Decomposition of Leaf Litter of Four Tree Species in A

8/2/2019 Decomposition of Leaf Litter of Four Tree Species in A

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Decomposition of leaf litter of four tree species in a subtropicalevergreen broad-leaved forest, Okinawa Island, Japan

Laode Alhamd, Syoko Arakaki, Akio Hagihara*

Laboratory of Ecology and Systematics, University of the Ryukyus, Okinawa 903-0213, Japan

Received 13 January 2003; received in revised form 16 September 2003; accepted 20 February 2004

Abstract

The leaf litter decomposition of four indigenous tree species, such as Castanopsis sieboldii, Schima wallichii, Elaeocarpus

japonicus, and Daphniphyllum teijsmannii, was monthly monitored using the litterbag technique over a 12-month period in a

subtropical evergreen broad-leaved forest of Okinawa Island, Japan. The decomposition rate constant (k) was 1.19 0.19 for D.teijsmannii, 1.09 0.07 for C. sieboldii, 0.94 0.05 for E. japonicus, and 0.66 0.05 (S.E.) yr1 for S. wallichii. Thedecomposition rate constant was significantly lower in S. wallichii than the other three species (P < 0.01). It might be attributed

to the low number of micro-fauna. The fastest rate of decomposition of the leaf litter of D. teijsmannii can be attributed to

collembola whose number was almost twice compared to the number of collembola observed in the other species leaf litters. The

remaining carbon of leaf litter decreased with increasing incubation time and its concentration was ca. 50% over one year. The

remaining nitrogen ofC. sieboldii, E. Japonicus, and D. teijsmannii showed three phases: leaching, net gain, and net loss, while

S. wallichii showed two phases without net loss phase. The leaf litter of D. teijsmannii, which had the highest initial N

concentration of 0.97%, showed the highest decomposition rate constant. Concerning the other species of leaf litters, however,

their initial N concentration did not reflect on their decomposition rate constant. The critical value of C/N ratio ranged from 31

for D. teijsmannii to 33 for C. sieboldii.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Decomposition rate constant; Leaf litter decomposition; Litterbag; Micro-fauna; Subtropical rain forest

1. Introduction

Decomposition of leaf litter, by which organicmatter and nutrients are returned to the forest soils,

is a primary mechanism and has received considerable

attention for sustainable soil fertility (Moretto et al.,

2001; Xuluc-Tolosa et al., 2003). The rate of litter

decomposition has been associated with the carbon

and nitrogen content (Fog, 1988; Kemp et al., 2003;

Meentemeyer, 1978; Swift et al., 1979). Complexes of

bacteria, fungi, and soil organisms have also an

important role in decomposing leaf litter. Themicro-fauna, which can move freely through the

litterbag net, have been shown to cause an increase

in weight loss (Berg et al., 1980; Berg and Staaf,

1981). The successional changes of soil organisms

have been demonstrated during the decomposition

process of various litters using the litterbag method

(Berg and Soderstrom, 1979). The roles of soil organ-

isms on nutrient cycle may be changed during decom-

position processes of litter (Hasegawa and Takeda,

1995; Warren and Zou, 2002).

Forest Ecology and Management 202 (2004) 111

* Corresponding author. Tel.: 81-98-895-8546;fax: 81-98-895-8546.E-mail address: [email protected] (A. Hagihara).

0378-1127/$ see front matter # 2004 Elsevier B.V. All rights reserved.doi:10.1016/j.foreco.2004.02.062


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Okinawan forests that are identified as subtropical

evergreen broad-leaved forests have high woody species

diversity including Castanopsis sieboldii (Makino)

Hatusima ex Yamazaki et Mashiba (Ito, 1997). InOkinawa, temperature and precipitation are high and

strong winds commonly occur together with a heavy

rain. These factors potentially contribute to the high

degree of nutrient supply through decomposition of

litters. However, studies on leaf litter decomposition

in subtropical rain forests in Okinawa, which are sub-

stantial to be performed for comprehending ecological

processes in the forests, have not yet been conducted.

The aims of this study were to determine the

remaining mass of leaf litter after decomposition, to

examine monthly changes in carbon (C), nitrogen (N),

and C/N ratio in decomposing leaves after the incuba-

tion, and to observe the number of micro-fauna in

process of the decomposition over one year.

2. Materials and methods

2.1. Study site

This study was carried out in a subtropical ever-

green broad-leaved forest in the northern part of

Okinawa Island, Japan (2684503000N and12880500000E). A general map of the study site is

shown in Fig. 1. Tanaka (1999) reported that trees

having DBH ! 4.5 cm in this area were mostlyoccupied by C. sieboldii (Makino) Hatusima ex Yama-

zaki et Mashiba, Elaeocarpus japonicus Sieb. et

Zucc., and Schima wallichii (DC.) Korthals, whose

percentages in number were 40%, 14%, and 10%,

respectively, and the other species were less than 6%.

Altitude and terrain-slope of the study area were

250 m above sea level and 24.58, respectively. The pH

of the soil was 4.35. Air moisture just above the forestfloor was approximately 90%. Monthly temperature

and rainfall distribution during the study period are

presented in Fig. 2. Mean monthly temperature ranged

from 16.4 8C to 28.2 8C and mean annual air tem-

perature was 22.9 8C. Annual rainfall was 2197 mm.

2.2. Litter decomposition

The leaf litter decomposition experiment was car-

ried out during a 12-month period from May 1999 to

May 2000. Four tree species were used in the experi-

ment: C. sieboldii, S. wallichii, E. japonicus, and

Daphniphyllum teijsmannii Zoll. ex Kurz. The decom-

position rates were evaluated using 25 cm 28 cmlitterbags with 2-mm mesh size constructed from

nylon net with 2-mm mesh size.

From March to April 1999, leaf litters were col-

lected in the study site by applying litterfall traps.

Collected leaf litter samples were immediately trans-

ported to the Laboratory of the University of the

Ryukyus, separated according to species, selected

in a wide range of leaf size, shape, and texture,

cleaned, and then air-dried to a constant weight at

a room temperature. Ten grams (12 replicates) of

each leaf litter type was weighed. All samples of leaf

litter were placed in litterbags. The top of the filled

litterbags was sealed and a plastic tag with an ID

number was wired to each litterbag. A total of 48

leaf litterbags were placed on the flat surface area in

May 1999 by utilizing metal pins to prevent move-

ment and to ensure a suitable contact between litter-

bags and organic soil layers. One litterbag from each

of theleaf littertypeswas retainedin the laboratoryto

determine the initial weight and chemical composi-

tion.

At monthly intervals from June 1999 to May 2000,

one litterbag was randomly retrieved from each leaflitter type. Each bag was placed into a separate poly-

ethylene bag and directly transferred to the laboratory.

Extraneous materials, including roots, were carefully

brushed off from the litterbags. Leaf residues were

oven-dried at 85 8C for 24 h and then weighed.

2.3. Chemical analysis

The leaf litter samples of each bag were milled to

determine the chemical contents (Janke & Kunkel

Gmbh & Co. KG, Type A 10 S11). A sample of10 mg was analyzed with an automatic gas chromato-

graph N.C.-Analyzer (Sumigraph, Model NC-80) to

determine the total concentration of carbon (C) and

nitrogen (N). Four replicates of each litterbag were

performed.

Remaining C and N after a given month incubation

were calculated by the following formula:

Remaining % LtCt

L0C0 100; (1)

2 L. Alhamd et al. / Forest Ecology and Management 202 (2004) 111


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where Lt is the mass of dry matter after a given

month, L0 is the initial mass of dry matter, Ct is the

concentration of C or N after a given month incuba-

tion, and C0 is the initial concentration of C or N in

litter.

2.4. Micro-fauna abundance

The abundance of micro-fauna in each litterbag

was extracted at a constant temperature (358

C)for three days by a modified Tullgren funnel and

collected in 90% ethanol. Then identification and

counting of these micro-fauna were performed

under a binocular microscope with a magnification

of 20.

2.5. Exponential decay model

The process of decomposing mass of leaf litter was

described using a single exponential decay model

(Olson, 1963), as follows:

Lt

L0 expkt; (2)

where L0 is the initial mass of dry matter,Lt is the mass

of dry matter after a given month incubation t, and kis

the decomposition rate constant.

2.6. Statistical analysis

The t-test was used for detecting a significantdifference in the decomposition rate constant among

the different species of leaf litter.

3. Results

3.1. Remaining mass

The loss of mass from decomposing leaf litter in

litterbags is described in Fig. 3. The remaining mass

Fig. 1. Map showing the study site (closed circle) in the northern part of Okinawa Island, Japan.

L. Alhamd et al. / Forest Ecology and Management 202 (2004) 111 3


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after 12 months incubation on the forest floor was

54%, 46%, 59%, and 61% to the initial mass for C.

sieboldii, S. wallichii, E. japonicus, and D. teijsman-

nii, respectively. The decay process was well-approxi-

mated by the exponential decay model given by

Eq. (2). As given in Table 1, the values of the decom-

position rate constant (k) were 1.19 0.19 for D.teijsmannii, 1.09 0.07 for C. sieboldii, 0.94 0.05for E. japonicus, and 0.66 0.05 (S.E.) yr1 for S.wallichii. The k-value for S. wallichii was significantly

low, as compared with the other species (P < 0.01).

3.2. Remaining C and N

The changes of remaining carbon followed a similar

pattern in all species, declining with increasing incu-

bation time during the process of decomposition, as

shown in Fig. 4. The carbon sharply decreased in the

first 2 months, reaching 3.2 g (71%) of C. sieboldii,

3.7 g (72%) of S. wallichii, 2.9 g (57%) ofE. japoni-

cus, and 2.8 g (54% of the initial C content) of D.

teijsmannii. During the later months, the decreasing

rate of carbon was comparatively low.

The remaining nitrogen decreased more slowly thancarbon during this study (Fig. 4). The nitrogen change

ofC. sieboldii showed a three-phase pattern: leaching

from the 1st to the 2nd month, net gain from the 3rd to

the 9th month, and net loss from the 10th to the 12th

month. On the other hand, the nitrogen change of S.

wallichii showed two phases: leaching from the 1st to

the 2nd month and net gain from the 3rd up to the 12th

month. The nitrogen change ofE. japonicus had three

phases: leaching in the first two months, net gain from

the 3rd to the 9th month, and net loss from the 10th to

Fig. 2. Monthly temperature and rainfall at the study site, from January 1999 to December 2000. The data were collected from the weather

station (Nago City, Okinawa) nearest to the study area.

Table 1

Annual decomposition rate constant (k) and 95% breakdown period of the four selected tree species during a 12-month period

Tree species k S.E. (yr1) n r2 95% breakdownperiod (year)

Castanopsis sieboldii 1.09 0.07 a,b 13 0.76 2.7Schima wallichii 0.66 0.05 c 13 0.86 4.5Elaeocarpus japonicus 0.94 0.05 b 13 0.84 3.2

Daphniphyllum teijsmannii 1.19 0.19 a 13 0.87 2.5

Values followed by different letters (a and b) in the same column are signi ficantly different (P < 0.01).



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the end of this study. The nitrogen change of D. teijs-

mannii had also three phases: leaching in the first one

month, net gain from the 2nd to the 7th month, and net

loss starting in the 8th and continuing to the 12th month.

3.3. Changes in C/N ratio

Fig. 5 shows the changes of C/N ratio in decom-

posing leaves of four tree species. The four species

showed a similar trend of C/N ratio, which decreased

progressively to the end of experiment. The C/N ratio

ofC. sieboldii sharply decreased with increasing N in

the 1st month (Fig. 4), gradually decreased until the

9th month, and then tended to 29 at the 12th month

incubation. The C/N ratio of S. wallichii decreased in

the first month and then slowly decreased to 29 at the

12th month. The C/N ratio of E. japonicus abruptly

decreased in the first three months, slowly decreaseduntil the 9th month, tended to increase until the 10th

month, and decreased again to 25. The C/N ratio ofD.

teijsmannii sharply decreased from the 1st to the 3rd

month and then slowly decreased down to 26.

3.4. Changes in faunal abundance

The number of micro-fauna in all litterbags was

counted. Both acari and collembola were the predo-

minant orders among 21 orders observed in the

Fig. 3. Percentage of remaining mass to initial mass in process of decomposition from May 1999 to May 2000. (a) C. sieboldii; (b) S.

wallichii; (c) E. japonicus; (d) D. teijsmannii. For the decomposition rate constant (k), see Table 1.



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litterbags. They contributed 82% and 14% of the total

micro-fauna for C. sieboldii, 67% and 28% for S.

wallichii, 73% and 21% for E.japonicus, and 59% and

35% for D. teijsmannii, respectively.

The densities of micro-fauna, in terms of the num-ber of individuals per gram of leaf litter residue, are

summarized in Table 2. The density of micro-fauna for

C. sieboldii had three peaks at 4, 7, and 11 months

after the incubation. The maximum value appeared in

the third peak with 72 individuals per gram of leaf

litter residue. On the other hand, the density for S.

wallichii showed a short-fluctuation pattern, in which

the peak of micro-fauna was reached at 5 months after

the incubation (37 individuals per gram of the residue

of leaf litter). The density for E. japonicus peaked at

11 months after the incubation with 138 individuals

per gram of the residue of leaf litter, which was

especially larger than those for the other three species.

The abundance of micro-fauna for D. teijsmannii

showed a similar trend to C. sieboldii and had threepeaks concentrating at 4, 7, and 10 months after the

incubation. The highest abundance arose at 10 months

after the incubation (113 individuals per gram of the

residue of leaf litter).

4. Discussion

The remaining mass of leaf litter decreased with

increasing incubation time (Fig. 3). It seems that

Fig. 4. Changes of the remaining carbon (*) and remaining nitrogen (*) of decomposing leaf litter after the incubation from May 1999 to

May 2000. Values are represented as mean S.E. (n 4). (a) C. sieboldii; (b) S. wallichii; (c) E. japonicus; (d), D. teijsmannii.



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there exist two stages in decomposition during this

study. Therate of decreasein all species was higherin

the first half than in the second half of decomposition

phase. Berg (1986) and Takeda (1995) also con-

cluded that the decomposition of leaf litter was

divided into two phases. In the first phase, the solublesubstances and non-lignified carbohydrates, e.g.

cellulose and hemicellulose, are decomposed by

saprotrophic fungi, while in the second decomposi-

tion phase, primarily lignin and lignified cellulose

remain. In addition, decomposing leaf litter is influ-

enced by the internal physicochemical properties of

the substrate and by the environmental factors under

which decomposition takes place (Gillon et al.,

1994). The estimated leaf decomposition of 95%

was faster in D. teijsmanii (2.5 years) than in C.

sieboldii (2.7 years), E. japonicus (3.2 years), and S.

wallichii (4.5 years) (Table 1). Since the full decom-

position of the leaf litters was longer than one year,

there is still a great need of conducting this investiga-

tion more than one year in this area. Kira and Shidei

(1967) reported that the duration for the 95% break-down of leaf litterwas 0.3 year afterdecomposition in

a tropical rain forest and 23.3 years in a subalpine

spruce forest.

Several studies have demonstrated that there are

significant contributions of soil micro-fauna on the

decomposition processes (Singh and Shekhar, 1989;

Tian et al., 1992). In the present study, the decom-

position rate constant k was significantly lower in S.

wallichii than the other three species (P < 0.01)

(Table 1). It may be attributed to the low number of

Fig. 5. Changes of the C/N ratio of decomposing leaf litter after the incubation from May 1999 to May 2000. Values are represented as mean

S.E. (n 4). (a) C. sieboldii; (b) S. wallichii; (c) E. japonicus; (d) D. teijsmannii.



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micro-fauna. The fastest rate of decomposition of the

leaf litter of D. teijsmannii can be attributed to col-

lembola whose number was almost twice compared to

the number of collembola observed in the other spe-cies leaf litters (Table 2). The highest k-value D.

teijsmannii was not significantly different from the

k-value of C. siebolldii. The result of both species

could be related to the similar abundance of micro-

fauna, which most likely influenced the decomposi-

tion of the leaf litters. The values of the decomposition

rate constant (Table 1), except the value ofS. wallichii,

were rather comparable to the mean value of 0.93 yr1

in temperate forests, but were much lower than the

mean value of 1.85 yr1 in tropical forests summar-

ized by Takeda (1996).

The remaining carbon of each species showed a

similar trend to the remaining mass, which decreased

with increasing incubation time (Fig. 4). It is sug-

gested that carbon content after monthly incubation

may be a factor in decomposition rate of leaf litter. In

addition, the mean C concentration of each leaf litter

type was ca. 50% over one year (Fig. 6).

The nutrient content of the leaves also affects therate of decomposition. Generally high levels of nutri-

ents, notably nitrogen, are expected to be able to

accelerate the decomposition process. Several studies

have shown a positive correlation between initial N

concentration and the decomposition rate constant

(Melillo et al., 1982; Vogt et al., 1991; Corteaux

et al., 1995; Mfilinge et al., 2002). In this study, the

leaf litter of D. teijsmannii, which had the highest

initial N concentration of 0.97% (Fig. 6), showed the

highest decomposition rate constant. Concerning the

other species, however, their initial N concentration

did not reflect on their decomposition rate constant

(Table 1).

Gosz et al. (1973) and Staff and Berg (1982) noticed

that nitrogen dynamics in decomposing leaf litter

Table 2

Numbers of micro-fauna colonizing in the residual of leaf litter of the four selected tree species in process of decomposition

Micro-fauna (g1

) Incubation time (month) Total (%)

2 3 4 5 6 7 8 9 10 11 12

Castanopsis sieboldiiAcari 19 28 52 44 34 61 26 24 57 66 33 444 (82)

Collembola 3 11 10 9 2 4 3 2 8 5 18 75 (14)

Others 1 2 3 2 2 2 2 1 2 1 4 22 (4)

Total 23 41 65 55 38 67 31 27 67 72 55 541

Schima wallichii

Acari 10 11 25 24 15 23 22 17 21 14 15 197 (67)

Collembola 3 4 7 12 4 4 6 6 11 13 13 83 (28)

Others 3 4 1 1 1 1 1 1 1 1 1 16 (5)

Total 16 19 33 37 20 28 29 24 33 28 29 296

Elaeocarpus japonicus

Acari 16 24 23 19 34 30 9 16 23 124 12 330 (73)Collembola 1 6 3 4 5 3 8 4 14 13 34 95 (21)

Others 7 1 1 1 2 6 2 2 2 1 1 26 (6)

Total 24 31 27 24 41 39 19 22 39 138 47 451

Daphniphyllum teijsmannii

Acari 8 2 27 23 1 38 2 21 69 40 42 273 (59)

Collembola 1 1 8 7 0 6 0 11 39 41 51 165 (35)

Others 1 2 3 3 0 2 1 0 5 2 8 27 (6)

Total 10 5 38 33 1 46 3 32 113 83 101 465



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showed three sequential phases: firstly, the initial

release phase in which leaching predominates; sec-

ondly, the net gain phase in which nitrogen is imported

into the residual material through the activity of

microorganisms, and thirdly, the net loss phase in

which an absolute decrease in the nutrient mass of

decomposing leaf litter occurs. In this study, nitrogenchanges of leaf litter after monthly incubation showed

two or three phases, such as leaching, net gain, and net

loss, in all species. Only two phases, i.e. without net

loss, were found in S. wallichii, but three phases

were observed in C. sieboldii, E. japonicus, and

D. teijsmannii (Fig. 4).

The C/N ratio of C. sieboldii was initially 57 and

then decreased to 52 by the end of the leaching phase

(second month) (Fig. 5). During the net gain phase, the

ratio further decreased from 52 to 33 (sixth month),

which might be recognized as a critical value of C/N

ratio for C. sieboldii. As shown in Fig. 7, the critical

value of S. wallichii reached 32 at 9 months after the

incubation, while those of E. japonicus and D. teijs-

mannii were 32 at 6 months and 31 at 9 months after

the incubation, respectively. The critical values

obtained in all species were achieved when the rangeof N concentration was 1.41.7% (Fig. 6). The present

critical values were a little bit lower than the respec-

tive values of 38 and 34 of Dipterocarpus baudii

leaves reported by Yamashita and Takeda (1998) in

two types of litterbags, 0.5 mm and 2.0 mm in mesh

size.

Acari and collembola were more dominant than the

other orders (Table 2). The number of acari of C.

sieboldii leaf litter was greater than those of the other

leaf litters for a 11-month collection, suggesting that a

Fig. 6. Changes of carbon (*) and nitrogen (*) concentrations after the incubation from May 1999 to May 2000. Values are represented as

mean S.E. (n 4). (a) C. sieboldii; (b) S. wallichii; (c) E. japonicus; (d) D. teijsmannii.



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rapid weight loss in C. sieboldii leaves might be

attributed to the presence of acari. On the other hand,

the low density of micro-fauna might not enhance the

decomposing rate of S. wallichii leaves (Table 1).

Acknowledgements

We are thankful to Prof. T. Shinzato and Dr. T.

Enoki, Subtropical Field Science Center at Yona,

University of the Ryukyus, for their help. We also

thank Prof. M. Tsuchiya for his suggestion in operat-

ing the N.C.-Analyzer. Thanks are due to Mr. B.

Tanaka for their invaluable cooperation in the field

works and Mr. B. Ranjeet for his correction of English.

We also thank two anonymous reviewers provided

many helpful comments on the manuscript. This study

was supported in part by Nippon Life Insurance

Foundation and a Grant-in-Aid for Scientific Research

(No. 12794001) from the Japanese Ministry of Educa-

tion, Culture, Sports, Science and Technology.

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Documents

Decomposition of Leaf Litter of Four Tree Species in A