variability of organic matter inputs affects soil moisture and soil biological parameters in a...

Variability of Organic Matter InputsAffects Soil Moisture and Soil

Biological Parameters in a EuropeanDetritus Manipulation Experiment

Istvan Fekete,1 Zsolt Kotroczo,2* Csaba Varga,3 Rita Hargitai,1 KimberlyTownsend,4 Gabor Csanyi,5 and Gabor Varbiro6

1Institute of Environmental Science, College of Nyıregyhaza, 4400 NyıregyhazaSostoi u. 31/B, Hungary; 2Department of Ecology,

University of Debrecen, 4032 DebrecenEgyetem ter 1, Hungary; 3Department of Land and Environmental Management, College ofNyıregyhaza, 4400 NyıregyhazaSostoi u. 31/B, Hungary; 4Department of Botany and Plant Pathology, Oregon State University, 104

Wilkinson Hall, Corvallis, Oregon 97331, USA; 5Vascular Medicine Institute, Department of Pharmacology & Chemical Biology,

University of Pittsburgh, 200 Lothrop Street, Pittsburgh, Pennsylvania 15261, USA; 6Department of Tisza River Research, Balaton

Limnological Research Institute of HAS, 4026 DebrecenBem ter 18/C, Hungary

ABSTRACT

Over the last three decades, increased temperatures

and reduced annual precipitation have resulted in

significant changes in several Central European

deciduous forests. These effects include changes in

soil moisture content and detritus production.

Within the framework of a detritus manipulation

experiment carried out in an old-growth Quercetum

petraea–cerris community, we examined how chan-

ges in detritus inputs affect soil moisture content

and microbial activity within six treatments. CO2

release and microbial enzyme activities are known

to be highly sensitive to environmental factors such

as soil moisture and detritus inputs. We applied

three detritus removal (No Litter, No Roots and No

Input) and two detritus addition (Double Litter

and Double Wood) treatments. Although the plots

received the same amount of precipitation, the

various detritus inputs caused significant differ-

ences in soil moisture. Treatments excluding living

roots had the highest moisture levels, while the

treatment excluding only aboveground detritus

inputs had the lowest. CO2 release, arylsulphatase

activity and saccharase activity showed significant

seasonal differences with the highest values occur-

ring in spring. Moisture content had a significant

positive correlation with CO2 release, and enzyme

activities of the plots were affected by the quantity

and quality of detritus inputs. Arylsulphatase

activity showed the strongest correlation with soil

moisture content (R = 0.62 in the control plot)

followed by CO2 release (R = 0.61) and finally sac-

charase activity (R = 0.42). We observed that there

was a remarkably weaker correlation between soil

moisture content and the three parameters in the

detritus removal treatments (R values between 0.56

and 0.13) than in the Control and detritus addition

treatments (R values between 0.72 and 0.42). The

correlation between the three parameters of interest

and soil moisture content weakens considerably

under drought conditions relative to the optimal

moisture range of soil moisture content for micro-

bial activity. If the amount of precipitation in the

Received 27 September 2011; accepted 15 April 2012;

published online 12 May 2012

Author contributionsIF: laboratory analyses, prepare the manuscript,

suggested statistical evaluation of the data, explanations and conclusions;

ZsK: organized field work and participated in the sampling program,

contributed to compiling the manuscript; CsV: contributed with discus-

sions and laboratory analyses and English translation; RH: data and sta-

tistical analyses; KT: contributed with discussions and improved the

English text and presentation; GCs: contributed and improved the English

text; GV: data and statistical analyses.*Corresponding author; e-mail:

[email protected]

Ecosystems (2012) 15: 792–803DOI: 10.1007/s10021-012-9546-y

� 2012 Springer Science+Business Media, LLC

792

area continues to decrease as anticipated, then litter

production and soil microbial activity may be

reduced.

Key words: CO2 release; soil moisture; enzyme

activity; detritus manipulation; DIRT; oak forest;

climate change.

INTRODUCTION

Since 1972, the Sıkf}okut forest, located in North

Eastern Hungary, has been the focus of extensive

investigation of forest ecosystems. In addition to

ecological examinations, research studies on plant

physiology, dendrology and climatology have been

conducted. These studies were conducted within

the framework of international programs such as

Man and the Biosphere and International Biological

Program. Examination of tree mortality is one of the

most important studies that have been carried out

in Sıkf}okut since the end of 1970s. Long term

meteorological data show clearly that the local

forest climate has become warmer and drier in the

last decades (Antal and others 1997). Climate

change has resulted in significant successional and

structural changes, and detritus production has

decreased compared to measurements taken in

1970s (Toth and others 2007)

Since the initial survey of the tree community in

Sıkf}okut in 1973, 68% of the most prevalent spe-

cies, sessile oak (Quercus petraea), have died (Bow-

den and others 2006). Changes in plant detritus

production combined with macro- and microcli-

matic changes have been shown to have an influ-

ence on microbial processes beyond the effects of

normal seasonal differences (Anderson and others

2004; Boerner and others 2005).

Soil moisture content positively and significantly

correlated with microbial biomass in soils of Q. pet-

raea forests (Baldrian and others 2010). Soil tem-

perature and moisture content have been shown to

affect the rate of soil CO2 release and enzyme

activities (Kang and Freeman 1999; Rustad and

others 2000; Tang and others 2006). Increased

temperature accelerates soil biological processes

only if soil moisture content is within a biologically

suitable range. Li and Sarah (2003b) reported a

decrease in soil enzyme activities under drier con-

ditions. Microbial activity reaches a maximum

when nearly one half to two-thirds of the pore

space is filled with water (Troeh and Thompson

2005). When soil moisture is less than optimum, it

is the lack of moisture, and in saturated soils, it is

the lack of oxygen that hinders the intensity of

microbially driven decomposition and nutrient-

transforming processes in the soil. This decrease

in the rate of microbial processes that recycle

nutrients causes reduction in available nutrients

(Sardans and Pennuelas 2005).

Soil enzyme activities are reliable indicators of

stress effects in ecosystems, thus providing the

opportunity to examine soil health conditions

(Sowerby and others 2005). We chose to look at

arylsulphatase and saccharase. Arylsulphatase

plays an important role in the nutrient cycle, con-

verting organic sulphur into mineral forms that can

be utilized by plants. Arylsulphatase activity cor-

relates significantly with soil organic matter and

moisture contents Strickland and Fitzgerald 1984;

Li and Sarah (2003a).

Saccharase is one of the enzymes responsible for

the decomposition of carbohydrates found in great

abundance in leaf litter (Kayang 2001). Saccharase

activity in the field reveals seasonal dynamics;

however; it is also considerably influenced by the

thickness of the plant detrital layer. A decrease in

soil moisture content reduces saccharase activity

(Li and others 2010). Our previous study has

revealed increased enzyme activities specifically of

phenoloxidase, saccharase and arylsulphatase dur-

ing the wetter spring and late autumn periods

compared to the drier months, at the Sıkf}okut site

(Fekete and others 2007, 2011).

Another important indicator of the intensity of

organic matter decomposition and soil microbial

activity is the extent of CO2 release (Gerenyu and

others 2005; Kotroczo and others 2008). The cli-

mate of a given area (or the weather in the short

term) influences the temporal pattern of maxima

and minima (Grogan and Chapin 1999). Just like

enzyme activity, the CO2 release in soils shows

seasonal dynamics. Soil moisture, temperature and

CO2 release were investigated by Russel and

Appleyard early in the twentieth century (Russel

and Appleyard 1915). Their findings revealed that

CO2 concentration of soil air was primarily deter-

mined by temperature during the cold months and

by soil moisture content in the warmer period.

Atkin and others (2000) and Wan and Luo (2003)

also found that seasonal variations in soil micro-

climate cause considerable differences in CO2

release. Substrate quality and quantity influence

soil CO2 release; the intensity of CO2 release is

determined by labile carbon supply available for

decomposing organisms (Raich and Tufekcioglu

2000). Wildung and others (1975) detected higher

Variability of Organic Matter Inputs 793

CO2 release above 15�C. The effect of soil moisture

on CO2 release is also influenced by the soil tem-

perature. According to Wildung and others (1975),

the increase of moisture content did not influence

the intensity of soil CO2 release significantly below

6�C. Under the climatic conditions of the temperate

zone, CO2 release reaches its maximum in spring

and summer (Gerenyu and others 2005) and

minimum in winter (Raich and others 2002). The

processes influencing soil moisture content and

organic substrate supply have significant impacts

on soil biological activity (Wan and Luo 2003).

Changes in detritus input have great impact on soil

organic matter content, soil moisture content, soil

temperature, pH and soil biological processes.

Many scientific studies report the impact of soil

moisture content on soil biological processes under

laboratory and field conditions (Nadelhoffer and

others 2004; Sayer 2006; Krakomperger and others

2008; Varga and others 2008).

We focused on CO2 release, saccharase and

arylsulphatase activities because they are the

widely used parameters for characterizing soil bio-

logical activity (Mader and others 1993; Albiach

and others 2000; Fierer and Schimel 2003; Zaller

and Kopke 2004; Nsabimana and others 2004;

Amaral and others 2011). These three factors have

been found to correlate strongly with soil moisture

and organic matter contents (Giardina and Ryan

2000; Wan and Luo 2003; Li and Sarah 2003b; Li

and others 2010).

The International Long-Term Ecological Research

(ILTER) DIRT Project including the Sıkf}okut DIRT

Project provided an appropriate framework for our

research. The DIRT project is derived from an

experiment started in forest and grassland ecosys-

tems at the University of Wisconsin in 1957 (Nielson

and Hole 1963). The Sıkf}okut DIRT Project is an

important part of a long term international project

that includes five more experimental DIRT sites

(Nadelhoffer and others 2004) in the USA (Harvard

Forest, Bousson Experimental Forest, H. J. Andrews

Experimental Forest, University of Michigan Bio-

logical Station) and one in Germany (Universitat

Bayreuth BITOK). The general purpose of the pro-

ject is to explore the relationship between the

modifications of detritus production and the changes

of climatic conditions and land use. Our further

objective was to examine the impact of detritus

quality (leaf, wood and root) and quantity on soil

biological activity, soil moisture content and the

relationship between these two factors. Our previ-

ous research revealed that organic matter content,

CO2 release, the rate of litter decomposition and

enzyme activities showed significant differences

because of the treatments applied (Fekete and others

2007, 2008; Kotroczo and others 2008; Varga and

others 2008). Changes in detritus quantity affect soil

ecological parameters such as soil temperature

and soil moisture content. Moreover, these

changes alter—sometimes decrease, sometimes

enhance—the effects of biotic components. The

purpose of this study was to examine the impact of

soil moisture content on enzyme activity and CO2

release in treatments differing in detritus inputs

within the framework of the DIRT project. Our

purpose was to discover whether different detritus

inputs would influence the moisture sensitivity of

soil biological processes. Moreover, we wished to

find the moisture range in which soil moisture

content correlates more strongly with enzyme

activities and CO2 release. We hypothesized that a

significant reduction in detritus input would

decrease the response of biological activity (together

with enzyme activities and CO2 release) to changes

in soil moisture content.

MATERIAL AND METHODS

Study Area and Experimental Design

The experimental site of 27 ha is located in the

southern part of the Bukk Mountains in North

Eastern Hungary at 325 m altitude. GPS coordi-

nates are N 47�56¢ E 20�25¢. This forest has been

protected since 1976, and is part of the Bukk

National Park at present. The annual precipitation

is about 550 mm, of which 20–25% falls in May–

June. This forest is a semi-natural stand (Quercetum

petraeae–cerris community) with no active man-

agement since 1976. Based on the data from 2003

to 2005, litter production consists of the following

tree species in decreasing order: Q. petraea, Quercus

cerris, Acer campestre, and Cornus mas. During the

same period the average leaf-litter production was

3326 kg ha-1 and the average amount of total

aboveground detritus (including branches, twigs,

fruit and buds) was 6572 kg ha-1 (Toth and others

2007). The soil type according to the WRB Soil

Classification is Cambisol.

The Sıkf}okut DIRT Project was launched in

November 2000. Six treatments were applied in the

experimental site. Detritus input was not manipu-

lated in the Control plot (C). There were two types

of detritus addition plots: double the normal

amount of leaf litter was applied to the Double

Litter (DL) plots, whereas in the Double Wood plot

(DW) the amount of wood detritus (branches, twigs

and bark) was doubled. In three treatments, detri-

tus inputs were removed: aboveground detritus

794 I. Fekete and others

from the No Litter plots (NL), living roots from the

No Roots plots (NR), and both aboveground detri-

tus and living roots from No Inputs plots (NI). The

detailed description of the treatments can be found

in Nadelhoffer and others (2004), Sulzman and

others (2005), Fekete and others (2007), and

Kotroczo and others (2008). Each plot is 7 9 7 m

(49 m2), and every treatment was replicated three

times. Plots were designed in a completely random

way and are characterized by the same soil com-

position, plants distribution and slope of land.

Soil Sampling and Measurements

Soil samples were collected randomly; five cores to

15 cm were taken from each plot. The cores were

extracted with an Oakfield auger (Oakfield Appa-

ratus Company, USA). The samples were homog-

enized and stored for one week at 4�C.

To measure soil temperature, one StowAway�

TidbiT� data-logger (Onset Computer Corporation,

USA) was placed 10 cm deep at the center of each

plot. We have been measuring soil temperature

since March 2001. The data-loggers take measure-

ments every hour. The data were downloaded once

a year.

Soil moisture content was determined by drying

the samples at 105�C for 24 h. Arylsulphatase

activity was measured 15 times and saccharase

activity 13 times between June 2004 and October

2006. Each treatment consisted of three plots, and

each sampling was replicated three times, and so

nine values were obtained at each measurement.

With the exception of three occasions, the samples

were taken at the same time. The examinations

were carried out during the growing season (sam-

pling ceased from December until March). Aryl-

sulphatase activity was measured as described

previously (Schinner and others 1996) using a

Perkin Elmer Lambda 5 UV–VIS spectrophotome-

ter. Saccharase activity was measured according to

Frankenberger and Johanson (1983).

The method of Jenkinson and Powlson (1976)

was used to measure soil CO2 release. It consists of

a laboratory examination of the soil samples and

shows the CO2 release of soil microorganisms (and,

to a lesser extent, that of the mesofauna living in

the soil). Production of CO2 was measured 13 times

from June 2004 to May 2007.

Applied Statistical Methods

The statistical analyses of the data were conducted

using Statistica 7.0 and Microsoft� Office 2003

Excel�. Random sampling and the independence of

sample elements were ensured by the experimental

procedure established. The homogeneity of the

variances was examined by Fmax-probe. Correlation

analyses, paired-sample t test and variance analyses

were also applied. Moisture contents of the plots

were compared by ANOVA. When groups were

significantly different, ANOVA were completed

with Tukey’s HSD test. A value of p £ 0.05 was

considered to be statistically significant. The

homogeneity of slopes was tested by one-way

ANCOVA (Analysis of Covariance). An F test for

the equality of slopes of regression lines was per-

formed. The treatments were divided into two

groups: one involved detritus input (DL, DW and

C), whereas the other involved detritus removal

(NL, NR and NI). The differences between the two

groups were analyzed by Principal Component

Analysis (PCA) using Past statistical software

(Hammer and others 2001).

RESULTS

Effect of Detritus Input on Soil MoistureContent

Soil moisture content was more uniform in NR and

NI treatments than in the others throughout the

year. Soil moisture content was higher by 35–50%

in root exclusion treatments (NR and NI) than in

the others during the drier summer and autumn

months. (The values measured before 22nd June

belong to the set of spring observations, whereas

those before 23rd September to the summer set).

The difference in soil moisture between treatments

was remarkably smaller in spring (Table 1). Even

the minimum values were higher in these two

treatments as compared to the other ones (NR =

25.9%, NI = 21.5%, C = 14.5%, NL = 13.5%, DL =

15.1% and DW = 13.8%). Although the lowest mean

moisture content was measured in the NL treatment,

it did not differ significantly from the values of the C,

DL and DW treatments. In drier periods, when soil

moisture content in C plots did not reach 25% soil

moisture content was significantly higher in root

exclusion treatments (NR, NI) as compared to the

four other treatments (p < 0.001; F(5;42) = 26.26)

(Tables 5, 6, 7).

Seasonal Dynamics of Soil BiologicalActivity

Measurements of soil CO2 release, enzyme activi-

ties and soil moisture content all had the highest

values in spring. The mean soil CO2 release value of

the six treatments in spring was significantly higher

(p < 0.001; N = 24) by 38.2% than in summer and


Tab

le1.

Seaso

nal

an

dTota

lM

ean

Valu

es

an

dSta

ndard

Err

ors

of

Ary

lsu

lph

ata

seA

ctiv

ity,Sacc

hara

seA

ctiv

ity,

Soil

CO

2R

ele

ase

an

dSoil

Mois

ture

Con

ten

tin

Term

sof

the

Tre

atm

en

ts

AS

pri

ng

Su

mm

er

Au

tum

nT

ota

l

CO

2re

lease

Mois

ture

CO

2re

lease

Mois

ture

CO

2re

lease

Mois

ture

CO

2re

lease

Mois

ture

DL

24.4

4±

1.4

229.1

9±

2.6

817.0

1±

1.1

217.0

4±

1.0

016.1

5±

1.0

918.2

8±

1.0

118.9

8±

0.9

021.2

5±

1.2

7

DW

23.8

0±

1.0

630.3

3±

2.4

015.3

0±

1.1

217.9

1±

0.9

015.6

3±

1.1

118.9

3±

1.1

518.0

4±

0.9

022.1

3±

1.2

5

C23.2

2±

1.0

428.5

6±

2.4

214.9

7±

1.2

017.7

0±

0.6

214.9

1±

0.9

319.3

1±

1.2

417.4

9±

0.8

521.6

6±

1.1

6

NL

17.4

5±

0.8

025.3

2±

1.9

911.7

1±

1.0

317.0

8±

0.7

013.1

9±

1.0

819.0

6±

1.4

314.0

5±

0.6

820.3

8±

0.9

9

NR

20.6

3±

1.3

235.1

6±

1.6

617.1

5±

1.4

631.2

4±

0.8

718.8

9±

1.3

732.0

7±

1.2

018.8

9±

0.8

232.7

6±

0.7

7

NI

19.0

4±

1.5

331.0

6±

2.0

416.7

6±

1.4

428.9

3±

0.9

916.8

4±

1.3

229.6

6±

1.1

717.4

9±

0.8

229.8

7±

0.8

2

BA

ryls

ulp

hata

seact

ivit

yM

ois

ture

Ary

lsu

lph

ata

seact

ivit

yM

ois

ture

Ary

lsu

lph

ata

seact

ivit

yM

ois

ture

Ary

lsu

lph

ata

seact

ivit

yM

ois

ture

DL

2.7

5±

0.3

333.5

±2.1

51.7

8±

0.1

422.4

±1.4

71.4

4±

0.1

918.3

±1.0

11.9

9±

0.1

624.2

9±

1.3

5

DW

3.0

7±

0.2

834.4

±1.3

01.7

6±

0.1

623.4

±1.4

91.6

4±

0.2

218.9

±1.1

52.1

5±

0.1

625.4

6±

1.2

5

C2.5

5±

0.2

832.4

±1.3

21.7

6±

0.1

322.6

±1.2

61.5

1±

0.2

219.3

±1.2

41.9

4±

0.1

424.7

8±

1.1

0

NL

1.7

4±

0.2

628.1

±1.2

01.0

3±

0.1

020.4

±1.1

30.8

8±

0.1

319.1

±1.4

31.2

2±

0.1

222.5

0±

0.9

3

NR

1.9

5±

0.2

537.3

±0.7

41.1

4±

0.0

832.1

±1.2

50.9

3±

0.1

032.1

±1.2

01.3

4±

0.1

133.8

5±

0.7

2

NI

1.5

6±

0.9

033.2

±0.8

01.0

8±

0.0

927.3

±1.0

21.0

1±

0.1

329.7

±1.1

71.2

2±

0.0

730.0

6±

0.6

7

CS

acc

hara

seact

ivit

yM

ois

ture

Sacc

hara

seact

ivit

yM

ois

ture

Sacc

hara

seact

ivit

yM

ois

ture

Sacc

hara

seact

ivit

yM

ois

ture

DL

4.4

0±

0.3

533.5

±2.1

33.8

1±

0.2

520.8

±2.3

24.0

2±

0.2

818.3

±1.1

84.0

1±

0.1

725.5

2±

1.5

7

DW

4.9

6±

0.2

834.0

±1.6

03.8

0±

0.1

823.1

±2.4

83.9

8±

0.3

318.9

±0.9

54.2

3±

0.1

726.7

7±

1.3

9

C4.5

7±

0.2

932.4

±1.3

74.0

7±

0.1

821.8

±1.7

74.4

0±

0.3

119.3

±1.3

54.3

4±

0.1

525.7

8±

1.2

5

NL

4.1

9±

0.3

328.1

±1.2

53.3

9±

0.2

319.0

±1.5

54.0

0±

0.4

019.1

±1.6

63.9

4±

0.1

923.2

5±

1.0

5

NR

3.8

2±

0.1

837.3

±0.6

93.4

3±

0.2

229.6

±0.5

83.7

0±

0.4

132.1

±1.2

93.6

2±

0.1

533.5

6±

0.7

6

NI

3.4

2±

0.2

933.2

±0.7

12.8

4±

0.3

025.5

±0.5

23.3

8±

0.3

229.7

±1.4

63.1

9±

0.1

630.1

4±

0.7

6

AC

O2

rele

ase

(mg

CO

2100

g-1

soil

10

days

-1),

Bary

lsu

lph

ata

se(l

gpN

Pg

soil

-1

h-

1),

Csa

cch

ara

se(m

ggl

uco

seg

soil

-1

24

h-

1).


by 39.6% than in autumn. The mean value of

arylsulphatase activity in spring was also signifi-

cantly higher (p < 0.001; N = 30) by 59.3% than in

summer and 83.5% than in autumn. Although

saccharase activity in spring was higher by 18.9%

than in summer and by 8.1% than in autumn, the

differences at this parameter were not significant.

In spring, mean CO2 efflux in DL, DW, C and NL

plots was higher by 12.1% than in NR and NI plots.

However, in autumn, CO2 efflux in root exclusion

treatments (NR and NI) was higher by 19.2% and

in summer by 15%. The mean saccharase activities

in DL, DW, C and NL plots were higher by 25.1%

than in root exclusion treatments in spring and by

15.8% in autumn. The mean arylsulphatase activ-

ity in DL, DW, C and NL plots were higher by 44%

than in root exclusion treatments in spring and by

41% in autumn.

The mean soil temperature was the highest in the

summer months (DL: 16.2�C, DW: 15.9�C, C:

15.8�C, NL: 16.4�C, NR: 17.2�C and NI: 16.9�C).

However, in our research, the relationship between

soil CO2 release and temperature could not be

demonstrated. Soil temperature measured at sam-

pling did not correlate with CO2 release according

to the statistical analyses. No correlation was found

between the enzyme activities and soil temperature

either.

Correlation Between Soil MoistureContent and Soil Biological Parameters

The relationship between CO2 release, enzyme

activity and moisture content was also shown by

regression analyses (Tables 2, 3, 4, 5, 6, 7). Soil

moisture content correlated the most strongly with

arylsulphatase activity, but the most weakly with

saccharase activity. Soil CO2 release and enzyme

activities correlated better with soil moisture con-

tent in control and litter addition treatments than

in litter removal ones. This correlation was the

strongest in the wet spring period.

In wetter periods, when soil moisture content in

C plots reached 25%, soil CO2 release and enzyme

activities were higher than in drier periods. With

higher soil moisture content, the parameters of

interest and moisture content exhibited higher

slope values and stronger correlations in the C, DL

and DW plots than in the plots involved in detritus

removal (Tables 2, 3, 4, 5, 6, 7). The strongest

Table 2. Relationship Between Soil Moisture Content and CO2 Release from 2004 to 2007

Spring Summer Autumn Total

R Slope R Slope R Slope R Slope

DL 0.88* 0.4242 0.23NS 0.5712 0.31NS 0.2161 0.72* 0.5205

DW 0.94* 0.4165 0.65* 0.5702 -0.44NS 0.5085 0.69* 0.5790

C 0.81* 0.2787 0.52NS 0.7179 -0.39NS 0.3326 0.61* 0.5582

NL 0.02NS 0.113799 0.34NS 0.6021 -0.32NS 0.1660 0.24NS 0.292599

NR 0.29NS 0.2077 0.34NS 0.4347 -0.08NS 0.4388 0.22NS 0.3687

NI 0.54NS 0.2449 0.42NS 0.7318 -0.04NS 0.4928 0.35NS 0.4793

R Pearson correlation coefficient.*p £ 0.05; NSp > 0.05; 99significant difference compared to control slope (one-way ANCOVA).

Table 3. Relationship Between Soil Moisture Content and Arylsulphatase Activity from 2004 to 2006



DL 0.79* 0.1217 0.78* 0.1481 0.43NS 0.0625 0.72* 0.0828

DW 0.76* 0.1299 0.77* 0.1813 0.52* 0.0990 0.70* 0.0897

C 0.73* 0.1338 0.59* 0.1674 0.47* 0.0880 0.62* 0.0794

NL 0.67* 0.0883 0.54* 0.1414 0.50NS 0.0478 0.56* 0.0697

NR -0.01NS 0.005299 -0.22NS 0.021699 0.19NS 0.0155 0.40* 0.0620

NI 0.75* 0.0865 0.15NS 0.011999 0.22NS 0.0222 0.39* 0.0405



correlation was observed in spring (Tables 2, 3, 4).

The difference in CO2 release and enzyme activity

between detritus removal treatments and the other

treatments was greater in the wetter periods than

in the drier periods. Moreover, CO2 release in NR

plots was higher than in other treatments in drier

periods.

As for soil CO2 release and enzyme activities,

statistically significant differences were detected

between the treatments among the drier and the

wetter periods (Tables 5, 6, 7). According to Tukey’s

HSD test, CO2 release was significantly higher

(F(5;66) = 4.89; p = 0.0007) in NR, NI and DL plots

than in NL. Among wet conditions significantly

higher (F(5;156) = 5.17; p = 0.0002) CO2 release was

measured in DL, DW and C plots as compared to

NL. Soil CO2 release in DL plots was not signifi-

cantly higher than in NI but the difference was

close to significant (p = 0.058). In drier periods,

arylsulphatase activity was significantly higher

(F(5;120) = 6.52; p < 0.0001) in C, DL and DW plots

than in NL. Moreover, it was significantly higher in

DW plots than in NI and NR. Among wet condi-

tions arylsulphatase activity was significantly

higher (F(5;138) = 8.46; p < 0.0001) in C, DL and

DW plots than in the litter removal treatments. In

drier periods, saccharase activity was significantly

higher (F(5;102) = 3.61; p = 0.005) in C plots than in

NI. However, in wetter periods, it was significantly

higher (F(5;120) = 4.21; p = 0.001) in C and DW

plots than in NI. According to principal component

analysis, although there is some overlap, the two

groups of treatments (detritus removal and detritus

input) showed remarkable differences (Figure 1).

Table 5. Total Mean Values and Standard Errors of Arylsulphatase Activity and Soil Moisture Content inTerms of the Treatments with Soil Moisture Content Below 25% (A) and Over 25% (B) in the Control andRelationship Between Soil Moisture Content and Arylsulphatase Activity from 2004 to 2006

Arylsulphatase activity

(lg pNP g soil-1 h-1)

Moisture (% w/w) R slope p (same) p (equal)

A

DL 1.41b ± 0.13 18.54a ± 1.22 0.42* 0.0744 NS NS

DW 1.42b ± 0.14 19.97ab ± 1.52 0.31 0.0571 NS NS

C 1.43b ± 0.13 19.61a ± 1.09 0.33 0.0762

NL 0.90a ± 0.11 18.25a ± 1.08 0.38 0.0388 0.011 NS

NR 1.04ab ± 0.09 29.66c ± 0.89 0.33 0.0343 >0.001 NS

NI 1.02ab ± 0.11 26.08bc ± 0.67 0.31 -0.0510 0.007 0.009

B

DL 2.49b ± 0.22 28.13a ± 1.76 0.61* 0.0803 NS NS

DW 2.64b ± 0.02 29.12a ± 1.45 0.68* 0.0937 NS NS

C 2.38b ± 0.19 28.23a ± 1.33 0.52* 0.0917

NL 1.48a ± 0.17 25.33a ± 1.08 0.49* 0.0789 0.003 NS

NR 1.59a ± 0.17 36.65b ± 0.60 0.27 0.0512 >0.001 NS

NI 1.35a ± 0.08 32.71ab ± 0.63 0.39* 0.0686 >0.001 NS

*There is significant relation between soil moisture content and arilsulphatase activity; p (same) ANCOVA test results between C and the given treatments; p (equal) significancetest of the equality of slopes. Different letters indicate significant difference.

Table 4. Relationship Between Soil Moisture Content and Saccharase Activity from 2004 to 2006



DL 0.77* 0.1264 0.26NS 0.0264 0.35NS 0.1069 0.43* 0.0676

DW 0.88* 0.1931 0.44NS 0.0362 0.66* 0.1427 0.64* 0.0749

C 0.77* 0.1678 -0.31NS 0.0522 0.56* 0.1184 0.42* 0.0762

NL 0.77* 0.1952 0.31NS 0.0393 0.44NS 0.0284 0.40* 0.0532

NR 0.24NS 0.0742 -0.03NS 0.0030 0.01NS 0.003899 0.13NS 0.0263

NI 0.47NS 0.1452 -0.09NS 0.0132 0.31NS 0.0748 0.31NS 0.0337



The detritus input treatments resulted in higher

CO2 release and enzyme activity values; whereas

detritus removal reduced those measured lower

values.

DISCUSSION

The significantly higher soil moisture content val-

ues in NR and NI plots can be explained by the fact

that at the beginning of the experiment plants were

removed and new plants were not permitted to

grow in these plots. Plants, especially large tree

species can take up large quantities of water from

soil to compensate for their transpiration water

deficit (Howard and Donovan 2007; Zeppel and

others 2010). In NR and NI treatments, roots were

excluded by inserting barriers around the plots to

prevent root growth into the area, which has

Table 6. Total Mean Values and Standard Errors of Saccharase Activity and Soil Moisture Content in Termsof the Treatments with Soil Moisture Content Below 25% (A) and over 25% (B) in the Control and Rela-tionship Between Soil Moisture Content and Saccharase Activity from 2004 to 2006

Saccharase (mg glucose

g soil-1 24 h-1)


A

DL 3.80ab ± 0.19 16.12a ± 0.74 0.08 -0.0181 NS NS

DW 3.69ab ± 0.15 17.42a ± 0.97 0.09 0.0444 NS NS

C 4.10b ± 0.19 17.89a ± 1.03 0.23 0.0516

NL 3.79ab ± 0.16 17.67a ± 1.65 0.05 0.0171 NS NS

NR 3.50ab ± 0.27 28.58b ± 1.12 0.27 -0.0596 NS NS

NI 3.03a ± 0.24 25.82b ± 0.97 0.16 -0.0470 0.011 NS

B

DL 4.20ab ± 0.22 28.81a ± 1.65 0.53* 0.0841 NS NS

DW 4.69b ± 0.18 29.89a ± 1.39 0.60* 0.0935 NS NS

C 4.55b ± 0.19 28.41a ± 1.26 0.54* 0.0840

NL 4.15ab ± 0.25 25.11a ± 1.06 0.55* 0.1099 NS NS

NR 3.72ab ± 0.19 35.21b ± 0.88 0.30 0.1579 0.003 NS

NI 3.31a ± 0.20 31.57ab ± 0.88 0.49* 0.1892 >0.001 NS

*There is significant relation between soil moisture content and saccharase activity; p (same) ANCOVA test results between C and the given treatments; p (equal) significance testof the equality of slopes. Different letters indicate significant difference.

Table 7. Total Mean Values and Standard Errors of CO2 Release and Soil Moisture Content in Terms of theTreatments with Soil Moisture Content Below 25% (A) and over 25% (B) in the Control and RelationshipBetween Soil Moisture Content and CO2 Release from 2004 to 2006

CO2 release (mg CO2 100

g-1 soil 10 days-1)


A

DL 16.45b ± 0.80 16.81a ± 0.51 0.22 0.4416 NS NS

DW 15.49ab ± 0.81 17.75a ± 0.75 0.47* 0.5056 NS NS

C 14.99ab ± 0.74 17.46a ± 0.50 0.16 0.2384

NL 12.50a ± 0.74 17.00a ± 0.67 0.15 0.2692 0.048 NS

NR 17.91b ± 1.01 30.35b ± 0.70 0.18 0.6194 NS NS

NI 16.02b ± 1.09 27.55b ± 0.77 0.50* 0.1747 0.021 NS

B

DL 24.70b ± 1.53 30.80ab ± 1.75 0.77* 0.8978 NS NS

DW 23.79b ± 0.76 32.67ab ± 1.41 0.87* 0.5883 NS NS

C 23.11b ± 1.18 31.22bc ± 1.36 0.66* 0.5604

NL 17.52a ± 0.92 27.77a ± 1.30 0.46 -0.3214 0.004 0.005

NR 21.10ab ± 1.24 38.26c ± 0.45 0.15 -0.4097 0.035 NS

NI 20.94ab ± 1.40 34.92bc ± 1.12 0.14 -0.1723 0.072 0.099

*There is significant relation between soil moisture content and CO2 release; p (same) ANCOVA test results between C and the given treatments; p (equal) significance test of theequality of slopes. Different letters indicate significant difference.


eliminated transpiration and its reducing effect on

soil moisture content.

The surface leaf litter layer also had an influence

on soil moisture content, though to a lesser, non-

significant extent. The litter layer has considerable

impact on soil microclimate (Sayer 2006). This

layer prevents soil from drying out, but in the case

of lower precipitation, the dry litter retains water

from soil. Bernhardt and others (2006) found that

the presence of greater litter decreased evaporation

because of the insulating properties of the litter.

The present study demonstrated that decreased

surface leaf litter decreased soil moisture content in

the area. Therefore, the annual mean moisture

content in NR was 11.9% higher than in NI and

9.2% higher in C than in NL.

The highest values of CO2 release and enzyme

activities were measured in the spring. This can be

attributed to the increased soil moisture content

because of snowmelt and spring rains (Conant and

others 2000). Wet soils provide favorable circum-

stances for the reproduction of microbes (to a cer-

tain extent) that contribute to soil CO2 release and

an increase in enzyme activities (Rastin and others

1988). Soil CO2 release in NR and NI plots lag

behind the means of other plots to the largest

extent in spring. This is explained by the fact that

there is no water deficit at the site in the spring

(Fuzy and others 2008). On the other hand, the

quantity of rhizosphere labile C supplied by pho-

tosynthesis available for soil CO2 release increases

in spring and summer (Wan and Luo 2003; Villanyi

and others 2006). This important part of the C

supply is absent from NR and NI plots, which

also decreases the CO2 efflux. This effect can be

observed in enzyme, mainly of saccharase, activity.

The roots, rhizosphere and ectomycorrhizal fungi

can enhance enzyme activities and CO2 release

in soil (Abuzinadeh and Read 1986; Courty and

others 2006). Lack of rhizosphere decreases CO2

release and enzyme activities in NR- and NI-treated

plots.

In spring, in contrast to other seasons, it was not

only the higher soil moisture content, but also the

decomposition of autumn litter rapidly accelerated

after the cold winter months, which contributes to

the increase in the quantity of available substrates.

This effect can sometimes be also realized during

the summer, thus enhancing the intensity of soil

CO2 release. That is why a higher concentration of

CO2 release was measured for some treatments in

the summer than the autumn in spite of the slightly

higher soil moisture content in autumn. In the

Andrews DIRT site, which contains the same

treatments as the Sıkf}okut DIRT site, soil CO2

release peaks were measured exclusively in sum-

mer (Sultzman and others 2005). This can be

explained by two facts. Firstly, the Andrews DIRT

site is located on the western slope of the Cascade

Mountain where the annual precipitation is about

Figure 1. Scatter plot view

of the data of the different

plots showing their scores

or correlations to the first

and second principal

components. The convex

hulls represent the

different treatment

groups (filled circle input

treatments with soil

moisture content <25%,

and addition symbol input


moisture content >25%,

open square removal


moisture content <25%,

multiplication symbol

removal treatments with

soil moisture content

>25%).


four times higher than in Sıkf}okut. Secondly, in the

Andrews DIRT site, soil CO2 release was measured

by a field method (IRGA) influenced by soil tem-

perature.

According to the statistical analyses, enzyme

activities and soil CO2 release correlated positively

with the soil moisture content; although there were

great differences between the treatments. In the

treatments involving detritus removal (NL, NR, and

NI), a much weaker correlation was found between

soil moisture content and both the enzyme activities

and soil CO2 release compared with the other three

treatments (DW, C and DL). This can be explained by

the fact that litter removal creates a smaller nutrient

supply in the soil. Our previous research showed that

the greater amount of detritus input of DL, DW and C

resulted in a significantly higher soil organic matter

content compared with treatments involving detri-

tus removal (Varga and others 2008). Therefore,

independent of the moisture conditions, the lower

nutrient supply does not allow the metabolism of

decomposers, which might intensify the CO2 release

and the enzyme activities of soils. The reduction in

detritus inputs (NR, NL and NI treatments) creates a

decrease in the quantities of exoenzymes and sub-

strates, which leads to the reduction of soil enzyme

activity of microbial origin (Ladd 1978). These pro-

cesses were observed in all of the enzymes examined

previously at Sıkf}okut: phosphatase, b-glucosidase

and phenoloxidase (Fekete and others 2007; Krak-

omperger and others 2008).

The correlations between soil moisture content

and enzyme activities, and moisture content and

CO2 release were the lowest in the NR and NI

treatments. In addition to the above mentioned

reasons, it can also be explained by the soil mois-

ture content of 34% in the NR and 30% in the NI

plots, which were 130–140% of the values mea-

sured in the other plots. The lower moisture con-

tent of the NL plots was caused by the lack of litter,

allowing for increased evaporation from the soil

surface. Moisture content throughout the year was

the most consistent in the NR plots. Here, the

highest value was 1.5 times as high as the lowest,

whereas in the other plots it was three times (with

the exception of the soil moisture content of NI).

The more consistent moisture content influenced

microbial processes to a lesser extent, which is

illustrated by the low value of R between the

examined parameters. The method, which

involved a laboratory experiment with a long

incubation period prevented the values of soil CO2

release and enzyme activities from correlating with

those of soil temperature. However, our previous

soda lime experiments in the field had revealed a

correlation between soil temperature and CO2

release among Sıkf}okut DIRT treatments (Kotroczo

and others 2008).

Litter removal substantially reduced biological

activity under conditions of optimal soil moisture

content. Below 25% moisture content, differences in

soil CO2 release and enzyme activities were low

between the treatments. These findings could be

explained by the insufficient moisture, which

resulted in less efficient decomposition activity of soil

microorganisms—despite the substrate availability.

That is why enzymeactivityand soil CO2 release in NL

resulted in smaller differences compared to Control

and detritus addition treatments (DL and DW) with

higher moisture content. On the other hand, the soils

inNRand NIare relativelywetter, even indry periods,

so that during the dry summer period, they can show

a higher activity of measured parameters.

However, with moisture content of the control

treatment above 25%, the effects of different litter

inputs are more obvious, the differences in activity

levels become greater (between the treatments), as

shown by our statistical analyses. Several research-

ers have previously found a significant correlation

between arylsulphatase and saccharase activities

and moisture content (Li and Sarah 2003a; Li and

others 2010). Luo and Zhou (2006) found lower soil

CO2 release under dry conditions and a maximal rate

at intermediate soil moisture levels. Gerenyu and

others (2005) found that the optimal water capacity

is 50–70%. This range corresponds to a moisture

content of 25–35% w/w. The results of regression

analysis showed that, above and below this range,

the correlation between soil moisture content and

the examined parameters weakens or breaks down

completely. In drier soils, both the metabolisms of

the decomposing microorganisms and the nutrient

transport become slower.

Excessive moisture content can also reduce soil

biological activity—decreasing CO2 release and

enzyme activity (Troeh and Thompson 2005; Lin

and others 2011). Under these circumstances, the

lack of oxygen can negatively affect soil biological

activity when moisture content is above the opti-

mum level. When the moisture content is above

35%, R and slope values were lower both between

moisture content and CO2 release, and moisture

content and arylsulphatase activity in the NR plots.

Regarding the NI plots within the same moisture

range, the correlation between moisture content

and CO2 release was not as strong; R and slope

values were lower.

ANOVA, Tukey’s HSD-test and regression anal-

ysis showed that the examined parameters (CO2

release, arylsulphatase and saccharase activities)


respond with different sensitivities to changes in

soil moisture content and detritus input. The sen-

sitivity of these changes decreases in the following

order: arylsulphatase activity > CO2 release >

saccharase activity.

CONCLUSION

Detritus and living roots greatly affect soil moisture

content. In the experimental site, the cleared plots

showed higher moisture contents because of the

lack of transpiration than the plots covered by

plants. Although evaporation from the vegetation-

free soil surface increases, it cannot compensate for

the lack of transpiration. Healthy functioning of soil

microbes requires a balance of the appropriate level

of soil moisture in addition to sufficient detritus

inputs to provide adequate nutrients. If either of

these factors are altered because of climate or land

use changes, then the activity of soil microorgan-

isms will considerably decrease, which might affect

soil nutrient supply and cycling. Our examinations

showed that increasing detritus input enhances the

stimulating effect of soil moisture content on

microbial activity, whereas detritus reduction hin-

ders this effect, or occasionally eliminates it. The

stimulating effect was the strongest around the

optimal range of soil moisture content. In drier or

wetter soils, the changes in moisture content

affected microbial activity to a lesser extent.

Moreover, correlation was not detectable in

extremely dry or wet soils, which illustrates the

negative effect of weather extremes on soil micro-

organisms. Global climate change increases the

frequency of weather extremes, which might neg-

atively affect soil biological activity as well.

ACKNOWLEDGEMENTS

This research was sponsored by the University of

Debrecen and College of Nyıregyhaza. Special

thanks are due to Bruce Caldwell, Kate Lajtha

(Oregon State University, Corvallis, USA) and

Janos Attila Toth (University of Debrecen, Debre-

cen, Hungary) for establishing the experiment and

supervising this study. The laboratory assistance of

Kovacs Laszlone is highly appreciated. The authors

also wish to thank Ms. Ildiko Huba and Mr. Peter

Fekete for the English version of this article.

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