Nutrient changes and release during decomposition of leaf litter in a Himalayan oak–conifer forest

Nutrient changes and release during decomposition of leaf litter in a Himalayan oak - conifer forest

UMA PANDEY AND J. S. SINGH Department of Botany, Kurnaun Urliversity, Naini Tnl 263002, Indin

Received April 29, 1983

PANDEY, U., and J . S . SINGH. 1984. Nutrient changes and release during decomposition of leaf litter in a Himalayan oak-conifer forest. Can. J. Bot. 62: 1824-1831.

Changes in nitrogen, calcium, water-soluble compounds, and total available carbohydrate in decomposing leaf litter of six tree and one shrub species, enclosed in nylon net bags and placed in a mixed oak conifer forest, were examined for a period of 487 days. The concentration of nitrogen increased during decomposition in all litter species. This increase was up to threefold in Aesculus irldica, Quercusjloribundn, and Qriercus leucotrichophorn. In most species the absolute increase in nitrogen mass was observed when decomposition had progressed up to 213 days. However, in Dnphrle cnrlrlabina and Ilex clipy;enn, the absolute mass of nitrogen was never greater than the initial mass at any stage of decomposition. The absolute mass of calcium in litter bags generally declined with time. The concentration of water-soluble compounds and of total available carbohydrates varied from species to species; both these constituents, however, continually decreased with the progress of decomposition. Within I year, the release of nitrogen, water-soluble compounds, and total available carbohydrates was 100% in D. cannubinn, A. indica, and I. dipyrena. In Cedrus deodarn, Q. jloribunda, and Q. leucotrichophora about 50% of total nitrogen input to the forest floor as litter fall was released by decomposition. In Cupressus torulosn only 14% of nitrogen falling as leaf litter was released during a period of 1 year.

PANDEY, U., et J . S. SINGH. 1984. Nutrient changes and release during decomposition of leaf litter in a Himalayan oak-conifer forest. Can. J. Bot. 62: 1824- 1831.

Les auteurs ont suivi, pendant une pCriode de 487 jours, les changements de I'azote, du calcium, des composCs hydrosolubles et des glucides disponibles totaux dans des litikres de feuilles en dCcomposition de six espkces arborescentes et une espkce arbustive; les litikres Ctaient placCes dans des sacs en filet de nylon, dans une foret mixte de ch&nes et conifkres. Chez toutes les espkces, la concentration de I'azote augmente durant la dCcomposition de la litikre; cette augmentation va jusqu'au triple pour les litikres d'Aesculus indicn, de Quercus floribunda et de Q~lercus leilcotrichophorn. Chez la plupart des espkces, I'augmentation absolue de la quantitC d'azote s'observe lorsque la dCcomposition a progress6 jusqu'a 213 jours. Cependant, chez Dnphne cannabina et Ilex dipyrenn, la quantitC absolue d'azote ne dCpasse jamais la quantitC initiale pendant la dCcomposition. La quantitC absolue de calcium dans les sacs de litikre diminue gCnCralement dans le temps. Les concentrations des composCs hydrosolubles et de glucides disponibles totaux varient d'une espkce a l'autre; cependant, ces deux classes de substances diminuent constamment mesure que la dCcomposition progresse. La libkration de I'azote, des composCs hydrosolubles et des glucides disponibles totaux atteint 100% en I an chez D. cnnnnbinn, A. indicn et I. rlipyrerln. Chez Cedrus deodnrn, Q . jloribunda et Q . leucotrichophora, environ 50% de I'azote total atteignant le plancher de la for&t sous forme de litikre est libCrC par la dCcomposition. Chez Cupressus tor~llosa, seulement 15% de I'azote de la litikre est libCrC en 1 an.

[Traduit par le journal]

Introduction In forested ecosystems, tree leaves are periodically or con-

tinually dropped on the ground. This leaf litter decomposes, releasing the nutrient into the soil for recirculation. The decomposition leads to chemical simplification of the various com- plex compounds resulting in the liberation of CO?, NH,, H?O, and mineral elements. According to MacLean and Wein (1978), the release of nutrients from forest litter through natural decomposition processes is recognized as being a very important part of the nutrient cycle whereby essential mineral elements tied up in the plant biomass are made available for further plant growth. Nutrient changes in the decomposing litter have been reported by Hayes (1965), Howard and Howard (1974), Anderson (1973a), Cromack and Monk (1975), MacLean and Wein (1978), and Jorgensen et al. (1980). The present paper deals with the nutrient concentration of decomposing litter and subsequent release of nutrients in important species of a mixed oak-conifer forest in Kumaun Himalaya. Decomposition rates for these litter species were presented earlier (Pandey and Singh 1982).

Materials and methods The study site is located at Naini Tal (29'24' N, 79'28' E) in a

protected reserve forest at an altitude of 2050 m on a northwest aspect. The site is covered with a mixed oak-conifer forest dominated by Crlpressus torrilosn D. Don. and Qriercris ,floribrlnrln Rehder. The

other important species are Ae.scrl/rls irlrlica Colebr., Quer-crls le~lco- trichophorn A. Camus, Ilex cli/)grenn Wall., and Cerlrrls rleoclnrn Roxb. The shrub layer is dominated by Arrlnrlinnrinfi~lcntn Nees and Dnphne cnrlrlnbinn Wall. Details of the vegetation, forest floor, and litter fall for the present site are given in Pandey and Singh (19810, 1981b).

The soil is derived from Krol limestone and contains 68% sand, 14% silt, and 18% clay. The surface soil has the following chemical composition (percent, + 1 SE): Kjeldahl nitrogen. 0.33 + 0.02; calcium, 2.17 k 0.12; organic carbon, 3.81 k 0.07.

Altitudinally, Naini Tal is located in a temperate environment but latitudinally i t is within the subtropical belt. The climate is markedly influenced by monsoon conditions. The mean monthly temperature ranges from 4.5 to 22°C. Climatically, the year is divisible into three seasons: summer (April to the first fortnight of June), rainy (second fortnight of June to September), and winter (Novembcr to February). March and October constitute transition periods between winter and summer seasons, and rainy and winter seasons, respectively. The annual rainfall averages 2488 mm, of which the greatest proportion (88%) occurs during the rainy season.

Preweighed, 5-g air-dried litter samples of seven species. namely A , inrlicn, Ce. rleorlr~rn, Cu. tor~llosa. D. car~r~nbinn, I. cIipyrenn, Q . ,floribur~rln, and Q. leucotrid~ophora were enclosed in nylon net bags (2 mm diameter apertures) and placcd on the forest floor on 10 February 1977 (Pandey and Singh 1982). Being an evergreen forest, leaf fall occurs throughout the year. Peak leaf fall in A . irlclicn, a deciduous species, occurs in September-October (Pandcy and Singh 198 1 b) . For this study, freshly fallcn leaves of the above species

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; o L , . t 3 L L L . 8 0 8 I L

030 120 210 300 390 480 0 30 I20 210 MO 390 480 D A Y S

4r ( g ~

0 1 1 . a o I L

0 30 120 210 300 390 480 DAYS

FIG. I . Changes in the concentration of nitrogen in leaf litter during decomposition. (a) Aesculus indica. (b) Cedrus deodara. (e) C U ~ ~ E S S L I S 10ru10sa. (d) Daphne cannnbina. (e) Ilex dipyretza. ( f ) Quercus jloribunda. (g) Quercus leuco~richophora. The bars represent 2 I SE.

were collected in October-November from the litter traps placed on the forest floor (Pandey and Singh 1981 b). The dry wcight equivalents were determined by oven-drying the stock litter samples. Three bags for each species were recovered periodically from the forest. brought to the laboratory, and the residual material was separated carefully from adhering soil particles, dried, weighed, and powdered (to pass through a sieve with I-mm pore size) for chemical analysis. Greatcr detail of experimental design is given in Pandey and Singh (1982). 'The residual litter samples were analyscd for total nitrogcn, calcium, water-soluble compounds (WSC), and total available carbohydratcs (TAC). WSC and TAC wcre determined for unwashed samples. All drying was done at 80°C to constant weight. The experiment was continued until 10 July 1978. The nitrogen content was determined by micro-Kjcldahl (Piper 1944). calcium content by titration after digestion in hot HN03 (Piper 1944), WSC according to Anderson (1973b), and TAC according to Smith (1969). WSC and TAC were determined on separate aliquots of the same stock sample.

Results In A . indica, D. cannabina, I . dipyr-ena, Q.flor-ibunda, and

Q. leucotrichophor-a there was almost a continuous increase in nitrogen concentration during decomposition, while in Ce. deodar-a and Cu. tor-ulosa an initial increase in the concentration was followed by a subsequent decrease (Fig. 1) . The differences in nitrogen concentration owing to species and to sampling dates were significant (P < 0.001); also, there was a significant interaction between species and dates ( P < 0.001) which indicated that the behaviour of litter s~ec ies in this

0 1 t 8 7 1 , ) ! . , 0 30 120 210 300 390 480 0 30 I20 210 300 390 480

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0 1 * * k

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DAYS

FIG. 2. Changes in the concentration of calcium in leaf litter during decomposition. (a) Aesculus indica. (b) Cedrrts deodara. (c) Cupres- sus lorulosa. (6) Daphne cant~abina. (e) 1le.y dipyrena. (f) Quercus jloribunda. (g) Quercus leuco~richophora. The bars represent t I SE.

position only D. cannabina, and after 12 1 days both D. cannabina and I . dipyr-ena were significantly different from other species. On 2 13th day only Cu. torulosn was different from other species. However, in the later stages, Ce. deodar-a and Cu. torulosa were significantly different from Q. jloribundr~ and Q. leucotrichophora. The nitrogen concentration increased significantly between days 12 1 and 304 in A . inrlica, and between days 12 1 and 2 13 in Ce. deorlarn, Q. ,floribunda, and Q. leucotrichophora.

To investigate whether nitrogen is lost from the leaves during decomposition or whether exogenous nitrogen enters the litter through immobilization, the following calculations were made. The absolute amounts (or mass in the sample) of nitrogen in the litter bags at various time intervals were calculated from the observed nitrogen concentrations and dry weights of the litter expressed as percentages of the initial weights of nitrogen present in the litterbags (Table 1). A value greater than 100% indicates a net gain in nitrogen, i.e., from an exogenous source, while a value less than 100% indicates that nitrogen is lost from the decomposing litter.

The total release of nitrogen from litter was 100% in A. indica within 335 days, 100% in D. cannrtbirla within 274 days, 100% in I. dipyrena within 304 days, 78% in C . deodara within 487 days, 73% in Cu. tor-ulosa within 487 days, and 90% in Q. floribunda and 70% in Q. leucotrichophora within 487 days.

regard varied across the dates. In the fresh leaf h e r , the nitro- Changes in calcium content gen content of A . indica, Ce. deodr~r-a. Cu. torulosa, Q . flori- The changes in the concentration of calcium did not show bunda, and Q. leucotr-ichophora was significantly different a uniform temporal pattern (Fig. 2). However, the differences from D. carznabina and I . dipyrena. After 29 days of decom- in percent calcium owing to species, to sampling dates, and the

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TABLE I . Nitrogen content of leaf material confined in litterbags

Period after Weight of litter Observed placement of remaining per litter bag Mass of N mass of N % change in

litter bans per litter bag as % of the mass (days)-

- Percent Grams (mg) initial mass of N

A. itldicn 0 100 4.34 48 - 0

29 97.35 4.23 50 104 4 121 80.32 3.49 48 100 0 213 32.68 1.42 33 69 -3 1 304 5.52 0.24 9 19 -8 1

(Total decomposition had occurred by 335 days)

Ce. deodnrn 0

29 121 2 13 304 395 487

Cu. rorulosn 0

29 121 213 304 395 487

D. cannabinn 0

29 121 2 13

100 4.41 113 -

93.65 4.13 95 84 29.71 1.3 1 39 35 0.45 0.02 0.6 0.5 (Total decomposition had occurred in 274 days)

I . dipyrena 0 100 4.6 1 8 8 - 0

29 93.06 4.29 67 76 - 24 121 54.23 2.50 48 55 - 45 2 13 18.01 0.83 17 19 -81

(Total decomposition by 304 days had occurred)

Q. floribunda 0 100

29 96.12 121 84.91 213 53.23 304 35.56 393 17.24 487 2.90

Q. leucorrichophorn 0 100

29 96.59 12 1 80.00 213 55.74 304 29.57 395 12.76 487 9.90

species-date interaction were significant (P < 0.001). In the later stages of decomposition (days 395-487) the difference fresh leaf litter and after 29 days of decomposition, the calcium between Ce. deodara and Cu. torulosa was not significant. content of Ce. deodara was significantly different from that of To quantify the loss of calcium during decomposition, calcu- Cu. torulosa, D . cannabina, and I . dipvrena. During days lations were made similar to those made for nitrogen, and 121 -213, Cu. torulosa was significantly different from the mass of calcium in the litter bags as percent of initial mass Ce. deodara, D . cannabina, and I . dipyrena. However, in the is given in Fig. 3A. It is evident that the greatest net release

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TABLE 2. Changes in the total amounts of nitrogen and calcium in the litterbags during the decomposition of leaf litter in certain species

Nutrient mass remaining (C/o of initial)

Decomposition Region Tree species time (months) Nitrogen Calcium Reference

New Hampshire, U.S. A.

North Carolina, U.S. A.

France

Australia

England

New Brunswick, Canada

Berlrla alleghenierl.sis Fagus grnndifulin Acer snccharum

Mixeel hcrrclwood litter Pirlrrs srrobrrs Fcrgrrs sylvnricn Fngus sylvaricn Qrrercrrs pefrnen Qrrercrrs perrcrea Errccrlyprrrs obliqucr Eucnlyprus obliqun Cnsrcrnea snrivn Fcrgrrs s?~lvaricn

Pirlrrs bnrrksinrza Pirlrrs Darlksicrna Acer rnbrrrm Acer rrrbrrrm Prrrr~us per~sylvnr1icn Prurlus per~sylvnr1icn Populus rrernuloides Popu1u.s rrernuloides Beruln pnpyrifern Berrrla pnpyrifern

Gosz er nl. (1973) Gosz el ell. (1973) Gosz el nl. ( 1973)

Cromack and Monk ( 1975) Cromack and Monk (1975) Lemee and Bichaut (1973) Lcmee and Bichaut (1973) Lemee and Bichaut (1973) Lcmee and Bichaut (1973) Attiwill (1968) Attiwill (1968) Anderson ( 19730) Anderson ( 19730)

MacLean and Wein ( 1978) MacLcan and Wein (1978) MacLean and Wein (1978) MacLean and Wein ( 1 978) MacLean and Wein ( 1 978) MacLean and Wein ( 1 978) MacLean and Wein (1978) MacLean and Wein (1978) MacLean and Wein (1978) MacLean and Wein (1978)

of calcium occurred in later periods of decomposition; the values were 100% (335 days) for A. itzclica, 78% (487 days) for C. deodcira, 82% (487 days) for Cu. torulosa, 100% (274 days) for D . cannabina , 100% (304 days) for I . dipyretza , 96% (487 days) for Q. ,floribuncla, and 87% (487 days) for Q. leucotrichophora.

Changes in water-sohtble compoutzcls The content of water-soluble compounds could be evaluated

up to a maximum period of 395 days for the slow-decomposing species and up to 121 days for the fast-decomposing ones (Fig. 4). Although the percent WSC fluctuated, a decreasing trend with time was evident in all species. In most species, this decrease started from the very beginning. However, while some species lost their WSC quickly, others did the same more gradually. Thus in the later stages of decomposition the amount of WSC was always very low in comparison to that in initial stages. The final detectable percentages of WSC in A. indica, Q. floribunda, and Q. 1eucotrichophor.n were higher (i.e., 6.66, 7.83. and 10.70%, respectively) compared with those of the two conifer species, namely Ce. cleodara (1.83%) and Clt. torulosa ( 1.67%).

Analysis of variance on these data indicated that the differences in percent WSC owing to species, sampling dates, and the species-date interaction were highly significant ( P < 0.001). More specifically, in the fresh leaf litter the WSC content in A. indica was significantly different from Ce. deodara, Cu. torulosa, and D . cantzabitza. In the later stages (after 29, 121, and 213 days of decomposition) significant differences occurred among the following three groups: (i) D. cannabitza and I . dipyrena, ( i i) Ce. deodara and

Cu. torulosa, and (iii) A . irzdica, Q . floributzcla, Q . leucotrichophora. The mass of WSC in the seven litter species decreased with time (Fig. 3B). Interestingly, the two conifer species lost WSC much more rapidly (90% loss in I2 1 days) than the broad-leaved oaks (90% loss in 304 days).

Changes in totrll available carbohydrates Changes in TAC concentration during different stages of

decomposition are shown in Fig. 5. During decomposition, the greatest decrease in the TAC content occurred in D. cannabinn followed by Q. floribunda, I. dipyrena, and Q. leucotrichophora. A lesser decrease in TAC content occurred in the two conifer species.

Analysis of variance indicated that the differences in percent TAC owing to species, sampling dates, and the species- date interaction were significant ( P < 0.001). The TAC concentration in the fresh leaf litter ofA. itzclica, Ce. deodclra, Q. floribunda, Q. leucotrichophorn, and I . clipyretza was significant~ different from that in Cu. torulosa and D . cannabinn. After 29 and 121 days of decomposition, Cu. torulosa and D . cantzabitza were different from all other species. After 2 13, 304, and 395 days of decomposition, A. itzclica, Ce. deodara, and Q. floribunda were similar among themselves and were different from Clt. torulosa and Q. leucotrichophora.

The loss of TAC from material placed for decomposition, with respect to initial value, during different intervals, is quan- tified in Fig. 3C. Although the loss was greater in the first sampling interval (29 days) for the two conifers as compared with the broad-leaved species, in subsequent periods the loss was much faster in the latter species. Thus, by day 304, while the conifers had lost only 74-76% of initial TAC. the broad-

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D A Y S

FIG. 3. Mass of nutrients in litterbags as percent of initial mass. (A) Calcium. (B) Water-soluble compounds. (C) Total available carbohydrates. ( a ) Aesculus indica. ( b ) Ceclrus cleo.ocl(ir(i. ( c ) Cilpress~ls torulosa. ( d ) Daphne canr~abina. ( e ) Ilex clipyrena. (f) Quercus jloribunda. ( g ) Querc~1.s leucotrichophora. Days: I = 29; 2 = 12 1 ; 3 = 213; 4 = 304; 5 = 395; 6 = 487.

leaved species had lost 87- 100%.

Discussion The concentration of N in the decomposing leaf litter in-

creased in all species except for Ce. deodara and Cu. torulosa, the increase being as much as threefold over the initial concentration in A. indica, Q. ji'oribunda, and Q. leucotrichophora. Increases in the concentration and in the mass of N in decomposing leaf litter have been observed by several researchers including Coldwell and Delong (1950), Gilbert and Bocock (19601, Bocock (1964), Will (1967), Hayes (1965), Anderson (19??,7), Gosz et al. (1973), Lemee and Bichaut (1973), and Howard and Howard (1974). These increases are often the consequences of three factors: a more rapid loss of carbon than of N (Ramacle and Vanderhoven 1973), an increase in the absolute amount of nitrogen (Jorgensen et al. 1980), and an immobilization of nitrogen by microorganisms (Aber and Melillo 1980, 1982; Melillo et al. 1982).

The absolute increases in the mass of N requires addition of N from exogenous sources. The possible sources include atmo-

L

0 X) 120 210 300 390 0 30 I20 210 300 393 DAYS

1

0 5 0 120 210 300 390 DAYS

FIG. 4. Changes in the concentration of total water-solublc compounds in the leaf litter during decomposition. ( a ) Aesculus inclica. ( b ) Cedr~rs deodara. ( c ) Cilpress~ls torillosa. ((1) Daphne ccinr~abir~a. ( e ) Ilex clipyrena. (J') Qilerc~ls j lorib~~r~cl(~. (g) Q~lercils leilcotricho- phora. The bars represent 2 1 SE.

spheric nitrogen (Olson 1933), atmospheric pecipitation, dust, insect frass (Bocock 1963), and nitrogen demand by the active heterotrophs (Gosz et al. 1973). Lemee and Bichaut (1973) and Hayes (1965) have attributed increases in the mass of nitrogen to translocation or fixation by microflora. Stark (1972) has shown that by concentration, protoplasmic movement, and au- tolysis, fungi may be able to move nutrients from one layer of soil to another. Ramacle and Vanderhoven (1973) reported maximal nitrogen fixation rate in theF horizon in a beech forest as 0.82 mg N - g dry weight-' . month-'.

According to Waksman and Tenny (1928), Tenny and Waksman (1929), and Waksman and Garretson (1931), for every unit of carbon oxidized by microorganisms, a certain amount of nitrogen must be assimilated. Anderson ( 1 9 7 3 ~ ) argued, therefore, that the addition of exogenous N to decomposing litter might accelerate the decomposition process.

In faster decomposing litter such as that of D. cannabina or I . dipyrena, however, an absolute increase in the mass of N was not apparent.

Values from other studies on changes in absolute amounts of certain nutrients during decomposition of leaf litter are summarized in Table 2 for comparison. It is evident that in several species the absolute amount of N was more than the initial N when decomposition had progressed for some time (e.g., up to 12 months), while the absolute amount was generally less than the initial N after 24 months. In the present study,

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-I a 0 3 0 1 2 0 2 1 0 3 0 0 3 9 0 030 120 210 300 390

k D A Y S 0

0 30 120 210 300 390 D A Y S

FIG. 5. Changes in the concentration of total available carbohydrates in leaf litter during decomposition. (a) Aescrtlrts indica. (b) Ceclrrts cleodara. (c) Cupress~ts torulosa. ( c f ) Daphr~e cnrlrzabirza . (e ) Ilex dipyrerla. ( j ' ) Querc~tsjloriburldc~. ( g ) Quer-cus leucotriclzo- phora. The bars represent + I SE.

in Ce. deodara, Cu. tonilosa, Q. Jlorib~trzda, and Q. leuco- triclzophora the mass of N expressed as percent of initial N was more than 100% at the end of 7 months but less than 100% at the end of the study. In the remaining three species, although the concentration of N in litter had increased over the initial concentration in certain periods, the absolute amount did not increase because of rapid weight loss.

Aber and Melillo (1980, 1982) and Melillo et al. (1982) demonstrated that decomposition can be described by an inverse linear relationship between the percentage of original mass remaining and the nitrogen concentration in residual material. This was true in our case for four species: A. irzdica, Y = 134.07 - 36.72X (r' = 0.94, P < 0.01); D. cnnnnbirza, Y = 395.03 - 124.14X ( r 2 = 0.85, P <: 0.05); Q. floriburzda, Y = 133.23 - 34.30X ( r 2 = 0.91, P < 0.01); Q . leucotrichophora, Y = 132.99 - 36.04X (r' = 0.86, P < 0.01), where Y is the percent weight remaining and X is the nitrogen content of the residual material (percent).

Aber and Melillo (1982) emphasized that a lignin-rich sub- strate provides more material for the production of perhumic substances and that much of the retained N is in the form of protein-lignin complexes rather than in microbial protein and, therefore, immobilization potential may be more a function of incomplete degradation than speed of decomposition.

The other three species, I. dipyrerzcl, CE . deorlara, and Cu. torulosa indicated an inverse relationship between percent weight remaining and nitrogen concentration, but the relationship was not statistically significant. The behaviour of Ca in the decomposing leaf litter was erratic and, in most cases, there was no pronounced decrease in the concentration for a larger part of the experimental period. Jorgensen et al. (1980) also reported that the concentration of Ca throughout the

decomposition period remained above or only slightly below that of the initial litter material. The erratic behaviour of Ca concentration was also noted by Gosz et al. (1973), Lemee and Bichaut (1973), Cromack and Monk ( 1975), and MacLean and Wein (1978). However, the mass of Ca in the litter bag declined owing to decomposition as reported in several studies (Table 2). Except for a few time intervals in Q. floriburzclc~ and Q . Ie~icotriclzophorc~, this was also true in the present study. MacLean and Wein (1978) observed increases in Ca content in decomposing branch litter of Acer, Prurzus, and Popuhis. Graustein et al. (1977) collected evidence from the litter layer of several forests to show that the associated fungi exude oxalic acid or oxalate abundantly enough to cause the precipitation of calcium. The producton of oxalate thus serves to retain calcium. The anaplerotic COz fixation might be involved in the synthesis of such Krebs tricarboxylic acid cycle intermediates in fungi (Caste and Hartman 1977).

Although the concentration of WSC and TAC varied from species to species, both these constituents continually decreased as decomposition progressed. This is understandable because most of the organic substances in plant leachates are soluble carbohydrates (Jensen 1974) and thus the TAC is mostly a leachable substance. The broad-leaved species lost their TAC more quickly than the conifer species.

In general, the loss of nutrients from the decomposing litter was greatest during the warm rainy season. The positive indi- vidual effects as well as the combined effect of rainfall and temperature on litter decomposition has already been discussed (Pandey and Singh 1982).

Pandey and Singh (1981b) estimated the amount of nutrients returned to the forest floor through the leaf fall in the species studied in the present paper. The total annual input and release of N , Ca, WSC, and TAC from the leaf litter are assessed in Table 3. The release was estimated by multiplying the input values by the fractional nutrient loss from litterbags in a year. Thus the release of N, Ca, WSC, and TAC was 100% in D. carzrzabina, A . inrlica, and I . dipyrena. In Ce. deoclara, Q. florib~irzda, and Q. leucotrichophora about half of the total N input was released by decomposition. In Cu. torulosa, only 14% of N falling as leaf litter was released during a period of 1 year. The annual release of Ca for Ce. cleohra, Cu. torulosa, Q . floriburzda, and Q . Ieucotrichophora exceeded three- quarters of the total calcium input. In these species, 95-99% of WSC and 78-95% of TAC were released within 1 year through decomposition. The massive input and release of WSC and TAC, which furnish readily available energy for microbial growth, would undoubtedly contribute to a fast turnover of the forest floor as was indeed reported for the present forest (Pandey and Singh 198 la) . The total annual release of nutrients on the site through decomposition relative to total input through litter fall amounted to 55% for N , 83% for Ca, 97% for WSC, and 92% for TAC. Compared with the present estimates, Jorgensen et al. (1980) reported an annual release of 6.9% N and 14.7% Ca in a 32-year-old Pirz~ls taeda plantation. The present study indicates a marked degree of functional diversity with respect to nutrient release. Thus, in this mixed forest, certain species release nutrients slowly while others do SO at a fast rate, pointing to the simultaneous occurrence of both slow and fast nutrient exchange pools. This functional diversity per- haps imparts a greater stability to mixed forest ecosystems as compared with monocultures.

Further, it would appear that the nutrients in the present

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TABLE 3. Annual input and release (kilograms per hectare) of nitrogen, calcium. water-soluble compounds, and total available carbohydrates owing to leaf litter and its decomposition

Water-soluble Total available Nitrogen Calcium compounds carbohydratc

Litter species Input Release Input Release Input Rclease Input Rclease

A . indico Ce. deodortr Cu. toruloso D. cotrnobitro I . dipyretrtr Q. jloribrrndtr Q. lerrcotrichophoro

Total Total release as

% of input

forest are released much more rapidly than in true latitudinally temperate forests (cf. Table 2).

Acknowledgements W e thank Dr. David C. Coleman, Natural Resource Ecology

Laboratory, Colorado State University, Fort Collins, C O , U.S.A. 80523, for reading the manuscript. Partial financial support from the Council of Scientific and Industrial Research, and the Department of Science and Technology, New Delhi, is gratefully acknowledged.

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Nutrient changes and release during decomposition of leaf litter in a Himalayan oak–conifer forest