Hydrologic alterations impact plant litter decay rate and ecosystem resilience in Mojave wetlands

Understanding ecosystem processes is vital for effective restoration of degraded ecosystems, especially wetlands. Restoration has become a necessity for management and conservation of the federally endangered Amargosa vole (Microtus californicus scirpensis) endemic to small, bulrush (Schoenoplectus americanus) dominated wetlands in the Mojave Desert. Recent data indicate catastrophic decrease of the vole population and its habitat from local alterations to hydrology, combined with diminished decomposition rates of bulrush, persistence of plant litter, and minimal plant growth except along narrow margins along stream edges. We conducted a series of three field and one greenhouse experiment(s) testing the effect of (1) moisture level on plant decay rate, (2) litter removal on plant regeneration, (3) the interactive effect of litter removal and moisture level increase on plant regeneration, and (4) potential germination rate of bulrush seeds under multiple hydrologic regimes to understand how hydrologic alteration and litter decay ultimately influences marsh regeneration. Results revealed decrease in water level caused a 20‐fold reduction in decomposition rates of a degraded marsh. Litter removal alone and in combination with water table restoration significantly and positively affected bulrush resprouting (p < 0.0001 for both). Seed bank experiments showed high rates of germination in saturated and flooded soil conditions, emphasizing the potential role of seedlings in ecosystem recovery. This study shows how the interaction of hydrologic change and decreased decomposition can shift an ecosystem toward limits of resilience. These results inform restoration strategies in arid‐region wetlands dominated by plants with slow litter decay where strategic litter removal may beneficially increase plant growth.     

Effects of elevated CO2 and nitrogen fertilization pretreatments on decomposition on tallgrass prairie leaf litter

Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C₄), Sorghastrum nutans (C₄), and Poa pratensis (C₃) plants that were grown in large open-top chambers under ambient or twice ambient CO₂ and with or without nitrogen fertilization (45 kg N ha⁻¹). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests that a large indirect effect of CO₂ on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However, there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C₄ grasses. We conclude that an indirect effect of CO₂ on decomposition and nutrient cycling could occur if CO₂ induces changes in the relative aboveground biomass of the prairie species.     

The decomposition of mangrove litter in a subtropical mangrove forest

Decomposition of Avicennia marina (Forsk.) Vierh. leaf and woody litter (twigs) was studied using litter bag experiments in a subtropical mangrove forest at two tidal levels (high and low) with different inundation regimes and during two seasons (summer and winter). Losses in dry weight were best described by a single exponential model which showed loss rates of both leaves and twigs were significantly higher low down on the shoreline (greater inundation) and in summer. The time (days) required for the loss of half of the initial dry weight (t ₅₀) was summer: high 59, low 44; winter: high 98, low 78. For twigs the values (days) were summer: high 383, low 179; winter; high 1327, low 1207. There is an exponential relationship between leaf litter t ₅₀'s and latitude which indicates the importance of temperature and therefore season, to the dynamics of organic cycling and export in mangrove systems.     

氮沉降对森林凋落物分解的影响

氮沉降增加作为全球变化的重要现象之一,已经并将继续对森林凋落物分解产生影响.综述了国内外氮沉降对森林凋落物分解影响及其机理的研究现状.氮沉降对凋落物分解的影响可分为直接影响和间接影响.氮沉降通过影响森林地被物组成和凋落物化学成分,间接影响凋落物分解.氮沉降对凋落物分解的直接影响表现为促进、无影响和抑制3种效果.分析了产生以上影响效果的作用机理,介绍了氮沉降对森林凋落物分解影响的研究方法,探讨了目前研究存在的问题,讨论了未来该方面研究的重点和方向.     

滇中亚高山地带性植被凋落物分解对模拟氮沉降的响应

模拟氮(N)沉降对凋落物分解特征的影响对研究森林生态系统物质循环响应大气N沉降的内在机理和应对N沉降全球化具有重要意义。从2018年2月至2019年1月,对滇中亚高山常绿阔叶林(Evergreen broad-leaf forest)和高山栎林(Quercus semecarpifolia forest)两种地带性植被进行模拟N沉降试验,利用尼龙网袋法对两种林型凋落叶和凋落枝进行原位分解试验,N沉降处理水平分别为对照CK(Control check, 0 g N m^-2 a^-1)、低氮LN(Low nitrogen, 5 g N m^-2 a^-1)、中氮MN(Medium nitrogen, 15 g N m^-2 a^-1)和高氮HN(High nitrogen, 30 g N m^-2 a^-1)。结果表明:常绿阔叶林凋落叶和凋落枝分解率分别为44.84%和21.96%,均高于高山栎林的35.97%(凋落叶)和17.5...     

桂林岩溶石山檵木群落不同恢复阶段凋落物层酶对凋落物分解的影响

该文选取桂林岩溶石山檵木群落不同恢复阶段(灌木阶段、乔灌阶段和小乔林阶段)作为研究对象,探究凋落物层酶对凋落物分解速率的影响。结果表明:不同恢复阶段凋落物经1 a分解后,凋落物剩余率分别为灌木阶段(59.58%)、乔灌阶段(61.79%)和小乔林阶段(62.02%)。不同恢复阶段凋落物分解速率随演替的进行而减小。3个不同恢复阶段凋落物层多酚氧化酶、脲酶、蔗糖酶活性均在12月份最低,多酚氧化酶活性均在3月份最高,脲酶和蔗糖酶活性均在6月份最高。3个恢复阶段纤维素酶活性变化规律趋势一致,均在6月份酶活性最高,灌木阶段纤维素酶活性在3月份最低,乔灌阶段和小乔林阶段纤维素酶活性均在9月份最低。3个不同恢复阶段的凋落物层酶活性在不同时期均表现为蔗糖酶脲酶纤维素酶多酚氧化酶。不同恢复阶段凋落物层酶活性对凋落物分解速率影响不同。灌木阶段凋落物层蔗糖酶活性与分解速率呈显著正相关(P 0.05),乔灌阶段脲酶活性与分解速率呈显著正相关(P 0.05),小乔林阶段各酶活性与分解速率相关不显著。蔗糖酶、脲酶和多酚氧化酶是影响灌木阶段凋落物分解速率的重要因素,脲酶、纤维素酶和多酚氧化酶是影响乔灌和小乔林阶段分解速率的重要因素。     

Advances in the effect of nitrogen deposition on grassland litter decomposition

Atmospheric nitrogen deposition has increased in the last several decades due to anthropogenic activities and global changes. Increasing nitrogen deposition has become an important factor regulating carbon cycle in grassland ecosystems. Litter decomposition, a key process of carbon and nutrient cycling in terrestrial ecosystems, is the main source of soil carbon pool and the basis of soil fertility maintenance. Elevated nitrogen deposition could affect litter decomposition by raising soil nitrogen availability, increasing the quantity and quality of litter inputs, and altering soil microorganism and soil conditions. Litter decomposition are complex biological, physical and chemical processes, which were affected by abiotic, biological factors and their interactions. The effects of nitrogen deposition on litter decomposition and the underlying mechanisms were discussed in this paper, including the aspactes of soil nitrogen availability, litter production, litter quality, microclimate, soil microorganism and enzyme activities. The main research contents, directions, methods and existing problems of litter decomposition in grasslands were discussed. We also discussed the prospect of future directions to study the interaction and feedback between nitrogen deposition and grassland ecosystem carbon cycling process.     

Biomass and litter dynamics in a Melaleuca forest on a seasonally inundated floodplain in tropical,northern Australia

Litterfall from a Melaleuca forest was investigated as part of chemical cycling studies on the Magela Creek floodplain in tropical, northern Australia. The forest contained two species of tree, Melaleuca cajaputi and Melaleuca viridiflora, with a combined average density of 294 trees ha^–1. The M. viridiflora trees had diameter breast height measurements ranging from 11.8 to 62.0 cm, median class 25.1–30.0cm and a mean value of 29.2±1.0 cm, compared to 13.0 to 66.3 cm, 30.1–35.0cm and 33.5±1.0cm for M. cajaputi trees. A regression model between tree height, diameter breast height and fresh weight was determined and used to calculate average tree weights of 775±1.6kg for M. viridiflora and 1009±1.6kg for M. cajaputi, and a total above-ground fresh weight of 263±0.3t ha^–1. The weight of litter recorded each month on the ground beneath the tree canopy ranged from 582±103 to 2176±376 g m^–2 with a monthly mean value of 1105±51 g m^–2. The coefficient of variation of 52% on this mean indicates the large spatial and temporal variability in litter distribution over the study site. This variability was greatly affected by the pattern of water flow and litter transport during the Wet season. Litterfall from the trees was evaluated using two techniques - nets and trays. The results from these techniques were not significantly different with annual litterfall collected in the nets being 705 ± 25 g m^–2 and in the trays 716±49 g m^–2. The maximum monthly amount of litterfall, 108 ±55g m^–2, occurred during the Dry season months of June–July. Leaf material comprised 70% of the total annual weight of litter, 480±29 g m^–2 in the nets and 495 ± 21 g m^–2 in the trays. The tree density and weight of litter suggest that the Melaleuca forests are highly productive and contribute a large amount of material to the detrital/debris turnover cycle on the floodplain.     

三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放

利用静态箱-碱液吸收法研究了三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放速率,讨论了影响CO2释放的环境因素,估算了枯落物分解的CO2释放对于总释放的贡献.结果表明,生长季,小叶章沼泽化草甸和小叶章湿草甸各部分CO2释放均具有明显的时间变化特征,温度和水分是重要制约因素.两类草甸湿地的平均土壤呼吸速率分别为4.33g·m-2·d-1和6.15g·m-2·d-1,枯落物分解的CO2平均释放速率分别为1.76g·m-2·d-1和3.10g·m-2·d-1,枯落物分解的CO2释放占总释放量的31%和35%,说明在碳素由地上植物碳库转移到地下土壤碳库的过程中,湿地枯落物是一个不可忽略的碳损失源.     

减雨对南亚热带马尾松人工林凋落物分解的影响

为探究气候变化背景下降雨格局改变对马尾松人工林凋落物分解及养分释放过程的影响,以南亚热带马尾松(Pinus massoniana)人工林为研究对象,设置穿透雨减少50%和不减雨(对照)处理,开展连续观测野外降水控制实验。采用凋落物分解袋法,研究了减雨处理对南亚热带马尾松人工林凋落叶分解速率及养分释放的影响,以及凋落叶分解速率的影响因素。结果表明:凋落叶分解2年后,减雨处理和对照林凋落叶残留率分别为38.09%和38.06%;凋落叶分解过程中碳元素表现为淋溶-富集-释放,而氮元素表现为富集,减雨50%在一定程度上促进了氮的富集,但未达到显著水平。相关分析表明,凋落叶的残留率与氮浓度和月积温呈显著负相关,与碳/氮呈显著正相关。本研究发现,减雨50%并未改变马尾松凋落叶分解速率和养分释放模式,凋落叶的残留率与氮浓度、碳/氮及月积温密切相关。     

Species control variation in litter decomposition in a pine forest exposed to elevated CO2

Net primary production and the flux of dry matter and nutrients from vegetation to soils has increased following four years of exposure to elevated CO₂ in a southern pine forest in NC, USA. This has increased the demand for nutrients to support enhanced rates of NPP and altered the conditions for litter decomposition on the forest floor. We quantified the chemistry and decomposition dynamics of leaf litter produced by five of the most abundant tree species in this ecosystem during the third and fourth growing seasons under elevated CO₂. The objectives of this study were to determine (i) if there were systemic or species‐specific changes in leaf litter chemistry associated with a sustained enhancement of plant growth under elevated CO₂; and (ii) whether the process of litter decomposition was altered by increased inputs of energy and nutrients to the forest floor in the plots under elevated CO₂. Leaf litter chemistry, including various C fractions and N concentration, was virtually unchanged by elevated CO₂. With few exceptions, plant litter produced under elevated CO₂ lost mass or N at the same relative rate as that produced under ambient CO₂. The relationship between initial litter chemistry and decomposition was not altered by elevated CO₂. The greater forest floor mass and nutrient content in the plots under elevated CO₂ had no consistent or long‐term effect on litter decomposition. Thus, we found no evidence that plant and microbial processes under elevated CO₂ resulted in systemic changes in mass loss or N dynamics during decomposition. In contrast to the limited effects of elevated CO₂ on litter chemistry and decomposition, there were large differences among species in initial litter chemistry, mass loss and N dynamics during decomposition. If the species composition of this forest community is altered by elevated CO₂, the indirect effect of a change in species composition will exert greater control over the long‐term rate of nutrient cycling than the direct effect of elevated CO₂ on litter chemistry and decomposition dynamics alone.     

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。     

Winter regulation of tundra litter carbon and nitrogen dynamics

Mass and nitrogen (N) dynamics of leaf litter measured in Alaskan tussock tundra differed greatly from measurements of these processes made in temperate ecosystems. Nearly all litter mass and N loss occurred during the winter when soils were mostly frozen. Litter lost mass during the first summer, but during the subsequent two summers when biological activity was presumably higher than it is during winter, litter mass remained constant and litter immobilized N. By contrast, litter lost significant mass and N over both winters of measurement. Mass loss and N dynamics were unaffected by microsite variation in soil temperature and moisture. Whether wintertime mass and N loss resulted from biological activity during winter or from physical processes (e.g., fragmentation or leaching) associated with freeze-thaw is unknown, but has implications for how future climate warming will alter carbon (C) and N cycling in tundra. We hypothesize that spring runoff over permafrost as soils melt results in significant losses of C and N from litter, consistent with the observed influx of terrestrial organic matter to tundra lakes and streams after snow melt and the strong N limitation of terrestrial primary production.     

凋落物多样性及组成对凋落物分解和土壤微生物群落的影响

凋落物分解是生态系统营养物质循环的核心过程,而土壤微生物群落在凋落物分解过程中扮演着极其重要且不可替代的角色。随着生物多样性的丧失日益严峻,探讨凋落物多样性及组成对凋落物分解和土壤微生物群落的影响,不仅有助于了解凋落物分解的内在机制,而且可为退化草原生态系统的恢复提供参考。以内蒙古呼伦贝尔草原退化恢复群落中的草本植物为研究对象,依据植物多度、盖度、频度和物种的重要值及其在群落中的恢复程度筛选出排序前4的羊草（Leymus chinensis）、茵陈蒿（Artemisia capillaris）、麻花头（Serratula centauroides）、二裂委陵菜（Potentilla bifurca）的凋落物为实验材料,通过设置3种凋落物多样性水平（1,2,4）,包括11种凋落物组合（单物种凋落物共4种,两物种凋落物混合共6种,四物种凋落物混合共1种）,利用磷脂脂肪酸（PLFA）方法来研究分解60 d后凋落物多样性及组成对凋落物分解和土壤微生物群落的影响。结果表明：（1）凋落物物种多样性仅对C残余率具有显著影响,表现在两物种混合凋落物C残余率显著低于单物种凋落物,而凋落物组成对所观测的4个凋落物分解参数（质量、C、N残余率以及C/N）均具有显著影响;（2）凋落物物种多样性对细菌（B）含量具有显著影响,而凋落物组成对真菌（F）含量具有显著影响,两者对F/B以及微生物总量均无显著影响;（3）冗余分析结果表明凋落物组成与凋落物分解相关指标（凋落物质量、C、N残余率及C/N）和土壤微生物（真菌、细菌含量）的相关关系高于凋落物多样性。（4）进一步建立结构方程模型（Structural Equation Model,SEM）发现,凋落物初始C含量对凋落物质量、C、N残余率及C/N有显著正的直接影响;凋落物木质素含量对凋落物质量、C、N残余率有显著正的直接影响;凋落物初始N含量对N残余率有显著正的直接影响,而对C残余率及C/N有显著负的直接影响;凋落物初始C/N对凋落物质量、N残余率有显著正的直接影响,而对C/N有显著负的直接影响。此外,凋落物初始C、N、木质素含量及C/N均对真菌含量具有显著正影响,并可通过真菌对凋落物质量分解产生显著负的间接影响。以上结果表明该退化恢复区域优势种凋落物分解以初始C、木质素为主导,主要通过土壤真菌影响凋落物的分解进程,这将减缓凋落物的分解速率进而减慢草原生态系统的进程。这些结果为凋落物多样性及组成对自身分解和土壤微生物群落的影响提供了实验依据,也为进一步分析凋落物分解内在机制以及草原生态系统的恢复提供了数据参考。     

长白山牛皮杜鹃凋落物分解及土壤动物的作用

凋落物分解是生态系统养分循环的重要环节。土壤动物对凋落物分解具有重要作用。有关高山常绿小灌木凋落物分解及土壤动物作用的研究鲜有报道。采用凋落物网袋法对长白山北坡岳桦林带(42°03'41.23″N,128°03'12.75″E,1900 m)牛皮杜鹃(Rhododendron chrysanthum)凋落物的分解过程进行了为期1a的野外观测与室内试验研究,采用4、2 mm和0.01 mm三种网孔凋落物袋来控制不同体型的土壤动物的参与,以研究凋落物的分解率、养分动态及土壤动物在凋落物分解中的作用。结果表明,4、2 mm和0.01 mm网孔凋落物分解率分别为34.19%、31.22%和25.45%。分解率表现出显著的季节差异性。从总体上来看,网袋内凋落物的总氮含量先增后减;C/N呈下降趋势。对分解起主要作用的优势类群是甲螨亚目和等节跳科。土壤动物总个体数与养分元素的释放关系显著,中小型土壤动物对有机碳的释放起到重要作用。截至2012年10月末试验结束,全部土壤动物对牛皮杜鹃凋落物分解质量损失的贡献率为25.57%,中小型土壤动物贡献率(16.88%)大型土壤动物贡献率(8.69%)。大型土壤动物和中小型土壤动物在牛皮杜鹃凋落物分解过程中所起的作用,具有不同步性。     

三江平原草甸湿地土壤呼吸和枯落物分解的CO2释放

利用静态箱-碱液吸收法研究了三江平原草甸湿地土壤呼吸和枯落物分解的CO₂释放速率,讨论了影响CO₂释放的环境因素,估算了枯落物分解的CO₂释放对于总释放的贡献。结果表明,生长季,小叶章沼泽化草甸和小叶章湿草甸各部分CO₂释放均具有明显的时间变化特征,温度和水分是重要制约因素。两类草甸湿地的平均土壤呼吸速率分别为4.33g•m^-2•d^-1和6.15g•m^-2•d^-1,枯落物分解的CO₂平均释放速率分别为1.76g•m^-2•d^-1和3.10g•m^-2•d^-1,枯落物分解的CO₂释放占总释放量的31%和35%,说明在碳素由地上植物碳库转移到地下土壤碳库的过程中,湿地枯落物是一个不可忽略的碳损失源。     

Lignin and nitrogen in the decomposition of leaf litter in a sub-tropical forest ecosystem at Shiroy hills in north-eastern India

The effect of the initial lignin and nitrogen contents of the leaves of five tree species, on their decomposition dynamics, was studied in the sub-tropical forest ecosystem existing at Shiroy hills. The decomposition dynamics of litter materials are described by inverse linear relationships between the percentage of the original biomass remaining and the nitrogen concentration in the residual material. Initial lignin and nitrogen were highly correlated with remaining biomass (r=0.94 and 0.77). The rate constants (K), for the annual leaf mass loss, ranged from −0.18 to −0.56. The values for initial lignin (%), initial nitrogen (%), the ratio between initial lignin, initial nitrogen and the annual decomposition rate constants were compared with similar results from other studies in various climatic zones of the world.     

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。     

森林凋落物分解重要影响因子及其研究进展

当前 ,森林凋落物分解被放在陆地生态系统碳平衡背景下进行研究 ,认识凋落物分解过程的影响因素和影响机理对理解地表碳平衡具有重要意义。凋落物在分解过程中 ,伴随有养分含量的变化 ,低品质凋落物在分解前期 (可达 2～ 3年 )会从环境中固定养分 ,特别是氮磷养分 ,而在后期则会释放出养分。凋落物本身的养分含量是影响分解速率的重要因素 ,高养分含量的凋落物分解快些 ,阔叶凋落物比针叶凋落物分解快些。有资料显示 ,在总分解率为2 9 4 %的构成中 ,理化因素、微生物因素与土壤动物因素对凋落物分解的贡献率分别为 7 2 %、8 0 %和 14 2 %。不同类型凋落物在分解过程中的土壤动物类群也不同 ,它也是造成凋落物分解速率不同的关键因素 ,通常阔叶树种凋落物分解过程中 ,会有更多的微节肢动物出现。CO2浓度升高将造成植物有机质含碳量与其它养分的比值升高 ,形成低品质的凋落物 ,从而间接影响凋落物分解速率 ,一般认为 ,全球CO2 浓度升高会加强土壤作为碳汇的功能。