ORIGINAL PAPER

Soil acidity and nutrient deficiency in central Amazonianheath forest soils

Flavio J. Luizao Æ Regina C. C. Luizao ÆJohn Proctor

Received: 21 February 2007 / Accepted: 21 May 2007 / Published online: 21 June 2007

� Springer Science+Business Media B.V. 2007

Abstract Experiments were carried out to test the

effects of liming and nutrient additions on plant

growth and soil processes such as C and N miner-

alisation in three contrasting forest types in central

Amazonia: the stunted facies of heath forest (SHF),

the tall facies of heath forest (THF) and the

surrounding lowland evergreen rain forest (LERF).

Calcium-carbonate additions increased soil respira-

tion in the field plots in the SHF; in laboratory

incubations, soil respiration was higher in the SHF

when soils were fertilised with N, and in THF and

LERF after S additions. The addition of N alone or in

different combinations generally induced a net

immobilisation of soil N. Net nitrification increased

during the incubation in SHF and THF soils fertilised

with N+P, and in LERF soils fertilised with either N,

or P, or CaCO3. In a field experiment using ingrowth

bags, a higher fine root production was observed in

all forest types when bags were fertilised with CaCl2or CaCO3, suggesting that Ca may be a limiting

nutrient in these soils. Calcium-carbonate addition in

a glasshouse bioassay experiment with rice showed

an overall positive effect on the survival and growth

of the seedlings. In other treatments where soil pH

was not raised, the rice showed acute toxicity

symptoms, poor root and shoot growth and high

mortality. Similar results were yielded in a field

experiment, using naturally established seedlings in

the field plots in SHF, THF and LERF. It is concluded

that the acute H+ ion toxicity is a major growth-

limiting factor for non-adapted plants in heath forest

soils in central Amazonia.

Keywords Campina � Campinarana � Heath forest �Nutrient limitation � Soil acidity

Introduction

Most of Amazonia that is not seasonally flooded is

covered by lowland evergreen rain forest (sensu

Whitmore 1984), often referred to in Brazil as terra

firme forest, and characterised by high species

diversity (Pires and Prance 1985). However other

forest formations that have a low species diversity,

low stature and high presence of scleromorphic

leaves, associated with white sandy soils (Spodosols),

occur locally throughout Amazonia in Brazil, south-

ern Venezuela, Ecuador, north-eastern Peru (Klinge

and Medina 1979; Anderson 1981; Proctor 1999), as

well as in Guyana and Suriname (Heyligers 1963;

Whitmore 1984). Several of these forest formations

F. J. Luizao (&) � R. C. C. Luizao

Departamento de Ecologia, Instituto Nacional de

Pesquisas da Amazonia, Caixa Postal 478, 69011-970

Manaus, Amazonas, Brasil

e-mail: fluizao@inpa.gov.br

J. Proctor

School of Biological and Environmental Sciences,

University of Stirling, Stirling FK9 4LA, Scotland, UK

123

Plant Ecol (2007) 192:209–224

DOI 10.1007/s11258-007-9317-6

present distinctive situations (e.g., caatinga located

on waterlogged sites in Venezuela vs. campina in

central Amazon on sites not subject to flooding).

However, these forest formations from the neotropics

(which could be collectively called caatinga), show

noticeable similarities in structure and physiognomy

amongst themselves, and to kerangas from the

palaeotropics, in Southeast Asia (Brunig 1968,

1970; Proctor et al. 1983; Whitmore 1984). Taking

into account that in Brazil there is another well-

known biome named caatinga (covering large areas

of the semi-arid region in north-eastern Brazil), the

use of an international nomenclature such as ‘heath

forest’ (sensu Whitmore 1984) seems more conve-

nient, and will be used henceforth. About 5–6% of

Amazonia is covered by heath forest (Anderson 1981;

Whitmore 1984) occurring on Spodosols with a layer

of mor humus of varying thickness. The stunted

facies of heath forest (referred to as SHF in this

article) is called campina in Brazil and often lacks the

mor humus layer; the taller facies (THF) is called

campinarana, and occurs next to high LERF. The

physiognomy of the SHF and THF formations could

correspond to facies of ‘caatinga’ in Venezuela

(Anderson 1981).

Heath forests grow on bleached white sands

(Richards 1996) and are generally characterised by

their short stature, slender trunks, thick leaves and

low species richness. There are several views as to

the causes of heath forests, but it is unlikely that a

single causal factor acts in isolation (Brunig 1968,

1970; Richards 1996). The four factors most com-

monly cited are: (i) drought (Brunig 1968; Klinge and

Medina 1979); (ii) waterlogging (Brunig 1968;

Bongers et al. 1985; Klinge and Medina 1979); (iii)

low nutrients (Brunig 1973, 1974; Jordan 1985;

Medina and Cuevas 1989; Richards 1996); and, (iv)

soil acidity and phenolics (Brunig 1968; Janzen 1974;

Proctor et al. 1983; Whitmore 1984; Proctor 1999).

However, the main factor or factors causing this

forest formation remain unclear (Miyamoto et al.

2007) and require further investigation.

The first two of the above hypotheses, drought and

waterlogging, are difficult to investigate experimen-

tally. However, on the basis of observations made in

heath forests occurring under different hydrological

situations, they have been discarded as the principal

causal factors. For example why does seasonal

waterlogging tend to cause savanna in much of

Brazil and not heath forests if waterlogging is an

important cause of heath forests?

The second two hypotheses (low nutrients, soil

acidity and phenolics) are more amenable to exper-

imental tests. Moreover, field studies in heath forest

in Brunei, analysing soil and litterfall nutrient

contents, have indicated a possible limitation by N,

but not by P for heath forest growth (Moran et al.

2000). In experimental tests, Ca addition (liming) has

generally been used to reduce acidity and fertiliser

applications to the soil can directly stimulate micro-

bial population and allow plant growth. The root

ingrowth technique, despite its shortcomings, offers

an opportunity to study fine root growth in relation to

mineral nutrient availability, and is particularly useful

for within-site comparisons amongst treatments

(Steen et al. 1991).

In order to test the hypothesis that nutrients, or low

pH, or both limited soil processes (such as soil

respiration and N transformations), fine root and plant

growth and survival were compared after the addition

of nutrients in two types of heath forest and in LERF.

It was hypothesised that (a) soil respiration, N

transformations, and roots and seedling growth would

respond to N but not P or other nutrient addition; and

(b) increasing soil pH through liming would cause a

significant response in soil processes, root growth,

and seedling growth and survival, and (c) the addition

of both lime and nutrients should produce the best

responses.

Materials and methods

Study site

The field study was carried out in central Amazonia

(2o360 S; 60o010 W), 60 km north of Manaus,

Amazonas State, Brazil, on a gradient of natural

vegetation from SHF through THF to high LERF.

The average annual rainfall in the area is 2,300 mm,

and a dry season occurs from June to November. The

soils are classified as Spodosols (SHF and THF) and

Ultisols (LERF). Selected features for soil profiles

under each forest type are given in Table 1. Species

richness in both heath forests is low (seven species ha�1

in SHF and 24 in THF) compared with 82 species ha�1

in the LERF. Above-ground biomass was estimated at

71 Mg ha�1 in SHF, 152 Mg ha�1 in THF and

210 Plant Ecol (2007) 192:209–224

123

409 Mg ha�1 in LERF (Luizao 1996). The Fabaceae

(Caesalpinioideae) has the highest basal area in all

three-forest types, followed by the Sapotaceae in the

SHF, by the Euphorbiaceae in the THF, and by the

Burseraceae in the LERF. A full description of the site

properties and the forests is given by Luizao (1996).

For soil and vegetation studies, three 50 m · 50 m plots

were delimited and used in each forest type. In each

plot, the four quadrants, measuring 25 m · 25 m, were

also marked. In the present work, two experiments

were carried out in the field (experiments 1 and 2) and

two in the laboratory (experiments 3 and 4).

Field experiments

Experiment 1: root ingrowth bags in the field

Nylon ingrowth bags of 12 cm · 12 cm and 1-mm

mesh were used. Two growth media were used in the

ingrowth bags: medium-sized vermiculite (3�6 mm)

and sieved sand from open SHF sites. They con-

trasted in that sand is inert with virtually no exchange

capacity, whilst vermiculite being a clay mineral has

a large exchange capacity (100–150 meq/100 g), its

pH is between 7 and 10, and naturally contains

exchangeable K+, Mg2+ and Fe2+ ions. The bags with

sand were placed on the soil surface (after the removal

of the litter layer) and the bags with vermiculite were

placed on the soil surface, and in the soil to a depth of

10 cm. In the SHF, the 10 cm depth corresponded to

either white sand in the open patches, or under closed

canopy, it incorporated the layer where organic

matter and fine roots concentrated. In the THF at

10 cm depth ingrowth bags were almost exclusively

in the litter layer and in the LERF, mostly in the

upper litter layer where a well-developed root mat

occurred.

There were six nutrient addition treatments

(Table 2), where the growth media were treated with

distilled water (control) or by either solutions or

suspensions of one of five nutrients: KCl, CaCO3,

NaHPO4, CaCl2 and urea (NH2CONH2). After 24 h

imbibition, the growth media were placed in the

nylon ingrowth bags. In each 25 m · 25 m quadrant

of the main field study plots (50 m · 50 m), one bag

was randomly placed, making it four replicate soil

bags of each nutrient treatment per plot. The bags

were left undisturbed for 117 d (all in the rainy

season) from 2 January to 19 May 1993. Then, all the

bags were removed, any outside roots shaved, and the

roots inside the bags (all <2-mm diameter) separated

by sieving and flotation. The roots were dried

(1058C) and weighed.

Experiment 2: the effect of nutrient addition on native

tree seedlings

In each forest type, two 8 m · 5 m plots were

delimited, either in small natural gaps (THF and

LERF) or in open areas alongside the ‘islands’ of

Table 1 Nutrient and acidity analyses of soil from the upper layers from the SHF, THF and LERF. Values are means of three pits

(Source: Luizao 1996, modified)

Depth*

(cm)

pHH2O N

(mg g�1)

C:N Ptotal

(mg g�1)

K+

(m-eqiv

100 g�1)

Na+

(m-eqiv

100 g�1)

Ca2+

(m-eqiv

100 g�1)

Mg2+

(m-eqiv

100 g�1)

CEC

(m-eqiv

100 g�1)

H+/Al3+

(m-eqiv

100 g�1)

SHF 0–5 3.7 0.28 25.4 165 0.15 0.03 0.08 0.26 1.84 >67.0

5–10 4.3 0.20 2.0 48 0.03 0.0 0.15 0.04 0.66 >24.0

20–30 4.9 0.30 0.5 17 0.0 0.0 0.08 0.01 0.28 7.50

THF 0–9 3.5 1.24 24.3 623 0.36 0.45 0.02 0.38 7.06 25.8

9–20 4.2 0.05 18.8 26 0.06 0.0 0.14 0.04 1.08 8.70

20–30 4.2 0.02 61.0 19 0.03 0.0 0.18 0.03 1.05 9.10

LERF 0–6 3.9 1.08 21.0 419 0.05 0.05 0.02 0.06 7.82 0.21

7–20 4.1 0.70 18.6 305 0.02 0.01 0.34 0.06 19.4 0.40

20–30 4.3 0.30 37.0 214 0.02 0.0 0.36 0.05 19.3 0.10

* The layer thickness varied according to the distribution of organic and mineral layers. The first of the three above layers was

predominantly organic (H); the second, mixed organic/mineral, and the third, an intrinsically mineral layer. Note that in SHF any

vestige of organic mixing in soil profile had disappeared after 10 cm in depth

Plant Ecol (2007) 192:209–224 211

123

vegetation (SHF). Only two replicate plots were used

because of the shortage of suitable natural gaps in the

THF and LERF. Fourteen 1 m · 1 m quadrats in each

plot were selected for experimental treatments on

seedlings already existing and measuring up to 30 cm

in height (thus, a wide variety of seedling species, and

likely of ages as well, was included in the experiment).

Seven nutrient addition treatments were applied (Table

2): (1) NH2CONH2, (2) Na2PO4, (3) KCl, (4) CaCl2,

(5) CaCO3, (6) a combination of 1, 2, 3 and 5, and a

control (no added nutrients). Two replicates of each of

the seven treatments were applied in each plot.

Treatments were randomly located in each plot.

Rates of fertilisation (Table 2) were similar to those

generally recommended by forestry nurseries in

Brazil (Reis 1989), and fell within the lower part of

ranges commonly used for mature trees elsewhere

(Tanner et al. 1990). The nutrients were added to the

soil on 1 March 1993, during the rainy season to

ensure that native seedlings did not dry out in the

months following treatment. Seedlings were assessed

at the beginning of the experiment and after 180 d,

and survival rate (final/initial numbers) and growth

quotient (final/initial height) determined.

The same 8 m · 5 m plots were used for soil

respiration measurements in response to nutrient

additions. Three composite samples (made up of five

sub-samples taken at random within the 1 m · 1 m

quadrats) were collected from the upper soil layer (0–

20 cm) from each treatment. In the SHF, the 0–20 cm

layer was generally mineral, slightly mixed with

some organic matter in the top 1–2 cm; in the THF

and the LERF, it generally included a humic layer

and a mixed organo-mineral layer, as well as a root

mat. Samples were cleaned of roots and litter, and the

fresh soil transferred into glass bottles. Bottles were

incubated in the dark for 10 d at 248C, and the

evolved carbon dioxide measured by using the

fumigation–incubation method of Jenkinson and

Powlson (1976). Sampling and measurements were

repeated after 60 d and 180 d from the beginning of

the experiment.

Laboratory experiments

Experiment 3: effect of nutrient addition on C and N

mineralisation and net nitrification

To test the effects of soil nutrient limitation on soil

respiration and N transformations nutrient additions

were made to soil under laboratory conditions. Soil

mineral samples were taken from the top 10 cm in

each of the three 50 m · 50 m plots of the three forest

types, bulked per forest type and carefully mixed. A

50-g sub-sample of each bulked sample was ran-

domly allocated to one of 12 treatments (Table 2).

The flasks were incubated in the dark at 248Cfor 10 d, and the evolved CO2 was measured by

titration according to the fumigation-incubation

method of Jenkinson and Powlson (1976). For

calculations of the N transformation N was extracted

from 5-g sub-samples, at the start of the incubation

Table 2 Nutrient addition treatments (all expressed on a kg ha�1 basis) applied to soils (and root ingrowth media in Experiment 1)

in the four experiments made in the field and in the laboratory

Treatment Experiment 1 (field)

Root ingrowth bags

Experiments 2 and 3 (field, native

seedlings; and lab, rice)

Experiment 4 (lab) Soil C and N

mineralisation

1 N as 150 kg of NH2CONH2 N as 150 kg of NH2CONH2 N as 150 kg of NH2CONH2

2 P as 50 kg of NaH2PO4 P as 50 kg of NaH2PO4 P as 50 kg of NaH2PO4

3 K as 60 kg of KCl K as 60 kg of KCl K as 60 kg of KCl

4 Ca as 2 000 kg of CaCl2 Ca as 2 000 kg of CaCl2 Ca as 2 000 kg of CaCO3

5 Ca as 2 000 kg of CaCO3 Ca as 2 000 kg of CaCO3 Ca as 2 000 kg of CaSO4

6 No added nutrients (control) NPKCa—combination of 1, 2, 3 and 5 S as 500 kg of Na2SO4

7 – No added nutrients (control) NP (combination of 1 + 2)

8 – – NK (combination of 1 + 3)

9 – – NCa (combination of 1 + 4)

10 – – NCa (combination of 1 + 5)

11 – – NS (combination of 1 + 6 above)

12 – – No added nutrients (control)

212 Plant Ecol (2007) 192:209–224

123

(initial mineral N), and after 10 d (incubated mineral

N) with 50-ml 2 M KCl. Concentrations of the

ammonium ion were determined colorimetrically by

flow injection, using a modified indophenol blue

method and the concentrations of nitrate ions were

determined by a similar technique using a modified

cadmium reduction method (Gine et al. 1980). Net

mineralisation and net nitrification were calculated

following Keeney (1982) and included the subtrac-

tion of the amount of nitrogen added in the N

treatments.

Experiment 4: glasshouse bioassay experiment

Humus (decomposing litter and raw humus material)

and the upper mineral soil layer were collected

separately from SHF, THF and LERF, air-dried and

sieved through a 2-mm mesh. Eight 7-cm diameter

(200-ml volume) pots were prepared for each of

seven treatments, and for each forest type and soil

depth. The seven treatments (Table 2) were the same

as those applied in the field (Experiment 2) and the

pots were watered with 20 ml freshly made nutrient

solutions or suspensions (Table 2). The pots were

randomly located on wooden benches inside a

glasshouse. Except for CaCl2, the rates of nutrient

additions were at the lower end of the recommended

range for cultivating acidic soils in Brazil (Anghinoni

and Volkeweiss 1984). Directly after applying the

nutrients, 10 seeds of dryland rice (Brazilian variety

IAC-47) were placed in the top 1-cm of soil. The pots

were kept moist and 10 d after planting germination

was assessed; 40 d later rice plants were assessed and

harvested. Shoot and root biomass, and plant survival

and mortality were determined.

Dryland rice was chosen as the test plant after an

attempt to grow a native tree species in field

conditions was unsuccessful due to heavy seedling

predation, despite showing high rates of germination

in all three forest types (Luizao 1996). Dryland rice

as a test plant is usually disease free, has a low soil

nutrient demand, and its seeds are readily available.

Despite that the Iban word kerangas (for heath forests

in Indonesia) means a site/soil where rice cannot

grow (Whitmore 1984), the authors considered its use

appropriate, since eventual positive responses in SHF

and THF soils could be attributed to the soil

amendments provided by nutrient additions.

Statistical analyses

In the field assays, nested analyses of variance (treat-

ments nested in plots) using GLM (General Linear

Model) were performed. In the laboratory incubations,

two-way analyses of variance were performed with

nutrient treatment and forest type as fixed factors. To

assess the effects of the nutrient additions in relation

to the control, one-way analyses of variance followed by

the Dunnett’s test were used to compare treatments to

control within each forest type. Data were transformed

(using square-root, logarithmic or arcsine transforma-

tions) to assure homogeneity of variance (Zar 1984).

Results

Field experiments

Experiment 1: root ingrowth bags at field plots

There was a large variability in the results obtained

from ingrowth bags. Significantly fewer roots were

found in the ingrowth bags in the SHF (nested

ANOVA, d.f. = 12; P < 0.001) than in the THF and

LERF. Fine root mass was significantly lower in the

bags filled with sand compared with those with

vermiculite (P < 0.001; Fig. 1). Within the vermiculite

bags, those buried within the soil showed a higher

production of fine roots compared with those placed on

the litter layer surface. In the SHF, the vermiculite

bags placed on the soil surface showed a significantly

higher production of fine roots than both the vermic-

ulite bags buried within the soil and the sand bags on

the soil surface (P < 0.001). Although variability was

high, CaCO3, CaCl2 and KCl increased fine root

growth in the THF (P < 0.05). In the LERF, CaCl2 and

CaCO3 were the only treatments which significantly

increased (both P < 0.001) fine root growth in

vermiculite-filled bags and at both depths.

Experiment 2: Effect of nutrient addition on the

growth of native tree seedlings

In the SHF plots, nutrient additions did not signifi-

cantly increase seedling survival compared to con-

trols (Fig. 2) and CaCl2 addition (nested ANOVA,

d.f. = 21; F = 6.52; P < 0.001) killed all the seedlings.

Plant Ecol (2007) 192:209–224 213

123

In the THF seedling survival was also significantly

reduced by CaCl2 (F = 4.0; P < 0.01), but increased

by NPK+CaCO3. In the LERF plots, none of the

nutrient additions influenced the survival rate of the

seedlings. The quotient of final/initial height was

significantly increased in SHF by NPK+CaCO3

(+27%). Nitrogen addition alone caused a mean

increase of 22% in seedling growth in relation to the

control, but the difference was not statistically

significant. In the THF, the final height of the

seedlings was generally lower than the initial height

(except after addition of NPK+CaCO3), but only

significantly so with CaCl2. In LERF no significant

differences in height were found between treatments.

No significant differences were found amongst

treatments for soil respiration (Table 3), with the

exception of the 60-d sampling time in SHF, where

respiration was significantly higher with the addition

of NPK+CaCO3 (nested ANOVA, d.f. = 21;

P < 0.05). In the same soil, there was a concomitant

increase (P < 0.001) in soil pH under the same

treatment.

SHF

0

1

2

3

4

5

KCl CaCO3 CaCl2 Urea NaH2 PO4 Control

Ro

tom

ass

(gabg

1-)

vermiculite, on surface

vermiculite, 10 cm deep

sand, on surface

THF

0

2

4

6

8

10

KCl CaCO3 CaCl2 Urea NaH2PO4 Control

Roo

tm

ass

(gba

g1-)

LERF

0

2

4

6

8

10

KCl CaCO3 CaCl2 Urea NaH2PO4 Control

Treatments

tooR

sam

s(g

gab1-)

* *

**

** *

**

****** *****

**

Fig. 1 Ingrowth bag experiment: dry mass of roots per bag

after 117 d in the bags containing vermiculite on the soil

surface, vermiculite at 10 cm depth in the soil and sand on the

soil surface, under different nutrient addition treatments. Bars

are means ± SE of four bags in each experiment and treatment

in each of the three replicate plots in the SHF, THF and LERF.

Significance levels for nested ANOVA with Dunnet’s test for

comparisons with the control are: *, 0.05; **, 0.01; ***, 0.001

0.0

0.4

0.8

1.2

1.6

2.0

N P K

aC

l 2C

aC

O3

C

PN

KI+

CaC

O3

Ctn oro

l

Gro

wth

nid

ex(f

ina

/lni

tiia

hlei

gh

t

SHF THF LERF

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

N P K

aC

l 2C

aC

O3

C

KP

NI+

CaC

O3

Ctnoro

l

Treatments

uS

vriv

laar

et

SHF THF LERF

*

*

****

***

*

**

Fig. 2 Field experiment: survival rate (quotient of final/initial

number of living native seedlings), and the growth (quotient of

final/initial height of the native seedlings) 180 d after nutrient

addition in the SHF, THF and LERF. Values are means with

SE (n values are variable and indicated above the bars). The

survival rate varies from 0 (no survival of seedlings) to 1 (all

survived). Growth quotients <1 indicate negative growth on the

average of the plots: quotients >1 indicate actual growth of

seedlings. Significant differences in relation to the control

(from nested ANOVA followed by Dunnet’s test) are indicated

by asterisks: * ,0.05; **, 0.01; ***, 0.001

214 Plant Ecol (2007) 192:209–224

123

Laboratory experiments

Experiment 3: effect of nutrient addition on C and N

mineralisation

Soil respiration. Soil respiration measurements varied

widely amongst soil types and treatments. Greater

increases in respiration after nutrient additions in

relation to the control were visible in SHF (Fig. 3),

but the differences were only significant in the

treatments N+P and N+Na2SO4 (one-way ANOVA,

P < 0.05). In the THF soils, respiration was signif-

icantly higher than the control in the treatments S and

N+S (P < 0.001). In the LERF soils, respiration was

significantly higher than the control in the treatments

S and N+K (P < 0.001) (Fig. 3).

Net nitrogen mineralisation and net nitrification.

The addition of N alone, or in all combinations (N +

Na2SO4; N+K; N+CaCO3; N+CaSO4; N+P) induced

net N immobilisation (P < 0.001) in SHF and THF

soils (Fig. 4). In the LERF soils, six out of the 12

treatments caused significant net immobilisation of

N: the addition of N alone; N+P; N+K; N+CaCO3;

N+CaSO4; N+Na2SO4 (P < 0.001), whereas two

treatments caused net mineralisation: CaSO4 and

CaCO3 (all P < 0.001) (Fig. 4).

Net nitrification rates were not affected by any of

the treatments in SHF soils (Fig 5). In the THF

soils, only N+P increased significantly net nitrifica-

tion (P < 0.001). In the LERF, the rates of net

nitrification were significantly different from the

control in seven out of the 12 treatments: an

increase with N, P and CaCO3; and a decrease with

KCl, Na2SO4, N+CaSO4 and N+Na2SO4 (all

P < 0.001) (Fig. 5).

Experiment 4: glasshouse bioassay experiment

Soil type and nutrient addition treatment generally had

a significant influence on the germination, survival and

growth of the dryland rice (Fig. 6). There was an

extreme stunting and early death of seedlings in SHF

and THF soils that had not received CaCO3. A

significantly higher shoot biomass of rice was found

with CaCO3 alone and with NPK+CaCO3 (F = 16.1;

P < 0.001) in SHF soils. In THF soils, only the addition

of CaCO3 (F = 7.66; P < 0.001) and in the LERF, only

the addition of NPK+CaCO3 increased shoot biomass

significantly. Root biomass was also significantly

higher after the addition of both CaCO3 and NPK+Ca-

CO3 (F = 9.23; P < 0.001) in SHF soil; after addition of

CaCO3 in THF soil (F = 5.91; P < 0.001); and no

significant effects of nutrient addition were found in

the LERF soils. The addition of CaCl2 inhibited

germination and killed most seedlings even in the

LERF soils (Fig. 6), although the few seedlings which

did survive in the SHF and THF soil grew well. The

addition of CaCl2 significantly increased seedling

mortality in all three soil types (F = 14.4, SHF;

F = 10.3, THF; F = 24.3, LERF; P < 0.001). In THF

soils, addition of NH2CONH2 also significantly

increased mortality (F = 10.3; P < 0.001).

Table 3 Soil respiration (mg C g�1 oven-dry soil) 60 d and 180 d after nutrient addition to field plots with already existing seedlings

in SHF, THF and LERF

Treatment Forest types

SHF THF LERF

60 d 180 d 60 d 180 d 60 d 180 d

N 56.0 ± 25.6 20.0 ± 2.20 91.4 ± 32.6 101 ± 22.4 52.1 ± 15.6 111 ± 3.70

P 20.1 ± 4.08 na 83.7 ± 12.2 na 57.3 ± 20.3 na

K 68.9 ± 17.0 na 60.9 ± 15.2 na 52.1 ± 11.3 na

NPK + CaCO3 104 ± 15.7* 66.6 ± 14.5 93.3 ± 21.6 110 ± 12.7 86.5 ± 8.45 103 ± 13.2

CaCl2 70.1 ± 20.6 na 91.1 ± 23.6 na 69.5 ± 17.3 na

CaCO3 41.9 ± 5.18 100 ± 3.43 105.5 ± 25.3 128 ± 20.6 92.3 ± 22.8 135 ± 41.6

Control 30.5 ± 6.12 57.1 ± 20.8 48.5 ± 11.3 128 ± 13.4 66.5 ± 6.12 90.4 ± 21.8

Values are treatment means ± SE at each time in each forest type of two replicate sub-plots within each of two plots (n = 4).

na = not analysed; * significant difference among treatments (P < 0.05)

Plant Ecol (2007) 192:209–224 215

123

Discussion

The pH in the three forest types was amongst the

lowest recorded for rain forests on acidic soils, but

the concentrations of nutrients (except for Na in SHF,

and Ca in all three forest types) in the surface soils

SHF

0

20

40

60

80

100

120 *

*

***

***

******

*** ***

***

tC

rl N +N

P

+N

K

+N

aC

CO

3

+N

aC

SO

4

+N

SO

4 P K

aC

CO

3

aC

SO

4

Na 2

SO

4N

a 2S

O4

Na 2

SO

4

So

lire

spria

t(

noi

µg

Cg

1-)

THF

0

30

60

90

120

tC

rl N +N

P

+N

K

+N

Ca

CO

3

+N

Sa

CO

4

+N

SO

4 P K O3

Ca

C

Sa

CO

4

So

lire

spir

ta

oi(

nµ

gC

g1-)

LERF

0

30

60

90

120

tC

rl N +N

P

+N

K

+N

aC

CO

3

+N

aC

SO

4

+N

SO

4 P K

aC

CO

3

aC

SO

4

Treatments

Soi

lres

pira

tion

(µC

g-g

)1

Fig. 3 Laboratory experiment: soil respiration (mg C g�1

oven-dry soil 10 d�1) under different nutrient addition

treatments (explained in the text) in SHF, THF and LERF

soils. Values are means ± SD (n = 3). Significance levels for

ANOVA within each forest type with Dunnet’s test for

comparisons with the control are: *, 0.05; **, 0.01; ***, 0.001

SHF

-120

-100

-80

-60

-40

-20

0

20

40

60

Ctr

l N

N+

P

N+

K

N+

Ca

CO

3

N+

Ca

SO

4

N+

SO

4 P K

Ca

CO

3

Ca

SO

4

Na 2S

O4

Na 2S

O4

Na 2S

O4

N m

iner

aliz

atio

n (µ

N g

-1)

N

min

eral

izat

ion

(µg

N g

-1)

N

min

eral

izat

ion

(µg

N g

-1)

***

***

***

***

***

***

THF

-120

-100

-80

-60

-40

-20

0

20

40

60

Ctr

l N

N+

P

N+

K

N+

Ca

CO

3

N+

Ca

SO

4

N+

SO

4 P K

Ca

CO

3

Ca

SO

4

***

***

***

***

****

**

***

LERF

-120

-100

-80

-60

-40

-20

0

20

40

60

Ctr

l N

N+P

N+K

N+C

aCO

3

N+C

aSO

4

N+S

O4 P K

CaC

O3

CaS

O4

***

***

***

***

***

***

***

***

Fig. 4 Laboratory experiment: net nitrogen mineralisation

(mg N g�1 oven-dry soil 10 d�1) under different nutrient

addition treatments in the SHF, THF and LERF soils. Values

are means ± SE (n = 9). Significance levels for ANOVA with

Dunnet’s test for comparisons with the control are: *, 0.05;

**, 0.01; ***, 0.001

216 Plant Ecol (2007) 192:209–224

123

are not exceptionally low (Luizao 1996). The most

striking difference observed between the heath forest

and the LERF soils was the dominance of H+ (instead

of Al3+) in the exchange complex, especially in the

SHF, where Al3+ concentrations were negligible and

the H+/Al3+ quotient was much higher (more than 300

times in upper soil layer) than in the LERF soils

(Luizao 1996; Proctor 1999; Table 1). However, the

biomass estimated for the LERF (409 Mg ha�1),

slightly higher than the range reported for forests on

Oxisols in Amazonia (Jordan 1985) suggests that

-7

-5

-3

-1

1

3

5 SHF

tC

rl N +N

P

+N

K

+N

CO

3a

C +N

Sa

CO

4

+N

SO

4 P K

Ca

CO

3

Sa

CO

4

Na 2

SO

4N

a 2S

O4

Na 2

SO

4

Ne

tti

nr

ficia

tn

oi(µ

gN

1-)

-3

0

3

6

9

12 THF

tC

rl N +N

P

+N

K

+N

CaC

O3

+N

CaS

O4

+N

SO

4 P K

aC

CO

3

aC

SO

4

Net

intr

ific

taio

n(µ

Ng

g1-)

-5

0

5

10

15

20 LERF

tC

rl N +N

P

+N

K

+N

Ca

CO

3

+N

Ca

SO

4

+N

SO

4 P K

CO

3a

C

SO

4a

C

Treatments

eN

tnitr

fici

ta

noi

(µN

gg

1-)

***

***

***

***

***

***

***

***

Fig. 5 Laboratory experiment: net nitrification (mg N g�1

oven-dry soil 10 d�1) under different nutrient addition

treatments in the SHF, THF and LERF soils. Values are

means ± SE (n = 9). Significance levels for ANOVA with

Dunnet’s test for comparisons with the control are: *, 0.05;

**, 0.01; ***, 0.001

0

2

4

6 ***

***

******

*******

**

***

***

*

****

*****

**

8

10

Mor

tatily

u-N

rea C

Kl

aC

Cl 2

aC

CO

3

PN

K+

aC

O3

C

Con

rtol

Con

rtol

Con

rtol

SHF THF LERF

0

20

40

60

80

100

120

N-

ruae

NaH

2PO

4N

aH2P

O4

CK

l

aC

l 2C

aC

O3

C

PN

K+

aC

O3

C

Sooht

ibmo

(ssa

gm

2-)

0

20

40

60

80

100

N-

ruae

aN

H2

O4

P

CK

l

aC

l 2C

aC

O3

C

PN

K+

aC

O3

C

Treatments

Ro

moibto(

ssag

m2-)

Fig. 6 Glasshouse experiment: number of dead rice seedlings,

and shoot and root dry mass (g m�2) in each treatment after

50 d, using soils from the SHF, THF and LERF. Values are

means and SE (n = 8), and significant differences in relation to

the control (from one-way ANOVA followed by Dunnet’s test)

are indicated by asterisks: *, 0.05; **, 0.01; ***, 0.001

Plant Ecol (2007) 192:209–224 217

123

there are no limitations for tree growth in that forest

type.

Two nutrient combinations caused a significant

increase in the SHF soil respiration: urea with

Na2PO3, and urea with Na2SO4 suggesting that N is

limiting microbial activities in the SHF. In turn, P and

S seemed to be important when enough N was

supplied. In THF soils, S, especially when combined

with N, seemed to be the nutrient which mostly

stimulated the activity of the microorganisms

whereas in LERF soils, additions of S, and the

combination N+K, stimulated soil respiration. En-

hanced microbial activity could be caused either by S

or by the added Ca or Na (Persson et al. 1989).

However, the latter is unlikely to be the case since Na

is at most a micronutrient whilst Ca did not produce

so positive a response when added as CaCO3. Thus,

the increase in microbial activity might be caused by

additions of S, which was somehow unexpected,

since over 95% of the forest topsoil S is organically

bound (David et al. 1982). These results indicate that

under certain conditions (e.g. adequate supply of

other nutrients) S may limit microbial decomposition.

Another possible explanation could be a potential

liming effect of S in the soil, but unfortunately there

was no separate S treatment in the experiments to

confirm the results.

High soil acidity has often been considered to be a

strong microbial inhibitor. When acidity is reduced

by liming a more diverse decomposer community

may establish, allowing a more efficient substrate

utilisation (Insam 1990). Contrary to that expectation,

though CaCO3 addition increased soil pH in the SHF,

its initial positive effect on soil respiration at the 60-d

sampling was not apparent at 180 d. In THF and

LERF soil respiration was not significantly influenced

by CaCO3, a similar result to that found by Persson

et al. (1990) in coniferous forest in Scandinavia.

They found no significant difference in soil respira-

tion between the controls and mineral soils which

received CaCO3, and that may indicate that not

enough liming material was applied to increase soil

pH in those forest types.

Low concentrations of N found in heath forest

leaves (Coomes and Grubb 1996) and litterfall

(Luizao 1996; Proctor 1999) have been used to

suggest that N may be unusually low in heath forests,

thus limiting plant growth (Coomes and Grubb 1996).

However, low N availability of soils may occur

because of immobilisation by microorganisms (Pers-

son et al. 1990). In the present study, in the soils of all

forest types, all treatments including N additions

resulted in a high net N immobilisation, which is a

consequence of increased activity of the soil

microbes (Persson et al. 1990). Since in the SHF

soils a significant pH increase was not followed by

enhanced net N mineralisation, it seems that low pH

is not the only factor influencing the N transforma-

tions. The addition of CaCO3 alone was effective in

enhancing net N mineralisation only in the LERF

soils. The general lack of an increase in net N

mineralisation in both the SHF and THF soils when

only CaCO3 was applied may be explained by an

increase in bacterial relative to fungal decomposition,

since there are strong indications that liming of forest

soils stimulates bacterial activity more than that of

fungi (Griffin 1985). In the present study N was

added as urea, and no significant changes in soil pH

were observed in the urea treatments, despite its

potential acidifying effect, as pointed out in exper-

iments made in eastern Amazonia in soils with a

similar texture and chemistry (Ludwig et al. 2001).

As an intermediate in microbial metabolism, urea

applied to the soil is very readily hydrolysed, and

much of it is transformed to ammonium ions and

immobilised in a few days.

Net nitrate production can only increase when

there is ammonium available for nitrifying microor-

ganisms. Therefore, the extent to which nitrate

production and leaching may increase depends on

whether liming stimulates mineralisation or immo-

bilisation of ammonium. An experiment using soil

solution concentration of nitrate in soil profile to

estimate nitrate leaching in Scandinavian forest soils

showed that leaching of NO3-N occurred in higher

concentrations below pH 4.5 as a direct effect of the

pH more than any other factors (Falkengren-Grerup

et al. 2006). In the present study, as the pH was not

elevated substantially in the SHF soils, nitrate

leaching may have occurred in the field assays, but

not in the 10-d incubation experiment in laboratory.

In this case, since N mineralisation was inhibited by

many of the added nutrients, no ammonium was left

for the nitrification process. In both SHF and THF

soils, net nitrification was inhibited (although not

significantly) by nearly all nutrients applied. Even the

addition of urea did not increase nitrification. Studies

have suggested that labile inhibitors of nitrification

218 Plant Ecol (2007) 192:209–224

123

may be responsible for delays in nitrate production

(Vitousek and Matson 1985) or for its complete

inhibition (White 1988).

The Ca status of the SHF, THF and LERF soils

was very low and the overall positive response of fine

root growth (in all bag positions, media and forest

types) to both CaCO3 and CaCl2 addition, suggests

that fine root growth is restricted by both soil pH and

low Ca. However, the positive effect of both Ca

treatments on the root mass in the heath forest soils

may have another explanation. First, increased fine

root production does not necessarily imply increased

plant growth (E.V.J. Tanner, pers. comm. 2002).

Plants might respond to fertilisation by first increas-

ing root production, and only much later showing any

increase in above-ground biomass (Silver 1994).

Also, the general increase in root growth in the bags

filled with vermiculite, especially in those buried in

the soil, suggest that the alkaline vermiculite used in

Brazil (pH = 8.8) had a positive effect on fine root

growth. The vermiculite used in the present work was

acquired from the only supplier in Brazil and with its

high pH value and an unquantified amount of cations

in its composition, certainly represented a confound-

ing factor for evaluating the effects of the nutrient

additions. However, it must be pointed out that the

two cations generally present in higher concentrations

in vermiculite (Mg2+ and Fe2+) were not evaluated in

the present work. Also, there was a control for the

experiment using vermiculite bags with no nutrient

addition, and further, the effect of nutrient additions

on vermiculite bags placed on soil surface were not

strikingly different from the ones with sand.

The results of the present study contrast with that of

Cuevas and Medina (1988), who worked in different

types of rain forest (tierra firme, tall caatinga and low

bana) at San Carlos, Venezuela. They found fine root

growth stimulated by the addition of N in tall caatinga

and low bana forests only on top of the root mat and

by P in tierra firme and bana forests and by Ca only in

the tierra firme forest (&LERF). Proctor (1995)

pointed out that owing to the very poor root growth

in the unfertilised treatments of Cuevas and Medina

(1988) their study did not allow them to reach firm

conclusions on the limiting nutrients in the tierra firme

and bana forests. Their data lend no support to the

view that N, P or K, are limiting for plant growth in

lowland evergreen rain forests, which confirms the

results of the present study.

The lack of response of fine roots to N, P and K

addition observed here is not surprising, and corrob-

orates the results of several recent ingrowth bag

studies carried out in tropical and temperate soils.

Studies carried out in Borneo at Barito Ulu, Central

Kalimantan, Indonesia (J. Proctor, unpublished),

found no response in a heath forest to P (but there

was a significantly increased fine root growth in

LERF in the presence of P). It seems that soil acidity

not only controls nutrient effects on plant growth but

it is also important for maintaining differences in

species composition such as was observed by Roem

et al. (2002) in heath land on nutrient-poor sandy soil

in the Netherlands. They showed that the influence of

nutrient availability on species composition in heath-

land was less important than soil acidity. To what

extent that control by acidity is effective is not

precisely known as in harsh environments, such as

the heath forests, some native species are able to deal

with nutrient limitations (stress tolerators), but may

rapidly respond in an opportunistic way when the

limitation is removed, assuming a behaviour properly

called as ‘latent competitors’ (Nagy and Proctor

1997). Such a strategy by certain heath forest species

would help explain the surprising results found by

Miyamoto et al. (2007) in a Bornean heath forest in

southern Central Kalimantan (basal area of

21.8 m2 ha�1) on bleached white sand, under an

annual rainfall regime of 3,200 mm. They recorded a

quick recovery in wood biomass after a strong

drought, caused by the El Nino phenomenon. Using

pulses of nutrients (in this case, possibly released by

dead wood and the extra litterfall produced by the

drought) the heath forest apparently became a more

productive system in the following years, allowing an

increase in primary productivity in response to

increased nutrient availability. The increase in nutri-

ent availability in this case may be paralleled by an

increase in soil pH caused by the release of Ca and

Mg from the dead wood as illustrated in former works

involving clearings produced by selective logging in

Brazilian Amazon. They showed that together with

some short term release of N and P from extra fine

litterfall, a considerable increase in Ca and Mg

availability in upper soil layer was observed after

1.5 years in response to the decomposition of dead

wood accumulated in patches of the clearings

produced by selective logging (Yano 2001; Pauletto

2006). These two basic cations, Ca and Mg, as well as

Plant Ecol (2007) 192:209–224 219

123

Mn, are present in higher concentrations in the coarse

litter fraction 2–10 cm in diameter (Pauletto 2006)

which may be decomposed within a couple of years,

resulting in a slight but important increase in soil pH,

causing a positive response in seedling and tree

growth.

In the present study, native seedlings in the field

experiment showed either no or a negative response

to N, P and K addition, as well as a high mortality

when CaCl2 was applied. The results in SHF and THF

were very similar to those of other studies carried out

in temperate forests on acidic sandy soils in Sweden

(Brunet and Neymark 1992; Falkengren-Krerup and

Tyler 1992, 1993; Staaf 1992) or elsewhere (Proctor

1999; Roem et al. 2002). They all found that any

addition of mineral nutrients was unsuccessful in

promoting plant survival or growth, unless the

treatment involved an increase in soil pH.

In the present study, overall, there were no

beneficial effects of the nutrient addition in the SHF

and THF, if not accompanied by an increase in soil

pH (by the addition of CaCO3), and a very limited

effect in the LERF. Thus, there was no direct

evidence of nutrient limitation for seedling growth

in the SHF and THF, and other factors must be

involved. The high toxicity induced by soil acidity

was likely to be the main cause for the death or poor

growth of seedlings in the nutrient addition treat-

ments.

In soils well supplied with Al, pH is controlled by

a complex hydrated Al-ion buffer system which sets a

lower limit to pH, preventing extreme acidity (with

values much below 4.0) and high H+ concentrations

(Rowell 1988; Fitter and Hay 1991). For soils of

similar pH there are large differences between

mineral and organic soils. In mineral soils exchange-

able Al limits exchangeable acidity, whilst in organic

soils the pH is maintained by the buffering ability of

the organically complexed Al. Along a transition

from mineral to organic soils the decrease in

exchangeable Al with increasing organic matter, is

paralleled by an increase in the exchangeable acidity.

The removal of the Al complexes by the addition of

bases (especially CaCl2, which was used in much

larger concentrations than the other major nutrients in

the present study) may have caused a decrease in the

soil pH, increasing the H+ toxicity. It must be

remembered that the amelioration of H+ toxicity by

Al3+ ions has been shown experimentally (Kinraide

1993), and that in acidic soils Al3+ ions may prevent

H+ from becoming an intrinsic toxin (Kinraide 2003).

Thus, Al3+ ions decrease solute leakage at low pH,

producing a growth enhancement (Foy 1984; Rowell

1988). In studies of Haplic Podzols in a boreal

coniferous forest in Sweden, Skyllberg (1991, 1999)

found that the humus layer (O horizon) had a pH

positively correlated with Al. In line with other

above-mentioned authors (e.g. Proctor 1999; Kinra-

ide 1993; 2003) Skyllberg suggested that in acid

humus layers and organic horizons with a pH below

4.0, Al cations act as any ‘base cation’ through an H+-

displacement at cation exchange sites. Thus, instead

of acidifying effects, Al ions in soil (at adequate

concentrations) would be beneficial, buffering the pH

at levels not toxic to plants, and the lack of

displacement of such ions cause strong toxicity for

plant roots. In Scotland, addition of low concentra-

tions of Al (2–5 mg l�1) to soils poor in Al ions

enhanced the growth of two races of Betula pendula

Roth originating from Al-poor soils (Kidd and

Proctor 2000). In Scandinavia, a pot experiment

using acid soil and raising its pH from 3.3 by

carbonate additions showed that the growth of

Bromus benekenii (Lange) Trimen. and nine other

species (out of a total of 17) was limited at pH <4.1

and the toxicity of H-ions to Bromus was confirmed

at pH 4.2 or lower (Falkengren-Grerup et al. 1995). In

the present study, the very low concentration of Al in

the heath forest soils, especially in the SHF, where

the mor humus is often lacking, may be a major

reason for the poor control of H+ toxicity.

The results of the glasshouse experiment using rice

seedlings overall confirmed those found in the field

study on native tree seedlings: the only general

positive effect on growth was caused by the addition

of CaCO3, whilst the addition of CaCl2 had a general

deleterious effect on seedlings, inducing high mor-

tality rates. The general coincidence of the results

observed in the glasshouse (using a cultivated crop)

with the field experiment (using several native

species) was reassuring.

The apparent contradiction of the strongly nega-

tive results for seedling growth in relation to the

positive responses of fine root growth to the addition

of CaCl2 (in the ingrowth bags) may have two

explanations. These results may indicate that most of

the roots penetrating the bags and responding posi-

tively to the CaCl2 additions originated from mature

220 Plant Ecol (2007) 192:209–224

123

plants (not seedlings), which might respond differ-

ently to nutrient addition. Most likely, though, the

fine roots were not adversely affected because there

was enough time for part of the CaCl2 (mainly the

chloride fraction) to be leached from the bags by

rainwater. In fact, 1,440 mm of rain fell during the

experiment, and January, the first month of the

experiment, had a rainfall mean of 108 mm per week.

After such selective leaching, the residual Ca may

have been beneficial for fine root growth.

The positive responses of fine root growth and the

soil respiration to additions of Ca to the soil seem to

be further pieces of evidence of limitations by this

element in the heath forest soils, after the apparent

limiting effect of Ca and Mn for soil and litter

organisms (Luizao 1994; 1996). However, that does

not imply that these elements are also limiting for

plant growth as a whole, since other factors may be

involved (Attiwill and Adams 1993). For instance,

Grubb (1989) suggested that in nutrient-poor soils, an

important interaction between shade and nutrients

(especially for P) occurs, and that was partly

confirmed in later bioassays in lowland dipterocarp

rain forests in Singapore. Highly positive responses

of two shrubby species were found when P was added

(Burslem et al. 1994), but seedlings of four shade-

tolerant species showed either no response or a

negative response to P additions (Burslem et al.

1995). They suggested P and major cations as

limiting factors in nutrient-poor soils (Burslem

et al. 1994), and those shade-tolerant tree seedlings

which have mycorrhizas are not limited by P supply

because of the mycorrhizas or because they have a

low demand for nutrients when growing in the shade

(Burslem et al. 1995). The latter suggestion was also

made by Denslow et al. (1987), who found positive

responses of seedling growth with complete nutrient

fertilisation on nutrient-richer soils, but no responses

of shrubby species to P additions. In fact, the

assessment of the actual nutrient requirements of

trees would be necessary for nutrient addition exper-

iments, but these requirements are virtually impossi-

ble to ascertain.

The results found in the present study for the

seedling survival and growth agree notably with

another study on Central Kalimantan heath forest

soils, also growing dryland rice in a pot experiment.

No seedling root growth was found in any treatment

in the heath forest organic soil, except when CaCO3

was added (Proctor 1999). It was speculated that poor

growth of rice on heath forest soils was due to toxins

in the soil and not due to a low soil nutrient status.

The negative effects of the humus layer included

in part of the pots in the present study may also be the

result of phenolic compounds (leached by the

frequent watering of the pots), affecting seedling

roots, especially in the heath forest soils. In Sarawak,

Brunig (1968, 1974) reported that heath forest soils

have high concentrations of secondary metabolites,

which may have two effects: production of toxic

effects on the vegetation, and reduction of available

N in the soil. Whitmore (1990) indicated that phenols

are abundant in heath forest leaves and litter, and

these may be toxic or inhibit uptake when they leach

into the soil. Soil phenolics directly affect germina-

tion and especially the growth of higher plants, and

concentrations of soluble phenolics are correlated

with organic matter content, and highest in the

superficial L and F organic layers (Kuiters 1990). In

the organic layers of the THF soils, evidence was

found of phenolic leachates, in the form of green-

brownish bubbles (Luizao 1994), certainly released

by the decomposition of either the litter on the soil

surface or the fine roots, the main originators of

phenolics in soil (Kuiters 1990).

However, in the field experiment, using pre-exist-

ing natural seedlings, and where controls showed no

strong mortality, the putative toxicity of phenolic

compounds would have interacted with the added

nutrients, making it still more difficult to explain the

mechanisms involved. The phenolic substances are

closely related to pH and soil nutrient status, and

although phenolics are generally not high enough to be

strongly acidic, they are more physiologically active

with H+ to produce the high mortality of seedlings in

the SHF and THF when the pH buffer was probably

swamped by the large additions of CaCl2.

Conclusions

It is possible that the soils in the SHF are nutrient limited,

considering that they have virtually no top organic layer

(where most of the nutrients are found in THF soils), and

that a better response, though not always significant, was

observed for SHF soils than for THF soils when

nutrients were added. Seedling mortality was less in

the SHF than in THF when N, P or NPK + CaCO3 were

Plant Ecol (2007) 192:209–224 221

123

added, whilst the shoot and root mass were higher in

SHF than in THF soils when NPK + CaCO3 were added.

There was little evidence of N or P limitation, as

generally suggested for acidic tropical soils, as the chief

cause of poor plant growth in SHF and THF. It is

possible to speculate that there was some evidence of

toxic effects of soil pH and secondary compounds, as

illustrated by the slight negative responses to the

inclusion of humus layer in the pots with heath forest

soils, and by the largely positive response to the addition

of CaCO3 to the soils. However, the question of limiting

factors for plant growth in heath forest soils is still an

unresolved one, and, thus, the view of Whitmore (1984)

that heath forests occur on sites which have a number of

unfavourable characteristics, acting together or sepa-

rately, is substantiated. Even not being frequent, drought

may occur; the extremely acid soils, with pH <4 at

surface would be toxic to many plants; the soil has low

amounts of Al and Fe sesquioxides, and consequently a

low ability to absorb H+; phenols occur at high levels in

leaves and litter, leaching into the soil; and, the amounts

of nutrients in fine litter are low and slowly cycling. All

these severe conditions, together or separately, restrict

the production of heath forest and select only those

species which are resistant to its many adverse condi-

tions.

Acknowledgements We wish to thank Claudio Yano and

Cilene Palheta Soares for helping in the laboratory and in the field;

two anonymous reviewers and Laszlo Nagy provided helpful

comments to improve the manuscript. The work was funded by

INPA/DFID (National Institute for Amazonian Research/

Department for International Development, UK) through the

project BIONTE (Biomass and Nutrients in the Tropical Rain

Forest) and by the European Community through the project

‘Organic Matter as Basis for Sustainable Use of Soils in Amazon’.

References

Anderson AB (1981) White-sand vegetation of Brazilian

Amazonia. Biotropica 13:199–210

Anghinoni I, Volkweiss SJ (1984) Recomendacoes de uso de

fertilizantes no Brasil. In: Espinoza W, Oliveira AJ (eds)

Anais do simposio sobre fertilizantes na agricultura Bra-

sileira. EMBRAPA, Brasılia

Attiwill PM, Adams MA (1993) Nutrient cycling in forests.

New Phytol 124:561–582

Bongers F, Engelen D, Klinge H (1985) Phytomass structure of

natural plant communities on spodosols in southern

Venezuela: the bana woodland. Vegetatio 63:13–34

Brunet J, Neymark M (1992) Importance of soil acidity to the

distribution of rare forest grasses in south Sweden. Flora

187:317–326

Brunig EF (1968) On the limits of vegetable productivity in the

tropical rain forest and the boreal coniferous forest. Ind

Bot Soc 46:314–322

Brunig EF (1970) Stand structure, physiognomy, and envi-

ronmental factors in some lowland forests in Sarawak.

Trop Ecol 11:26–43

Brunig EF (1973) Species richness and stand diversity in

relation to site and succession of forests in Sarawak and

Brunei (Borneo). Amazoniana 4:293–320

Brunig EF (1974) Ecological studies in the kerangas forests of

Sarawak and Brunei. Borneo Literature Bureau, Kuching

Burslem DFRP, Grubb PJ, Turner IM (1995) Responses to

nutrient addition among shade-tolerant tree seedlings of

lowland tropical rain forest in Singapore. J Ecol 83:113–

122

Burslem DFRP, Turner IM, Grubb PJ (1994) Mineral nutrient

status of coastal hill dipterocarp forest and adinandra

belukar in Singapore: bioassays of nutrient limitation. J

Trop Ecol 10:579–600

Coomes DA, Grubb PJ (1996) Amazonian caatinga and related

communities at La Esmeralda, Venezuela: forest struc-

ture, physiognomy and floristics, and control by soil fac-

tors. Vegetatio 122:167–191

Cuevas E, Medina E (1988) Nutrient dynamics within Ama-

zonian forest. II. Fine root growth, nutrient availability

and leaf litter decomposition. Oecologia 76:222–235

David MB, Mitchell MJ, Nakas JP (1982) Organic and inor-

ganic sulfur constituents of a forest soil and their rela-

tionship to microbial activity. Soil Sci Soc Amer J

46:847–852

Denslow JS, Vitousek PM, Schultz JC (1987) Bioassays of

nutrient limitation in a tropical rainforest soil. Oecologia

74:370–376

Falkengren-Grerup U, Tyler G (1992) Nutrient conditions

limiting survival and growth of Galium odoratum (L.)

Scop. in acid forest soil. Acta Oecol 13:169–180

Falkengren-Grerup U Tyler G (1993) Experimental evidence

for the relative sensitivity of deciduous forest plants to

high soil acidity. For Ecol Manage 60:311–326

Falkengren-Grerup U, Brunet J Quist ME (1995) Sensitivity of

plants to acidic soils exemplified by the forest grass

Bromus benekenii. Water Air Soil Poll 85:1233–1238

Falkengren-Grerup U, ten Brink DJ Brunet J (2006) Land use

effects on soil N, P, C and pH persist over 40–80 years of

forest growth on agricultural soils. For Ecol Manag

225:74–81

Fitter AH, Hay RKM (1991) Environmental physiology of

plants, 2nd edn. Academic Press, Oxford

Foy CD (1984) Physiological effects of hydrogen, aluminium,

and manganese toxicities in acid soil. In: Adams F (ed)

Soil acidity and liming, 2nd edn. American Society of

Agronomy, Madison

Gine MF, Bergamin-Filho H, Zagatto EAG et al (1980)

Simultaneous determination of nitrate and nitrite by flow

injection analysis. Anal Chim Acta 114:192–197

Griffin DM (1985) A comparison of the roles of bacteria and

fungi. In: Leadetter ER, Poindexter ED (eds) Bacteria in

nature: bacterial acitivities in perspective. Plenum Press,

New York

Grubb PJ (1989) The role of mineral nutrients in the tropics: a

plant ecologist’s view. In: Proctor J (ed) Mineral nutrients

222 Plant Ecol (2007) 192:209–224

123

in tropical forests and savannas. Blackwell Scientific

Publications, Oxford

Heyligers PC (1963) Vegetation and soil of a white-sand sa-

vanna in Suriname. Verhandelingen der koninklijke Ne-

derlandse Akademie van Wetenschappen, AFD.

Natuurkunde. N.V. Noord-Hollandshce, Uitgevers Ma-

atschappij, Amsterdam

Insam H (1990) Are the soil microbial biomass and basal

respiration governed by climatic regimes? Soil Biol Bio-

chem 22:525–532

Janzen DH (1974) Tropical blackwater rivers, animals and mast

fruiting by the Dipterocarpaceae. Biotropica 6:69–103

Jenkinson DS, Powlson DS (1976) The effects of biocidal

treatments on metabolism in soil. V. A method for mea-

suring soil biomass. Soil Biol Biochem 8:209–213

Jordan CF (1985) Nutrient cycling in tropical forest ecosys-

tems. John Wiley and Sons, Chichester

Keeney DR (1982) Nitrogen availability indices. In: Page AL,

Miller RH, Keeney DR (eds) Methods of soil analysis Part

2, 2nd edn. American Society of Agronomy, Madison

Kidd PS, Proctor J (2000) Effects of aluminium on the growth

and mineral composition of Betula pendula Roth. J Exp

Bot 51:1057–1066

Kinraide TB (1993) Aluminium enhancement of plant

growth in acid rooting media. A case of reciprocal

alleviation of toxicity by two toxic cations. Physiol

Planta 88:619–625

Kinraide TB (2003) Toxicity factors in acidic forest soils: at-

tempts to evaluate separately the toxic effects of excessive

Al3+ and H+ and insufficient Ca2+ and Mg2+ upon root

elongation. Eur J Soil Sci 54:323–333

Klinge H, Medina E (1979) Rio Negro caatingas and camp-

inas. Amazonas states of Venezuela and Brazil. In:

Spetch RL (ed) Heathland and related shrublands. Eco-

systems of the World 9A. Elsevier Scientific, Amster-

dam. pp 483–487

Kuiters AT (1990) Role of phenolic substances from decom-

posing forest litter in plant-soil interactions. Acta Bot

Neerl 39:329–348

Ludwig B, Khanna PK, Anurugsa B et al (2001) Assessment of

cation and anion exchange and pH buffering in an Ama-

zonian Ultisol. Geoderma 102:27–40

Luizao FJ (1996) Ecological studies in three contrasting forest

types in central Amazonia. Ph.D. thesis, University of

Stirling

Luizao RCC (1994) Soil biological studies in contrasting types

of vegetation in central Amazonian Rain Forests. Ph.D.

thesis, University of Stirling

Medina E, Cuevas E (1989) Patterns of nutrient accumulation

and release in Amazonian forests of the upper Rio Negro

basin. In: Proctor J (ed) Mineral nutrients in tropical

forests and savannas. Blackwell Scientific Publications,

Oxford

Miyamoto K, Rahajoe JS, Kohyama T (2007) Forest structure

and primary productivity in a Bornean heath forest. Bio-

tropica 39:35–42

Moran JA, Barker MG, Moran AJ et al (2000) A comparison of

the soil water, nutrient status, and litterfall characteristics

of tropical heath and mixed-dipterocarp forest sites in

Brunei. Biotropica 32:2–13

Nagy L, Proctor J (1997) Plant growth and reproduction on a

toxic alpine ultramafic soil: adaptation to nutrient limita-

tion. New Phytol 137:267–274

Pauletto D (2006) Estoque e producao de liteira grossa em

submetida ao manejo florestal no noroeste de Mato

Grosso. Dissertacao de mestrado, Universidade do

Amazonas

Persson T, Wiren A, Andersson S (1990) Effects of liming on

carbon and nitrogen mineralization in coniferous forest.

Water Air Soil Poll 54:351–354

Pires JM, Prance GT (1985) The vegetation types of Brazilian

Amazon. In: Prance GT, Lovejoy TE (eds). Amazonia.

Pergamon Press, Oxford

Proctor J (1995) Rainforests and their soils. In: Primack RB,

Lovejoy TE (eds) Ecology, conservation, and manage-

ment of Southeast Asian rainforests. Yale University

Press, New Haven

Proctor J (1999) Heath forests and acid soils. Bot J Scotl

51:1–14

Proctor J, Anderson JM, Chai P et al (1983) Ecological studies

in four contrasting lowland rain forests in Gunung Mulu

National Park, Sarawak. I. Forest environment, structure

and floristics. J Ecol 71:237–260

Reis EL (1989) Processo de obtencao de mudas de seringueira

em tubetes. 1. Avaliacao do desenvolvimento das plan-

tulas com diferentes adubacoes. Agrotropica 1:194-197

Richards PW (1996) The tropical rain forest: an ecological

study, 2nd edn. Cambridge University Press, Cambridge

Roem WJ, Klees H, Berendse F (2002) Effects of nutrient

addition and acidification on plant species diversity and

seed germination in heathland vegetation. J Appl Ecol

39:937–948

Rowell DL (1988) Soil acidity and alkalinity. In: Wild A (ed)

Russel’s soil conditions and plant growth. Longman Sci-

entific, Essex

Silver WL (1994) Is nutrient availability related to plant

nutrient use in humid tropical forests? Oecologia 98:336–

343

Skyllberg U (1991) Seasonal variation of pHH2O and pHCaCl2 in

centimeter-layers of mor humus in a Picea abies (L.)

Karst. stand on till soils in northern Sweden. Scand J For

Res 6:3–18

Skyllberg U (1999) pH and solubility of aluminium in acid

forest soils: a consequence of reactions between organic

acidity and aluminium alkalinity. Europ J Soil Sci 50:95–

106

Staaf H (1992) Performance of some field-layer vegetation

species introduced into an acid beech forest with mor soil.

Acta Oecologica 13:753-765

Steen E (1991) Usefulness of the mesh bag method in quan-

titative root studies. In: Atkinson D (eds) Plant root

growth: an ecological perspective. Blackwell Scientific

Publications, Oxford

Tanner EVJ, Kapos V, Freskos S et al (1990) Nitrogen and

phosphorus fertilization of Jamaican montane forest trees.

J Trop Ecol 6:231–238

Vitousek PM, Matson PA (1985) Causes of delayed nitrate

production in two Indiana forests. For Sci 31:122–131

Yano CY (2001) Efeitos da liteira fina sobre a disponibilidade

de nutrientes e o crescimento de plantulas em areas de

Plant Ecol (2007) 192:209–224 223

123

extracao seletiva de madeira na Amazonia Central.

Dissertacao de mestrado, Universidade do Amazonas

White CS (1988) Nitrification inhibition by monoterpenoids:

theoretical mode of action based on molecular structures.

Ecology 69:1631–1633

Whitmore TC (1984) Tropical rain forests of the Far East, 2nd

edn. Clarendon Press, Oxford

Whitmore TC (1990) An introduction to tropical rain forests.

Clarendon Press, Oxford

Zar JH (1984) Biostatistical analysis. Prentice-Hall, Engle-

wood Cliffs

224 Plant Ecol (2007) 192:209–224

123