湿地枯落物分解及其对全球变化的响应

综述了当前湿地枯落物分解及其对全球变化响应的研究动态。湿地枯落物分解研究已随研究方法的改进而不断深化;当前湿地枯落物分解过程研究主要集中在有机质组分和元素含量变化特征的探讨上;湿地枯落物分解同时受生物因素（即枯落物性质以及参与分解的异养微生物和土壤动物的种类、数量和活性等）和非生物因素（即枯落物分解过程的外部环境条件,包括气候条件、水分条件、酸碱度与盐分条件以及湿地沉积的行为与特征等）的制约;模型已成为湿地枯落物分解研究的重要手段,对其研究也在不断深化。还讨论了湿地枯落物分解对于全球变化的响应,指出全球变暖、大气CO2浓度上升、干湿沉降及其化学组成改变可能对枯落物分解产生的直接、间接和综合影响。最后,指出了当前该领域研究尚存在的问题以及今后亟需加强的几个研究方面。     

Distinct responses of soil respiration to experimental litter manipulation in temperate woodland and tropical forest

Global change is affecting primary productivity in forests worldwide, and this, in turn, will alter long‐term carbon (C) sequestration in wooded ecosystems. On one hand, increased primary productivity, for example, in response to elevated atmospheric carbon dioxide (CO₂), can result in greater inputs of organic matter to the soil, which could increase C sequestration belowground. On other hand, many of the interactions between plants and microorganisms that determine soil C dynamics are poorly characterized, and additional inputs of plant material, such as leaf litter, can result in the mineralization of soil organic matter, and the release of soil C as CO₂ during so‐called “priming effects”. Until now, very few studies made direct comparison of changes in soil C dynamics in response to altered plant inputs in different wooded ecosystems. We addressed this with a cross‐continental study with litter removal and addition treatments in a temperate woodland (Wytham Woods) and lowland tropical forest (Gigante forest) to compare the consequences of increased litterfall on soil respiration in two distinct wooded ecosystems. Mean soil respiration was almost twice as high at Gigante (5.0 μmol CO₂ m^?2 s^?1) than at Wytham (2.7 μmol CO₂ m^?2 s^?1) but surprisingly, litter manipulation treatments had a greater and more immediate effect on soil respiration at Wytham. We measured a 30% increase in soil respiration in response to litter addition treatments at Wytham, compared to a 10% increase at Gigante. Importantly, despite higher soil respiration rates at Gigante, priming effects were stronger and more consistent at Wytham. Our results suggest that in situ priming effects in wooded ecosystems track seasonality in litterfall and soil respiration but the amount of soil C released by priming is not proportional to rates of soil respiration. Instead, priming effects may be promoted by larger inputs of organic matter combined with slower turnover rates.     

Interactive responses of grass litter decomposition to warming,nitrogen addition and detritivore access in a temperate old field

Plant litter decomposition has been studied extensively in the context of both climate warming and increased atmospheric N deposition. However, much of this research is based on microbial responses, despite the potential for detritivores to contribute substantially to litter breakdown. We measured litter mass-loss responses to the combined effects of warming, N addition and detritivore access in a grass-dominated old field. We concurrently assessed the roles of litter treatment origin vs. microenvironment (direct warming and N-addition effects) to elucidate the mechanisms through which these factors affect decomposition. After 6 weeks, mass loss increased in N-addition plots, and it increased with detritivore access in the absence of warming. After 1 year, warming, N addition, and detritivore access all increased litter mass loss, although the effects of N addition and warming were non-additive in the detritivore-access plots. For the litter-origin experiment, mass loss after 6 weeks increased in litter from N-addition plots and warmed plots, but unlike the overall decomposition response, the N-addition effect was enhanced by detritivore access. Conversely, for the microenvironment experiment, detritivore access only increased mass loss in unfertilized plots. After 1 year, detritivore access increased mass loss in the litter-origin and microenvironment experiments, but there were no warming or N-addition effects. Overall, our results provide support for a substantial role of detritivores in promoting litter mass loss in our system. Moreover, they reveal important interactions between litter origin, microclimate and detritivores in determining decomposition responses to global change.     

山地森林表层土壤酶活性对短期增温及凋落物分解的响应

为了探究贡嘎山地区暗针叶林表层土壤酶活性对增温及凋落物分解的响应,采用开顶式生长箱(open top chamber)和加热电缆(OTC-cable)联合增温的方式模拟增温,同时定位监测实验小区地表空气、表层土壤温湿度的变化;不同类型(A:75%峨眉冷杉针叶+25%杜鹃荚蒾灌木叶凋落物,B:55%峨眉冷杉针叶+45%杜鹃荚蒾灌木叶凋落物)凋落物在模拟增温和自然对照条件下分解4年,研究土壤过氧化氢酶、多酚氧化酶和脲酶活性的变化。结果表明:增温使得地表空气和表层土壤温度分别增加了2.84℃和1.83℃;使得空气相对湿度和土壤含水量分别降低了5.27%和1.55%。针叶比例高会抑制凋落物分解,约13%;增温促进凋落物分解且对针叶比例高的促进作用更加明显,增幅均超过10%。增温总体上降低了土壤过氧化氢酶和脲酶活性,而对多酚氧化酶活性的影响表现为增大。针叶比例降低的凋落物分解对3种土壤酶活性的影响大致趋势是增大,幅度在15%以上。增温和凋落物类型之间的交互作用显著。随着土壤深度增加,土壤过氧化氢酶和多酚氧化酶活性增大,而脲酶活性降低。增温和不同类型凋落物分解对表层土壤酸碱性无显著作用。在土壤含水量较低的情况下,土壤水分对酶活性影响较大。贡嘎山峨眉冷杉林表层土壤酶对温度的敏感性不仅因酶类型、土壤深度而存在差异,也随增温时间、土壤水分条件而有所不同。     

Effects of shrub encroachment on the anuran community in periodically flooded grasslands of the largest Neotropical wetland

In many parts of the world, replacement of natural grasslands by woody plants has resulted in a decrease of pasture areas and in habitat loss for a variety of animal species, including amphibians. Wetlands are especially susceptible to invasive plants, both native and exotic, but the effects of such invasions on animal assemblages remain poorly understood. Here, we present information on the impact of selected environmental variables, especially coverage by the native shrub Combretum laxum Jacq., on the structure of an anuran assemblage in the Pantanal, a huge flood‐pulsed South American wetland. Anurans were surveyed during the rainy season in 17 plots, which differed in extent of C. laxum coverage, leaf litter volume, soil moisture and distance to permanently wet areas. Effects of these environmental variables on the species number, relative abundance and composition of the anuran assemblage were evaluated using multivariate statistical analyses. We captured 1203 anurans, of 21 species from four families. Both the number of species and the relative abundance of anurans were lower in plots with greater C. laxum coverage, which also influenced anuran species composition. Number of species was highest in plots located closest to permanently wet areas, which provide protection from desiccation and other resources during the Pantanal dry season, and so could be considered source areas of anurans. While many anuran species were negatively affected by the homogenization of the landscape caused by shrub encroachment, some seemed to be favoured in such circumstances. For these, dense shrub encroachment into natural grasslands may provide safer migratory routes to permanently wet habitats. Thus, at the mesoscale, a mosaic of areas with different levels of coverage by C. laxum (shrub islands) may aid anuran assemblages in the Pantanal wetlands, facilitating the maintenance of higher beta and gamma diversity.     

Seasonal influx and decomposition of autochthonous macrophyte litter in a north temperate estuary

An 18-month study was undertaken to determine the seasonal contribution and detrital processing of autochthonous plant litter in the Great Bay Estuary System of New-Hampshire-Maine, USA and adjacent open coast. Four species were studied: the halophytes, Spartina alterniflora Loisel. and Zostera marina L. and the seaweeds, Ascophyllum nodosum (L.) Le Jolis and Fucus vesiculosus L. v. spiralis Farlow. Monthly strand line collections at estuarine and open coastal sites provided information on the seasonal influx of litter derived from each species. Detrital inputs from S. alterniflora and Z. marina were maximal in the spring and summer, respectively. Seaweed litter was abundant (35 to 85% of the total strand line) throughout the year. The seaweeds contributed 1 to 3 times as much detrital material as the vascular plants within the Estuary, and 50 times as much on the open coast. In situ measurements of decomposition, using nylon, mesh bags, were made for each species under several environmental conditions. Seaweeds decomposed 3 to 10 times faster than vascular plant litter under similar conditions. Decomposition rates and changes in the nutrient content of litter were dependent on surrounding environmental conditions. Continual nutrient depletion occurred in litter within the strand line. Nitrogen and phosphorus enrichment were observed under submerged conditions and were attributed to microbial activity and rapid leaching of carbonaceous substrates. A computer simulation model was developed to validate the field data and to predict seasonal detrital carbon input by each species. The significance of autochthonous input is discussed in relation to other detrital sources.     

Differential responses of litter decomposition to warming,elevated CO2, and changed precipitation regime

Plant and Soil - This study was performed to determine if the contribution of biological N2 fixation (BNF) associated with Brazilian sugarcane cultivars could be increased by the inoculation with...     

外源氮添加对温带荒漠地表凋落物分解及养分释放的影响

采用分解网袋法,在古尔班通古特沙漠南缘设置对照N₀(0 g N·m^-2·a^-1)、N₅(5 g N·m^-2·a^-1)、N₁₀(10 g N·m^-2·a^-1)和N₂₀(20 g N·m^-2·a^-1)4个施N处理,研究外源N添加对多枝柽柳、盐角草及两者混合凋落物分解过程及养分释放的影响,分析氮沉降对荒漠生态系统凋落物分解的影响。结果表明: 各物种凋落物的分解速率存在显著差异,经过345 d的分解,多枝柽柳、盐角草及混合物在不同N处理间的分解速率分别为0.64～0.70、0.84～0.99和0.71～0.81 kg·kg^-1·a^-1。凋落物分解过程中,N、P均表现为养分的直接释放,试验结束时,N₀、N₅、N₁₀和N₂₀处理单种凋落物及其混合物N分别释放60.6%～67.4%、56.7%～62.6%、57.4%～62.3%、46.8%～63.0%,P分别释放51.9%～77.9%、59.9%～74.7%、53.0%～79.9%、52.3%～76.4%。N处理对单种凋落物及其混合物的分解影响不显著,但各种凋落物的养分动态对N添加的响应不同,N处理抑制了盐角草N、P释放及混合凋落物P释放,而对多枝柽柳无影响。在温带荒漠,适量的N输入对凋落物分解速率影响不大,但可能会延缓个别物种养分向土壤系统的归还。     

荒漠草原土壤微生物矿化对灌丛引入过程及水分的响应

以宁夏荒漠草原封育草地（封育14年）、放牧地为对照,开展不同年限（3a、12a、22a）和间距（40 m、6 m、2 m）柠条地（Caragana korshinskii）灌丛引入过程土壤微生物矿化及对不同水分梯度（自然降雨、前期饱和、持续干旱）响应特征研究。结果表明：灌丛地0-20 cm和0-100 cm土层土壤全氮含量均高于放牧地且随年限和密度增加呈增高趋势,分别为0.28-0.42、0.27-0.42 g/kg和0.28-0.51、0.27-0.51 g/kg,但在22年且密度增至2 m间距的灌丛地与封育草地相比差异不显著或呈降低趋势;微生物量氮变化分别为0.041-0.057、0.041-0.081 mg/kg,且22年灌丛地呈显著降低,2 m间距灌丛地呈显著增加,但均显著低于封育草地0.079 mg/kg和放牧地0.103 mg/kg （P<0.05）;真菌/细菌比值随灌丛地年限和密度增加变化为0.06-0.33,均高于封育草地0.04和放牧地0.03（P<0.05）,微生物变化改变了灌丛地的矿化过程,相较封育草地0.003 mg kg^-1 d^-1和放牧地-0.068 mg kg^-1 d^-1的净矿化速率,不同年限/间距灌丛地虽分别降低为-0.155--0.084、-0.116--0.061 mg kg^-1 d^-1,但均表现为前期加速硝化过程,使得硝态氮则随年限和密度增加呈增加趋势显著高于两样地,而铵态氮变化则较为稳定;封育草地对干旱具缓冲作用,持续矿化,而放牧地和灌丛地净矿化速率对水分降低响应积极,分别降低280.3%和440.2%,其中放牧地和灌丛地以硝化作用变化尤为显著,特别是灌丛地则随干旱加剧净硝化速率均呈显著降低趋势（P<0.05）,其净矿化速率变化以硝化过程占主导。     

The influence of litter quality and micro-habitat on litter decomposition and soil properties in a silvopasture system

Studies to understand litter processes and soil properties are useful for maintaining pastureland productivity as animal husbandry is the dominant occupation in the hot arid region. We aimed to quantify how micro-habitats and combinations of litters of the introduced leguminous tree Colophospermum mopane with the grasses Cenchrus ciliaris or Lasiurus sindicus influence decomposition rate and soil nutrient changes in a hot desert silvopasture system. Litter bags with tree litter alone (T), tree + C. ciliaris in 1:1 ratio (TCC) and tree + L. sindicus 1:1 ratio (TLS) litter were placed inside and outside of the C. mopane canopy and at the surface, 3–7 cm and 8–12 cm soil depths. We examined litter loss, soil fauna abundance, organic carbon (SOC), total (TN), ammonium (NH₄–N) and nitrate (NO₃–N) nitrogen, phosphorus (PO₄–P), soil respiration (SR) and dehydrogenase activity (DHA) in soil adjacent to each litter bag. After 12 months exposure, the mean residual litter was 40.2% of the initial value and annual decomposition rate constant (k) was 0.98 (0.49–1.80). Highest (p < 0.01) litter loss was in the first four months, when faunal abundance, SR, DHA and humidity were highest but it decreased with time. These variables and k were highest under the tree canopies. The litter loss and k were highest (p < 0.01) in TLS under the tree canopy, but the reverse trend was found for litter outside the canopy. Faunal abundance, litter loss, k, nutrient release and biochemical activities were highest (p < 0.01) in the 3–7 cm soil layer. Positive correlations of litter loss and soil fauna abundance with soil nutrients, SR and DHA demonstrated the interactions of litter quality and micro-habitats together with soil fauna on increased soil fertility. These results suggest that a Colophospermum mopane and L. sindicus silvopasture system best promotes faunal abundance, litter decomposition and soil fertility. The properties of these species and the associated faunal resources may be utilised as an ecosystem-restoration strategy in designing a silvopasture system. This may help to control land degradation and increase productivity sustainably in this environment.     

Contribution of litter layer to soil greenhouse gas emissions in a temperate beech forest

Background and aims

The litter layer is a major source of CO₂, and it also influences soil-atmosphere exchange of N₂O and CH₄. So far, it is not clear how much of soil greenhouse gas (GHG) emission derives from the litter layer itself or is litter-induced. The present study investigates how the litter layer controls soil GHG fluxes and microbial decomposer communities in a temperate beech forest.

Methods

We removed the litter layer in an Austrian beech forest and studied responses of soil CO₂, CH₄ and N₂O fluxes and the microbial community via phospholipid fatty acids (PLFA). Soil GHG fluxes were determined with static chambers on 22 occasions from July 2012 to February 2013, and soil samples collected at 8 sampling events.

Results

Litter removal reduced CO₂ emissions by 30 % and increased temperature sensitivity (Q₁₀) of CO₂ fluxes. Diffusion of CH₄ into soil was facilitated by litter removal and CH₄ uptake increased by 16 %. This effect was strongest in autumn and winter when soil moisture was high. Soils without litter turned from net N₂O sources to slight N₂O sinks because N₂O emissions peaked after rain events in summer and autumn, which was not the case in litter-removal plots. Microbial composition was only transiently affected by litter removal but strongly influenced by seasonality.

Conclusions

Litter layers must be considered in calculating forest GHG budgets, and their influence on temperature sensitivity of soil GHG fluxes taken into account for future climate scenarios.

     

草地利用方式对土壤呼吸和凋落物分解的影响

草地利用方式影响植被群落结构和土壤微环境, 制约草地生态系统碳循环。该文通过测定温带草原在放牧、割草、围封3种利用方式下湿润年(2012年)和干旱年(2011年)的凋落物产量、质量及其分解速率和土壤碳通量, 分析了草地利用方式对土壤呼吸和凋落物的影响, 探讨了凋落物对土壤呼吸的贡献机制。结果表明: 在干旱年份, 放牧样地土壤呼吸最大, 分别达到割草和围封样地的1.5倍和1.29倍; 在湿润年份, 割草样地土壤呼吸最大, 为309 g C∙m^-2∙a^-1, 明显高于放牧样地和围封样地。不论干旱年还是湿润年, 围封样地凋落物产量都大于放牧样地和割草样地。3种利用方式下湿润年土壤呼吸和凋落物分解均比干旱年增强。因此, 水分是温带草原植物生长和生态系统碳循环的主要限制因子, 草地利用方式则显著影响凋落物生产和分解。进一步分析表明, 经过两年的分解, 同一样地内凋落物质量C:N下降, N含量和木质素:N升高, 土壤呼吸与凋落物产量、凋落物分解速率以及木质素:N正相关, 而与凋落物C:N负相关。     

Effects of grassland-use on soil respiration and litter decomposition

 草地利用方式影响植被群落结构和土壤微环境, 制约草地生态系统碳循环。该文通过测定温带草原在放牧、割草、围封3种利用方式下湿润年(2012年)和干旱年(2011年)的凋落物产量、质量及其分解速率和土壤碳通量, 分析了草地利用方式对土壤呼吸和凋落物的影响, 探讨了凋落物对土壤呼吸的贡献机制。结果表明: 在干旱年份, 放牧样地土壤呼吸最大, 分别达到割草和围封样地的1.5倍和1.29倍; 在湿润年份, 割草样地土壤呼吸最大, 为309 g C·m^–2·a^–1, 明显高于放牧样地和围封样地。不论干旱年还是湿润年, 围封样地凋落物产量都大于放牧样地和割草样地。3种利用方式下湿润年土壤呼吸和凋落物分解均比干旱年增强。因此, 水分是温带草原植物生长和生态系统碳循环的主要限制因子, 草地利用方式则显著影响凋落物生产和分解。进一步分析表明, 经过两年的分解, 同一样地内凋落物质量C:N下降, N含量和木质素:N升高, 土壤呼吸与凋落物产量、凋落物分解速率以及木质素:N正相关, 而与凋落物C:N负相关。     

Decomposition of cellulose,soil organic matter and plant litter in a temperate grassland soil

The formation of mor humus in an experimental grassland plot, which has been acidified by long-term fertiliser treatment, has been studied by comparing the rates of cellulose, soil organic matter and plant litter decay with those in an adjacent plot with near-neutral pH and mull humus. The decomposition of cellulose filter paper in litter bags of 5 mm, 1-mm and 45-μm mesh size buried at 3 to 4 cm depth the plots was followed by measuring the weight loss and changes in glucose content over a 6 month period. Soil pH was either 5.3 or 4.3. Decomposition of native soil organic matter and plant litter in soil from the same plots were followed using CO₂ evolution in laboratory microcosms. Cellulose weight loss at pH 5.3 was greatest from the 5-mm mesh bags and least from the 45-um mesh bags. At pH 4.3 there was little weight loss from bags and no significant differences in weight loss between bags with different sized mesh. There was, however, a reduction in the glucose content of the hydrolysed and derivatised filter paper with time. The decomposition rate of native soil organic matter in the low pH soil was increased to that observed in the less acid soil when the pH of the former was increased from 4.3 to 5.3. The increase in decomposition rate of added plant litter in the more acid soil as a result of CA(OH)₂ addition was only 60% of that observed in the soil with pH 5.3. These data support the hypothesis that the absence of soil animals and the restricted microbial decomposition in the acidic soil was responsible for mor humus formation.     

森林凋落物分解及其对全球气候变化的响应

凋落物分解是重要的森林生态系统过程之一,受到气候、凋落物质量、土壤生物群落等生物和非生物因素的综合调控．迄今,有关不同森林生态系统和不同树种地上部分的凋落物动态、凋落物分解过程中的养分释放动态、生物和非生物因素对凋落物分解的影响等研究报道较多,但对地下凋落物的分解研究相对较少．近年来,森林凋落物分解对以大气CO2浓度增加和温度升高为主要特征的全球变化的响应逐步受到重视,但其研究结果仍具有很多不确定性．因此,未来凋落物生态研究的重点应是凋落物分解对土壤有机碳固定的贡献、地上／地下凋落物的物理、化学和生物学过程及其对各种生态因子（例如冻融、干湿交替）及交互作用的响应、凋落物特别是地下凋落物分解对全球气候变化的响应机制等方面．     

祁连山东缘高寒草甸灌丛化对植被群落与土壤理化特性的影响

为明晰祁连山东缘高寒草甸灌丛化对其植被群落与土壤理化特性的影响,选取甘肃省天祝藏族自治县高寒草甸灌丛化区域,调查其植被,采集土壤测定理化性质,分析植被与土壤的互馈关系。结果表明:高寒草甸植被的均匀度指数、高度、盖度、地上生物量、土壤含水率随灌丛化过程增加(P<0.05),而多样性指数和容重均降低;全磷含量在各土层以灌丛区最高,但C ∶ P和N ∶ P以草甸区最高;土壤N ∶ P<14表明土壤养分主要受限于氮;土壤脲酶和过氧化氢酶活性在草甸区各土层显著高于灌丛区(P<0.05);冗余分析显示前两个排序轴的累计解释量为54.88%,土壤过氧化氢酶与植被特征拟合的结果最好(Pr=0.010),表明高寒草甸灌丛化过程中土壤过氧化氢酶受植被特征的制约最大。可见,高寒草甸灌丛化显著影响了植被群落结构与土壤理化特性,在祁连山生态保护和管理中应该予以重视。     

Plant community and tissue chemistry responses to fertilizer and litter nutrient manipulations in a temperate grassland

Human-mediated nutrient amendments have widespread effects on plant communities. One of the major consequences has been the loss of species diversity under increased nutrient inputs. The loss of species can be functional group dependent with certain functional groups being more prone to decline than others. We present results from the sixth year of a long-term fertilization and litter manipulation study in an old-field grassland. We measured plant tissue chemistry (C:N ratio) to understand the role of plant physiological responses in the increase or decline of functional groups under nutrient manipulations. Fertilized plots had significantly more total aboveground biomass and live biomass than unfertilized plots, which was largely due to greater productivity by exotic C₃ grasses. We found that both fertilization and litter treatments affected plant species richness. Species richness was lower on plots that were fertilized or had litter intact; species losses were primarily from forbs and non-Poaceae graminoids. C₃ grasses and forbs had lower C:N ratios under fertilization with forbs having marginally greater %N responses to fertilization than grasses. Tissue chemistry in the C₃ grasses also varied depending on tissue type with reproductive tillers having higher C:N ratios than vegetative tillers. Although forbs had greater tissue chemistry responses to fertilization, they did not have a similar positive response in productivity and the number of forb species is decreasing on our experimental plots. Overall, differential nutrient uptake and use among functional groups influenced biomass production and species interactions, favoring exotic C₃ grasses and leading to their dominance. These data suggest functional groups may differ in their responses to anthropogenic nutrient amendments, ultimately influencing plant community composition.     

Differential responses of auto‐ and heterotrophic soil respiration to water and nitrogen addition in a semiarid temperate steppe

Evaluating how autotrophic (SR_A), heterotrophic (SR_H) and total soil respiration (SR_TOT) respond differently to changes of environmental factors is critical to get an understanding of ecosystem carbon (C) cycling and its feedback processes to climate change. A field experiment was conducted to examine the responses of SR_A and SR_H to water and nitrogen (N) addition in a temperate steppe in northern China during two hydrologically contrasting growing seasons. Water addition stimulated SR_A and SR_H in both years, and their increases were significantly greater in a dry year (2007) than in a wet year (2006). N addition increased SR_A in 2006 but not in 2007, while it decreased SR_H in both years, leading to a positive response of SR_TOT in 2006 but a negative one in 2007. The different responses of SR_A and SR_H indicate that it will be uncertain to predict soil C storage if SR_TOT is used instead of SR_H to estimate variations in soil C storage. Overall, N addition is likely to enhance soil C storage, while the impacts of water addition are determined by its relative effects on carbon input (plant growth) and SR_H. Antecedent water conditions played an important role in controlling responses of SR_A, SR_H and the consequent SR_TOT to water and N addition. Our findings highlight the predominance of hydrological conditions in regulating the responses of C cycling to global change in the semiarid temperate steppe of northern China.