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.     

Decomposition and substrate quality of leaf litters and fine roots from three exotic plantations and a native forest in the southwestern highlands of Ethiopia

Substrate quality and decomposition (measured as CO₂ release in laboratory microcosms) of fresh leaf litter and fine roots of Cupressus lusitanica, Pinus patula, Eucalyptus grandis and native forest trees were studied. Changes in litter chemistry in each forest stand were analysed by comparing fresh leaf litter (collected from trees) and decomposed litter from the forest floor. Elemental concentrations, proximate fractions including monomeric sugars, and cross polarisation magic-angle spinning (CPMAS) ¹³C NMR spectra were analysed in leaf litters, decomposed litter and fine roots. Leaf litters and fine roots varied in their initial substrate chemistry with Ca concentration in leaf litters being higher than that in fine roots. In each stand, fine roots had a higher acid unhydrolysable residue (AUR) (except for the Pinus stand), higher holocellulose concentration and lower concentration of water-soluble extractives (WSE) and dichloromethane extractives (NPE) than fresh leaf litter. Likewise, ¹³C NMR spectra of fine roots showed lower alkyl and carboxyl C, and higher phenolic (except P. patula), aromatic and O-alkyl C proportions than leaf litters. Compared with fresh leaf litter, decomposed litter had lower concentrations of potassium, holocellulose, WSE, NPE, arabinose and galactose, similar or higher concentrations of Mg, Ca, S and P, and higher concentrations of N and AUR. CPMAS ¹³C NMR spectra of decomposed litter showed a higher relative increase in signal intensity due to methoxyl C, aromatic C, phenolic C and carboxylic C compared with alkyl C. In a microcosm decomposition study, the proportion of initial C remaining in leaf litter and fine roots significantly fitted an exponential regression model. The decomposition constants (k) ranged between 0.0013 and 0.0030 d⁻¹ for leaf litters and 0.0010-0.0017 d⁻¹ for fine roots. In leaf litters there was a positive correlation between the k value and the initial Ca concentration, and in fine roots there was an analogous positive correlation with initial WSE. Leaf litters decomposed in the order Cupressus>native forest>Eucalyptus∼Pinus, and fine roots in the order Pinus>native forest>Cupressus∼Eucalyptus. In each stand the fine root decomposition was significantly lower than the leaf litter decomposition, except for the P. patula stand where the order was reversed.     

Decomposition and Nutrient Release from Litter Fall in the Semi‐arid Tropics of Sudan

In Sudan, tree plantations remain the first choice and are widely used in protecting arable lands from sand movement. Decomposition and nutrient changes from leaves of some agroforestry trees (Eucalyptus microtheca, Ficus spp., and Leucaena leucocephala) and litter fall from guava (Psidium guajava) and mango (Magnifera indica) were monitored (in a 12‐week litter‐bag experiment). Rate of dry‐matter weight loss from guava (0.098 wk^?1) was significantly (P < 0.01) faster than from mango residues (0.04 wk^?1). Corresponding values for Leucaena, Eucalyptus, and Ficus were 0.0533, 0.0524, and 0.0438 wk^?1, respectively. In general, micronutrients tend to accummulate during a decomposition period. Potassium (K) was the only element found to be consistently lost by leaching very rapidly from all litters. Nitrogen (N) was released at a significantly (P < 0.03) higher rate from Leucaena (0.0558 wk^?1) compared to Ficus (0.0399 wk^?1) and Eucalyptus (0.0301 wk^?1). Mobility of nutrients from the litters was in the order of K > phosphorus (P) = N > calcium (Ca) > magnesium (Mg). It is concluded that ficus and mango leaves are suitable for improving quality of arid soils through buildup of soil organic matter and supplying easily released organic sulfur (S) (environmentally sound management practice) whereas litter from guava is suitable for temporary nutrient correction. Mixing of guava and mango residues may slow fast decomposition of the former.     

小五台山地区主要林分枯落物分布特征及水源涵养能力

为评估小五台山地区主要林分的水源涵养能力,同时为筛选水源涵养树种提供新思路,通过浸泡法和模拟降雨法,对小五台山地区7种典型林分枯落物分布特征及水源涵养能力进行研究。结果表明:(1)林分枯落物覆盖面积和厚度均表现为阔叶林大于针阔叶混交林、针叶林,其最大分别为青杨纯林和蒙古栎纯林,且厚度表现出坡下大于坡上的特征;(2)枯落物蓄积量为油松纯林＞青杨纯林＞油松×蒙古栎混交林＞白桦纯林＞粉桦×云杉混交林＞蒙古栎纯林＞椴树纯林,其中半分解层大于未分解层;(3)枯落物吸持能力表现为半分解层大于未分解层,且针阔叶混交林和大部分阔叶林大于针叶林,其中青杨纯林的最大,最大持水量、有效拦蓄量和最终吸持量分别为1.69,1.37,0.41 mm;(4)所有林分枯落物持水率均表现为浸泡法大于模拟降雨法,只采用传统的浸泡法会导致研究结果偏大。各林分枯落物水源涵养能力表现为阔叶林和针阔混交林优于针叶林,其中青杨纯林和白桦纯林水源涵养能力最强,在今后水源涵养林的树种筛选中可考虑多选择青杨和白桦等阔叶树。     

Effects of fungal inocula on the decomposition of lignin and structural polysaccharides in Pinus sylvestris litter

 Litter bags containing sterile Scots pine (Pinus sylvestris) needles (19.8% lignin, 26.5% cellulose and 0.34% N) were inoculated with two species of fungi in the laboratory and then placed in the litter layer of a pine plantation. Marasmius androsaceus, which can degrade lignocellulose, was initially displaced by other fungal colonisers and was not detected in the litter after 2–3 months; but was re-isolated from the needles after 12 months. Trichoderma viride, which is a cellulolytic species and also antagonistic to other fungi, dominated the litter throughout the experiment. The control litter was naturally colonised by litter fungi. After 12 months, mass losses were similar at 52% for M. androsaceus and 48% for T. viride, compared with 36% for the control litter colonised by a more complex fungal community. Lignin concentrations increased with time in control litter and with T. viride because mass losses of carbohydrates were greater than those of lignin. Litter inoculated with M. androsaceus showed significant lignin decomposition throughout the experiment but cellulose concentrations showed a proportional increase in the first 6 months, suggesting that the fungus was preferentially exploiting hemicellulose and non-structural carbohydrates. Analysis of TFA-extractable sugars (mainly from hemicellulose) and CuO-derived phenylpropanoid moieties from lignin confirmed the differential patterns of resource decomposition which were not evident from total mass losses. During the initial stages of decomposition, T. viride was as effective in utilising structural polysaccharides as the complex fungal community in the control litter. Furthermore, M. androsaceus not only exhibited unexpectedly low cellulolytic activity but also facilitated lignin depolymerisation after the fungus was no longer detectable in the litter. The pre-inoculation of litter with these two fungal species therefore affected the overall dynamics of decomposition at a biochemical level. This study illustrates the importance of understanding the effects and interactions of specific fungi, rather than assumptions about the functional competence of diverse communities, on the processes of litter decomposition. Received: 5 July 2000     

Effect of litter quality on its decomposition in broadleaf and coniferous forest

Recently there has been much interest in the effect of litter mixing as well as the effect of different forest habitats on the decomposition process. Our aim was to test two hypotheses: high quality litter promotes decomposition of poor quality litter, and litter decomposes faster in broadleaf than in coniferous forest. We conducted a litter mixing experiment using litterbags placed in two forest floors, in which treatments consisted of litter monocultures of each of two campy species (Castanopsis eyrei and Pinus massoniana), as well as mixtures of these two species. The results showed that C. eyrei leaves decomposed significantly faster in the coniferous habitat than in their native habitat. On the other hand, P. massoniana needles decomposed significantly faster in their native coniferous habitat than in the broadleaf habitat. In our experiment we found that the mixture had different effect on different quality litter. P. massoniana needles (poor quality) had a positive effect on the decomposition of C. eyrei leaves (high quality), while C. eyrei leaves had a negative effect on the decomposition of P. massoniana needles in the mixture case in both broadleaf and coniferous habitats. The diversity of the fungi identified from different litters varied among treatments and the mass loss was positively correlated with the Shannon–Weaver diversity index of fungi. It is suggested that fungi may be one of the major drivers to control the decomposition process.     

Litter decomposition reduces either N2O or NO production in strongly acidic coniferous and broad-leaved forest soils under anaerobic conditions

Purpose

The beneficial effect to the environment of nitrate (NO₃ ^?) removal by denitrification depends on the partitioning of its end products into nitrous oxide (N₂O), nitric oxide (NO), and dinitrogen (N₂). However, in subtropical China, acidic forest mineral soils are characterized by negligible denitrification capacity and thus reactive forms of N could not be effectively converted to inert N₂, resulting in a negative environmental consequence. In this study, the influences of C input from litter decomposition on denitrification rate and its gaseous products under anoxic conditions in the acidic coniferous and broad-leaved forest soils in subtropical China were investigated using the acetylene (C₂H₂) blockage technique in the laboratory.

Materials and methods

The coniferous and broad-leaved forest soils with and without litter addition were incubated under anaerobic conditions for 244 h. There were three treatments for each forest soil including addition of 0.5 and 1% corresponding litter (gram of litter per gram of soil) and the control without addition of litter.

Results and discussion

The results showed that litter addition into the broad-leaved forest soil had no effect on average rates of denitrification (calculated as the sum of NO, N₂O, and N₂), whereas in the coniferous forest soil, the addition resulted in a significant increase in average denitrification rate. In the broad-leaved forest soil, both rates of litter addition decreased the production of NO but increased the production of N₂, and high rates of litter addition into the coniferous forest soil promoted the reduction of N₂O to N₂.

Conclusions

Increased decomposition of litter in the forest soils could effectively reduce N₂O and NO production through denitrification under anaerobic conditions.     

太行山典型区域不同林分类型枯落物水文效应

采用样地调查和室内浸泡法,对河北易县洪崖山自然保护区葫芦峪林场6种不同林分类型枯落物的水文效应进行研究。结果表明:6种林分类型枯落物的蓄积量范围为5.25～15.70 t/hm~2,蓄积量总体为阔叶林刺槐最大,针阔混交林次之,针叶林最小,各林分半分解层蓄积量总体大于未分解层(油松纯林、黑枣和油松混交林未分解层大于半分解层);最大持水量范围为10.55～25.04 t/hm~2,阔叶林栓皮栎(25.04 t/hm~2)最大,刺槐纯林(23.66 t/hm~2)次之,针叶林油松(10.55 t/hm~2)最小;最大持水率范围是171.19%～260.20%,针叶林油松最大,侧柏最小;有效拦蓄量范围为6.25～17.60 t/hm~2,阔叶林栓皮栎(17.60 t/hm~2)最大,刺槐纯林次之(17.30 t/hm~2),针叶林侧柏(6.25 t/hm~2)最小;有效拦蓄率略有不同,针叶林油松最大,其值为180.29%,阔叶林栓皮栎(162.98%)次之,针阔混交林黑枣和油松最小,其值为77.22%。综合研究分析表明,栓皮栎和刺槐的枯落物层持水能力较佳,该地区栓皮栎林和刺槐林枯落物层水源涵养能力优于其他4种林分类型的枯落物。     

Decomposition and nutrient content of litter in a fertilized eucalypt forest

The decomposition and nutrient content of litter was studied for 2 years in regrowth Eucalyptus diversicolor forest to which N (0, 200 kg ha^-1 year^-1) and P (0, 30, 200 kg ha^-1) had been applied. The P addition increased, and the N addition decreased, the rate of dry weight loss of decomposing litter. Analysis of the coefficients of a double exponential decay model with components describing the release of labile and resistant fractions indicated that decomposition of the resistant component of litter was most affected by the fertilizer additions. Treatment with N reduced the rate of loss of this component and increased its half-life by approximately 30%, whereas P treatment increased its rate of decay and decreased its half-life by approximately 30%. P accumulated in litter during decomposition. P uptake and retention was greater in P-treated than untreated plots. The application of N reduced P accumulation in litter. An accumulation of N also occurred during decomposition, the amount of N imported into litter being greater on plots treated with N fertilizer. Treatment with N affected the amount of S in decomposing litter. Litter on N-treated plots either accumulated more S or released it more slowly than litter on plots not treated with N. The application of N as NH₄NO₃ decreased forest-floor litter pH, increased litter layer mass (by 15%), and increased the amount of N (by 34%) and S (by 32%) stored in the forest floor. Treatment with P reduced the amount of N (by 22%) stored in the litter layer. The application of 200 kg P ha^-1 in the absence of N increased the store of P in the litter layer by 80%, but when N and P were applied together the amount of P in the litter was not significantly different between P treatments.     

Effects of surface fire on litter decomposition and occurrence of microfungi in a Cymbopogon polyneuros dominated grassland

Abstract

Litter decomposition rate, changes in macronutrients such as nitrogen (N), phosphorus (P) and potassium (K) from different grades of litter decomposition and occurrence of soil microfungi were investigated in a Cymbopogon polyneuros-dominated tall grass ecosystem from a burned and an unburned site in southern India. The litter decomposition rate was higher at the burned site than at the unburned site. This rate was also higher when the litter was mixed with the mineral soil material than leaving the litter unaffected on the soil surface. The concentrations of N, P, and K in the litter decreased as a result of progressed litter decomposition. Occurrence of microfungi identified from the different decomposition grades of the Cymbopogon polyneuros litter was higher at the burned site compared to the unburned site. Microfungal species present at both sites showed only minor differences.     

Influence of elevated ecosystems levels on litter decomposition and mineralization

Litter decomposition was studied at two forested watersheds in east Tennessee which differed primarily in their past history of atmospheric S input. Cross Creek Watershed, located near a large coal-fired power plant, has received greater S inputs than the more remote Camp Branch Watershed. Decomposition was estimated through the measurement of forest floor respiration, litter microflora populations, litter and soil microarthropod populations, and litter nutrient status. Average forest floor respiration rates were very similar, 6.78 g CO₂ m^?2 day^?1 or 2472 g m^?2 yr^?1 at Camp Branch and 6.86 g CO₂ m^?2 day^?1 or 2505 g M^?2 yr^?1 at Cross Creek. Fractional loss rates provided estimates of annual decay rates (k) of 0.35 and 0.39 for Camp Branch and Cross Creek, respectively. Litter decomposition was estimated to contribute 23% of the total CO₂ output at Camp Branch and 26% at Cross Creek, while root respiration accounts for about 43 to 46%. Bacterial and fungal populations were about equal in size at both watersheds, with bacteria averaging 100 × 106 g^?1 of litter and fungi 23 × 106 g^?1 of litter. Total numbers of arthropods averaged 34% greater at Camp Branch. Acarina populations averaged 59% higher at Camp Branch, while Collembola numbers were about equal at the two watersheds. Nutrient mobility in the litter and soil was similar at both watersheds. The order of decreasing mobility was K, Mg, Ca, S, N, and P. Litterfall nutrient concentrations were slightly higher for all elements at Cross Creek, resulting in greater litter concentrations of Ca and Mg. Litter concentrations of S and N, however, were significantly greater at Camp Branch, indicating watershed differences in the loss rates and cycling processes of these elements. There were no differences between the loss rates or litter concentrations of P, K, and Na at either site. Overall, decomposition was similar at the two watersheds. Historic S inputs do not appear to have had a major effect on decomposition rate or decomposer organisms with the possible exception of lowered arthropod populations at Cross Creek.     

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.     

多因素干扰下森林公园枯落物水文效应

为探究森林公园植被的水源涵养能力,为森林公园植被配置和经营管理提供依据,研究选取天龙山森林公园6种林分(油松、山杨、刺槐、油松—侧柏混交林、侧柏—油松—杏树混交和灌木林)为研究对象,通过测定林下枯落物厚度、蓄积量、持水性能和干扰度等指标,研究不同林分类型枯落物水文效应。结果表明:(1)所有林分枯落物干扰度范围为无到中度,厚度范围为0.57~2.63 cm,山杨最厚,侧柏—油松—杏混交林最薄;蓄积量范围为7.20~16.30 t/hm²,油松—侧柏混交林最大,侧柏—油松—杏混交林最小。(2)6种林分除山杨林以外,半分解层最大持水量均大于未分解层持水量,其中油松—侧柏最大,山杨最小;未分解层最大持水率均大于半分解层,刺槐最大,灌木林最小。枯落物的总最大持水量为20.02~27.90 t/hm²,总最大持水率为187.40%~277.89%,针阔混交林的持水率较高。(3)山杨有效拦蓄量最大,为15.05 t/hm²,而油松最小,为12.33 t/hm²;侧柏—油松—杏混交林的拦蓄率最大;(4)枯落物持水量、持水率与时间分别为对数和幂函数关系,均在泡水2 h达到极值。综合对比6种林分,轻度干扰的山杨水文效益最优,中度干扰的油松纯林、油松—侧柏混交林最差;阔叶树种水文效应较优于针叶树种,针阔混交优于纯林。研究结果可为森林公园植被管理和水土保持效益评价提供参考依据。     

浙江省天台县不同森林类型枯落物及土壤水文特性

[目的]掌握浙江省天台县不同森林枯落物和土壤的持水能力,为该区域今后在森林水源涵养等方面提供科学依据。[方法]采用野外调查和室内浸泡法,对天台县8种森林类型(毛竹林、阔叶混交林、针阔混交林、针叶混交林、马尾松林、杉木林、黑松林、木荷林)枯落物及林下土壤持水性进行了研究。[结果] 8种森林类型的枯落物蓄积量在8.05～23.84 t/hm~2之间;最大持水量变化范围为14.59～35.15 t/hm~2,其大小排序为:木荷林针阔混交林阔叶混交林马尾松林杉木林黑松林毛竹林针叶混交林;8种森林类型林下枯落物持水量与浸泡时间之间变化规律基本一致,持水量与浸泡时间呈对数函数关系,不同森林类型林下枯落物吸水速率与浸泡时间呈幂函数关系;各森林类型土壤容重介于0.83～1.21 g/cm~3,土壤持水力变化范围为200.74～575.70 t/hm~2,其大小依次为:黑松林针阔混交林木荷林杉木林毛竹林马尾松林阔叶混交林针叶混交林。[结论]阔叶林以及含有阔叶树种的森林类型枯落物以及林下土壤持水能力均较强,其中土壤持水能力最强的为黑松林。     

红壤侵蚀地植被恢复后土壤水分特征及其凋落物碳归还模式

[目的]研究退化恢复地土壤水分物理性质和凋落物碳归还的关系,理解不同植被恢复措施的理水调水功能。[方法]采用野外调查与室内分析相结合的方法,研究了南方红壤侵蚀地典型植被恢复模式(柑橘林、封育林、木荷×马尾松林混交林、阔叶林)土壤(0—80cm土层)水分特征及其凋落物碳归还。[结果](1)不同植被恢复模式土壤含水量随土壤水吸力的增大而减小,其剖面平均含水量在15与2.5kPa水吸力条件下相比,下降幅度的大小依次为:柑橘林(45.92%)封育林(45.10%)木荷×马尾松林混交林(38.79%)阔叶林(31.20%);(2)土壤含水量随土层深度的增加而降低,各植被恢复模式在不同水吸力条件下底层(60—80cm)土壤含水量与表层(0—10cm)的相比,柑橘林的变化幅度为30.11%~9.72%,封育林为31.81%~24.46%,木荷×马尾松林混交林为24.46%~5.49%,阔叶林为8.21%~0.24%;在不同土层或不同水吸力条件下,阔叶林土壤含水量下降的幅度均最小;(3)不同模式凋落物碳归还总量大小依次为:木荷×马尾松林混交林(1 915.79kg/hm2)阔叶林(1 414.84kg/hm2)封育林(1 212.32kg/hm2)柑橘林(633.88kg/hm2),阔叶林阔叶碳归还量和饱和含水量均大于木荷×马尾松林混交林,阔叶碳归还量和饱和含水量表现出更大的一致性。[结论]阔叶林土壤保水持水性能最佳,且阔叶碳归还对土壤饱和含水量的影响大于其他组分。     

Home-field advantage of litter decomposition and nitrogen release in forest ecosystems

Litter decomposition is a major fundamental ecological process that regulates nutrient cycling, thereby affecting net ecosystem carbon (C) storage as well as primary productivity in forest ecosystems. Litter decomposes in its home environment faster than in any other environment. However, evidence for this phenomenon, which is called the home-field advantage (HFA), has not been universal. We provide the first HFA quantification of litter decomposition and nutrient release through meta-analysis of published data in global forest ecosystems. Litter mass loss was 4.2 % faster on average, whereas nitrogen (N) release was 1.7 % lower at the home environment than in another environment. However, no HFA of phosphorus (P) release was observed. Broadleaf litter (4.4 %) had a higher litter mass loss HFA than coniferous litter (1.0 %). The positive HFA of N release was found in the coniferous litter. Mass loss HFA was significantly and negatively correlated with the initial lignin:N litter ratio. The litter decomposition and N release HFAs were obtained when mesh size ranged from 0.15 mm to 2.0 mm. The HFA of litter decomposition increased with decomposition duration during the early decomposition stage. The HFA of N release was well correlated with mass loss, and the greatest HFA was at mass loss less than 20 %. Our results suggest that the litter decomposition and N release HFAs are widespread in forest ecosystems. Furthermore, soil mesofauna is significantly involved in the HFA of litter decomposition.     

小流域水土保持生态修复区森林枯落物的持水性能

 在山东省邹城市刘庄小流域水土保持生态修复区内,对5种森林植被类型的枯落物持水性能进行了研究。结果表明:①枯落物层具有明显的蓄水、保水作用。不同森林类型枯落物最大持水率为850%～1982%,其中阔叶林明显高于针叶林;但由于针叶林具有较大的枯落物蓄积量,因此,针叶林仍能维持较高的蓄水功能。不同森林类型枯落物最大持水量为154～253mm,其中针阔混交林和针叶林高于阔叶林,具体顺序为麻栎+侧柏>侧柏>赤松+侧柏>麻栎>刺槐。②不同森林类型枯落物持水量和吸水速率,随时间的动态变化规律基本相似。随浸水历时的延长,枯落物持水量呈增加趋势,但当枯落物在水中浸泡8h时,持水量达到较大值,之后增加浸泡时间 ,持水量增加幅度较为平缓。不同森林类型枯落物吸水速率,在前4h内变化最快,以后逐渐变缓,24h时吸水基本停止。③不同森林类型枯落物有效拦蓄水深为0 61～143mm,针阔混交林>阔叶林>针叶林;具体顺序为麻栎侧柏>刺槐>麻栎>侧柏>赤松+侧柏。     

Photoacceleration of plant litter decomposition in an arid environment

In arid ecosystems, abiotic processes facilitate the physical and chemical degradation of plant litter to the extent that decomposition models that use climatic and litter composition variables as surrogates for microbial activity are not predictive. The purpose of this study was to estimate the potential contribution of photodegradation to the decomposition of plant litters that varies in architecture and chemical composition. Litter of Pinus edulis, Juniperus monosperma and Populus deltoides were exposed to ambient and attenuated sunlight, with and without supplemental water additions, at a riparian forest site along the Middle Rio Grande (New Mexico, USA). Mass loss, elemental composition, and microbial extracellular enzyme activities (EEA) were measured over 639 days. The composition of the fungal communities associated with the decomposing litters was compared by analyses of fungal ITS nrDNA sequences. Litter exposed to ambient sunlight had greater mass loss rates than shaded litter, independent of the water treatment: Populus increased by 100%, Pinus by 86% and Juniperus by 46%. The increases were proportional to exposed litter surface area per g dry mass. EEA potentials, particularly oxidative activities, were low in comparison to those measured in mesic ecosystems. For Populus litter, the principal driver of photoacceleration appeared to be photodegradation of cellulose; for Pinus, it was photodegradation of polyphenols; for Juniperus accelerated mass loss was associated with photodegradation of both polysaccharides and polyphenols. Fungal community composition varied by litter type, but the dominant colonizers were yeasts and dark-septate hyphal taxa; a finding consistent with the low enzymatic oxidation potential. This study shows that photochemical oxidation can supplement enzymatic oxidation and increase decomposition rates. As a result, organic matter decomposition in arid ecosystems is not restricted to periods of high moisture availability as is plant production. This decoupling may partly account for the low soil organic matter content of these ecosystems.     

Effects of sulfuric,nitric, and mixed acid rain on litter decomposition,soil microbial biomass,and enzyme activities in subtropical forests of China

Acid rain pollution is changing gradually from sulfuric acid rain (SAR) to mixed acid rain (MAR) and then to nitric acid rain (NAR) with the rapidly growing number of motor vehicles. The influences of changed acid rain types on ecosystem functions, particularly on litter decomposition, remain unclear. Two dominant litter types from a coniferous forest and a broad-leaved forest were incubated in microcosms with original forest soils and treated by five types of acid rain with different SO₄²⁻ to NO₃⁻ ratios (1:0, 5:1, 1:1, 1:5, and 0:1). During a six-month incubation period, litter mass losses, soil microbial biomass, and enzyme activities were investigated. Results showed that various acid treatments inhibited litter decomposition, soil microbial biomass, and most enzyme activities, and the inhibitory effects of NAR were more significant than those of SAR and MAR. The resistance to external acid of microbial communities in broad-leaved forest was higher than that in coniferous forest. NAR and MAR treatments slowed down soil carbon (C), nitrogen (N), and phosphorus (P) mineralization by attenuating the correlations between litter mass losses and the enzymes involved in C, N, and P cycling. Results reveal that the ratio of SO₄²⁻ to NO₃⁻ in acid rain is an important factor which profoundly influences litter decomposition process. In the future, a decreasing ratio of SO₄²⁻ to NO₃⁻ in acid rain will be observed in subtropical forests. Thus, soil C would accumulate as a consequence of future acid precipitation, and this may seriously affect the balance of ecosystem C, N flux.     

Effects of tree species and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey

Leaf litters from beech (Fagus orientalis Lipsky.) and oak (Quercus robur L.), and needle litters from fir (Abies nordmanniana Spach.) and pine (Pinus sylvestris L.) trees were collected from north-facing site and south-facing site and at three slope positions (top, middle and bottom) on each aspect that varied in soil chemical characteristics (soil pH, cation exchange capacity and base saturation). The litters were analysed for initial total carbon, nitrogen, acid detergent fibre, lignin and cellulose concentrations. Nitrogen, acid detergent fibre and lignin concentrations and carbon:nitrogen and lignin:nitrogen ratios varied significantly within and between species according to soil chemical characteristics on aspects and slope positions. Litter decomposition was studied in the field using the litterbag technique. The litters were placed on two aspects and at three slopes on each aspect in October 2001, and were sampled every 6-month for 2 years. The main effects of aspect, species and slope position on decomposition rates were all statistically significant. Oak leaf litter showed highest decomposition rates, followed by pine, fir and beech litter, and the litters placed on north-facing site decomposed faster than those on the south-facing site. The litters placed at the top slope position decomposed slower than at those at either the bottom or middle positions. Initial lignin concentrations explained most of the variation in decomposition rates between species, and within species for the aspects and the slope positions, but the explained variance showed differences between aspects and slope positions. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.