Nitrogen dynamics of decomposing hardwood leaf litter in a central himalayan forest

Soil Bid. Biochem. Vol. 17. No. 6, pp. 827-830, 1985 Printed in Great Britain. All rights reserved

Copyright 8

0038-0717185 $3.00 + 0.00 1985 Pergamon Press Ltd

NITROGEN DYNAMICS OF DECOMPOSING HARDWOOD LEAF LITTER IN A CENTRAL HIMALAYAN FOREST UPADHYAY

V. P. Department

of Botany,

Kumaun

(Accepfed

and J. S. University,

SINGH*

Naini

Talk-263

002. India

15 February 1985)

Summary-The N dynamics in four decomposing broadleaf litter species of a mixed broadleaf forest in Central Himalaya was followed for a period of 578 days. The C:N ratio above which net immobilization and below which net mineralization took place, differed among species. Once the nitrogen release phase started, the release was in proportion to the weight loss.

INTRODUCTION

Several authors have suggested that the N content, the C-to-N ratio, the lignin content and the lignin-toN ratio determine the rate of litter decomposition (Waksman and Gerretsen, 1931; Fogel and Cromack, 1977; Berg and Staaf, 1980, 1981; Aber and Melillo, 1982). During the initial stages of decomposition, N controls the rate of decomposition, but with time lignin exerts a major influence (Pandey and Singh, 1982). In litter with a high lignin concentration, the N-controlled decomposition phase tends to be shortened (Berg and Staaf, 1980). We have investigated the N dynamics in four species of decomposing hardwood leaf litter from a mixed broadleaf forest in Central Himalaya. MATERIALS

AND METHODS

The site situated at 1350m altitude, 79”28’N lat. and 29”2 1‘E long. in the Central Himalaya, supports a mixed evergreen broadleaf forest. Quercus leucotrichophora A. Camus, Lyonia ovalifolia (Wall.) Drude., Symplocos ramosissima Wall., Quercus glauca Thumb., and Rhododendron arboreum Sm. are fairly well represented with scattered emergent trees of Pinus roxburghii Sarg. The rocks comprise thicklybedded hard compact sandstone associated with purple, red and green slates. The soil is residual, sandy loam with 82% sand, 10% silt and 8% clay; total soil N is 0.3% and organic C 3.5%. Climate is characterized by a summer monsoon and the year is divisible into three distinct seasons: rainy (mid-June-September), winter (NovemberFebruary) and summer (April-June). Temperature ranges between 8’ and 24°C and annual rainfall is 2005 mm. Litter species and methods Mature leaves of L. ovalijolia, Q. glauca, R. arboreum and Q. leucotrichophora were collected in May 198 1. Although leaf fall in this forest is perpetual, the

*Present address: Department of Botany, Banaras Hindu University, Varanasi-221 005, India.

peak fall is in May-June. The leaves were air-dried in the shade and 5 g samples were enclosed in 10 x 10 cm nylon mesh bags. The mesh size (1 mm) was large enough to permit aerobic microbial activity and free entry of small soil animals. For each of the four species 180 bags were randomly placed on the forest floor at the beginning of the rainy season of 1981 on 7 July. Five replicates (5 g each) from the stock litter sample were oven-dried at 60°C to calculate the dry weight of the enclosed litter. Three litter bags were recovered randomly every month for a year. At the end of the year, litter bags still remained for R. arboreum and Q. leucotrichophora and some of these bags were recovered every 122 and 90 days. respectively. The recovered material was carefully separated from soil particles, weighed, dried at 60°C to constant weight and reweighed. Then the samples were ground in a Wiley Mill and analysed for N (microKjeldah1; Piper, 1944). C-to-N ratios were calculated assuming C concentrations of approximately 50% of ash-free weight (McBrayer and Cromack, 1980). Lignin was estimated by using HCl-activated trig01 (Edwards, 1973). The trigol-lignin method was found superior to the Klason lignin method, as the regression coefficients involving trigol-lignin were less divergent, with smaller standard deviations, compared to Klason lignin (Edwards, 1973).

RESULTS AND DISCUSSION

Decomposition of Q. glauca and L. ovalifolia was faster throughout the decay period. N concentration increased 2.4 times in the residual litter from the initial in 365 days in L. ovalifolia and in 304 days in Q. gluuca. Decomposition was almost complete (90%) after 396 and 365 days, respectively, for the above two species, and after 608 days for R. arboreum and 520 days for Q. leucotrichophora. In the latter two species, the concentration of N was, respectively 2.4 times and 2.1 times that of the initial after 578 and 487 days (Table 1). The relationship between y0 weight remaining and N concentration in residual material was inverse (Fig. 1). L. ovalifolia and Q. leucotrichophora, having initial N concentration, respectively, of 0.80 and 1.15% showed a corresponding net release of 41 and 25% of

827

and

V. P. UPADHYAY

828 Table Days elapsed 0

62 123 184 243 304 365 487 578

I. Cumulative

weight loss and increase

Lyonia ovalijolia Weight N cont. loss (%) (%) 0.00 54.48 + 0.39 61.67 f 4.87 68.90 k 0.92 80.58 rt:0.89 85.98 +_ I .61 96.29 k 0.65

0.80 f 0.02 1.05 * 0.05 1.13 fO.O1 1.17*0.03 1.25 + 0.01 1.72 + 0.08 1.89 + 0.04

in N concentration

0.94 f 0.04 1.87+0.01 1.94 * 0.005 2.12 * 0.01 2.14 5 0.09 2.24 + 0.02

the initial N mass during the first 62 days of exposure in the litter bags. In L. ovalifoliu the release of N was more rapid than in Q. leucotrichophora. In both cases, N release and weight loss continued to the end of the experiment (Fig. 2). Q. glauca and R. arboreum showed an absolute increase in N mass during the first 62 days of decomposition; this increase was 5 and 21% over the initial N mass, respectively. Thereafter, both species released N and continued to do so to the end of the experiment. The relative increase in N concentration during decomposition is a well known phenomenon (Bocock, 1963; Gosz et al., 1973; Pandey and Singh, 1982) and usually occurs independently of whether or not there is an absolute increase of N mass. In our study, all litter species exhibited an increase in N concentration during decomposition (Fig. l), but the absolute in-

.

arboreum

%

remaining

0.00 0.70 f 0.01 25.26 f 2.50 0.70 * 0.01 1.20 * 2.02 36.43 f 2.68 40.14k6.71 1.24 f 0.01 44.78 k 1.44 1.26f 0.005 59.91 + 1.23 1.30 * 0.02 72.41 f 1.10 I .52 f 0.03 90.26 k 0.76 I .68 * 0.02 95.46 + 1.04 1.68 * 0.02

Quercus leucotrichophora Weight N cont. loss (%) (%) 0.00 31.85 f 5.05 39.80 + 3.48 48.70 f 3.11 55.74 + 3.61 72.26 k 2.14 87.05 f 0.71 97.45 f 0.20

1.15 kO.03 1.23 k 0.01 1.34 + 0.08 1.53 kO.01 1.74+_O.ll 1.78 f 0.05 1.95+ 0.02 2.42 k 0.01

1\ Quercus

Quercus

glauca

leucotrichophoro

N

10 residual

material

(Y) of the residual material as a function of N concentration (X): Lyonia r = 0.844, P < 0.01. Quercus glauca; Y = 165.40 -66.97X; r = 0.979, arboreum; Y = 178.16 - 99.1583 r = 0.959, P < 0.01. Quercus leucotrichophora; Y = 159.01 - 68.32X; r = 0.948. P < 0.01.

ooalifolia; Y = 125.68 - 69.66X; P < 0.01. Rhododendron

(% + 1 SE1

l\

20 c

Fig. 1. 7; weight

decomaosition

crease in N mass was observed only in Q. glauca and R. arboreum. Gosz et al. (1973) also found an increase in N mass in Quercus petraea but not in Fraxinus excelsior, Corylus avellana and Alnus glutinosa. Similarly, Anderson (1973) found an increase of N mass in Fagus sylvatica, but not in Castanea sativa. In Q. glauca and R. arboreum, N accumulated until about 4547% of the dry weight had been lost. Howard and Howard (1974) and Staaf and Berg (1977) reported that N accumulated in decomposing litter until about 35% of the dry weight had been lost for decomposing deciduous and Scats pine leaf litter, respectively. The initial concentration of N may determine whether or not there will be accumulation. Further, the N concentration for accumulation varies with the species and the system. Gosz et al. (1973) observed accumulation in litter which had initially up to 0.9%

Lyon10 ovalifol/a

Rhodouendron

during

Rhododendron arboreum Weight N cont. loss (%) (%)

Quercus glauca Weight N cont. loss (%) (%) 0.00 47.08 k 2.77 69.38 + 6.29 75.59 + 2.47 79.86 f 1.28 89.09 + 0.36

J. S. SINGH

Nitrogen dynamics in decomposing litter

t-

Rhododendron

829

Ouercus

gloffco

orboreum

140 r

I50

450

300

Days

Fig. 2. % N mass and % weight

remaining

N. Anderson (1973) found that no accumulation occurred at 0.8% whereas it took place at 0.6% N. Howard and Howard (1974) noted a small increase even at 3.03% initial G. In &r study, Q. gZauca and R. arboreum having initial N concentration, respectively of 0.9 and 0.7% accumulated N, whereas L. ovalifolia and Q. feucotrichophora with initial concentration of 0.8 and 1.15%, respectively, did not show accumulation. If the accumulation is considered a microbial process, it would depend on the microbial activity, and therefore, be related to weight loss of the substrate. Berg and Staaf (1981) found a strong correlation between weight loss and absofute amount of N uptake during the accumuIation phase for Scats pine needles. According to Flaig et al. (1959), lignin and some humification products decompose slowly and therefore, cause an increase in the absolute content of N in decomposing litter. Coldwell and Delong (1950) found an increase in N mass of 12 and 5%, respectively, for beech and birch leaves after 17 months

300

150

600

600

450

elapsed

during different periods of decomposition.

of incubation, whereas poplar and maple showed a decrease of 6 and 17%, respectively. This increase and release of N was linearly related with initial iignin Quercus

90

glauca

.

60 / 30

/' i

I

I

1

30

60

Hhododendron

1

90

orboreum

90

Table 2. Initial lignin level and N accumulated during the decomuosition of different soecies Species Lyon& aual~alia~ Quercus glauca” Rhododendronarboreum* Quercus leucotrichophora” Shorea robustah Ma/lotusphilippeak b Pinus roxburghiib Quercus lanuginosab Quercusfloribundab Myrica esculentab

Lignin

Accumulated N (T(,of initial N mass)

15.8 10.8 17.9 16.7 9.3 5.3 23.4 17.0 17.4 17.2

0 105 121 0 102 0 117 102 122 126

*Present study. bResults of Upadhyay and Singh (1984).

30

30

Total amount

N released ot

90

60

critical

(%

of

N level

)

Fig. 3. The relationship between weight loss of litter (as % of amount at critical N level; Y) and total N released (as % of amount at critical N level; A’): Quercus glauca; Y = - 3.30 + 0.977X; r = 0.996, P < 0.01. Rhododendron arboreum; Y = -6.23 + 0.969X; r = 0.997, P c 0.01.

V. P. UPADHYAYand J. S. SINCH

830

Table 2 illustrates the initial lignin level and N accumulated during decomposition for certain litter species of Himalayan forests. It is apparent that species having 17% or more of initial lignin accumulated more N during decomposition compared to those having lower lignin contents. Toth et al. (1974) recorded losses of N from the litter with low lignin contents and an a~umulation in those with a high lignin content. The nitrogen content of litter at which N release begins varies considerably. It has been suggested that the release of N from litter takes place at a C-to-N ratio of about 20-30 corresponding to 2.5-1.7x N (Lutz and Chandler, 1947). Q. gluuca started releasing N at C-to-N ratio of 25 whereas R. arboreum did so at C-to-N ratio 41. The critical N level from which the release started was 1.9 and 1.3%, respectively, for Q. glauca and R. arboreum. Once the release phase began in Q. glattca and R. arboreum, there was no further accumulation of N. There existed a strong positive relationship between % weight loss and % N release in the residual material of these two species (Fig. 3). concentration.

Acknowledgements-We

gratefully acknowledge

financial

support from the Department of Science and Technology, New Delhi, India.

REFERENCES Aber J. D. and Melillo J. M. (1982) Nitrogen immobilization in decaying hardwood leaf litter as a function of initial nitrogen and lignin content. Canadian Joltrnal of 3otuny 60, 22622269.

Anderson J. M. (1973) The breakdown and decomposition of sweet chestnut (Casranea sutiua Mill) and beech (Fugns syh~uticu L). leaf litter in two deciduous woodland soils: I. Breakdown, leaching and decomposition. Oecologia 12, 251-274. Berg B. and Staaf H. (1980) Decomposition rate and chemical changes of Scats pine needle litter. II. Influence of chemical composition. In Structure und Function of Northern Cont$erous Forests. An Ecosystem Study (T.

Persson, Ed.). Ecological

Bulletins

(Stockholm)

32,

373-390.

Berg B. and Staaf H. (1981) Leaching, accumulation and release of nitrogen in decomposing forest litter. In Terrestrial Nitrogen Cycles (F. E. Clark and T. Rosswall, Eds). Ecological Bulletins (Stockholm)

33, 163-178.

Bocock K. L. (1963) Changes in the amount of nitrogen in

decomposing leaf litter in sessile oak (Quercus petraeu). Journal of Ecology 51, 555-566.

Coldwell B. B. and Delong W. A. (1950) Studies on the composition of deciduous forest tree leaves before and after partial decomposition. Scienti$c Agriculture 30, 456466.

Edwards C. S. (1973) Determination of lignin and cellulose in forages by extraction with triethylene glycof. Journal of the Science of Food and Agriculture 24, 381-388.

Flaig W., Schobinger U. and Deuel H. (1959) Umwandlung von Lignin in Huminsauren bei der Verrottung von Weizenstroh. Chemishe Berichute 9, 1973-1982. Fogel R. and Cromack K. Jr (1977) Effect of habitat and substrate quality on Douglas fir litter decomposition in Western Oregon. Canadian Journal of Botuny 55, 1632-1640. Gosz J. R., Likens G. E. and Bormann

F. H. (1973) Nutrient release from decomposing leaf and branch litter in the Hubbard Brook forest. New Hampshire. Ecological Monographs 43, 173-191.

Howard P. J. A. and Howard D. M. (1974) Microbial decomposition of tree and shrub leaf litter. I. Weight loss and chemical composition of decomposing litter. O&OS 25, 341-352. Lutz H. J. and Chandler R. F. (1947) Forest Soils. Wiley, New York. McBrayer J. F. and Cromack K. Jr (1980) Effect of snowpack on oak-litter breakdown and nutrient release in a Minnesota forest. Pedobiologiu 20, 47-54. Pandey U. and Singh J. S. (1982) Leaf-litter decomposition in an oak-conifer forest in Himalaya: the effects of climate and chemical composition. Forestry 55, 47-59. Piper C. S. (1944) Soil and Plant Analysis. Interscience, New York. Staaf H. and Berg B. (1977) Mobilization of plant nutrients in a Soots pine forest mor in Central Sweden. S&U Fennicu 11, 210-217.

Toth J. A., Papp L. B. and Lenkey B. (1974) Litter d~om~sition in an oak forest ecosystem (Quercetum petrueu Cerris) of Northern Hungary studied in the frame work of “Sikfokut project”. In ~~odegrudutjon et Humzficatz’on.(G. Kilbertus, 0. Reisinger, A. Mouray and J. A. Cansela de Fonseca. Eds), pp. 41-58. Rapport due ler Colloque International Pierron, Sarreguimenes. Upadhyay V. P. and Singh J. S. (1984) Litter decomposition. In An Integrated Ecological Study of Eastern Kumaun Himalaya with Emphasis on Natural Resources

(J. S. Singh and S. P. Singh, Eds), pp. 227-263. Department of Science and Technology,- New Delhi, Kumaun University. Naini Tal. India. Waksman S. A. and-F. C. Gerretsen (1931) Influence of temperature and moisture upon the nature and extent of decomposition of plant residues by microorganisms. Ecology 12, 33-60.