Ecological Engineering 73 (2014) 454–460

Dynamics of decomposition and nutrient release of leaf litter inKandelia obovata mangrove forests with different ages in JiulongjiangEstuary, China

Ting Li a,b, Yong Ye a,*aKey Laboratory of the Ministry of Education for Coastal and Wetland Ecosystem, College of the Environment and Ecology, Xiamen University, Xiamen,Fujian,Chinab South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China

A R T I C L E I N F O

Article history:Received 7 June 2014Received in revised form 12 September 2014Accepted 29 September 2014Available online xxx

Keywords:MangroveKandelia obovataLeaf litterDecompositionNutrient releaseForest age

A B S T R A C T

Rates of in-situ decomposition and nutrient (organic C, N and P) release of leaf litter were seasonallycompared among three planted Kandelia obovata mangrove forests (K12, K24 and K48 with forest ages of12, 24 and 48 years, respectively) and one natural mature K. obovata forest (KM) in Jiulongjiang Estuary,China. The average values of half-time (T50) of leaf litter decomposition in spring, summer, autumn andwinter were 29.8, 18.7, 23.9 and 47.4d, respectively. Decomposition rates were lower in the older forests(with T50 values of 30.1 and 31.1d averaged by all seasons in K48 and KM, respectively) than in theyounger ones (with T50 values 29.8 and 28.8d averaged by all seasons in K12 and K24, respectively),especially in summer and autumn. The annual mean T50 of nutrient release of leaf litter duringdecomposition followed an order of KM > K48 > K24 > K12. During leaf litter decomposition, C releaseswere very similar to dry weight losses, while N releases were slower and P releases were much faster thandry weight losses. With the development of restored mangrove forests, decomposition and nutrientrelease of leaf litter became slow, which may increase the chance of leaf litter being exported into thesurrounding waters.

ã 2014 Elsevier B.V. All rights reserved.

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Ecological Engineering

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1. Introduction

Mangrove forests are extremely open and productive ecosys-tems providing large amounts of energy and organic matter toestuarine and coastal systems via litter fall and decomposition(Lugo and Snedaker, 1974; Mackey and Smail, 1996; Ye et al., 2011).Litter fall has been estimated to account for 30–60% of totalprimary production of mangrove forests (Bunt et al., 1979). Thehigh productivity was often attributed to rapid litter decomposi-tion and efficient recycling of nutrient elements in mangroveforests (Bosire et al., 2005). Most of mangrove primary production,mainly consisting of mangrove leaves, becomes available toconsumers after senescence and breakdown. Decomposition oflitter fall is one of the basic functions of forest ecosystems (Harley,1971; Ananda et al., 2008). The rate and extent of in situdecomposition governs how much of organic matter and nutrientsis recycled within the mangrove forest, and how much is exportedto near-shore waters (Boulton and Boon, 1991 Zhou et al., 2010).

* Corresponding author. Tel.: +86 592 2880249; fax: +86 592 2880249.E-mail address: yeyong@xmu.edu.cn (Y. Ye).

http://dx.doi.org/10.1016/j.ecoleng.2014.09.1020925-8574/ã 2014 Elsevier B.V. All rights reserved.

The importance of mangrove litter fall and its decomposition in themaintenance of debris-based food webs in the coastal waters andtheir significance for coastal fisheries were indicated (Golley et al.,1962; Odum et al., 1975; Lee, 1995; Ashton et al., 1999).

Despite the value and importance of mangrove forests, theseecosystems have been under severe pressure from rapidlyincreasing human population, large scale deforestation practicesand conversion of forests into aquaculture farms (Alongi 2002; Yeet al., 2011; Gross et al., 2014). In order to compensate the losses ofmangrove forests and to enhance biological functions of coastalzones, vegetation restoration projects have been carrying out inJiulongjiang Estuary, China in the past decades (Chen et al., 2007;Chen and Ye, 2011), but to achieve the ultimate goal of ecosystemfunction restoration there still has a long way to go and the changesin litter decomposition with forest restoration stages should befully understood.

Decomposition of mangrove leaf litter has been studied innumerous subtropical and tropical regions (e.g. Valk and Attiwill,1984; Woodroffe and Moss, 1984; Benner et al., 1986; Robertson,1988; Tam et al., 1990; Ananda et al., 2008). Faster decompositionrates result in nutrient retention, while slow decomposition ratesincreases the chance of leaf litter being exported (Ashton et al.,

Fig. 1. Maps of (A) Caoputou, the study area, and (B) positions of the four studiedmangrove forests K48, K24 and K12 for K. obovata forests aged 48, 24 and 12 years,and KM for one natural mature K. obovata forest.

T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460 455

1999 Zhou et al., 2010). Most published information is on generasuch as Rhizophora and Avicennia, but data on species such asKandelia obovata commonly found in subtropical regions are scanty(Tam et al., 1998), and studies associated with the progress ofvegetation restoration are even rare. Therefore, the present studyfocused on the question how decomposition and nutrientdynamics of leaf litter of K. obovata, a species widely distributedand commonly used in mangrove restoration in China, differamong mangrove forests with forest ages.

2. Study area and methods

2.1. Study area

From March 2010 to February 2011, field experiments werecarried out along the southern coastline of Jiulongjiang Estuarynear Caoputou Village (24�24 0N, 117�55 0E), Fugong Town, LonghaiCounty, Zhangzhou City, Fujian Province of China (Fig. 1A). Theclimate of this region is a southern subtropical maritime (Table 1),with annual mean air temperature of 21.0 �C. In this region, winterlasts from December to February, and the low air temperaturesusually appear in December or January. Spring months (fromMarch to May) are wet season with relatively long rain periods andmost of rainfall during hot seasons (summer from June to August orautumn from September to November) is derived from typhoons.

To protect the sea bank in this area, several mangroveplantations (mainly the species K. obovata) have been successfullycarried out since 1960s so that there are planted K. obovatamangrove forests with different ages. In this study, the selectedthree K. obovata forests were planted in 1962 (K48), 1986 (K24) and1998 (K12) with ages of 48, 24 and 12 years (up to the year 2010),

Table 1Monthly mean climate parameters from December 2009 to November 2010.

Parameter Dec Jan Feb Mar Apr

Temperature (�C) 15.6 15.1 16.2 18.1 19.6

Rainfall(mm) 29.7 41.5 110.3 18.2 78.1

Data from the local weather bureau of Longhai County about 17 km from the study are

respectively (Fig. 1B). In addition, one natural mature K. obovataforest (KM) was also selected as the succession endpoint ofrestored mangroves (Fig. 1B). The floors of these forests are notinundated during neap tides. Tides are semidiurnal with anaverage range of 4 m and the mean salinity of open water adjacentto the mangrove forests is about 17.1 psu (Chen et al., 2007). Thesefour forests were subjected to roughly equivalent tidal elevationfrom field observation and are inundated by high tides for 6–8 daysevery month.

In order to completely represent the litter decompositioncondition in these K. obovata forests, mudflat of each forest wasdivided into three tide stripes, each ranging around 50 m. Sedimentand vegetation surveys for these four forests were conducted ineach tide strip of each forest in April 2010. One sediment samples(5–25 cm deep) was collected in the middle zone of each stripe todetermine moisture, total organic C content, total N content andpH value (Table 2). Density, height and basal diameter of adult treeswere recorded within one quadrat of 25 m2 in the middle zone ofeach stripe (Table 3).

2.2. Leaf litter decomposition experiments

Decomposition experiments were seasonally conducted in eachof the four chosen K. obovata forests by the litterbag method (Fellet al., 1984) in March 2010, June 2010, September 2010 andFebruary 2011, representing spring, summer, autumn and winter,respectively. In each season, newly fallen leaves with yellow colorwere randomly picked from each forest. The leaves were washedclean and air-dried for 12 h so that no surface water remained andthen about every 20 g leaves were placed into each nylon litter bag(18 � 25 cm2) with mesh size of 1 mm. The litter bags were securelytied to aerial roots of K. obovata trees so that they were kept to layon the mud surface during the experiments. Totally 63 bags wereprepared for each forest, with 21 bags (7 bags a group fixed on3 random position) at each tide stripe. Three litter bags weresampled at each tide stripe (one at each position) of each followingtime, days 0 (not incubated on mud surface), 3, 7, 14, 21, 28 and35 in spring, summer and autumn, and days 0, 7, 14, 21, 28, 42and 56 in winter. These samples were brought to the laboratoryand gently washed in a sieve to remove sediment. The washed leaflitter was immediately dried at 60 �C for 48 h, the final dry weightwas recorded, then ground in a mill and passed through the100-mesh sieve. The powders were stored under desiccantconditions for chemical analyses.

2.3. Chemical analyses

Subsamples of leaf litter were digested with sulfuric acid andhydrogen peroxide. N contents were determined by the microKjeldahl method and P contents were assayed by the ascorbic acid-antimony reducing phosphate colorimetric method. Organic Ccontents were analyzed by the method from Walkley and Black(1934). The initial dry weight values of leaf litter were converted bythe moisture contents and fresh weight of leaf litter in the day0 bags. All of the chemical analyses were done in laboratory atabout 20 �C. Three samples were tested for each sampling event ateach stripe.

May Jun Jul Aug Sep Oct Nov

24.1 26.5 30.1 29.4 27.2 23.8 19.7268.9 119.3 63.4 8.2 157.8 192.8 14.5

a.

Table 2Sediment parameters (5–25 cm deep) in the studied K. obovata forests (mean � SE,n = 3). TN (%) and TOC (%) are contents of total nitrogen and total organic carbon insediments.

Forest pH TN (%) TOC (%)

K12 7.05 � 0.48 0.080 � 0.011 1.59 � 0.08K24 6.35 � 0.48 0.092 � 0.012 1.73 � 0.14K48 6.16 � 0.34 0.101 � 0.023 1.92 � 0.21KM 5.50 � 0.74 0.088 � 0.025 1.89 � 0.50

Table 3Characteristics of plant communities of the studied K. obovata forests (n = 3).

Forest Stem diameter (cm) Stem height (m) Tree density (ind hm�2)

K12 5.4 � 0.2 4.5 � 0.2 10978 � 1487K24 6.7 � 0.1 5.9 � 0.4 15387 � 12K48 9.7 � 0.4 7.1 � 0.7 10233 � 318KM 12.0 � 1.8 7.0 � 0.4 9733 � 400

456 T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460

2.4. Statistical analysis

The relationship between the percentage of initial dry weightremaining in litter bags and sampling time was best fitted by thenegative single exponential model (with correction factor):

Xt ¼ ae�kt

where Xt is the percentage of the initial material remaining afterdecomposition time (t), a is the correction factor and k is adecomposition coefficient. The times required for the decomposi-tion of the half the initial material (T50) were determined by theequation T50 = ln (a/50)/k. Differences in litter decomposition ratesand changes in nutrients (organic C, N, P) among the four forests(K12, K24, K48 and KM) and four seasons (spring, summer, autumnand winter) with decomposition time series of 1, 2, 3, 4 and5 weeks were tested by repeated measures two-way analysis ofvariance (ANOVA) with decomposition time as within-subjectfactor, forest age and season as between-subject factors. One-wayANOVA test was employed to evaluate any difference in T50 amongthe four forests in each season. The same test was used to assessany difference in litter decomposition rate, initial concentrations ofnutrients and nutrient release in leaf litter among the four forests.All analyses were performed by SPSS16.0 and Excel 2003 forWindows.

Table 4Results of repeated measures ANOVA for dry weight loss during decomposition ofleaf litter in the studied K. obovata forests.

Source of variation df MS F p

Within-subjectTime 4 0.951 3017.056 0.000Time � age 12 0.004 11.358 0.000Time � season 12 0.021 66.027 0.000Time � age � season 36 0.002 7.746 0.000Error 128 0.000Between-subjectAge 3 0.009 14.474 0.000Season 3 0.551 902.692 0.000Age � season 9 0.006 9.876 0.000Error 32 0.001

Within-subject factor is decomposition time; between-subject factors are forest ageand season. Decomposition time refers to the number of weeks (1, 2, 3, 4 and 5) leaflitter bags were in the field.

3. Results

3.1. Leaf litter decomposition

There were significantly interactive effects of forest age, seasonand decomposition time on dry weight losses during leaf litterdecomposition (Table 4), and the highly significant effect ofdecomposition time suggests that dry weight loss changedsignificantly in leaf litter over the incubation period. Decomposi-tion rates varied not only within the incubation period, but alsoamong forests and seasons. Statistical significance of ‘forest bytime’ and ‘season by time’ interaction suggest that rate and patternof decomposition of K. obovata leaf litter were significantlydifferent at harvest times over the total incubation period, whenthe younger forests compared with the older forests or the hotterseasons compared with the colder seasons.

Leaf litter of K. obovata in each forest degraded rapidly in thefirst 3 weeks, with about 30% of litter dry weight loss from the litterbag (Fig. 2). The decomposition rate of leaf litter reached itsmaximum within two weeks. At the end of the incubation(5–7 weeks), leaf materials of K. obovata were difficult to beidentified and the residues were intermingled with sedimentinside the bags, so the field decomposition experiment is hard toproceed any longer with this litter bag method. The decompositionpatterns observed in different seasons and different forests weresimilar, with very rapid early losses.

Such decomposition patterns were better described by simplenegative exponential 2 Equations than simple linear regressionequations as R (coefficient of determination) values of theexponential regression were higher than the linear regression(Tam et al., 1998), so exponential equations were used to createfitting curves of leaf litter decomposition (Table 5). Despite thesimilarity in litter decomposition pattern among the four K.obovata forests, mean half-time of leaf decomposition (T50) valueswere significantly different among the four forests in each seasonexcept for winter (p < 0.001, F = 20.659 in spring; p = 0.005,F = 9.802 in summer; p = 0.002, F = 13.699 in autumn; p > 0.05 inwinter according to one-way ANOVA). Mean T50 was 29.8 d inspring,18.7d in summer, 23.9 d in autumn and 47.4 d in winter withan order of increasing degradation rate as summer > autumn >spring > winter. There were higher decomposition rates and moresignificant differences among seasons at the early periods of theexperiment than the remaining periods. Decomposition rates werelower in the older forests (with T50 values of 30.1 and 31.1daveraged by all seasons in K48 and KM, respectively) than in theyounger ones (with T50 values 29.8 and 28.8d averaged by allseasons in K12 and K24, respectively), especially in summer andautumn. Averaged by all of the forests and seasons, T50 value of dryweight loss during decomposition of leaf litter was 29.9d.

3.2. Nutrient releases

The nutrient (organic C, N, P) contents in K. obovata leaf litterwere analyzed during the decomposition processes. The initialvalues of the contents of C, N and P in leaf litter at the beginning ofdecomposition decreased with the increasing forest age and C:Nratios of younger forests (K12 and K24) were significantly higherthan those of older forests (K48 and KM), but there were notsignificant differences in any of these parameters between K48 andKM (Table 6). There were significant effects of forest age, seasonand decomposition time on nutrient releases duing leaf litterdecomposition (Tables 7–9). Nutrient releases of organic C, N and Pduring decomposition experiments were closely paralleled withdry weight losses (Figs. 3–5). The loss percentages of C were verysimilar to those of dry weight losses, while the loss percentages ofN were slightly lower and the loss percentages of P were faster than

K24

0

20

40

60

80

0 7 14 21 28 35 42 49 56 63

K48

0

20

40

60

80

0 7 14 21 28 35 42 49 56 63Time ( days)

Dry

wei

ght l

oss (

%)

K12

0

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0 7 14 21 28 35 42 49 56 63D

ry w

eigh

t los

s (%

)

KM

0

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80

0 7 14 21 28 35 42 49 56 63Time ( days )

SpringSumm erAutumnWint er

Fig. 2. Loss percentages of initial dry weight during decomposition of leaf litter in the studied K. obovata forests (n = 3).

Table 5Simple negative exponential regression equations (X = ae�kt) on % of litter massremaining in litter bags (X) against time (t) during decomposition of leaf litter in thestudied K. obovata forests.

Season Forest R2 k T50 (n = 3)

Spring K12 0.969 0.023 32.2 � 1.27cK24 0.962 0.026 26.9 � 0.69aK48 0.938 0.023 29.9 � 0.41bKM 0.993 0.023 30.3 � 0.71b

Summer K12 0.982 0.038 16.9 � 0.72aK24 0.965 0.031 18.1 � 1.19abK48 0.969 0.031 19.1 � 0.99bcKM 0.986 0.032 20.7 � 0.51c

Autumn K12 0.914 0.025 22.0 � 1.33aK24 0.944 0.025 23.2 � 0.58abK48 0.926 0.024 24.1 � 0.51bKM 0.947 0.023 26.1 � 0.52c

Winter K12 0.901 0.013 47.9 � 1.32aK24 0.903 0.013 46.9 � 2.52aK48 0.886 0.013 47.4 � 2.90aKM 0.934 0.013 47.3 � 2.76a

R, coefficient of determination; k, decomposition constant; T50, half life time.Different letters after T50 data in the same season indicate statistically significantdifferences among forests in each season at the level of 0.05.

Table 6Initial contents of nutrients in leaf litter at the beginning of decomposition in thestudied K. obovata forests.

Forest C (%) N (%) P (%) C:N

K12 45.28 � 0.84b 1.06 � 0.02c 0.122 � 0.003b 42.80 � 0.29cK24 44.50 � 0.65b 0.91 � 0.03b 0.109 � 0.003a 49.01 � 1.41bK48 43.15 � 0.51a 0.72 � 0.04a 0.104 � 0.003a 60.06 � 3.46aKM 43.29 � 0.17a 0.70 � 0.05a 0.101 � 0.009a 61.71 � 4.26a

Different letter indicate statistically significant differences among forests at thelevel of 0.05.

Table 7Results of repeated measures ANOVA for C losses during decomposition of leaf litterin the studied K. obovata forests.

Source of variation df MS F p

Within-subjectTime 4 0.934 4103.597 0.000Time � age 12 0.004 16.024 0.000Time � season 12 0.028 122.040 0.000Time � age � season 36 0.002 8.452 0.000Error 128 0.000Between-subjectAge 3 0.008 8.408 0.000Season 3 0.535 573.446 0.000Age � season 9 0.010 10.626 0.000Error 32 0.001

Table 8Results of repeated measures ANOVA for N losses during decomposition of leaf litterin the studied K. obovata forests.

Source of variation df MS F p

Within-subjectTime 4 1.057 557.205 0.000Time � age 12 0.006 3.208 0.000Time � season 12 0.042 22.126 0.000Time � age � season 36 0.003 1.710 0.016Error 128 0.002Between-subjectAge 3 0.179 62.354 0.000Season 3 0.429 149.330 0.000Age � season 9 0.024 8.412 0.000Error 32

T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460 457

those of dry weight losses. More rapid releasing of organic C, N andP from decomposed leaves were found in summer and autumnthan in winter and spring, indicating more nutrients were releasedand exported to the surrounding waters in hot seasons. For Nconcentrations in the residual litter materials during decomposi-tion (Fig. 4), there were general increases from the 2nd to the 3rd orthe 4th weeks of leaf litter decomposition in Spring, Summer andAutumn. After these periods, the N remaining in litter materialsdeclined steadily. P remaining in the residual litter material rapidly

decreased during the first 3 weeks and then decreased gradually(Fig. 5). After 35 days’ decomposition, the nutrients releases fromleaf litter were around 54% for organic C, 50% for N and 66% for P inspring, 68% for C, 62% for N and 76% for P in summer, 57% for C, 53%for N and 68% for P in autumn, and 41% for C, 29% for N and 49% for Pin winter.

The decomposition patterns of nutrients in K. obovata leaf litterwere also described by simple negative exponential 2 Equations

Table 9Results of repeated measures ANOVA for P losses during decomposition of leaf litterin the studied K. obovata forests.

Source of Variation df MS F p

Within-subjectTime 4 1.016 495.825 0.000Time � age 12 0.004 1.712 0.071Time � season 12 0.017 8.097 0.000Time � age � season 36 0.001 0.622 0.950Error 128 0.002Between-subjectAge 3 0.023 4.859 0.007Season 3 0.559 116.932 0.000Age � season 9 0.010 2.167 0.052Error 32 0.005

Within-subject factor is decomposition time; between-subject factors are forest ageand season. Decomposition time refers to the number of weeks (1, 2, 3, 4 and 5) leaflitter bags were in the field.

Spring

10

30

50

70

90

110

0 10 20 30 40

% C

rem

aini

ng

K12 K24K48 KM

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30

50

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% C

rem

aini

ng Winter

10

30

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0 20 40 60Time (days)

Fig. 3. Remaining percentages of organic C during decomposition of leaf litter in the studied K. obovata forests (n = 3).

Spring

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% N

rem

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K12 K24K48 KM

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ng Winter

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0 20 40 60Time (d ays)

Fig. 4. Remaining percentages of N during decomposition of leaf litter in the studied K. obovata forests (n = 3).

458 T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460

(Table 10). The four forests had significantly different T50 values ofreleases of C, N and P during decomposition of leaf litter, withlarger differences in N releases than those in C and P releases.Generally, T50 values of nutrient releases increased with forest age,indicating that the longer the forest grows, the slower the nutrients

releases during decomposition of leaf litter. Averaged by data in thefour forests, T50 values of releases of C, N and P duringdecomposition of leaf litter were 29.4, 40.4 and 21.2d.

4. Discussion

Mangrove litter has been reported to be quickly decomposedwith rapid decreases in dry weight and high leaching rates in thefirst few weeks of exposure in the field (Valk and Attiwill, 1984;Mfilinge et al., 2005). In the present study, the highestdecomposition rate occurred in the 2nd week in winter and inthe first week in other seasons, and then followed by slowerdecreases for the rest of the experiment period. This quickdecomposition at early stage might be related to leaching ofsoluble organic materials and inorganic compounds such as

soluble sugars (Steinke et al., 1993). A slower loss of dry weightreflected the loss of more resistant materials (Steinke et al., 1990).The decomposition pattern in the present study was similar tothose observed in previous studies (Twilley et al., 1986; Mackeyand Smail, 1996; Wafar et al., 1997; Imgraben and Dittmann, 2008).

Spring

10

30

50

70

90

110

0 10 20 30 40%

P re

mai

ning

K12 K24K48 KM

Summ er

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30

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Autumn

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% P

rem

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ng Winter

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0 20 40 60Time (d ays)

Fig. 5. Remaining percentages of P during decomposition of leaf litter in the studied K. obovata forests (n = 3).

T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460 459

Leaf litter decomposition can be influenced by not only seasons(Mackey and Smail, 1996) but also spatial scales such as tidal levels(Lee, 1989; Mackey and Smail, 1996; Dick and Osunkoya, 2000;Mfilinge et al., 2002). The decomposition rates in both summer andwinter from K. obovata forests in Jiulongjiang Estuary in China inthe present study, with T50 of dry weight losses of 18.7 and 47.4drespectively, were much slower than those with correspondingvalues of 13 and 42d from mangrove forests of the same species inHong Kong (Tam et al., 1990), about 2�-latitude and 2 �C annualmean air temperature less than the area of the present study.The decomposition rates of leaf litter in each of the four mangroveforests in the present study were more rapid in summer than thosein winter because activities of microbes increased in hot seasons,as reported in other mangrove forests (Lin, 1999).

Earlier studies indicated that initial nutrients level of litter, inparticular N content, has a controlling influence on litterdecomposition rates (Melillo et al., 1982; Twilley et al., 1997).Decomposition rates generally increase for litter with high leaf Ncontent (Pelegraí et al., 1997). Fenchel et al. (1998) suggested thathigh initial N content or low C:N ratio in litter would result in highmicrobial assimilation and mineralization efficiencies, and lessimmobilization effects, hence accelerate the decomposition oflitter fall. Certainly, we observed a steady enrichment of litter N in

Table 10Simple negative exponential regression equations (X = ae�kt) on % of annual litternutrients remaining in litter bags (X) against time (t) during decomposition of leaflitter in the studied K. obovata forests.

Nutrient Forest R2 k T50 (n = 3)

C remaining K12 0.992 0.023 28.6 � 0.57aK24 0.985 0.022 28.8 � 1.09aK48 0.985 0.022 29.2 � 0.63aKM 0.989 0.022 30.9 � 1.02b

N remaining K12 0.988 0.022 32.3 � 0.68aK24 0.949 0.020 36.9 � 0.84bK48 0.903 0.014 51.1 � 3.24 dKM 0.979 0.017 41.1 � 1.82c

P remaining K12 0.979 0.032 19.4 � 0.74aK24 0.962 0.028 21.3 � 0.43abK48 0.964 0.028 21.4 � 1.13abKM 0.978 0.029 22.5 � 1.60b

R, coefficient of determination; k, decomposition constant; T50, half life time.Different letters after T50 data for the same nutrient indicate statistically significantdifferences among forests at the level of 0.05.

the first 3 weeks of decomposition and N quantity declined muchslower than organic C and P. This may be due to the rapid releasesof soluble forms of P from litter by leaching (Steinke et al., 1993;Tam et al., 1998).

The decomposition of leaf litter is greatly associated with thesurrounding environment which can be largely changed with thedevelopment of a restored forest. At different stages of a restoredmangrove ecosystem, many factors such as litter production,microbiological activity, inundation condition, aerobic condition ofsediment, faunal communities and litter nutritional values alsochanged (Clough et al., 2000; Morrisey et al., 2003; Nga et al., 2005;Chen et al., 2007; Ye et al., 2013). The present study showed thatinitial N and P levels in leaf litter declined as the increase in forestage of K. obovata forests. This is in line with findings from Nga et al.(2005) that mangrove plants in younger forests (7 and 11 years) areable to take up more N and P than those in older forests (17 and24 years) and the formers produce a large quantity of higherquality litter as input to the aquatic system. Hong and San (1993)concluded that old trees produce much woody materials, such asstems, branches and reproductive parts, while young trees producemore leaves. Clough et al. (2000) even indicated that the leaf areaindex (LAI) decreased with the increase in mangrove forest age,resulting in more closed canopy in young forests than in old ones.Chen et al. (2007) showed that younger forests (4 and 7 years)generally had more macro-benthic fauna species than older ones(19 and 43 years). In a conclusion, litter decomposition rate isinevitably to show some differences with the development of arestored mangrove forest, as is indicated by the present study thatlitter decomposition rates are directly correlated to the age of themangrove forests. We found that leaf litter lose its dry weight andnutrients (organic C, N, P) significantly faster in younger forests(K12, K24) than in older forests (K48, KM), especially during thehotter and wetter seasons (summer and autumn). With thedevelopment of restored mangrove forests, slower decompositionand nutrient release of leaf litter may increase the chance of leaflitter being exported into ocean.

Acknowledgements

The work described in this paper is supported by the grantsfrom National Natural Science Foundation of China (Project no.

460 T. Li, Y. Ye / Ecological Engineering 73 (2014) 454–460

41076049 and 41276077). We thank Baipeng Pang and Yantao Gufor their dedicating work in the field and/or laboratory.

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