Leaf Decomposition in a Dry Season Irrigation Experiment in Eastern Amazonian Forest Regrowth

Leaf-litter decomposition is a major component of carbon and nutrient dynamics in tropical forest ecosystems, and moisture availability is widely considered to be a major influence on decomposition rates. Here, we report the results of a study of leaf-litter decomposition of five tree species in response to dry-season irrigation in a tropical forest regrowth stand in the Brazilian Amazon; three experiments differing in the timing of installation and duration allowed for an improved resolution of irrigation effects on decomposition. We hypothesized that decomposition rates would be faster under higher moisture availability in the wet season and during dry-season irrigation periods in the treatment plots, and that decomposition rates would be faster for species with higher quality leaves, independent of treatment. The rates of decomposition ( k ) were up to 2.4 times higher in irrigated plots than in control plots. The highest k values were shown by Annona paludosa (0.97 to 1.26/yr) while Ocotea guianensis (0.73 to 0.85/yr) had the lowest values; intermediate rates were found for Lacistema pubescens (0.91 to 1.02/yr) and Vismia guianensis (0.91 to 1.08/yr). These four tree species differed significantly in leaf-litter quality parameters (nitrogen, phosphorus, lignin, and cellulose concentrations, as well as lignin:nitrogen and carbon:nitrogen ratios), but differences in decomposition rates among tree species were not strictly correlated with leaf-litter quality. Overall, our results show that dry-season moisture deficits limit decomposition in Amazonian forest regrowth.     

Comparison of Leaf Litter Decomposition Rates in Restored and Mature Riparian Forests on the Sacramento River, California

One of the largest riparian restoration projects in the United States is currently taking place in California on the Sacramento River. Nearly 2,000 ha of land adjacent to the river channel have been revegetated with native riparian species in an effort to reestablish riparian forests. The objective of this study was to compare leaf litter decomposition rates in restored riparian forests to those in mature, naturally established riparian forests, in order to monitor the development of this ecosystem function in restored forests. Leaf litter decomposition rates were measured over 1 year in six restored riparian forests (4, 7, and 9 years old) and two mature remnant riparian forests (>50 years old), in order to test two hypotheses: (1) decomposition rates of restored and mature forests are significantly different and (2) decomposition rates in the chronosequence of restored forests are moving along a trajectory, approaching the decomposition rates characteristic of mature forests as they age. Statistical analyses revealed no significant differences in annual decay rates among the four different forest ages and no trajectory among leaf litter decomposition rates in restored forests. These results suggest that a functionally equivalent process of leaf litter decomposition occurs in both restored and naturally established forests and show promise for the efficiency of nutrient cycling processes in these restored forests.     

天童国家森林公园常见植物凋落叶分解的研究

 选择天童地区常绿阔叶林及其退化群落常见植物种为对象,着重探讨分解速率和基质营养含量以及比表面积(Specific Leaf Area, SLA)的关系,并试图通过单独分解试验和混合分解试验的比较,从物种、功能群角度探讨凋落叶多样性和分解这一生态系统过程的关系,为深入研究常绿阔叶林常见植物种的营养策略、群落养分循环等奠定基础,也为植被恢复、森林生态系统管理提供理论依据。结果表明：所有凋落叶随时间进程失重率增大,但失重率并不与时间呈线性相关;凋落叶分解后N、P均发生了变化,大多数凋落叶在分解初期N、P均发生了积累,营养元素的释放和富集与凋落叶初始营养状况无明显的相关性。凋落叶的年分解系数与凋落叶中的初始N含量有较高的相关性,而与初始P含量则无显著的相关性;凋落叶的分解速率与成熟叶的面积无相关性,而与其SLA有很强的相关性。通过模型分析,天童地区大多数常见树种凋落叶分解95%需1～4年,平均是2.54年;分解率最高的物种为山鸡椒(Litsea cubeba),其值为6.280,最低的为黄丹木姜子(Litsea elongata),其值为0.558。凋落物混合对分解有很大的影响,虽在初期对分解有阻碍作用,但长期是促进的。若不考虑功能群差异,则可得出多样性的增加有利于分解的结论。功能群数目的增加在凋落物分解前期对分解起促进作用,但这种作用随分解的进展逐渐减小。混合物种的特性往往是决定分解过程的最重要的因素。     

松嫩草原优势植物羊草立枯体分解的研究

在羊草草原上当年羊草的枯死体大部分以立枯体的形态存在,立枯量约占枯死量的７５．３４％。立枯体与凋落物的分解速率的季节变化趋势基本相同,均呈抛物线型。每月凋落物的分解速率均大于立枯体分解速率,二者最小值均出现在１０月份。其中立枯体分解速率最大值出现在７月,凋落物出现在８月。立枯体和凋落物损失率的季节变化曲线均呈指数形式,立枯体的所损失量约占凋落物损失量的７７．１１％。立枯体的分解与水热因子均呈指数正     

Leaf litter decomposition in a southern Sonoran Desert ecosystem, northwestern Mexico: Effects of habitat and litter quality

Leaf litter decomposition of dominant woody perennial species in the three most common habitats of the southern Sonoran Desert was studied using the litter-bag method. Our objective was to assess the influence of litter quality on decomposition rates in three contrasting desert environments. The hypotheses were: (1) decomposition rates within the same litter type are faster in more mesic habitats, (2) decomposition rates are lower in higher lignin content or lower nutrient quality substrates, and (3) species-rich substrates enhance decomposition rates. For all litter types and habitats, a rapid loss of mass occurred during the summer rains at the start of the experiment, but total loss within the same litter type differed significantly among habitats. Decay rates were not higher in the more mesic habitat, but in the dry plains where solar irradiance and termite activity were highest. While termite activity was less important in the arroyos and absent in the hillsides habitats, proliferation of fungal mycelium in these sites was much higher than in the plains, suggesting that biotic and abiotic factors act both independently of litter richness. Lignin content seems to be an important factor controlling the loss of litter, because decay rates were inversely related to litter initial lignin content in all three habitats. Leaf litter diversity did not enhance rates of decomposition. The leaf litter mixture had k-values similar to the most recalcitrant monospecific litter in all three habitats, indicating a neutral or even antagonistic role of species-specific compounds in decomposition rates.     

Mixing effects on litter decomposition rates in a young tree diversity experiment

Litter decomposition is an essential process for biogeochemical cycling and for the formation of new soil organic matter. Mixing litter from different tree species has been reported to increase litter decomposition rates through synergistic effects. We assessed the decomposition rates of leaf litter from five tree species in a recently established tree diversity experiment on a post-agriculture site in Belgium. We used 20 different leaf litter compositions with diversity levels ranging from 1 up to 4 species. Litter mass loss in litterbags was assessed 10, 20, 25, 35, and 60 weeks after installation in the field. We found that litter decomposition rates were higher for high-quality litters, i.e., with high nitrogen content and low lignin content. The decomposition rates of mixed litter were more affected by the identity of the litter species within the mixture than by the diversity of the litter per se, but the variability in litter decomposition rates decreased as the litter diversity increased. Among the 15 different mixed litter compositions in our study, only three litter combinations showed synergistic effects. Our study suggests that admixing tree species with high-quality litter in post-agricultural plantations helps in increasing the mixture's early-stage litter decomposition rate.     

Rates of litter decomposition in terrestrial ecosystems: global patterns and controlling factors

Aims We aim to construct a comprehensive global database of litter decomposition rate (k value) estimated by surface floor litterbags, and investigate the direct and indirect effects of impact factors such as geographic factors (latitude and altitude), climatic factors (mean annual tempePlrature, MAT; mean annual precipitation, MAP) and litter quality factors (the contents of N, P, K, Ca, Mg and C:N ratio, lignin:N ratio) on litter decomposition.Methods We compiled a large data set of litter decomposition rates (k values) from 110 research sites and conducted simple, multiple regression and path analyses to explore the relationship between the k values and impact factors at the global scale.Important findings The k values tended to decrease with latitude (LAT) and lignin content (LIGN) of litter but increased with temperature, precipitation and nutrient concentrations at the large spatial scale. Single factor such as climate, litter quality and geographic variable could not explain litter decomposition rates well. However, the combination of total nutrient (TN) elements and C:N accounted for 70.2% of the variation in the litter decomposition rates. The combination of LAT, MAT, C:N and TN accounted for 87.54% of the variation in the litter decomposition rates. These results indicate that litter quality is the most important direct regulator of litter decomposition at the global scale. This data synthesis revealed significant relationships between litter decomposition rates and the combination of climatic factor (MAT) and litter quality (C:N, TN). The global-scale empirical relationships developed here are useful for a better understanding and modeling of the effects of litter quality and climatic factors on litter decomposition rates.     

海南岛中部丘陵地区植被恢复过程中凋落物动态及土壤碳氮含量变化

为探究海南岛中部丘陵地区植被恢复过程中凋落物分解动态和土壤碳氮含量变化,采用时空互代法,在琼中湾岭地区同时具有经自然恢复的草丛、灌丛、次生林和人工恢复的马占相思林4种植物群落的两个山坡采用凋落物袋法进行凋落物交互分解实验。结果表明:4类型凋落物在同一样地中分解时,灌丛凋落物肖梵天花分解速率最高;同一种类凋落物在4个样地中分解时,在灌丛样地的分解率较高,而在3个自然植被样地中,分解速率为灌丛>草丛>次生林,显示随着植物群落进展演替的进程,凋落物分解速率呈现先增加后降低的趋势;马占相思凋落物和在马占相思林样地分解凋落物的分解率均低于次生林。土壤碳氮含量变化不显著,但有随植被恢复进程而增加的趋势。     

陆地生态系统凋落物分解对全球气候变暖的响应

陆地生态系统凋落物分解是全球碳收支的一个重要组成部分, 主要受气候、凋落物质量和土壤生物群落的综合控制。科学家们普遍认为全球气候变化将对陆地生态系统凋落物分解产生复杂而深远的影响。该文结合凋落物分解试验的常用方法——缩微试验、原位模拟实验和自然环境梯度实验, 归纳现有研究结果, 意在揭示全球气候变化对陆地生态系统凋落物分解的直接影响(温度对凋落物分解速率的影响)和间接影响(温度对凋落物质量、土壤微生物群落及植被型的影响)的普遍规律。各种研究方法都表明: 在水分条件理想的情况下, 温度升高往往能加快凋落物的分解速率; 原位模拟实验中, 凋落物分解速率因物种、增温方法和地理方位而异; 全球气候变化能改变凋落物质量, 但可能不会在短期内影响凋落物的分解速率; 凋落物质量和可分解性的种间差异远大于增温所引发的表型响应差异, 那么, 气候变化所引发的植物群落结构和物种组成的变化将对陆地生态系统凋落物分解产生更强烈的影响; 土壤生物群落如何响应全球气候变化, 进而怎样影响凋落物分解过程, 这些都还存在着极大的不确定性。     

Do non-native Platanus hybrida riparian plantations affect leaf litter decomposition in streams?

In forest headwater streams where the riparian canopy limits autochthonous primary production, leaf litter decomposition is a key process controlling nutrient and carbon cycling. Any alteration of the riparian vegetation may influence litter decomposition and detrital food webs. We evaluated the effect of non-native Platanus hybrida riparian plantations on leaf litter decomposition in Mediterranean streams. The experiment was conducted in six headwater streams; three lined by native riparian vegetation and three crossing P. hybrida plantations. We have characterized the processing rates of alder leaves and the assemblages of shredder macroinvertebrates and fungi. Litter decomposition was significantly faster in the P. hybrida than in the reference streams. Although the dissolved inorganic nitrogen concentration was higher in P. hybrida, no significant effect was observed in decomposition rates. Differences in decomposition rates reflected the macroinvertebrate and shredder colonization in alder litter, with higher abundance and richness in the P. hybrida streams. However, aquatic hyphomycete sporulation rate was higher in reference streams, suggesting that the variation in decomposition rates is a direct consequence of shredder abundance. Our findings support part of the substrate quality-matrix quality (SMI) hypothesis, which expects that high-quality litter will show increased decomposition rates in a low-quality litter matrix.     

Characteristics of the biochemical composition of plant litter at different stages of decomposition (according to thermal analysis data)

The composition of samples of needles, leaves, sheaved cottongrass (Eriophorum vaginatum) tissues, and the L horizon of the forest floor of different degree of decomposition, isolated from the plant litter in southern taiga ecosystems, was studied by thermal analysis. It was established that plant litter decomposition is accompanied by structural changes in celluloses and that the decomposition rates of hemicellulose and structured cellulose vary at different stages of decomposition. The structural specificity and incongruent thermal decomposition of grass lignocellulose were observed in all samples of plant material. The rates at which the content of components of the plant litter decreased depended on the type and stage of decomposition of plant material. The decomposition rate of biochemical components tended to increase in better drained soils.     

Thermochemical pretreatment of lignocellulose to enhance methane fermentation: I. Monosaccharide and furfurals hydrothermal decomposition and product formation rates

Over a pH range 1-4 and temperatures from 170 to 230 degrees C, the decomposition rates of xylose, galactose, mannose, glucose, 2-furfural, and 5-hydroxymethyl-2-furfural (5-HMF) were pseudo first order. The effect of temperature and pH on the pseudo first-order decomposition rate constants was modeled using the Arrhenius equation and acid-base catalysis, respectively. Decomposition rates of the monosaccharides were minimum at a pH 2-2.5. Above pH 2.5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid catalysis at below ca. pH 3.5. The hydrothermal conversion of glucose to its decomposition products during thermochemical Pretreatment can be modeled as a combination of series and parallel reactions. The formation rates of identified soluble products from glucose decomposition, 5-HMF and levulinic acid, were also functions of temperature and pH. The rate of 5-HMF formation relative to glucose decomposition decreased as the pH increased from 2.0 to 4.0, with levulinic acid formation only detected when the pH was 2.5 or less. For glucose decomposition, humic solids accounted for ca. 20% of the decomposition products.     

Global patterns in fine root decomposition: climate,chemistry, mycorrhizal association and woodiness

Fine root decomposition constitutes a critical yet poorly understood flux of carbon and nutrients in terrestrial ecosystems. Here, we present the first large‐scale synthesis of species trait effects on the early stages of fine root decomposition at both global and local scales. Based on decomposition rates for 279 plant species across 105 studies and 176 sites, we found that mycorrhizal association and woodiness are the best categorical traits for predicting rates of fine root decomposition. Consistent positive effects of nitrogen and phosphorus concentrations and negative effects of lignin concentration emerged on decomposition rates within sites. Similar relationships were present across sites, along with positive effects of temperature and moisture. Calcium was not consistently related to decomposition rate at either scale. While the chemical drivers of fine root decomposition parallel those of leaf decomposition, our results indicate that the best plant functional groups for predicting fine root decomposition differ from those predicting leaf decomposition.     

帽儿山森林落叶分解消耗与土壤动物关系的研究

１引言森林凋落物分解是森林生态系统物质循环和能量流动的重要环节,枯枝落叶分解是由多种因素作用的复杂过程．研究枯枝落叶在自然环境下的分解消耗及其与土壤动物的关系具有重要的生态学意义［４］,并对林业生产、营造人工林有一定的指导作用．在枯枝落叶分解研究中,...     

土壤湿度对东北3种主要树种凋落物分解的影响

结合丰林国家自然保护区原始阔叶红松林1998-2017年表层(0～10 cm)土壤湿度监测数据,评估了全球变化背景下土壤湿度变化对东北主要森林树种红松、臭冷杉和白桦凋落物分解的影响.结果表明: 在同一土壤湿度水平下,凋落物分解速率随着凋落物质量的增加而增大,即表现为白桦>臭冷杉>红松.凋落物的分解速率随着土壤湿度的降低而减小.白桦、臭冷杉和红松3种凋落物的土壤湿度敏感性指数(M₁₀)分别为0.782、0.789和0.827,土壤湿度水平每降低10%,初始分解速率分别减小21.8%、21.1%和17.3%.高质量凋落物(高氮含量、低碳氮比、低木质素含量)的分解速率对土壤湿度变化的响应更敏感.凋落物分解速率在不同凋落物类型间的差异随着土壤湿度的降低而缩小.近20年间,原始阔叶红松林土壤湿度呈显著减少趋势,对凋落物分解表现为抑制作用.在全球变化背景下,随着气温的升高,土壤湿度将继续降低,对凋落物的抑制作用会进一步增强,并将部分抵消因温度升高所带来的凋落物分解速率增大的压力.     

几种水生植物腐解过程的比较研究

研究水生植物腐烂分解过程及其养分动态对认识水生态系统物质循环过程具有重要意义。通过室内植物分解模拟试验,对6种水生植物的腐解过程及腐解残余物成分的变化进行了比较研究。结果表明,在64 d的腐解过程中,浮叶植物的分解速率最快,沉水植物其次,挺水植物最慢;同种植物的分解速率及残余物成分变化在不同生物量密度组间存在一定差异,但总体趋势一致。分解过程中,植物残余物中P、纤维素、木质素含量的变化趋势种间差异较小,总体上P含量先迅速下降后缓慢上升,纤维素含量先下降后趋于稳定,木质素含量先上升后趋于稳定;植物残余物中C、N、半纤维素含量在分解初期种间的变化趋势不同,而分解后期则均为C含量上升,N、半纤维素含量趋于稳定。相关性分析结果表明,总体上,在整个分解周期中,初始N、P含量越大分解越快,初始纤维素、半纤维素、木质素含量、C/N、C/P、木质素/N等越大分解越慢;植物腐解不同阶段的质量指标对分解速率的影响有所不同,在分解前期,残余物中N含量越高分解越快,半纤维素含量、C/N、木质素/N越高,分解越慢,而后期木质素含量越高分解越慢,其它因子影响较小。     

Linkages between grazing history and herbivore exclusion on decomposition rates in mineral soils of subalpine grasslands

Background & aims

Herbivore-driven changes to soil properties can influence the decomposition rate of organic material and therefore soil carbon cycling within grassland ecosystems. We investigated how aboveground foraging mammalian and invertebrate herbivores affect mineral soil decomposition rates and associated soil properties in two subalpine vegetation types (short-grass and tall-grass) with different grazing histories.

Methods

Using exclosures with differing mesh sizes, we progressively excluded large, medium and small mammals and invertebrates from the two vegetation types in the Swiss National Park (SNP). Mineral soil decomposition rates were assessed using the cotton cloth (standard substrate) method between May and September 2010.

Results

Decomposition displayed strong spatio-temporal variability, best explained by soil temperature. Exclusion of large mammals increased decomposition rates, but further exclusion reduced decomposition rates again in the lightly grazed (tall-grass) vegetation. No difference among treatments was found in the heavily grazed (short-grass) vegetation. Heavily grazed areas had higher decomposition rates than the lightly grazed areas because of higher soil temperatures. Microbial biomass carbon and soil C:N ratio were also linked to spatio-temporal decomposition patterns, but not to grazing history.

Conclusions

Despite altering some of the environmental controls of decomposition, cellulose decomposition rates in the SNP’s subalpine grasslands appear to be mostly resistant to short-term herbivore exclusion.     

Effect of small reservoirs on leaf litter decomposition in Mediterranean headwater streams

Leaf litter decomposition is a crucial process providing matter and energy to communities inhabiting headwater streams. This process could be affected by many man-made landscape transformations and its response can vary depending on the climate setting. In this study, we test the hypothesis that the presence of small headwater reservoirs decreases litter decomposition downstream, as reported for temperate Oceanic climatic regions, and that this effect is more accentuated in the Mediterranean. The effect of small dams on the decomposition of alder (Alnus glutinosa) leaves was studied in four headwater streams in Catalonia (NE Spain). The presence of a dam affected litter decomposition rates in three of the four streams studied, and this depended on reservoir typology. In those with seasonal surface release, decomposition rates were slower downstream from the dams, but in the case of a continuous hypolimnetic release, it was faster, with higher DIN and temperature and abundance of shredders. Alder litter decomposition rates were twice those reported for Oceanic climatic conditions. In Mediterranean headwaters, the effect of small dams will even be more evident at an annual scale due to the diminished flow rates in summer and this effect will be more pronounced than in the more Oceanic.     

N concentration controls decomposition rates of different strains of ectomycorrhizal fungi

The decomposition of soil organic matter in forest ecosystems is important in two ways. First, soil organic matter is the largest pool of C in terrestrial ecosystems, so understanding global carbon cycling requires an appreciation of the factors that control the size of that pool and the fluxes through it. Among these factors are those that control the rate of organic matter decomposition. Second, organic matter decomposition is the major process controlling the supply of nutrients to plants. In some ecosystems ectomycorrhizal fungi comprise a surprisingly large fraction of soil organic matter. However, little is known of the rates of decomposition of ectomycorrhizal fungi, or of the factors that control those rates. Therefore, we set out to examine the relationship between N concentrations and decomposition rates of ectomycorrhizal fungi using a wide variety of strains isolated from a Pinus resinosa plantation. We found that substantial variation among strains existed in decomposition rate, and that decomposition rate was highly correlated with tissue N concentration. We conclude, therefore, that the structures of ectomycorrhizal fungal communities may be ecologically important in terms of ecosystem C and N dynamics.     

降水强度变化对天山云杉地表凋落物和细根分解的影响

为了探明不同降水条件下干旱区山地森林主要优势树种凋落物分解特征,采用野外模拟试验,通过设计3种降水强度处理[ZP（去除降水）、CK（自然降水,对照）、DP（双倍降水）],研究了降水强度变化对天山云杉地表凋落物（叶和枝）和细根分解的影响。研究结果表明：分解24个月后对照凋落叶、凋落枝和细根干重损失率比去除降水损失率分别高24.79%、2.54%和23.09%,比双倍降水损失率低7.04%、0.68%和10.70%,去除降水对凋落叶和细根分解的抑制作用显著,对凋落枝抑制作用较微弱,双倍降水对分解具有促进作用,但仅对细根分解的促进作用显著。对照和双倍降水处理下凋落叶和细根月平均分解率均表现为双峰型曲线,凋落枝为单峰曲线,去除降水处理下地表凋落物和细根月平均分解率相对平缓。木质素和纤维素残留率也表现为去除降水 > 对照 > 双倍降水。不同降水处理下分解过程中N元素释放模式不同,但C释放模式基本一致。相关分析表明,凋落物月分解率与0~10 cm土层温度的相关性不显著（P>0.05）,但与土壤含水量间为线性极显著正相关（P<0.05）。我们研究结果发现云杉凋落物与根系分解对降水强度变化存在明显差异,未来气候变化对土壤碳周转影响应该充分考虑这种器官间差异。