Decomposition dynamics of Phragmites australis litter inLake Burullus, Egyptpsbi_389 47..56

EBRAHEM M. EID,* KAMAL H. SHALTOUT† and YASSIN M. AL-SODANY*1

*Botany Department, Faculty of Science, Kafr El-Sheikh University, 33516 Kafr El-Sheikh, and †Botany Department, Faculty ofScience, Tanta University, 31527 Tanta, Egypt

Abstract

This study estimated the decomposition rate and nutrient dynamics of Phragmites aus-tralis litter in Lake Burullus (Egypt) and investigated the amount of nutrients releasedback into the water after the decomposition of the dead tissues. Phragmites australisdetritus decomposition was studied from April to September 2003 utilizing the leaf, stem,and rhizome litterbags technique with coarse mesh (5 mm) bags on five sampling datesand with nine replicate packs per sample. All samples were dried, weighed and analyzedfor N, P, Ca, Mg, Na, and K concentrations. The exponential breakdown rate of leaves(-0.0117/day) was significantly higher than that of rhizomes (-0.0040/day) and stems(-0.0036/day). N, Na and K mineralization were the highest from leaf litter, followed byrhizomes and stems, while P, Ca and Mg mineralization were the highest from rhizomes,followed by leaves and stems. The dead shoot biomass at the end of 2003 amounted to4550 g DM/m2 which enters the decomposition process. By using the decay rate of 0.0117and 0.0036/day for the leaves and stems, 3487 g DM/m2 is decomposed in a year, leavingonly 1063 g DM/m2 after 1 year. This is mainly equivalent to releasing the followingnutrients into surrounding water (in g/m2): 24.4 N, 1.1 P, 15.5 Ca, 3.5 Mg, 11.3 Na and16.7 K. In conclusion, the present study indicates a significant difference in relation to thetype of litter; these breakdown rates were generally greater than most rates reported inprevious studies that used the same technique and mesh size.

Keywords: breakdown, litter, Mediterranean lakes, Phragmites australis, wetlands.

Received 12 July 2011; revision received 20 May 2012; accepted 1 June 2012

Introduction

Common reed, Phragmites australis (Cav.) Trin. ex Steudel,is a cosmopolitan angiosperm that is believed to be one ofthe most widely distributed species in the world, rangingall over Europe, Asia, Africa, America, and Australia(Holm et al. 1977). It has broad ecological amplitude, andgrows on soils with different pH, salinity, fertility, andtexture (Eid et al. 2010a). It inhabits shores, littoral zones,and peat bogs with different trophic levels (Haslam 1973;Shaltout & Al-Sodany 2008; Eid et al. 2010a).

Phragmites australis occurs in all Egyptian phytogeo-graphical regions (Täckholm 1974; Zahran & Willis 2009).It has been recorded in the main habitats of Burullus

wetland such as shore and open water of the lake, islets,salt marshes, drains, and sand sheets. Its stands along theshores of this lake and around its islets, which representthe most common vegetation type in Lake Burullus (Shal-tout & Al-Sodany 2008). Reed beds, along the deltaicMediterranean coast of Egypt, are important for winter-ing, foraging, refuge, and breeding of the migrant birds(Kassas 2002). Also, these stands probably play an impor-tant role in the nutrient budget of the Mediterraneancoastal waters and lakes (Eid et al. 2010a,b). The reed bedsalso create a suitable shelter for fishes (particularly fry andjuveniles; Khalil & El-Dawy 2002). This type of habitat isbecoming rare and threatened (Shaltout & Khalil 2005).Thus, Lake Burullus was declared in 1998 as one ofthe Egyptian protected areas and registered as one ofthe Ramsar sites in Egypt (Kassas 2002).

In wetland ecosystems, a considerable part of theorganic material produced is formed by emergent macro-phytes, which play an important role in the detritus food

Correspondence: Ebrahem M. EidEmail: ebrahem.eid@sci.kfs.edu.eg1 Present address: Biology Department, Faculty of Science, TaifUniversity, Taif, Saudi Arabia

Plant Species Biology (2014) 29, 47–56 doi: 10.1111/j.1442-1984.2012.00389.x

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© 2012 The Society for the Study of Species Biology

chain (Gessner & Newell 1997) by supplying an importantnutrient source (van Dokkum et al. 2002). Hence, litterbreakdown is considered a pivotal process in the metabo-lism of wetland ecosystems (Webster et al. 1995; Wallaceet al. 1997), and it provides important information onwetland functioning (nutrient cycling and energy flow;Robinson & Gessner 2003). Phragmites australis occupiesabout 20% of Lake Burullus area (= 8200 ha) with a highprimary production on the order of 54 t/ha (Eid et al.2010b). Such plants of a high primary production canextract large amounts of nutrients from their environ-ment. Consequently, wetland plants could be used toreduce the nutrient content of domestic, industrial, andagricultural wastewater (e.g. Hammer 1989). The recyclingof nutrients is an important function in the aquaticecosystems; hence the dynamics of nutrient cyclingshould be understood in order to properly managehealthy wetland ecosystems that are to be used for pro-ductive purposes such as biomass production or waste-water treatment.

Phragmites australis has a dormant period each year(December–February) during which the shoots die andthe resulting dead matter is returned to the lake substrate.

This material gradually decomposes through a combina-tion of leaching, weathering, and biological actions (Eid2012), and thus the metals and nutrients within the planttissues have the potential to be released back into theenvironment and can provide a short-term sink in thewater of Lake Burullus. However, the rates at which thismaterial decomposes and the release of metals and nutri-ents within Lake Burullus remain poorly understood (Eidet al. 2010b). Thus, the aim of the present study wastwofold: (i) to estimate the decomposition rate and nutri-ent dynamics of P. australis litter at different time intervalsand with coarse-mesh (5 mm) litter bags, using samples ofleaves, stems, and rhizomes, in one of the eutrophic fresh-water coastal Mediterranean lagoons; and (ii) to investi-gate the amount of nutrients released back into the waterafter the decomposition of the dead tissues. We tested thenull hypothesis that the litter components of P. australis(leaves, stems, and rhizomes) have the same rate ofdecomposition and nutrient release. It is important tounderstand the effect of P. australis decomposition on theaquatic ecosystem and could be a precise instrument forformulating efficient strategies related to the managementof P. australis in the Egyptian wetlands.

31° 18` 23``

31° 21` 5``

31° 23` 47``

31° 26` 29``

31° 29` 11``

31° 31` 53``

31° 34` 35``

31° 37` 17``

30` 00``30°

34` 44``30°

37` 54``30°

41` 03``30°

44` 12``30°

47` 21``30°

50` 30``30°

53` 40``30°

56` 50``30°

00` 00``31°

03` 00``31°

06` 19``31°

09` 29``31°

12` 18``31°

Mediterranean Sea

Western Basin

RashidBranch

N 0 5 km

Middle Basin

Eastern Basin*

**

Fig. 1 Map of Lake Burullus (Egypt) indicating the location of the three sampling sites (shown by asterisks).

48 E . M . E I D E T A L .

© 2012 The Society for the Study of Species Biology Plant Species Biology 29, 47–56

Materials and methods

Study area

Lake Burullus is one of the Egyptian northern lakes that isconnected with the Mediterranean Sea through a naturaloutlet called Al-Bughaz. It is bordered to the north by theMediterranean Sea and to the south by agricultural landsof the Nile Delta (Fig. 1). The lake extends for a distance of47 km along a NE–SW axis, with an oblong shape of atotal area of 410 km2. Its main basin can be classified intoeastern, middle, and western basins. The western basin isthe narrowest with a width of � 5 km (in north–southdirection), while the middle basin is the widest with amaximum width of 14 km. The depth of this lake variesbetween 20 cm close to the shore of the eastern basin and200 cm at the middle basin and near the outlet to the sea.A marine sand bar separates the Mediterranean coastfrom the lake shore, with a width that varies between afew hundred meters near the sea outlet to a maximum of6 km in the west. Some 30 islets of different sizes aredistributed within the lake, where they form physical iso-lations between the basins of the lake (Shaltout & Khalil2005).

The main human activity in Lake Burullus is fish pro-duction, with fish yield of 52 000 t/year (Khalil &El-Dawy 2002). Lake Burullus is one of the major disposalareas for agricultural drainage water in Egypt, receivingabout 4 billion m3 of drainage water per year from the NileDelta agricultural lands (El-Shinnawy 2002). It is an alka-line, shallow, brackish, and polluted lake (Table 1). TheMediterranean deltaic coast, in which this lake occurs,belongs to the arid region where the climatic conditionsare warm summers (20–30°C) and mild winters (10–20°C)with an aridity index that ranges between 0.20 and 0.03(UNESCO 1977).

Sampling and mass loss experiment

Samples of leaves, stems, and rhizomes were collectedfrom Lake Burullus in March 2003 using five randomlydistributed quadrats (0.5 ¥ 0.5 m), within a quadrat allP. australis shoots were cut off at ground level and sepa-rated into leaves and stems (without leaf sheath). Rhi-zomes were dug in the same quadrats and down to 0.5 mdepth (the deepest point of rhizome penetration; Eid et al.2010b), and they were washed with lake water till theybecame free from sediment. In the laboratory, sampleswere carefully washed with tap water and then air-driedin the laboratory for 1–2 weeks. The experimental periodstarted when most senescent leaves and culms of the reedplants of the previous growing season were expected tofall down onto the lake sediments. The timing and collect-ing method were chosen to reflect the natural decompo-sition in the lake water (Eid 2012). A random subsample ofleaves, stems, and rhizomes (old and young) materialwere oven-dried at 105°C to constant weight to estimatethe initial oven-dry weight of each bag. Air-dried leaves(9.0 g), stems without leaf sheath (10.0 g), and rhizomes(50% old and 50% young) (10.0 g), were cut to 10 cmpieces, weighed to the nearest milligram and confined inplastic litterbags of 10 ¥ 15 cm with a large enough mesh(5 mm) to allow fluent transport of water, sediments, andorganisms. On April 1, 2003, 135 litterbags were preparedto represent the stems, leaves, and rhizomes (45 litterbagsper organ). Fifteen subsets were prepared; each of ninelitterbags (three bags per organ) bound together withnylon thread, and attached to a bar for incubating 25 cmbelow the water line. Five bars were fixed in each of threesites that represent the eastern basin of Lake Burullus(Fig. 1). One bar was collected monthly from each site(May–September 2003). In the laboratory, the litterbags

Table 1 Characteristics of the commonreed stands (� standard deviation) in LakeBurullus, where the present study wascarried out (Eid et al. 2010b)

Lake Burullus Minimum Maximum Mean

Water characteristicsWater level (cm) 53 � 6 94 � 4 71 � 4Transparency (cm) 20 � 1 60 � 6 53 � 5pH 8.4 � 0.2 8.9 � 0.1 8.7 � 0.1Temperature (°C) 15.1 � 0.7 28.8 � 1.1 23.5 � 4.4Salinity (ppt) 4.0 � 0.7 7.0 � 0.8 5.0 � 0.7Dissolved oxygen (mg/DM3) 8.0 � 2.2† 9.5 � 2.2† 8.7 � 2.3†Total nitrogen (mg/DM3) 173 � 27 361 � 46 250 � 29Total phosphorus (mg/DM3) 20 � 5 204 � 54 81 � 23

Reed characteristicsShoot density (m-2) 76 � 6 228 � 10 139 � 59Shoot height (cm) 169 � 3 364 � 6 265 � 82Culm diameter (mm) 7 � 2 13 � 3 10 � 3Total above-ground biomass (kg/m2) 4.6 � 0.5 7.0 � 0.6 5.4 � 0.6

† Value as in Shaltout and Khalil (2005).

D E C O M P O S I T I O N O F P . A U S T R A L I S 49

Plant Species Biology 29, 47–56 © 2012 The Society for the Study of Species Biology

were thoroughly rinsed with tap water and briefly withsterilized water to remove sediments, lake water, andanimals. Thereafter, the contents were dried at 105°C toconstant weight, and then weighted.

Litter nutrient concentrations

Nutrients were extracted from 0.5–1.0 g of the remainingmass (leaves, stems, and rhizomes) using concentratedHNO3 and HClO4 acids (87:13, v/v; Jones 2001). Ca, Naand K were analyzed using the flame photometer(CORNING M410; Corning Co. Ltd, UK), Mg by atomicabsorption (Shimadzu AA-6200; Shimadzu Co. Ltd,Japan) and P and N by spectrophotometer (CECIL CE1021; Cecil Instruments Ltd, UK) using the ammonium-molybdate and Indo-phenol blue methods, respectively(Allen 1989).

Calculation and data analysis

The data of the three sites were collated, which resulted innine replicates per organ at each sampling date. Thepercentage of the remaining dry mass of P. australiswas calculated using the equation: dry mass remaining

(%) = (Mt/M0) ¥ 100; where Mt is the litter dry massremaining after time t and M0 is the original mass. The drymass remaining was used to determine the decay rateaccording to the single exponential decay model:Mt/M0 = e-kt, where k is the breakdown coefficient (Olson1963). To calculate k, linear regressions of ln (Mt/M0)versus time (0, 30, 60, 90, 120 and 150 days) were per-formed. This model is based on the assumption that thedecomposition rate at time t is proportional to the mass attime t (Gamage & Asaeda 2005). We used the regressionprocedures to evaluate statistical relationships betweenthe time (days) as an independent variable, x, and thepercent of dry mass remaining as a dependent variable, y,of P. australis in Lake Burullus. Nutrient content was cal-culated by multiplying the mass remaining of plant litter(g) by its nutrient concentration (mg nutrient/g litter).Nutrient contents were then expressed as a percent of theinitial content at the beginning of the experiment. We usedthe regression procedures to evaluate statistical relation-ships between the time (days) as an independent variable,x, and the percent of the nutrient content remaining as adependent variable, y. The dead shoot biomass at the endof 2003 amounted to 4550 g DM/m2, which enters thedecomposition process (581 g DM/m2 for leaves and

Fig. 2 Dry mass remaining (%) � stan-dard deviation (vertical bar, n = 9) ofPhragmites australis litter in Lake Burullus,day 0 (April 1, 2003): , stem; ,leaf; , rhizome.Day

0 30 60 90 120 150

Dry

mas

s re

mai

nin

g (

%)

10

20

30

40

50

60

70

80

90

100 Stem: y = 92.79*e(-0.0033*x), R 2 = 0.859, F = 24.5, P = 0.008

Leaf: y = 92.59*e(-0.0189*x), R 2 = 0.879, F = 29.0, P = 0.006

Rhizome: y = 89.51*e(-0.0039*x), R 2 = 0.775, F = 13.8, = 0.021P

Table 2 Breakdown rates of Phragmitesaustralis litter in Lake Burullus. k: exponen-tial breakdown coefficient (day-1): M0, esti-mated initial dry mass (g); Mt, remainingdry mass after time t (g); SD, standarddeviation; R2, coefficient of determination

Litter type k � SD M0 � SD Mt � SD R2

Leaf - 0.0117 � 0.0009 9.02 � 0.31 1.57 � 0.21 0.879Rhizome - 0.0040 � 0.0003 10.00 � 0.34 5.52 � 0.22 0.775Stem - 0.0036 � 0.0002 10.00 � 0.35 5.80 � 0.20 0.859

50 E . M . E I D E T A L .

© 2012 The Society for the Study of Species Biology Plant Species Biology 29, 47–56

3969 g DM/m2 for stems; Eid et al. 2010b). By using thedecay rate of 0.0117 and 0.0036/day1 for the leaves andstems, respectively, 3487 g DM/m2 is decomposed in ayear, leaving only 1063 g DM/m2 after 1 year. The nutri-ent release (g/m2) into the surrounding water was calcu-lated by multiplying the decomposed dry mass in a year(g DM/m2) with the initial nutrient concentration (mg/g1). Estimation of the nutrient content mineralization rate(k, day-1) was calculated based on the changes in litternutrient contents between the initial and final collectiondate using Olson’s (1963) exponential model. To identifydifferences in the decomposition rates of the litter types(leaves versus stems versus rhizomes), one-way anova

was performed with SPSS 15.0 software (SPSS, 2006).Nutrient concentrations and nutrient contents data ofP. australis litters were subjected to two-way anova usingSPSS 15.0 software (SPSS, 2006) to test the differencesbetween litter types over time. The data were tested forvariance homogeneity and normality of distribution andwhen necessary log-transformed.

Results

Mass loss

Changes in dry mass of P. australis leaves, stems, andrhizomes litter versus time are presented in Figure 2. Inthe first month, the mean percentage of mass loss approxi-mated 65.2% in leaves, 32.2% in rhizomes, and 24.5% instems (Fig. 2). In the 150-day study period, leaves lost 83%of their original mass, approximately twice as much asstems (42%) and rhizomes (45%) lost. Our null hypothesiswas not supported because there were significant differ-ences (P < 0.001) in the rates of the decompositionbetween leaves, stems, and rhizomes in the litter of P. aus-tralis. All regressions of the percent dry mass remaining(y) against time (x) were significant (Fig. 2). Estimatedbreakdown coefficients of leaves, stems and rhizomesranged from 0.0036 to 0.0117 per day (Table 2). Decompo-sition rates obtained for reed litter at Lake Burullus weregenerally greater than most of the rates reported in pre-vious studies that used similar methods (Table 3).

Litter nutrient concentrations

Concentrations of N, P, Mg, and Na were found to differsignificantly (P < 0.05) between the different componentsof P. australis litter (Table 4). Litter concentrations of N, P,Na, and K were found to fluctuate significantly (P < 0.05)with time. Initial N, P, and K concentrations in leavesexceeded those in stems and rhizome, while initial Ca,Mg, and Na concentrations in rhizome exceeded thosein stems and leaves (Fig. 3). During the first month, allnutrient concentrations decreased in the components of T

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D E C O M P O S I T I O N O F P . A U S T R A L I S 51

Plant Species Biology 29, 47–56 © 2012 The Society for the Study of Species Biology

Table 4 Results of two-way anova

(F-value) of nutrient concentration (mg/g)of Phragmites australis litter in LakeBurullus

Effect df N P Ca Mg Na K

Litter type 2 29.0*** 4.6* 2.0ns 9.2** 53.6*** 2.7ns

Time 5 7.1** 5.7* 2.0ns 1.3ns 33.6*** 52.1***Litter type ¥ Time 10 15.0*** 142.9*** 25.2*** 67.0*** 4.5*** 76.1***

Litter type: stem, leaf and rhizome; time: 0, 30, 60, 90, 120 and 150 days; d.f., degrees offreedom. * P < 0.05, ** P < 0.01, *** P < 0.001, ns, not significant (i.e. P > 0.05).

N

Co

nc

en

tra

tio

n (

mg

g-1

)

0

2

4

6

8

10

12

14

16

18P

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

K

Day

0 30 60 90 120 1500

2

4

6

8

10

12

14

16Na

Day

0 30 60 90 120 150

Co

nc

en

tra

tio

n (

mg

g-1

)

0

1

2

3

4

5

6

7

8

9

Ca

Co

nc

en

tra

tio

n (

mg

g-1

)

0

1

2

3

4

5

6

7

8

9 Mg

0

1

2

3

4

5

6

7

8

Fig. 3 Nutrient concentration (mg/g) � standard deviation (vertical bar, n = 9) of Phragmites australis litter in Lake Burullus, day 0 (April1, 2003): , stem; , leaf; , rhizome.

52 E . M . E I D E T A L .

© 2012 The Society for the Study of Species Biology Plant Species Biology 29, 47–56

P. australis litter following submersion in the lake. Afterthat, N, P, Na, and K concentrations increased, then theydecreased later (Fig. 3).

Litter nutrient contents

In the present study, all nutrient contents were found tofluctuate significantly (P < 0.01) with time (Table 5). Ournull hypothesis was not supported because there weresignificant differences (P < 0.05) in the nutrient contentsof N, Ca, Mg, and K between leaves, stems, and rhizomesin P. australis litter. At the end of the decompositionperiod (150 days), only 2.1–35.8% of nutrient contentsremained in the leaves component of the litter; 3.1–46.3%of nutrient contents remained in stems; 2.6–27.2% ofnutrient remained in rhizomes (Fig. 4). Most regressionsof the percent nutrient content remaining (y) against time(x) were significant (Fig. 4). N, Na, and K mineralizationwere the highest from leaves, followed by rhizomes andstems, while P, Ca, and Mg mineralization were highestfrom rhizomes followed by leaves and stems (Table 6).

Discussion

The results of the present study suggest two major com-ponents of P. australis litter decomposition: first, rapidleaching of soluble organic compounds, which accountsfor the sharp drop in the dry mass during the first month(Fig. 2), and nutrient elements producing dissolvedorganic matter available to microorganisms; second,physical and biological breakdown of plant litter. The rateof leaching is highly variable and depends on the leafspecies (Cummins et al. 1989). Two thirds of the reed leafdetritus was lost in the first month. Most likely, this is dueto the leaching of easily soluble compounds from leaves(van Dokkum et al. 2002). According to the relevant litera-ture, P. australis rhizomes had a similar exponentialbreakdown rate (k) to the leaves and a higher rate that canbe compared to stems (Dinka et al. 2004; Ágoston-Szabóet al. 2006); but in the present study, rhizomes had anexponential breakdown rate comparable to the stems anda lower rate that can be compared to leaves. Our studysuggests that the lower decomposition rate of P. australisstems in litter comparable to the leaves in litter may be

explained by the lower nutrient concentrations of stems,with a high fiber content and highly sclerenchymatoustissue (Gessner 2000). High fiber content would lead todifferences in the activity of microbial decomposers(Dinka et al. 2004). Substantially lower microbial activityin decomposing P. australis stems, which is comparable toleaves, has been observed by Andersen (1978) and Dinkaet al. (2004). The lower decomposition rate of P. australisrhizomes in litter, which is comparable to leaves in litter,may be explained by the different contents of rhizomelitter bags in the present study; it consisted of old andyoung rhizomes materials pooled together. Old rhizomesare less susceptible to herbivores, mechanical damage,and desiccation compared with leaves (Asaeda & Nam2002), and therefore the mass loss rate of rhizomes waslower than that of leaves.

Decomposition rates of reed in litter in Lake Burulluswere generally greater than most of the rates reported inthe other previous studies for the same species (Table 3).This could be due to the high water concentrations of Nand P in our study area. Decomposition rates are typicallyfaster when nutrient availability is high, either in the watercolumn, or in the plant tissue itself (Webster & Benfield1986; Peterson et al. 1993). Many of the previous studies(Andersen 1978; Suberkropp & Chauvet 1995; Bayo et al.2005) found that N and/or P concentration in water havebeen demonstrated as key factors for determining micro-bial activity, and therefore decomposition rates of plantlitter are different in different types of aquatic ecosystems.Differences also may be partially due to the timing ofexperiment deployment (Asaeda & Nam 2002). InWrubleski et al.’s (1997), with deployment of litter bags inspring, as opposed to winter, resulting in a faster rate ofmass loss. In addition, the favorable thermal and aerobicconditions in the water during the present study (April–September, the warmer months) might contribute to theexplanation of this high breakdown rate, where watertemperature is known to have a strong influence on leaflitter decomposition (Hanson et al. 1984). According toSchlesinger (1997), the decomposition rate doubles withevery 10°C increase in temperature. The use of dried orfresh samples (Gessner 1991) and the timing of materialcollection can also contribute to the observed variance ofreed decay rate (Pinna & Basset 2004).

Table 5 Results of two-way anova

(F-value) of nutrient content (%) of Phrag-mites australis litter in Lake Burullus

Effect df N P Ca Mg Na K

Litter type 2 7.6* 0.9ns 5.5* 4.2* 2.3ns 7.5*Time 5 32.2*** 26.1*** 28.2*** 10.5** 144.1*** 5557.0***Litter type ¥ Time 10 13.2*** 96.9*** 6.8*** 46.7*** 3.8** 0.5ns

Litter type: stem, leaf and rhizome; time: 0, 30, 60, 90, 120 and 150 days; d.f., degrees offreedom. * P < 0.05, ** P < 0.01, *** P < 0.001, ns, not significant (i.e. P > 0.05).

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Plant Species Biology 29, 47–56 © 2012 The Society for the Study of Species Biology

In the present study, all nutrient concentrationsdecreased in the litter of P. australis following submersionin the lake and that could be due to the leaching of solublematerial during the early phase (Gessner 2001). After that,

N, P, Na, and K concentrations increased, which agreeswith previous macrophyte litter submersion studies (e.g.,Polunin 1982; Hietz 1992; Dinka et al. 2004). The increaseof N concentration is thought to be due to fixation of N

N

Nu

trie

nt c

on

ten

t rem

ain

ing

(%)

0

20

40

60

80

100

Days vs Stem_N Days vs Leaf_N Days vs Rhizome_N StemLeafRhizome

P

0

20

40

60

80

100

StemLeafRhizome

Ca

Nu

trie

nt c

on

ten

t rem

ain

ing

(%)

0

20

40

60

80

100Mg

0

20

40

60

80

100

Na

Day

0 30 60 90 120 150

Nu

trie

nt c

on

ten

t rem

ain

ing

(%)

0

20

40

60

80

100K

Day

0 30 60 90 120 1500

20

40

60

80

100

Stem: y = 89.40*e(-0.0091*x)

, R 2 = 0.804, F = 16.4, P = 0.016

Leaf: y = 97.42*e(-0.0363*x)

, R 2 = 0.892, F = 33.1, P = 0.005

Rhizome: y = 88.42*e(-0.0121*x)

, R 2 = 0.661, F = 7.8, P = 0.049

Stem: y = 99.95*e(-0.0838*x)

, R 2 = 0.980, F = 195.6, P = 0.000

Leaf: y = 99.99*e(-0.1183*x)

, R 2 = 0.982, F = 214.1, P = 0.000

Rhizome: y = 102.89*e(-0.0275*x)

, R 2 = 0.951, F = 77.1, P = 0.001

Stem: y = 67.79*e(-0.0018*x)

, R 2 = 0.038, F = 0.2, P = 0.712

Leaf: y = 82.56*e(-0.0137*x)

, R 2 = 0.542, F = 4.7, P = 0.095

Rhizome: y = 89.60*e(-0.0203*x)

, R 2 = 0.670, F = 8.1, P = 0.046

Stem: y = 99.99*e(-0.1096*x)

, R 2 = 0.997, F = 1166.8, P = 0.000

Leaf: y = 99.99*e(-0.1298*x)

, R 2 = 0.999, F = 2776.0, P = 0.000

Rhizome: y = 99.98*e(-0.0873*x)

, R 2 = 0.994, F = 635.4, P = 0.000

Stem: y = 99.72*e(-0.0084*x)

, R 2 = 0.935, F = 57.8, P = 0.002

Leaf: y = 100.36*e(-0.0102*x)

, R 2 = 0.913, F = 41.8, P = 0.003

Rhizome: y = 95.29*e(-0.0090*x)

, R 2 = 0.919, F = 45.2, P = 0.003

Stem: y = 88.34*e(-0.0068*x)

, R 2 = 0.763, F = 12.9, P = 0.023

Leaf: y = 86.11*e(-0.0132*x)

, R 2 = 0.611, F = 6.3, P = 0.067

Rhizome: y = 80.16*e(-0.0107*x)

, R 2 = 0.529, F = 4.5, P = 0.101

Fig. 4 Nutrient content remaining (%) � standard deviation (vertical bar, n = 9) of Phragmites australis litter in Lake Burullus, day 0 (April1, 2003): , stem; , leaf; , rhizome.

54 E . M . E I D E T A L .

© 2012 The Society for the Study of Species Biology Plant Species Biology 29, 47–56

from the atmosphere or water by microorganisms (Mason1976). The microorganisms cause transformation in litterquality (e.g., increase in N concentration) that influencesdecomposition dynamics (Webster & Benfield 1986). Theincrease in P, Na, and K concentrations in the reed littermight be attributed to the uptake by microorganisms fromthe surrounding water (Mason & Bryant 1975; Dinka et al.2004), the colonization and proliferation of microorgan-isms on the decomposing litter (Dinka et al. 2004), and thedifferent fiber compounds decomposing at different ratesover the study period (Ágoston-Szabó et al. 2006).

Nutrient content remaining in P. australis litter at theend of the experiment was presented in Figure 4. Theremaining nutrient contents might be accumulated in thesediment, and can have consequences on the quality andquantity of the sediment organic matter. Further study isneeded for the process of determining the consequencesof the accumulation in sediment on the quality and quan-tity of the sediment organic matter. The dead shootbiomass decomposed after 1 year is mainly equivalent toreleasing the following nutrients into the surroundingwater (in g/m2): 24.4 N, 1.1 P, 15.5 Ca, 3.5 Mg, 11.3 Na and16.7 K. Thus, emergent macrophytes such as P. australisspecies could be a major source of available nutrients in anaquatic ecosystem.

In conclusion, the breakdown rate of leaves in thepresent study was significantly higher than that of rhi-zomes and stems; these breakdown rates were generallygreater than most of the rates reported in previous studiesthat used similar methods. The results of the presentstudy suggest two major components of P. australis litterdecomposition: first, rapid leaching of soluble organiccompounds; and second, physical and biological break-down of plant litter. Decomposing P. australis litter withinwetlands can provide a short-term sink for available nutri-ents in aquatic ecosystems and might be accumulated inthe sediment and can have consequences on the qualityand quantity of the sediment organic matter. Thus, werecommend harvesting and removing the plant materialsimmediately at the end of the growing season to avoidleaching of nutrients from the plant materials to the sedi-ment and water. Harvested plant material could be usedas roof or fencing materials.

Acknowledgments

The first author is most grateful to Mr F. El-Shamly, themanager of Burullus Protected Area for permission andhelp during the field study. We thank the anonymous tworeviewers for their useful comments on an earlier version,and Dr A. H. Salama for English revision.

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