陆地生态系统混合凋落物分解研究进展

凋落物分解在陆地生态系统养分循环与能量流动中具有重要作用,是碳、氮及其他重要矿质养分在生态系统生命组分间循环与平衡的核心生态过程。自然生态系统中,植物群落大多具有较高的物种丰富度和多样性,其混合凋落物在分解过程中也更有可能发生养分传递、化学抑制等种间互作,形成多样化的分解生境,多样性较高的分解者类群以及复杂的级联效应分解,这些因素和过程均对研究混合凋落物分解过程、揭示其内在机制形成了极大的挑战。从构成混合凋落物物种丰富度和多样性对分解生境、分解者多样性及其营养级联效应的影响等方面,综合阐述混合凋落物对陆地生态系统凋落物分解的影响,探讨生物多样性在凋落物分解中的作用。通过综述近些年的研究发现,有超过60%的混合凋落物对其分解速率的影响存在正向或负向的效应。养分含量有差异的凋落物混合分解过程中,分解者优先利用高质量凋落物,使低质量的凋落物反而具有了较高的养分有效性,引起低质量凋落物分解加快并最终使混合凋落物整体分解速率加快;而凋落物物种丰富度对土壤动物群落总多度有轻微的影响或几乎没有影响,但是对线虫和大型土壤动物的群落组成和多样性有显著影响,并随着分解阶段呈现一定动态变化;混合凋落物改变土壤微生物生存的理化环境,为微生物提供更多丰富的分解底物和养分,优化微生物种群数量和群落结构及其分泌酶的活性,并进一步促进了混合凋落物的分解。这些基于植物-土壤-分解者系统的动态分解过程的研究,表明混合凋落物分解作用不只是经由凋落物自身质量的改变,更会通过逐级影响分解者多样性水平而进一步改变分解速率和养分释放动态,说明生物多样性确实在一定程度上调控凋落物分解及其养分释放过程。     

Review of mixed forest litter decomposition researches

The litter plays an important role in forest ecosystems. Decomposition of mixed leaf litters has recently become an active research area because it mimics the natural state of leaf litters in most of forests. Many studies reported effects of mixing litters on their decomposition, ranging from positive, negative to neutral. In this paper decomposition mechanisms of mixed litters concluded by researchers were summarized. Firstly, plant litter quality had been recognized as an important factor to affect decomposition rate. Some studies showed a positive significant correlation between initial N, P concentration and non-additive effect in litter mixture decomposition. Secondly, it has been suggested that litter mixture could increase abundance and diversity of fauna and microbial decomposers, especially fungi. Thirdly, compared with single litter decomposition, the nutrient exchange between different litter species is often considered as one of main non-additive effects observed in litter mixture. Some results showed that the active transport of nutrients by fungal hyphae derived positive effect on the decomposition of litter mixture. The multiple factors such as, leaf litter species, investigation method and plot, were also analyzed. In conclusion, it is necessary to enhance a further research on factors in mixed litter decomposition and an interaction between various factors due to the complex relationship. We are looking forward to using these theories of mixed litter decomposition to direct practical forest management.     

Review of mixed forest litter decomposition researches

The litter plays an important role in forest ecosystems. Decomposition of mixed leaf litters has recently become an active research area because it mimics the natural state of leaf litters in most of forests. Many studies reported effects of mixing litters on their decomposition, ranging from positive, negative to neutral. In this paper decomposition mechanisms of mixed litters concluded by researchers were summarized. Firstly, plant litter quality had been recognized as an important factor to affect decomposition rate. Some studies showed a positive significant correlation between initial N, P concentration and non-additive effect in litter mixture decomposition. Secondly, it has been suggested that litter mixture could increase abundance and diversity of fauna and microbial decomposers, especially fungi. Thirdly, compared with single litter decomposition, the nutrient exchange between different litter species is often considered as one of main non-additive effects observed in litter mixture. Some results showed that the active transport of nutrients by fungal hyphae derived positive effect on the decomposition of litter mixture. The multiple factors such as, leaf litter species, investigation method and plot, were also analyzed. In conclusion, it is necessary to enhance a further research on factors in mixed litter decomposition and an interaction between various factors due to the complex relationship. We are looking forward to using these theories of mixed litter decomposition to direct practical forest management.     

全球气候变暖对凋落物分解的影响

凋落物分解作为生态系统核心过程,参与生态系统碳的周转与循环,影响生态系统碳的收支平衡,调控生态系统对全球气候变暖的反馈结果。全球气候变暖通过环境因素、凋落物数量和质量以及分解者3个方面,直接或间接地作用于凋落物分解过程,并进一步影响土壤养分周转和碳库动态。气候变暖可通过升高温度和改变实际蒸散量等环境因素直接作用于凋落物分解。气候变暖可引起植物物种短期内碳、氮和木质素等化学性质的改变以及群落中物种组成的长期变化从而改变凋落物质量。在凋落物分解过程中,土壤分解者亚系统作为主要生命组分(土壤动物和微生物)彼此相互作用、相互协调共同参与调节凋落物的分解过程。凋落物分解可以通过改变土壤微生物量、微生物活动和群落结构来加快微生物养分的固定或矿化,以形成新的养分利用模式来改变土壤有机质从而对气候变化做出响应。未来凋落物分解的研究方向应基于大尺度跨区域分解实验和长期实验,关注多个因子交互影响下,分解过程中碳、氮养分释放、地上/地下凋落物分解生物学过程与联系、分解者亚系统营养级联效应等方面。     

全球变化对陆地生态系统枯落物分解的影响

了解枯落物分解对大大二氧化碳浓度增高,气候变暖和降水变化的反应,对深入理解陆地生态系统土壤有机物形成和碳的固化能力（Carbonh sequestration)十分重要。通过分析业已发表的文献,实验室根系分解实验和美国西北部针叶林叶片的分解实验,旨在评估大气二氧化碳浓度增高,气候变暖和降水化对陆地生态系统枯落物分解的可能影响,大气二氧化碳浓度增高可通过降低枯落物质量和增加草原生态系统土壤水分间接地影响枯落物分离,根据17项研究结果,大气二氧化碳浓度加倍可导致木本和草本枯落物平均氮含量降低19．6％和9．4％;木质素／氮化值增高36．3％和5．5％,枯落物质地的降低通常导致枯落物分解减慢。气候变暖一般加速枯落物的分解,但是用于表示这种促进作用的Q10随着温度的增高而降低,全球降水变化对陆地生态系统枯落物分解的影响不但取决于现有水分条件而且还以决于降水变的程度。以美国西北部地的针叶林为例,降水改变对森林生态系统枯落物分解的影响将是 多元的,有的增加,有的降低,而有的相对不变,最后,指出了今后 在方该领域有待加强的几个研究方面。     

Effect of litter substrate quality and soil nutrients on forest litter decomposition: A review

Forest litter plays an important role in determining nutrient cycling, balance and maintaining ecosystem function of forest ecosystems. Studies have shown that litter substrate quality is one of the most important factors affecting litter decomposition in a given area. It is, hence, important to understand the factors controlling litter decomposition in the late decomposition stage and determining organic matter changes over the duration of litter decomposition. Decomposition rate of mixed litter may differ with that of a single specie litter. Supply of soil nutrients is an important factor controlling litter decomposition rate, because the essential nutrients in soil or litter material influence community and activity of decomposers (soil organisms). There were clear relationships among soil nutrient, litter substrate quality, and decomposition. Soil nutrient contents were positively correlated with litter substrate quality, showing that higher contents of soil nutrient were accompanied with good quality of litter substrate, and lower soil nutrients with poor litter quality. The effects of soil fertility on litter decomposition rate varied with environmental conditions. It was reported that litter quality regulates the early stage of carbon decomposition and its accumulation in soil, however, it could not predict the long-term dynamics of soil organic carbon. Hence, the formation and stabilization of soil organic carbon are controlled by the quantity of litter input and its interaction with the soil circumstances rather than by the litter quality. The present paper reviewed the research findings about litter decomposition related to litter substrate quality and soil nutrients, including short-term and long-term litter decomposition, decomposition of single-species vs. mixed-litter decomposition and litter nutrients release. The present paper aimed to clarify the relationship between soil nutrients and litter decomposition, which will help to understand forest succession, forest water conservation and soil re-production capacity.     

Effect of nitrogen addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes of Northeast China

Wetland ecosystems store a large amount of organic carbon (C) in soils, due to the slow decomposition rates of plant litter and soil organic matter. Increased nitrogen (N) availability induced by human activities and global warming may accelerate litter decomposition and affect soil organic C dynamics in wetlands. In the present study, we investigated the effect of N addition on decomposition of Calamagrostis angustifolia litters from freshwater marshes in the Sanjiang Plain of Northeast China under field and laboratory conditions. First, we assessed the changes in initial litter chemical composition and subsequent decomposition following three years of N addition at the rate of 24 g N m⁻² year⁻¹ under field conditions. Our results showed that N addition increased litter N concentration and decreased C/N ratio, and thus stimulated litter decomposition. Secondly, we examined the effect of increased N availability (0, 25, 50 and 100 mg N g⁻¹ litter) on litter decomposition under laboratory conditions. Increased exterior N availability also enhanced microbial respiration and increased litter mass loss under both waterlogging and non-waterlogging conditions. In addition, waterlogging conditions inhibited microbial respiration and suppressed litter mass loss. These findings demonstrated that N addition increased litter decomposition rates through improved litter quality and enhanced microbial activity in freshwater marshes of Northeast China. This implies that increased N availability accelerates litter decomposition rates, and thus may cause substantial losses of soil C and diminish and even reverse the C sink function of wetlands in the Sanjiang Plain of Northeast China.     

Nitrogen transfer in litter mixture enhances decomposition rate,temperature sensitivity,and C quality changes

Background and aims

Litter decomposition is a critical process in terrestrial ecosystems and, since in natural conditions plant litter occurs in mixtures, understanding the interactive effects of mixed litter is of great ecological relevance. In this context, we test the hypothesis that N transfer between high quality litter to N-poor substrates are at the base of synergistic interactions, positively affecting litter decay rate, temperature sensitivity, and changes of organic C quality.

Methods

We carried out a manipulative experiment using four organic substrates, encompassing a wide range of biochemical quality (Hedera helix and Quercus ilex leaf litter, cellulose strips and woody sticks), each decomposing either separately or in matched pair mixtures for 360 days. Organic substrates were characterized for mass loss, C and N content and by ¹³C CPMAS NMR to assess biochemical quality changes.

Results

Litter response to mixing was related to the biochemical quality of the components in the mixture: additive when substrates with similarly high (H. helix and Q. ilex) or low (cellulose and wood) N content were paired, but synergistic when substrates with contrasting N content were associated (either of the two leaf litters with either cellulose or wood). Overall, no antagonist effects were observed in this experiment. Interestingly, decomposition of cellulose and wood showed an higher temperature sensitivity, compared to monospecific substrates, when paired with N rich materials. Significant N transfer was found from N rich litter to N poor substrates and ¹³C CPMAS NMR showed rapid changes of C quality of cellulose and wood sticks only when paired with N rich litter.

Conclusions

Our findings support the hypothesis that mixing litters of different quality, with quality expressed in terms of C/N ratio and N content, increases decomposition rate and temperature sensitivity of the lower quality substrates.     

When will litter mixtures decompose faster or slower than individual litters? A model for two litters

Litter mixtures often decompose at a different rate than the average of the individual litters, but, so far, the underlying mechanisms are not understood. We propose here an explanation based on a model with two litters. The model describes the carbon and nitrogen mineralisation of the litters. The decomposition rates of the litters become linked because the growth efficiency (production‐to‐assimilation ratio) of the decomposers responds to the amount of inorganic nitrogen (initial plus mineralised) in the surrounding environment. The model shows that, when in a mixture, one litter decomposes always faster and the other one always slower compared to when they decompose on their own. The relative changes in decomposition rates are also equal and consequently the decomposition rate for the whole mixture can be expected to lie between the rates of the two individual litters. The mixture decomposes faster than the average of the two litters separately when the litter of the higher quality also mineralises nitrogen fastest. If the litter of the higher quality instead has the smallest nitrogen mineralisation rate, the mixture decomposes slower. The model predictions are consistent with observations from 23 published experimental litter‐mixture studies.     

Do physical plant litter traits explain non‐additivity in litter mixtures? A test of the improved microenvironmental conditions theory

The decomposition rates of plant litter mixtures often deviate from the averaged rates of monocultures of their component litter species. The mechanisms behind these non‐additive effects in decomposition of litter mixtures are lively debated. One plausible explanation for non‐additive effects is given by the improved microenvironmental condition (IMC) theory. According to this theory, plant litter species, whose physical characteristics improve the microclimatic conditions for decomposers, will promote the decomposition of their co‐occurring litter species. We tested the IMC theory in relation to leaf litter and soil moisture in two contrasting moisture conditions in a dry subarctic mountain birch forest with vascular plant leaf litters of poor and high quality. The non‐additive effects in mass loss of litter mixtures increased when moisture conditions in litter and soil became more favourable for plant litter decomposition. The sign of this increase (antagonistic or synergistic) in non‐additive effects was more predictable for litter mixtures of poor litter quality. Although the specific mechanisms underlying the IMC theory depended on the litter quality of the litter mixtures, a standardized water holding capacity (WHC) was the litter trait most closely related to the non‐additive effects in mixtures of both poor and high quality litter types. Furthermore, we found that higher dissimilarity in WHC traits between the component litter species in a mixture increased synergistic effects in litter mixtures under limiting moisture conditions. However, under improved moisture conditions, increased antagonistic effects were observed. Thus, we found clear support for the IMC theory and showed that climatic conditions and leaf litter physical traits determine whether the non‐additive effects in litter mixtures are antagonistic or synergistic. Our study emphasizes the need to include litter physical traits into predictive models of mixing effects on plant litter decomposition and in general suggests climate specificity into these models.     

Interactions between Litter Lignin and Nitrogenitter Lignin and Soil Nitrogen Availability during Leaf Litter Decomposition in a Hawaiian Montane Forest

Previous work in a young Hawaiian forest has shown that nitrogen (N) limits aboveground net primary production (ANPP) more strongly than it does decomposition, despite low soil N availability. In this study, I determined whether (a) poor litter C quality (that is, high litter lignin) poses an overriding constraint on decomposition, preventing decomposers from responding to added N, or (b) high N levels inhibit lignin degradation, lessening the effects of added N on decomposition overall. I obtained leaf litter from one species, Metrosideros polymorpha, which dominates a range of sites in the Hawaiian Islands and whose litter lignin concentration declines with decreasing precipitation. Litter from three dry sites had lignin concentrations of 12% or less, whereas litter from two wet sites, including the study site, had lignin concentrations of more than 18%. This litter was deployed 2.5 years in a common site in control plots (receiving no added nutrients) and in N-fertilized plots. Nitrogen fertilization stimulated decomposition of the low-lignin litter types more than that of the high-lignin litter types. However, in contrast to results from temperate forests, N did not inhibit lignin decomposition. Rather, lignin decay increased with added N, suggesting that the small effect of N on decomposition at this site results from limitation of decomposition by poor C quality rather than from N inhibition of lignin decay. Even though ANPP is limited by N, decomposers are strongly limited by C quality. My results suggest that anthropogenic N deposition may increase leaf litter decomposition more in ecosystems characterized by low-lignin litter than in those characterized by high-lignin litter. Received 26 October 1999; accepted 2 June 2000.     

Litter stoichiometric traits of plant species of high-latitude ecosystems show high responsiveness to global change without causing strong variation in litter decomposition

? High-latitude ecosystems are important carbon accumulators, mainly as a result of low decomposition rates of litter and soil organic matter. We investigated whether global change impacts on litter decomposition rates are constrained by litter stoichiometry. ? Thereto, we investigated the interspecific natural variation in litter stoichiometric traits (LSTs) in high-latitude ecosystems, and compared it with climate change-induced LST variation measured in the Meeting of Litters (MOL) experiment. This experiment includes leaf litters originating from 33 circumpolar and high-altitude global change experiments. Two-year decomposition rates of litters from these experiments were measured earlier in two common litter beds in sub-Arctic Sweden. ? Response ratios of LSTs in plants of high-latitude ecosystems in the global change treatments showed a three-fold variation, and this was in the same range as the natural variation among species. However, response ratios of decomposition were about an order of magnitude lower than those of litter carbon/nitrogen ratios. ? This implies that litter stoichiometry does not constrain the response of plant litter decomposition to global change. We suggest that responsiveness is rather constrained by the less responsive traits of the Plant Economics Spectrum of litter decomposability, such as lignin and dry matter content and specific leaf area.     

Litter decomposition of a pine plantation is affected by species evenness and soil nitrogen availability

Background and aims

Litter decomposition is a key process controlling flows of energy and nutrients in ecosystems. Altered biodiversity and nutrient availability may affect litter decomposition. However, little is known about the response of litter decomposition to co-occurring changes in species evenness and soil nutrient availability.

Methods

We used a microcosm experiment to evaluate the simultaneous effects of species evenness (two levels), identity of the dominant species (three species) and soil N availability (control and N addition) on litter decomposition in a Mongolian pine (Pinus sylvestris var. mongolica) plantation in Northeast China. Mongolian pine needles and senesced aboveground materials of two dominant understory species (Setaria viridis and Artemisia scoparia) were used for incubation.

Results

Litter evenness, dominant species identity and N addition significantly affected species interaction and litter decomposition. Higher level of species evenness increased the decomposition rate of litter mixtures and decreased the incidence of antagonistic effects. A. scoparia-dominated litter mixtures decomposed faster than P. sylvestris var. mongolica- and S. viridis-dominated litter mixtures. Notably, N addition increased decomposition rate of both single-species litters and litter mixtures, and meanwhile altered the incidence and direction of non-additive effects during decomposition of litter mixtures. The presence of understory species litters stimulated the decomposition rate of pine litters irrespective of N addition, whereas the presence of pine litters suppressed the mass loss of A. scoparia litters. Moreover, N addition weakened the promoting effects of understory species litters on decomposition of pine litters.

Conclusions

Pine litter retarded the decomposition of understory species litters whereas its own decomposition was accelerated in mixtures. Nitrogen addition and understory species evenness altered species interaction through species-specific responses in litter mixtures and thus affected litter decomposition in Mongolian pine forests, which could produce a potential influence on ecosystem C budget and nutrient cycling.     

模拟干旱和磷添加对热带低地雨林叶凋落物分解的影响

凋落物是植物在其生长发育过程中新陈代谢的产物,是土壤有机质输入的重要途径,凋落物分解是生态系统养分循环的关键过程之一。在全球气候变化背景下,热带地区干旱事件发生的频率和强度均在增加,同时,普遍认为热带地区受磷(P)限制,所以探讨干旱胁迫和土壤磷可用性对热带地区叶凋落物分解的影响及两者是否存在交互效应十分必要,有助于了解干旱对该区叶凋落物分解的影响机制以及是否受土壤磷调控。依据植物多度、碳固持类型、叶质地,以海南三亚甘什岭热带低地雨林的4个树种叶凋落物(铁凌 Hopea exalata、白茶树 Koilodepas bainanense、黑叶谷木 Memecylon nigrescens、山油柑 Acronychia pedunculata)为实验材料,依托2019年在该区建成的热带低地雨林模拟穿透雨减少、磷(P)添加双因素交互控制实验平台,包括干旱(D -50%穿透雨)、P添加(P +50Kg P hm^-2a^-1)、模拟干旱×P添加(DP -50%穿透雨×+50Kg P hm^-2a^-1)、对照(CK)4个处理,且4种处理随机分布于3个区组,即设置了3个重复。使用常规的凋落物分解袋法探究实验处理对4个树种叶凋落物的分解系数、碳(C)、氮(N)元素动态变化的影响。结果表明:不同树种的叶凋落物因基质质量不同分解存在差异。模拟干旱处理对叶凋落物C、N损失产生抑制作用,但是对不同树种叶凋落物的抑制作用不同,原因是干旱处理通过抑制土壤分解者活动、减弱凋落物的物理破碎作用,间接抑制凋落物分解,并且由于高质量(含N量高)凋落物受微生物分解者影响较大,所以该凋落物分解受干旱抑制程度较大;P添加处理对叶凋落物C损失存在促进作用、N损失存在抑制作用,原因是土壤中P含量的升高,提高了微生物分解高C物质的能力,以及当土壤中P含量较高时,间接抑制微生物通过分解凋落物获取养分或者促进微生物优先完成自身生长代谢需要而不是合成分解凋落物所需要的酶,导致叶凋落物N损失下降;模拟干旱与P添加处理存在显著交互效应,P添加处理缓解或反转了干旱胁迫对叶凋落物分解的抑制作用。以上结果表明,不同基质质量的凋落物分解存在差异,对干旱胁迫的响应不同;在叶凋落物分解过程中,P添加促进C损失、抑制N损失;此外,在热带低地雨林,土壤中P可用性变化可调节干旱对凋落物分解的影响。     

No bottom-up effects of food addition on predators in a tropical forest

Several studies in temperate forests have demonstrated effects of litter addition on decomposers and predators. However, adding litter does not allow separating the effects of food availability and habitat space. We investigated the response of decomposers and predators to increased food resources and space in forests of the southern Mata Atlântica of Brazil. In two forest ecosystems representing an early successional stage of secondary forests and old-growth forest, we added nutrient-rich organic material, artificial litter of no nutritional value, or a combination of both to the soil surface of 120 plots to separate the effects of habitat space and food on soil food webs. We sampled litter- and soil-dwelling arthropods after three months using pitfall traps, soil sample extraction, and sticky traps just above the soil. Adding artificial litter had no positive effect on any of the 17 analyzed arthropod groups. Combining all sampled arthropods the effect was even significantly negative. Adding food had a positive effect on the abundance of decomposers, but not predators. We found no interactions between added artificial litter and added organic material. Our results suggest that the soil fauna in tropical forests is food limited. The lack of a bottom-up effect on predators suggests that they are not predominantly regulated by the abundance of epigeic prey but rather by competition or predation.     

放牧对青藏高原东部两种典型高寒草地类型凋落物分解的影响

为认识放牧对青藏高原东部中生性的高寒草甸草地和半湿生的沼泽草地凋落物分解的影响,在这两种草地上分别设置了围栏和放牧样地,研究了其各自的混合凋落物样品和4个优势物种(发草Deschampsiacaespitos、鹅绒委陵菜Potentilla anserine、木里苔草Carexmuliensis、藏嵩草Kobresiatibetica)凋落物的分解和养分释放动态,这4个优势物种也大致代表了当地沼泽草地生态系统在放牧和气候变暖驱动下逆行演替不同阶段的优势物种类群。结果表明,各优势物种凋落物的分解速率有显著差异;放牧在总体上促进了凋落物的分解,但不同物种的响应有所不同;放牧对凋落物C的释放影响不显著或有抑制作用,但对N、P的释放具有一定促进作用。对各优势物种凋落物分解和养分释放模式的分析表明,群落逆行演替过程中,凋落物分解和C释放加速,可能促进沼泽湿地退化的正反馈效应。草甸草地的退化标志物种鹅绒委陵菜具有较高的凋落物质量和分解速度,反映了中生条件下植物应对牲畜啃食采用"逃避"而非"抵抗"策略的趋向。     

Actual litter decomposition rates in salt marshes measured using near-infrared reflectance spectroscopy

Near-infrared reflectance spectroscopy (NIRS) has been widely applied as a holistic tool to investigate decomposition processes in terrestrial ecosystems. The objectives of this research were to determine the potential of NIRS to predict (1) the halophytic litter chemistry (i.e., carbon and nitrogen content) during decomposition, and (2) the stage of decomposition of halophytic litter. Decomposition experiments were conducted in the laboratory with microcosms placed under a wide range of physical characteristics and in the field with litterbags located along the elevation gradient (i.e., low to upper marsh). Microcosm experiments were used to calibrate the predictive equations. These calibration equations were then applied to the field data to test their capacity to predict %C, %N, and litter mass loss (LML). NIRS can be successfully applied to predict chemical composition of halophyte litter during decomposition processes. We hypothesized that the use of litterbags in the field might lead to a 20–40% overestimation of the decay rate as fine organic debris are lost through the meshes of the litterbags. NIRS can be used as a fast and nondestructive method to more accurately predict decay rates, and thus microbial consumption in aquatic environments.     

Effects and mechanism of plant litter on grassland ecosystem: A review

Plant litter is dead, above and below ground; organic material i.e. leaves barks, needles, twigs and roots. Plant litter plays a key role in nutrient cycling and community organization in grassland ecosystems. Litter can have important consequences on recruitment of plant species through modification of biological, physical, and chemical features of microenvironment. Plant litter offers a major input of organic matter to the soil which modifies soil chemistry, hence impacts nutrient cycling. At early stages of litter decomposition, a particular amount of carbon is transporting to the soil nutrient pool. In terrestrial ecosystems, plant litter regulating biogeochemical cycles, maintain soil fertility, nutrient availability, and therefore influence plant growth, diversity, composition, structure, and productivity. Litter can also impact plant above net plant productivity and below net plant productivity in grassland ecosystem. Plant litter accumulation and decomposition can impact plant species composition and community structure through temperature, light and nutrient availability. The effects of plant litter on vegetation may be negative, positive or neutral due vegetation variability, study duration, habitat, latitude, quantity and quality of litter. These diverse effects of plant litter on grassland ecosystem might be due to, management practice type, management intensity, climate type, timing, precipitation and soil nutrient pool etc. Current review attempts to describe prominent effects of plant litter on vegetation, seed germination, soil fertility, Productivity, species composition, community structure and mechanism in grassland ecosystem.     

N2-Fixing Red Alder Indirectly Accelerates Ecosystem Nitrogen Cycling

Symbiotic N₂-fixing tree species can accelerate ecosystem N dynamics through decomposition feedbacks via both direct and indirect pathways. Direct pathways include the production of readily decomposed leaf litter and increased N supply to decomposers, whereas indirect pathways include increased tissue N and altered detrital dynamics of non-fixing vegetation. To evaluate the relative importance of direct and indirect pathways, we compared 3-year decomposition and N dynamics of N₂-fixing red alder leaf litter (2.34% N) to both low-N (0.68% N) and high-N (1.21% N) litter of non-fixing Douglas-fir, and decomposed each litter source in four forests dominated by either red alder or Douglas-fir. We also used experimental N fertilization of decomposition plots to assess elevated N availability as a potential mechanism of N₂-fixer effects on litter mass loss and N dynamics. Direct effects of N₂-fixing red alder on decomposition occurred primarily as faster N release from red alder than Douglas-fir litter. Direct increases in N supply to decomposers via experimental N fertilization did not stimulate decomposition of either species litter. Fixed N indirectly influenced detrital dynamics by increasing Douglas-fir tissue and litter N concentrations, which accelerated litter N release without accelerating mass loss. By increasing soil N, tissue N, and the rate of N release from litter of non-fixers, we conclude that N₂-fixing vegetation can indirectly foster plant–soil feedbacks that contribute to the persistence of elevated N availability in terrestrial ecosystems.     

季节性冻融期间亚高山森林凋落物的质量变化

凋落物质量是影响凋落物分解的重要生物因子,其在季节性冻融期间的变化可能对亚高山森林生态系统过程产生显著的影响。因此,采用凋落物分解袋法,研究了岷江冷杉(Abies faxoniana)和白桦(Betula platyphylla)凋落物质量在一个季节性冻融期间(2006年10月至2007年4月)的变化。季节性冻融期间,岷江冷杉和白桦凋落物的木质素(L)和纤维素的降解率为全年降解的70%-75%,岷江冷杉和白桦凋落物的C/N、L/N和纤维素/N均显著增加,而纤维素/P均有所降低。岷江冷杉凋落物的C/P和L/P有所增加,但白桦凋落物的C/P和L/P有所降低。可见,季节性冻融期间,亚高山森林凋落物的质量发生了较为显著的变化,其显著影响了亚高山凋落物分解过程。