Fungal colonization as affected by litter depth and decomposition stage of needle litter

The present study was designated to evaluate the relative effects of litter depth and decomposition stage of needles on fungal colonization of needle litter in field experiments. The experiment was carried out in coniferous temperate forests in central Japan. Needle litter of Chamaecyparis obtusa and Pinus pentaphylla var. himekomatsu at two decomposition stages (recently dead and partly decomposed) were placed into the organic layer at two depths (on the surface of and beneath the litter layer). Fungal colonization of needles after 1 year was examined in terms of hyphal abundance and frequency of fungal species. Total and live hyphal length on needles were affected by the litter depth and (or) the decomposition stage of needles. Length of darkly pigmented hyphae on needles was 1.7-2.6 times greater beneath the litter layer than on the litter surface regardless of the decomposition stage of needles. Length of clamp-bearing hyphae in Pinus pentaphylla was 5.0-5.2 times greater in partly decomposed needles than in recently dead needles regardless of the litter depth. Frequencies of Pestalotiopsis spp. and Cladosporium cladosporioides were higher on recently dead needles than on partly decomposed needles and (or) were higher on the litter surface than beneath the litter layer. Frequencies of Trichoderma, Penicillium, and Umbelopsis species generally were higher on partly decomposed needles than on recently dead needles and were higher beneath the litter layer than on the surface.     

辽西低山丘陵区针叶林与阔叶林枯落物持水性对比

为对比分析辽西低山丘陵区针叶林与阔叶林枯落物的持水性差异,为辽西森林植被恢复提供科学依据和技术支撑,选取3个针叶林(红松林、油松林、兴安落叶松林)和3个阔叶林(榆树林、山杨林、紫椴林)下的枯落物作为研究对象,采用野外现场采样与室内浸水相结合的方法对枯落物的持水特性进行测定.结果表明:针叶林平均蓄积量大于阔叶林,其中针叶林蓄积量在14.65 ～ 17.75 t/hm2,阔叶林在8.44 ～ 16.92 t/hm2;针叶林枯落物平均厚度(2.79 cm)大于阔叶林(2.44 cm);针叶林最大持水率在148.88％ ～ 173.19％,阔叶林在145.42％ ～156.91％;针叶林有效拦蓄水量为19.47～25.59 t/hm2,阔叶林有效拦蓄水量为10.56～ 22.04 t/hm2,表现为针叶林下枯落物的拦蓄能力更强;针叶林半分解层拦蓄水量显著大于未分解层,阔叶林未分解层拦蓄水量大于半分解层;阔叶林未分解层吸水速率大于针叶林.     

Succession of collembolan communities during decomposition of leaf and root litter: Effects of litter type and position

Little is known about the collembolan community involved in the decomposition of fine root (≤2.0 mm in diameter) litter, which is largely different from leaves in both litter quality and position. The collembolan communities involved in root and leaf litter decomposition were compared in a litterbag experiment in a coniferous forest of Chamaecyparis obtusa. A two-factor experiment (litter type × litter position) was conducted to evaluate the relative effects of litter quality and position. Litterbags of roots and leaves were each placed at two positions (on the soil surface and in the soil), and were collected at seven different times over three years. Abundance and biomass of Collembola involved in root decomposition in the soil were higher than those involved in leaf decomposition on the soil surface, and the collembolan community composition largely differed between these two types of litterbag. Differences between root and leaf decomposition were mainly caused by litter position, but effects of litter type were also detected at species-level. Species that preferred roots were abundant at an early stage of litter decomposition in the soil. Because the early stage of decomposition in the soil is naturally achieved only by root litter initially deposited in the soil, root litter may function as an essential resource for certain species. The results of this study indicate that root litter contributes to collembolan community organization as a spatially and qualitatively different resource than leaf litter. This also suggests that root litter is decomposed via different soil faunal processes than leaf litter.     

No ‘home’ versus ‘away’ effects of decomposition found in a grassland-forest reciprocal litter transplant study

Plant litter often decomposes faster in the habitat from which it was derived (i.e. home) than when placed in foreign habitats (i.e. away), which has been called the home-field advantage (HFA) of litter decomposition. We tested whether the HFA of litter decomposition is driven by decomposer communities being specialized at decomposing litter in their home habitat, by reciprocally transplanting litter from grassland to early-successional forest. Unexpectedly, we found an overall disadvantage for at-home decomposition despite large differences in litter quality (lignin:N) between the two habitats. We found more evidence for habitat specialization among secondary decomposers (mites) than the primary decomposers (bacteria and fungi), suggesting that soil animals may be important in driving HFA patterns where they do exist. Grass litter decomposition in forest slowed down and became more fungal-based, while tree litter decomposition in grassland increased yet showed no shift to being bacterially-based, relative to ‘at home’ decomposition. This suggests a biological explanation for why a positive HFA was not observed. Our results highlight that both environmental context and soil biology can play an important and sometimes counter-intuitive role in modifying decomposition. A better understanding of the interaction between all three primary drivers of decomposition (the environment, litter quality and soil organisms) is necessary for reliable prediction of decomposition at global scales.     

Amounts and degradability of dissolved organic carbon from foliar litter at different decomposition stages

Litter is one of the main sources of dissolved organic carbon (DOC) in forest soils and litter decomposition is an important control of carbon storage and DOC dynamics. The aim of our study was to evaluate (i) effects of tree species on DOC production and (ii) relationships between litter decomposition and the amount and quality of DOC. Five different types of leaves and needles were exposed in litterbags at two neighboring forest sites. Within 12 months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory. In the collected litter percolates we measured DOC concentrations and recorded UV and fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules. Furthermore, we investigated the biodegradability of DOC from fresh and decomposed litter during 6 weeks incubations. Fresh sycamore maple litter released the largest amounts of DOC reaching about 6.2% of litter C after applying precipitation of 94 mm. We leached 3.9, 1.6, 1.0 and 3.3% carbon from fresh mountain ash, beech, spruce and pine litter, respectively. In the initial phase of litter decomposition significantly decreasing DOC amounts were released with increasing litter mass loss. However, after mass loss exceeds 20% DOC production from needle litter tended to increase. UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter. However, for deciduous litter the relationship was less obvious. We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds. Biodegradability of DOC from fresh litter was very high, ranging from 30 to 95% mineralized C. DOC from degraded litter was on average 34% less mineralizable than DOC from fresh litter. Taking into account the large DOC production from decomposed needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.     

Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species.Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed.Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.     

Decomposition of beech leaves (Fagus sylvatica) and spruce needles (Picea abies) in pure and mixed stands of beech and spruce

The decomposition of spruce needles and beech leaves was investigated in a 30- and 120-yr-old beech, spruce and mixed (beech/spruce) forest using 1 mm mesh litterbags. The mass loss, content of C, N and water and microbial biomass, basal respiration and specific respiration of the litter materials were analyzed after exposure for 1.5, 3, 6, 9, 12, 18 and 24 months in the field. Decomposition of both types of litter was faster in beech than in spruce stands and after 24 months loss of C from litter materials was at a maximum in beech stands (>60%) and considerably less in the spruce and mixed stands (ca. 40%). Generally, spruce needles decomposed more rapidly than beech leaves, but the faster decay was not associated with higher N concentrations. Rather, N was accumulated more rapidly in beech leaves. Concomitantly, in beech stands microbial biomass of beech leaves exceeded that of spruce needles indicating that beech leaves consist of more favorable resources for microorganisms than spruce needles. Differences in decomposition between beech leaves and spruce needles were most pronounced in beech stands, intermediate in mixed stands and least pronounced in spruce stands. Decomposition, N content and microbial biomass in litter materials exposed in the 120-yr-old stand consistently exceeded that in the 30-yr-old stand indicating adverse conditions for litter decay in regrowing stands. Generally, mixed stands ranked intermediate between spruce and beech monocultures for most of the variables measured indicating that the adverse conditions for litter decay and microorganisms in spruce forest are effectively counteracted by admixture of beech to spruce monocultures. It is concluded that the accumulation of litter materials in spruce forests is not due to the recalcitrance of spruce needles to decay. Rather, adverse environmental conditions such as high polyphenol contents in the litter layer of spruce stands retard decomposition processes; spruce needles appear to be more sensitive to this retardation than beech leaves.     

Changes in the lignin fraction of spruce and pine needle litter during decomposition as studied by some chemical methods

Changes in the lignin fraction of spruce and pine needle litter were followed by four different methods: Klason lignin, phloroglucinol lignin, dioxane-water-HCl-lignin and alkaline CuO oxidation. The decomposition patterns of the lignins studied were different, the largest differences between the methods being obtained for the spruce needles. Depending on the method used, between 36 and 46% of the original amount of lignin remained in the pine needles and about 30–61% in the spruce needles after 3 yr of decomposition. The decomposition rates of the various lignin pools were highly correlated with the loss in mass of the litter. The phloroglucinol lignin was decomposed significantly faster (P < 0.001) in the spruce needles than in the pine needles for as long as the decomposition process was followed. During decomposition of the litter, the residual amount of Klason lignin was correlated with the residual amounts of the other lignins. The application of the different methods to litter decomposition studies is discussed.     

Saprotrophic fungi transform organic phosphorus from spruce needle litter

Fungal decomposition of and phosphorus transformation from spruce litter needles (Picea abies) were simulated in systems containing litter needles inoculated with individual saprotrophic fungal strains and their mixtures. Fungal strains of Setulipes androsaceus (L.) Antonín, Chalara longipes (Preus) Cooke, Ceuthospora pinastri (Fr.) Höhn., Mollisia minutella (Sacc.) Rehm, Scleroconidioma sphagnicola Tsuneda, Currah & Thormann and an unknown strain NK11 were used as representatives of autochthonous mycoflora. Systems were incubated for 5.5 months in laboratory conditions. Fungal colonization in systems and competition among strains were assessed using the reisolation of fungi from individual needles. After incubation, needles were extracted with NaOH and extracts were analysed using ³¹P nuclear magnetic resonance spectroscopy (NMR). Needle decomposition was determined based on the decrease in C:N ratio. Systems inoculated with the basidiomycete S. androsaceus revealed substantial decrease in C:N ratio (from 25.8 to 11.3) while the effect of ascomycetes on the C:N ratio was negligible. We suppose that tested strains of saprotrophic ascomycetes did not participate substantially in litter decomposition, but were directly involved in phosphorus transformation and together with S. androsaceus could transform orthophosphate monoesters and diesters from spruce litter needles into diphosphates, polyphosphates and phosphonates. These transformations seem to be typical for saprotrophic fungi involved in litter needle decomposition, although the proportion of individual phosphorus forms differed among studied fungal strains. Phosphonate presence in needles after fungal inoculation is of special interest because no previous investigation recorded phosphonate synthesis and accumulation by fungi. Our results confirmed that the ³¹P NMR spectroscopy is an excellent instrumental method for studying transformations of soil organic phosphorus during plant litter decomposition. We suggest that polyphosphate production by S. androsaceus may contribute to the phosphorus cycle in forest ecosystems because this fungus is a frequent litter colonizer that substantially participates in decomposition.     

不同生境条件下西藏原始冷杉林凋落物分解特征与土壤养分的关系

[目的]研究不同生境条件下(林内、林外、林缘)藏东南急尖长苞冷杉林(Abies georgei var.smithii)凋落物分解特征与土壤养分特征之间的关系,为深入了解高寒高山森林生态系统物质循环过程提供依据。[方法]采用野外分解袋法和室内分析相结合,在林内、林外、林缘3种不同生境条件下对藏东南急尖长苞冷杉林凋落物进行了原位分解试验。[结果]分解速率总体上呈现出:林内林缘林外的特点,逐月分解率的变异系数表现为:林内(34.83%)林缘(57.35%)林外(72.09%);Olson指数衰减模型的模拟结果显示不同生境条件下(林内、林缘、林外)凋落物分解50%需要的时间为2.11,2.52,2.34 a,分解95%需要的时间为8.96,10.01,10.84 a;3种不同生境土壤养分在空间上差异显著,林内生境中与凋落物分解速率呈现极显著相关的土壤养分因子有土壤总有机碳(TOC)含量、N含量、土壤微生物量碳(SMBC)含量、土壤微生物量氮(SMBN)含量以及W_C∶W_N值;林外、林缘生境中与凋落物分解速率相关性最大的为土壤TOC含量,其次为W_C∶W_N值。[结论]生境条件的差异对凋落物分解速率有显著影响,在不同的生境条件下对凋落物分解影响起主导作用的土壤养分因素不同,凋落物—土壤生物地化循环紧密联系,相互作用关系复杂,生境作用效应突出。     

Immobilization of avian excreta-derived nutrients and reduced lignin decomposition in needle and twig litter in a temperate coniferous forest

The possible effects of excreta of the Great Cormorant Phalacrocorax carbo on decomposition processes and dynamics of nutrients (N, P, Ca, K, Mg) and organic chemical components (lignin, total carbohydrates) were investigated in a temperate evergreen coniferous forest near Lake Biwa in central Japan. Two-year decomposition processes of needles and twigs of Chamaecyparis obtusa were examined at two sites, control site never colonized by the cormorants (site C) and colonizing site (site 2). Mass loss was faster in needles than in twigs. Mass loss of these litter types was faster at site C than at site 2, which was ascribed to the decreased mass loss rate of acid-insoluble ‘lignin’ at site 2. Net immobilization of N, P, and Ca occurred in needles and twigs at site 2; whereas at site C, mass of these elements decreased without immobilization during decomposition. Duration of immobilization phase of these nutrients at site 2 was estimated to be 1.6 to 2.5 years in needles and 19.6 to 23.5 years in twigs. Immobilization potential (maximum amount of exogenous nutrient immobilized per gram initial material) was similar between needles and twigs for N and Ca but was about 10 times higher in twigs than in needles for P. δ¹³C in needles was relatively constant during the first year and then increased during the second year, whereas δ¹³C in twigs was variable during decomposition. Acid-insoluble fraction was depleted in ¹³C compared to whole needles (1.6-2.1‰) and twigs (2.0-2.5‰). δ¹⁵N of needles and twigs and their acid-insoluble fractions approached to δ¹⁵N of excreta during decomposition at site 2. This result demonstrated the immobilization of excreta-derived N into litter due to the formation of acid-insoluble lignin-like substances complexed with excreta-derived N. No immobilization occurred in K and Mg and their mass decreased during decomposition at both sites. Based on these results of nutrient immobilization during decomposition and on the data of litter fall and excreta amount at site 2, we tentatively calculated stand-level immobilization potential of litter fall and its contribution to total amount of N and P deposited as excreta. Thus, the potential maximum amount immobilized into litter fall (needles and twigs) was estimated to account for 5-7% of total excreta-derived N and P.     

我国南亚热带几种人工林的生物物质循环特点及其对土壤的影响

通过对杉木、马尾松、红荷木、格木四种人工林的三年定位研究,初步获得了四种林木对主要营养元素的生物吸收和归还特点、对土壤养分状况、水分状况、微生物状况和土壤酶活性的影响等一系列资料。初步阐明了四种林木凋落物的数量及主要营养元素含量,研究了四种林木凋落物的分解特点。从而为进一步研究林木混交提供了科学依据。研究表明,阔叶树种与针叶树种相比,在改善土壤理化性状、提高土壤生产力等方面都表现出明显的优点。     

Mass loss and nutrient release during litter decay in peatland: The role of microbial adaptability to litter chemistry

In peatlands the reduced decomposition rate of plant litter is the fundamental mechanism making these peat-accumulating ecosystems effective carbon sinks. A better knowledge of litter decomposition and nutrient cycling is thus crucial to improve our predictions of the effects of anthropogenic perturbation on the capacity of peatlands to continue to behave as carbon sinks. We investigated patterns of plant litter decomposition and nutrient release along a minerotrophic-ombrotrophic gradient in a bog on the south-eastern Alps of Italy. We determined mass loss as well as P, N, K, and C release of seven vascular plant species and four moss species after 1 year in both native and transplanted habitats. Hence, differences in litter decay were supposed to reflect the degree of adaptability of microbial communities to litter quality. Polyphenols/nutrient and C/nutrient quotients appeared as the main parameters accounting for decomposition rates of Sphagnum litter. In particular, litter of minerotrophic Sphagnum species decomposed always faster than litter of ombrotrophic Sphagnum species, both in native and transplanted habitats. Decomposition rates of vascular plant litter in native habitats were always higher than the corresponding mass loss rates of Sphagnum litter. Minerotrophic forbs showed the fastest decomposition both in native and transplanted habitats in accordance with low C/P and C/N litter quotients. On the other hand, C/P quotient seems to play a primary role also in controlling decomposition of graminoids. Decomposition of deciduous and evergreen shrubs was negatively related to their high lignin content. Nitrogen release from Sphagnum litter was primarily controlled by C/N quotient, so that minerotrophic Sphagnum litter released more N than ombrotrophic Sphagnum litter. Overall, we observed slower N release from litter of ombrotrophic vascular plant species compared to minerotrophic vascular plant species. No single chemical parameter could predict the variability associated with different functional groups. The release of K was very high compared to all the other nutrients and rather similar between ombrotrophic and minerotrophic litter types. In Sphagnum litter, a higher C/P quotient was associated with a slower P mineralisation, whereas a faster P release from vascular plant litter seems primarily associated with lower C/P and polyphenols/P quotients.     

Experimental evidence for the interacting effects of forest edge,moisture and soil macrofauna on leaf litter decomposition

Forest ecosystems have been widely fragmented by human land use. Fragmentation induces significant microclimatic and biological differences at the forest edge relative to the forest interior. Increased exposure to solar radiation and wind at forest edges reduces soil moisture, which in turn affects leaf litter decomposition. We investigate the effect of forest fragmentation, soil moisture, soil macrofauna and litter quality on leaf litter decomposition to test the hypothesis that decomposition will be slower at a forest edge relative to the interior and that this effect is driven by lower soil moisture at the forest edge. Experimental plots were established at Wytham Woods, UK, and an experimental watering treatment was applied in plots at the forest edge and interior. Decomposition rate was measured using litter bags of two different mesh sizes, to include or exclude invertebrate macrofauna, and containing leaf litter of two tree species: easily decomposing ash (Fraxinus excelsior L.) and recalcitrant oak (Quercus robur L.). The decomposition rate was moisture-limited at both sites. However, the soil was moister and decomposition for both species was faster in the forest interior than at the edge. The presence of macrofauna accelerated the decomposition rate regardless of moisture conditions, and was particularly important in the decomposition of the recalcitrant oak. However, there was no effect of the watering treatment on macrofauna species richness and abundance. This study demonstrates the effect of forest fragmentation on an important ecosystem process, providing new insights into the interacting effects of moisture conditions, litter quality, forest edge and soil macrofauna.     

Decomposition and macroinvertebrates in experimental litter along a secondary chronosequence of tropical montane forest

This paper presents the results of a decomposition experiment performed in a secondary chronosequence of tropical montane cloud forest in Mexico. The experiment was designed to explore whether the age of the forest influences the decomposition process and macroinvertebrate community independently of the quality of the decomposition resources. Fresh Pinus chiapensis needles and Persea americana leaves were set to decompose in each of four successional stages (15, 45, 75 and 100 years old). Results do not support the hypothesis that decomposition rate declines with increasing nutrient deficiency as forest succession proceeds. However, the chemical composition in decomposing leaves differed between successional stages. Higher availability of Ca in the 15-year-old forest appears to promote a positive feedback in the release of this nutrient from Persea americana leaves. Additionally, in old forests, a soil community that is more capable of breaking down recalcitrant material (acid detergent lignin) appears to have developed compared to early successional stages. The diversity of macroinvertebrates and abundance of predatory (Aranea and Diplura), detrivorous (Diplopoda) and geophagous (Enchytaeidae) taxa were different between boxes placed in different successional stages. We conclude that the decomposition and associated biota differ between successional stages. Apart from differences in litter quality, other factors associated with the age of the forest, such as small differences in soil temperature and long-lasting effects of disturbance, may also play influential roles.     

重庆缙云山典型林分的坡面糙率系数及影响因素

根据2008年4月实测数据,以三峡库区重庆缙云山4种典型林分（马尾松纯林、马尾松阔叶混交林、常绿阔叶林和楠竹林）为研究对象,并以农耕地作对照,在野外径流小区实验的基础上,通过曼宁公式,对重庆缙云山林地坡面糙率系数n值进行研究。结果表明：地表糙率系数n值介于0.0079-0.2704之间,其中,马尾松纯林的糙率系数n值最小,马尾松阔叶混交林的糙率系数n值最大,大小排序为马尾松阔叶混交林〉阔叶林〉楠竹林〉马尾松纯林;糙率系数n（y）与枯落物厚度（x）的关系为Y=0.0205e^0.5436x,R^2=0.9237;地表水分渗透量（y）随着糙率系数n（x）增加而增大,其关系式为y=37.25lnx＋188.47,R^2=0.7782。     

Litter decomposition and faunal activity in Mediterranean forest soils: effects of N content and the moss layer

Accumulation of soil carbon is mainly controlled by the balance between litter production and litter decomposition. Usually In Mediterranean forests there are contrasting conditions in the distribution of faunal activity and the moss layer that may have different effects on litter decomposition. Decomposition and faunal activity were studied by exposing litter of contrasting quality (Pinus halepensis Mill. and Quercus ilex L.) for 3.5 yr in three Mediterranean pine forests of the eastern Iberian Peninsula. The effects of mosses on decomposition and on faunal activity were studied by exposing P. halepensis litter either on moss patches or directly on the forest floor. Faecal pellet production was used as an indication of faunal activity. Water availability or soil characteristics seem to limit faunal activities in the drier sites. Faecal pellets were not found during the first stages of decomposition and in all sites they appeared when about a 30% of the initial litter had decomposed. Under wet conditions faecal pellet production was very high and a mass balance suggested that soil faunal activity may result in a net flow of organic matter from the lower organic horizons to the surface Oi horizon. Mosses slightly increased mass loss of pine litter probably as a consequence of high potentially mineralizable nitrogen in the Oa horizon of moss patches and also, perhaps, as a consequence of the higher moisture content measured in the Oi horizon needles sampled among the mosses. In contrast, moss patches reduced faunal activity. The effect of litter quality on mass loss was not always significant, suggesting an interaction between litter quality and site conditions. During the first stages of decomposition there was N immobilisation in P. halepensis litter (poorer in N) and N release from Q. ilex litter (richer in N). In conclusion, in these forests soil microclimate and/or N availability appear to be more important controlling litter decomposition than the distribution of faunal activity.     

Effects of nitrogen addition and litter properties on litter decomposition and enzyme activities of individual fungi

Litter decomposition is an important process of C and N cycling in the soil. Variation in the response of litter decomposition to nitrogen (N) addition (positive, negative or neutral) has been observed in many field studies. However, mechanism about variability in individual fungal species response to N addition has not yet been well demonstrated in the literature. Therefore, the objective of this study was to investigate the effects of N addition and litter chemistry properties on litter decomposition and enzyme activities of individual fungi. Three fungal species (Penicillium, Aspergillus, and Trichoderma) were isolated from a subtropical mixed forest soil. An incubation experiment was conducted using the individual fungi with two types of litter (leaf of Pinus massoniana and needle of Cryptocarya chinensis) and different N addition levels (0, 50 and 100 for N-deficient treatments, and 500 and 1000 μg N for N-excessive treatments). Cumulative CO₂-C, enzyme activities, and lignin and cellulose loss were measured during the incubation period of 60 days. Litter decomposition and enzyme activities significantly varied with the fungal species, while the N addition and litter types greatly affected fungal enzyme activities. The N treatments significantly increased lignin-rich needle decomposition by lignocellulose decomposers (Penicillium and Aspergillus) but did not affect their leaf decomposition. On the contrary, The N treatments stimulated leaf decomposition by cellulolytic species (Trichoderma) but did not affect its needle decomposition. Correlation analysis showed that lignin in the litter was the key component to affect litter decomposition. Activities of N-acetyl-β-glucosaminidase and phenol oxidase were both positively correlated to litter decomposition. The fungi (Penicillium and Aspergillus) with higher production of N-acetyl-β-glucosaminidase showed higher litter decomposition ability. The low N addition levels stimulated Penicillium and Aspergillus litter decomposition, but they still required more N source (e.g., litter N source) to support decomposition. Depressed fungal litter N uptake (lower N-acetyl-β-glucosaminidase activities) only occurred at the highest N addition level. Litter decomposition of Trichoderma depended more on external N and its litter decomposition capability was the lowest among the three species.     

黄土丘陵区不同林分类型枯落物层及其林下土壤持水能力研究

研究了青海省黄土丘陵区13种林分类型的枯落物层持水能力,并以荒山荒坡作为对照样地研究其表层土壤物理性质与持水能力.结果表明:不同植被类型,枯落物层平均蓄积量为混交林>针叶林>阔叶林,而平均最大持水量为混交林>阔叶林>针叶林,枯落物层平均厚度和平均有效持水量呈现相同规律,为阔叶林>混交林>针叶林;其土壤表层的总孔隙度、非毛管孔隙度均与枯落物层平均蓄积量呈现相同规律,且有林地土壤有效持水量是对照样地荒山荒坡的2.47～4.07倍.     

Leaf litter fall and litter decomposition under Eucalyptus and coniferous plantations in Gambo District,southern Ethiopia

Abstract

Litter fall and its decomposition rate play an important role in nutrient recycling, carbon budgeting and in sustaining soil productivity. Litter production and the decomposition rate were studied on commonly planted broad-leaved Eucalyptus (Eucalyptus globulus, Eucalyptus camaldulensis, Eucalyptus saligna) and coniferous (Juniperus procera, Cupressus lusitanica, Pinus patula) plantation species and compared with the adjacent broad-leaved natural forest. The production of litter was recorded by litter traps and the decomposition rate was studied by nylon net bag technique. Litter production under broad-leaved plantation species and natural forest (that varied from 9.7 to 12.6 Mg ha^?1 y^?1) was significantly higher (p<0.05) than that under coniferous species (that varied from 4.9 to 6.6 Mg ha^?1 y^?1). The average concentration of C and N in fresh mature leaves was higher than in leaf-litter fall, implying that both C and N were either sorbed in the plant system or lost through decomposition, leaching or erosion during the leaf-litter fall period. The amount of N, which potentially returned to the soil through the leaf-litter fall, tended to be higher in natural forest than in Eucalyptus plantations. The residual litter mass in the litter bag declined with time for all species. The annual dry matter decay constant (k) varied from 0.07 m^?1 in Pinus patula to 0.12 m^?1 in Eucalyptus saligna. The half-time (t_0.5) decay varied from 6.0 for Eucalyptus saligna to 9.7 months for Pinus patula. The results suggest that the decomposition rate in Pinus patula was relatively lower than the other species and the litter production under broad-leaved Eucalyptus was comparatively higher than that in coniferous species. Overall the litter decomposition was fast for all species. The higher litter production and its relative faster rate of decomposition is a positive aspect to be considered during species selection for the restoration of degraded habitats given other judicious management practices such as prolonging the rotation period are adhered to.