Variations in leaf litter decomposition across contrasting forest stands and controlling factors at local scale

Aims Litter decomposition is a critical pathway linking the above- and belowground processes. However, factors underlying the local spatial variations in forest litter decomposition are still not fully addressed. We investigated leaf litter decomposition across contrasting forest stands in central China, with objective to determine the spatial variations and controlling factors in forest floor leaf litter decomposition in relation to changes in forest stands in a temperate forest ecosystem.Methods Leaf litter decomposition was studied by using litterbag method across several typical forest stand types in Baotianman Nature Reserve, central China, including pure stands of Quercus aliena var. acuteserrata, Q. glandulifera var. brevipetiolata and Q. variabilis, respectively, and mixed pine/oak stands dominated by Pinus armandii and Q. aliena var. acuteserrata, as well as stands of pure Q. aliena var. acuteserrata trees ranging in stand age from ~40 to>160 years. Measurements were made on litter mass remaining and changes in litter chemistry during decomposition over a 2-year period, along with data collections on selective biotic and environmental factors. A reciprocal transplant experiment involving Q. aliena var. acuteserrata and Q. variabilis was concurrently carried out to test the occurrence of 'home-field advantage (HFA)' in local forests when only considering contrasting oak tree species. Correlation analyses and path analyses were performed to identify the dominant drivers and their relative contributions to variations in leaf litter decomposition.Important findings Significant variations were found in the rate of leaf litter decomposition among stands of different tree species but not among stand age classes. The values of decay constant, k, varied from 0.62 in Q. aliena var. acuteserrata stands to 0.56 in Q. variabilis stands. The reciprocal litter transplant experiment showed that the rate of leaf litter decomposition was on average 5% slower in home-fields than on reciprocal sites. Path analysis identified litter acid-unhydrolyzable residue (AUR) to N ratio, soil microbial biomass carbon (MBC), soil pH and soil organic carbon (SOC) as most prominent factors controlling the rate of leaf litter decomposition, collectively accounting for 57.8% of the variations; AUR/N had the greatest negative effect on k value, followed by weaker positive effects of SOC and MBC. Our findings suggest that tree species plays a primary role in affecting forest floor leaf litter decomposition by determining the litter quality, with site environment being a secondary factor contributing to the local variations in leaf litter decomposition in this temperate forest ecosystem.     

Nitrogen addition stimulates forest litter decomposition and disrupts species interactions in Patagonia,Argentina

Nitrogen (N) deposition and biodiversity loss are important drivers of global change, with uncertain consequences for carbon (C) and nutrient turnover in terrestrial ecosystems. We evaluated the simultaneous effects of N deposition and plant diversity on litter decomposition within a temperate forest in Patagonia. We identified ‘tree triangles’ created by the intersection of three tree‐canopies that directly controlled micro‐environmental conditions on the forest floor, and combined it with an N addition treatment. Triangles were composed of one or three Nothofagus species (N. dombeyi, N. obliqua or N. nervosa). We placed litterbags containing litter of each of the Nothofagus species and litterbags containing a mixture of the three species within all triangles and assessed mass loss over 2 years. We used a standard litter type in all triangles to independently evaluate triangle effects on decomposition. N addition had strong and positive effects on decomposition with an average 46% increase in the decomposition constant. Litter species significantly differed in their response to N addition; litter with higher lignin content and lower labile C content had larger increase in decomposition due to fertilization. Also, N addition disrupted two types of species interactions that control decomposition. The affinity relation between litter and decomposers, that enhanced decomposition of home litter (‘home‐field advantage’) that was demonstrated to be significant for all three Nothofagus species, disappeared with N addition. Second, N addition modified litter species interactions, transforming neutral effects of litter mixtures to positive, nonadditive effects on mass loss. Finally, N addition stimulated N release from decomposing litter which was modulated by plant species effects. Together, these results suggest that N addition to unpolluted forests increases C loss, contrary to what has been observed for temperate forests in industrialized areas of the world, and that alterations in nutrient pools have effects on species interactions, including the elimination of affinity effects for decomposition.     

长白山阔叶红松林主要树种凋落叶分解速率及其与叶性状的关系

阔叶红松林是我国东北地区地带性顶级森林群落,对维持区域生态系统稳定性具有重要作用。对阔叶红松林内主要树种凋落叶分解过程及影响因素进行研究,有助于增加长白山阔叶红松林生态系统的基础数据,为明确阔叶红松林的养分循环和物质流动提供依据。选取了长白山阔叶红松林内30个常见乔灌树种和16个凋落叶性状,采用野外分解袋法和室内样品分析等方法研究了长白山阔叶红松林内主要树种凋落叶分解速率及其与凋落叶性状的关系。1年的野外分解实验表明,30个树种的凋落叶重量损失率表现出较大差异。不同树种凋落叶的重量损失率在20.56%—92.11%之间,以红松(Pinus koraiensis)质量损失率最低,东北山梅花(Philadelphus schrenkii)质量损失率最高。不同生活型树种的凋落叶在质量损失率上存在显著差异,以灌木树种凋落叶的质量损失率最高,小乔木次之,乔木树种质量损失率最低。Olson模型拟合结果表明,不同树种凋落叶的分解速率k以红松最低,瘤枝卫矛(Euonymus verrucosus)最高,分别为0.24和1.64。不同树种分解50%和95%所需的时间分别在0.43—2.86年,1.83—...     

Diversity and functioning of fungi associated with leaf litter decomposition in Asian forests of different climatic regions

The pattern of diversity and functioning of fungi associated with leaf litter decomposition in Asian forests of different climatic regions was investigated by performing meta-analysis of published data for seven tree species in subalpine, temperate, subtropical and tropical forests. Fungal assemblages were examined by using common standard isolation-culture methods, and the abilities of individual fungal species to decompose leaf litter were examined with pure culture decomposition tests. The climatic patterns of diversity, assemblage structure and genus composition depended on the method of isolation: the washing method revealed no consistent pattern, whereas the surface sterilization method showed lower diversity and greater relative abundance of dominant fungal species within the assemblages in cooler climates. The decomposing ability of species within fungal assemblages was greater in warmer than in cooler climates and in broad-leaved than in coniferous tree species. In particular, the greatest abilities to cause mass loss were found among fungi with ligninolytic activity in broad-leaved tree species in warmer climates.     

中国温带和亚热带8个树种叶和吸收根协同分解

叶和细根(2mm)是森林生态系统的分解主体,二者是否协同分解,将极大影响所属植物在生态系统碳(C)循环中的物种效应。已有研究显示,叶和细根的分解关系具有极大的不确定性,认为很大程度上归因于细根内部具有高度的异质性,导致叶和细根在功能上不相似。为此,使用末梢1级根和细根根枝作为研究对象,它们在功能上同叶类似,称为吸收根。通过分解包法,分别在黑龙江帽儿山和广东鹤山,研究了2个阔叶树种和2个针叶树种(共8个树种)的叶和吸收根持续2a多的分解。结果发现,分解速率k(a~(-1),负指数模型)在8个树种整体分析时具有正相关关系(P0.05),在相同气候带或植物生活型水平上是否相关,受叶的分解环境及吸收根类型的影响;N剩余量整体上并不相关,亚热带树种的叶和细根根枝的N剩余量在分解1a后高度显著正相关,温带树种的叶和1级根的N剩余量在分解2a后显著高度正相关。本研究中,根-叶分解过程是否受控于相同或相关的凋落物性质是决定根-叶分解是否相关的重要原因,其中分解速率与酸溶组分正相关、与酸不溶组分负相关。比较已有研究,总结发现,根-叶分解关系受物种影响较大,暗示气候变化导致物种组成的改变将极大影响地上-地下关系,也因此影响生态系统C循环。     

亚热带不同树种凋落叶分解对氮添加的响应

为探究不同质量凋落物对氮(N)沉降的响应, 该研究采用尼龙网袋分解法, 在亚热带福建三明格氏栲(Castanopsis kawakamii)自然保护区的米槠(Castanopsis carlesii)天然林, 选取4种本区常见的具有不同初始化学性质的树种凋落叶进行模拟N沉降(N添加)分解实验(施N水平为对照0和50 kg·hm ^-2·a ^-1)。研究结果表明: 在2年的分解期内, 对照处理的各树种凋落叶的分解速率依次为观光木(Michelia odora, 0.557 a ^-1)、米槠(0.440 a ^-1)、台湾相思(Acacia confusa, 0.357 a ^-1)、杉木(Cunninghamia lanceolata, 0.354 a ^-1); N添加处理凋落叶分解速率依次为观光木(0.447 a ^-1)、米槠(0.354 a ^-1)、杉木(0.291 a ^-1)、台湾相思(0.230 a ^-1), 除杉木凋落叶外, N添加显著降低了其他3种凋落叶分解速率。N添加不仅使4种树木凋落叶分解过程中的N释放减慢, 同时还抑制凋落叶化学组成中木质素和纤维素的降解; N添加在凋落叶分解过程中总体上提高β-葡萄糖苷酶(βG)和酸性磷酸酶活性, 对纤维素水解酶的活性影响不一致, 而降低β-N-乙酰氨基葡萄糖苷酶活性和酚氧化酶活性。凋落叶分解速率与凋落叶中的碳获取酶(βG)活性以及其化学组分中的可萃取物含量极显著正相关, 与初始碳浓度、纤维素和木质素含量极显著负相关, 与初始N含量没有显著相关性。凋落物类型和N添加的交互作用虽未影响干质量损失速率, 但对木质素和纤维素的降解具有显著效应。综上所述, 化学组分比初始N含量能更好地预测凋落叶分解速率, 而N添加主要通过抑制分解木质素的氧化酶(如PHO)来降低凋落叶分解速率。     

Increasing Red Maple Leaf Litter Alters Decomposition Rates and Nitrogen Cycling in Historically Oak-Dominated Forests of the Eastern U.S.

Without canopy-opening fire disturbances, shade-tolerant, fire-sensitive species like red maple (Acer rubrum L.) proliferate in many historically oak-dominated forests of the eastern U.S. Here, we evaluate potential implications of increased red maple dominance in upland oak forests of Kentucky on rates of leaf litter decomposition and nitrogen (N) cycling. Over 5 years, we evaluated mass loss of leaf litter and changes in total N and carbon (C) within six leaf litter treatments comprised of scarlet oak, chestnut oak, and red maple, and three mixed treatments of increasing red maple contribution to the leaf litter pool (25, 50, and 75% red maple). Over a 1.5-year period, we conducted a plot-level leaf litter manipulation study using the same treatments plus a control and assessed changes in net nitrification, ammonification, and N mineralization within leaf litter and upper (0–5 cm depth) mineral soil horizons. Red maple leaf litter contained more “fast” decomposing material and initially lost mass faster than either oak species. All litter treatments immobilized N during initial stages of decomposition, but the degree of immobilization decreased with decreasing red maple contribution. The leaf litter plot-level experiment confirmed slower N mineralization rates for red maple only plots compared to chestnut oak plots. As red maple increases, initial leaf litter decomposition rates will increase, leading to lower fuel loads and more N immobilization from the surrounding environment. These changes may reduce forest flammability and resource availability and promote red maple expansion and thereby the “mesophication” of eastern forests of the U.S.     

亚热带森林树种多样性对凋落叶分解胞外酶活性的影响

森林生物多样性与生态系统功能关系是当前群落生态学的热点研究领域。然而, 以往研究更多聚焦在森林植物多样性丧失对群落生产力的影响, 而对森林凋落物分解的相关研究稍显不足。森林凋落叶分解的快慢直接受控于凋落物分解者分泌的胞外酶的活性, 后者更是指示森林生态系统养分循环的重要指标之一。本研究依托我国江西亚热带森林生物多样性与生态系统功能控制实验, 通过对不同植物多样性梯度样方内目标树种凋落叶胞外酶活性、理化性质以及腐生真菌的分析, 探索树种多样性丧失对胞外酶活性的影响及其调控机制, 以探讨森林树种多样性对地表、地下生态过程和功能的影响。结果表明, 样方水平树种多样性丧失显著影响胞外酶的活性, 除单种样方外, 随着样方水平树种丰富度的增加, 胞外酶活性呈现出增长趋势; 与碳周转相关的α-葡萄糖苷酶(AG)、β-葡萄糖苷酶(BG)、纤维二糖水解酶(CB)在树种多样性最大时活性达到最高; 而木糖苷酶(XS)以及与氮、磷和顽拗有机养分分解相关的N-乙酰-β-氨基葡萄糖苷酶(NAG)、酸性磷酸酶(AP)和多酚氧化酶(PPO)在树种多样性较低时活性较高。针对目标树种周围的邻居树种多样性进一步分析发现, 各胞外酶活性随着邻居树种多样性的变化呈“单峰”响应趋势, 酶活性大多在邻居树种丰富度为6时呈现峰值。研究发现真菌分解者在胞外酶活性对植物多样性的响应上可能存在重要的调控作用, 可以推测树种多样性通过改变腐生真菌分解者的群落结构和多度, 从而影响胞外酶活性。     

Limit values for decomposition and convergence process of lignocellulose fraction in decomposing leaf litter of 14 tree species in a cool temperate forest

We examined limit values for decomposition and lignocellulose index (LCI, the ratio of acid-soluble holocellulose to acid-soluble holocellulose plus acid-insoluble lignin and lignin-like substances) in leaf litter decomposition of 14 tree species over 3 years. The study was carried out on upper (moder) and lower parts (mull) of a forest slope that showed different humus accumulation forms in a cool temperate forest in Japan. Limit values for accumulated mass loss of litter ranged from 46.8% to 94.1% and were not different between the sites. Limit values were positively correlated to initial LCI and lignin content. Final values of LCI of 14 litter types at the end of the study period showed a convergent trend among litter types at 0.25–0.26 as compared to their initial values (0.41 mean). The final LCI was not different between the sites. A review of limit values and initial and final values of LCI in leaf litter of temperate and boreal forests indicated that the limit values and final LCI in litter types in Japan were lower than those in Europe and North America, which can be primarily ascribed to lower initial LCI in Japan.     

Factors regulating litter mass loss and lignin degradation in late decomposition stages

We studied late-stages decomposition of four types of coniferous needle and three types of deciduous leaf litter at two sites, one nutrient-poor boreal and one nutrient-rich temperate. The late stage was identified by that reached by litters at the onset of net loss of lignin mass, i.e. at about 1 year after the incubation when the highest amount of lignin had been detected; the study extended over the following 2 year period. Decomposition rates were significantly lower at the boreal than at the temperate site and did not differ between needle litter and leaf litter. In the boreal forest: (1) mass-loss was positively correlated with N and Mn release, (2) Mn concentration at the start of the late stage was positively correlated with lignin decay, (3) Ca concentration was negatively correlated to litter mass loss and lignin decay. In the temperate forest neither lignin, N, Mn, and Ca concentration at the start of the late stage, nor their dynamics were related to litter decomposition rates and lignin decay. In leaf litter mass-loss and lignin decay were positively correlated with N and Ca release and with Ca concentration. In needle litter mass-loss was positively correlated to Mn release and N concentration negatively with lignin decay. We concluded that Ca, N and Mn have different roles in controlling lignin decay depending on type of litter and site conditions.     

Slow decomposition and limited nitrogen release by lower order roots in eight Chinese temperate and subtropical trees

Background and aims

Roots of the lowest branch orders have the highest mortality rate, and may contribute predominately to plant carbon (C) and nutrient transfer into the soil. Yet patterns and controlling factors of the decomposition of these roots are poorly understood.

Methods

We conducted a two-year field litterbag study on different root orders and leaf litter in four temperate and four subtropical tree species.

Results

Five species showed slower decay rates in lower- (order 1–2) than higher-order (order 3–5) roots, and all species showed slower decay rates in lower-order roots than leaf litter. These patterns were strongly related to higher acid-insoluble fraction in lower- than higher-order roots, and in roots than in leaf litter, but were unrelated to initial N concentration. Litter N was predominantly in recalcitrant forms and limited amount of N was released during the study period;only 12 % of root N and 26 % of leaf litter N was released in 2 years.

Conclusions

We conclude that the slow decomposition of lower-order roots may be a common phenomenon and is mainly driven by their high acid-insoluble fraction. Moreover, litter N, especially root N, is retained during decomposition and may not be available for immediate plant uptake.     

Mixing Effects of Understory Plant Litter on Decomposition and Nutrient Release of Tree Litter in Two Plantations in Northeast China

Understory vegetation plays a crucial role in carbon and nutrient cycling in forest ecosystems; however, it is not clear how understory species affect tree litter decomposition and nutrient dynamics. In this study, we examined the impacts of understory litter on the decomposition and nutrient release of tree litter both in a pine (Pinus sylvestris var. mongolica) and a poplar (Populus × xiaozhuanica) plantation in Northeast China. Leaf litter of tree species, and senesced aboveground materials from two dominant understory species, Artemisia scoparia and Setaria viridis in the pine stand and Elymus villifer and A. sieversiana in the poplar stand, were collected. Mass loss and N and P fluxes of single-species litter and three-species mixtures in each of the two forests were quantified. Data from single-species litterbags were used to generate predicted mass loss and N and P fluxes for the mixed-species litterbags. In the mixture from the pine stand, the observed mass loss and N release did not differ from the predicted value, whereas the observed P release was greater than the predicted value. However, the presence of understory litter decelerated the mass loss and did not affect N and P releases from the pine litter. In the poplar stand, litter mixture presented a positive non-additive effect on litter mass loss and P release, but an addition effect on N release. The presence of understory species accelerated only N release of poplar litter. Moreover, the responses of mass loss and N and P releases of understory litter in the mixtures varied with species in both pine and poplar plantations. Our results suggest that the effects of understory species on tree litter decomposition vary with tree species, and also highlight the importance of understory species in litter decomposition and nutrient cycles in forest ecosystems.     

Response of Litter Decomposition to Simulated N Deposition in Disturbed, Rehabilitated and Mature Forests in Subtropical China

The response of decomposition of litter for the dominant tree species in disturbed (pine), rehabilitated (pine and broadleaf mixed) and mature (monsoon evergreen broadleaf) forests in subtropical China to simulated N deposition was studied to address the following hypothesis: (1) litter decomposition is faster in mature forest (high soil N availability) than in rehabilitated/disturbed forests (low soil N availability); (2) litter decomposition is stimulated by N addition in rehabilitated and disturbed forests due to their low soil N availability; (3) N addition has little effect on litter decomposition in mature forest due to its high soil N availability. The litterbag method (a total of 2880 litterbags) and N treatments: Control-no N addition, Low-N: −5 g N m⁻² y⁻¹, Medium-N: −10 g N m⁻² y⁻¹, and High-N: −15 g N m⁻² y⁻¹, were employed to evaluate decomposition_. Results indicated that mature forest, which has likely been N saturated due to both long-term high N deposition in the region and the age of the ecosystem, had the highest litter decomposition rate, and exhibited no significant positive and even some negative response to nitrogen additions. However, both disturbed and rehabilitated forests, which are still N limited due to previous land use history, exhibited slower litter decomposition rates with significant positive effects from nitrogen additions. These results suggest that litter decomposition and its responses to N addition in subtropical forests of China vary depending on the nitrogen status of the ecosystem.     

Decomposition of organic chemical components in relation to nitrogen dynamics in leaf litter of 14 tree species in a cool temperate forest

Decomposition of lignin, holocellulose, polyphenols and soluble carbohydrates was investigated in relation to nitrogen (N) dynamics in leaf litter of 14 tree species. The influence of organic chemical components and N on litter mass loss rate was then evaluated for 14 litter types. The study was carried out over a 3-year period on upper and lower parts of a forest slope in a cool temperate forest in Japan. The decomposition processes were divided into early and late phases based on N immobilization and mobilization. Mass loss rate of whole litter and organic chemical components was similar for the upper and lower sites. Litter mass loss was faster in the immobilization phase than in the mobilization phase in each of 14 litter types, which was ascribed to the decreased mass loss of holocellulose, polyphenols and soluble carbohydrates in the mobilization phase as compared to the immobilization phase. Mass loss rate of lignin was not different between the phases. Litter mass loss rate in the immobilization and mobilization phases was negatively correlated to lignin content and positively correlated to contents of polyphenols and soluble carbohydrates at the start of these phases, but was not correlated to holocellulose and N contents in either phase.     

Boreal peat properties link to plant functional traits of ecosystem engineers

Aims

Warming has the potential to alter plant litter mass loss and nutrient release during decomposition. However, a great deal of uncertainty remains concerning how other factors such as litter species or substrate quality might modify the effects of increased temperature on decomposition. Meanwhile, the temperature sensitivity of plant litter decay in tropical and subtropical forest ecosystems remains poorly resolved.

Methods

This study was designed to assess the effects of experimental warming on litter decomposition and nutrient release of two contrasting tree species (Schima superba and Machilus breviflora) by translocating model forest ecosystems from the high-elevation sites to the lower-elevation sites in subtropical China. Translocating model mountain evergreen broad-leaved forest (MEBF) to the altitude of 300 m and 30 m increased the average monthly soil temperature at 5 cm depth by 0.88 and 1.84 °C, respectively during the experimental period. Translocating model coniferous and broad-leaved mixed forest (CBMF) to the altitude of 30 m increased the average monthly soil temperature at 5 cm depth by 0.85 °C.

Results

We found that experimental warming accelerated litter decomposition in both model forest types, and the promoting efficiency was greater when the temperature increased. The litter with high quality (Schima superba) had stronger response to warming than low quality litter (Machilus breviflora). Warming accelerated Na, K, Mg, P, N and Ca release from Schima superba litter, but only simulated Ca release from Machilus breviflora litter. Overall, litter decomposition was controlled by the order: soil temperature > litter quality > soil moisture > litter incubation forest type under experimental warming in the subtropical China.

Conclusion

We conclude that leaf litter decomposition was facilitated by experimental warming in subtropical China. Litter species might modify the effects of increased temperature on litter decomposition; however, forest type has no effect on litter decomposition.

     

Effects of temperature and litter type on fungal growth and decomposition of leaf litter

The dependence of fungal decomposition of leaf litter on incubation temperature and litter types used as substrata was assessed under pure culture conditions. Isolates of Xylaria sp., a major ligninolytic fungus in cool temperate forests in Japan, were used as the fungal material. Xylaria sp. is mesophilic; maximum growth and decomposition occurred at 25°C. In the temperature test, the decomposition pattern of beech leaf litter by three isolates of Xylaria sp. changed at a threshold at 25°C. Cellulolytic activity increased with temperature from 5 to 25°C, whereas above 25°C ligninolytic activity increased at the expense of cellulolytic activity, leading to suppressed overall decomposition as a result of the higher temperature. The mass loss of leaf litter caused at 20°C by an isolate of Xylaria sp. was variable among 15 litter types and was correlated negatively with acid-unhydrolyzable residue (AUR) content and positively with total carbohydrate content for the 15 litter types. The effects of temperature and litter type on the growth and decomposition of leaf litter by Xylaria sp. may have implications for changes in fungal decomposition of leaf litter that would be predicted in response to future environmental changes.     

Factors influencing leaf litter decomposition: an intersite decomposition experiment across China

The Long-Term Intersite Decomposition Experiment in China (hereafter referred to as LTIDE-China) was established in 2002 to study how substrate quality and macroclimate factors affect leaf litter decomposition. The LTIDE-China includes a wide variety of natural and managed ecosystems, consisting of 12 forest types (eight regional broadleaf forests, three needle-leaf plantations and one broadleaf plantation) at eight locations across China. Samples of mixed leaf litter from the south subtropical evergreen broadleaf forest in Dinghushan (referred to as the DHS sample) were translocated to all 12 forest types. The leaf litter from each of other 11 forest types was placed in its original forest to enable comparison of decomposition rates of DHS and local litters. The experiment lasted for 30 months, involving collection of litterbags from each site every 3 months. Our results show that annual decomposition rate-constants, as represented by regression fitted k-values, ranged from 0.169 to 1.454/year. Climatic factors control the decomposition rate, in which mean annual temperature and annual actual evapotranspiration are dominant and mean annual precipitation is subordinate. Initial C/N and N/P ratios were demonstrated to be important factors of regulating litter decomposition rate. Decomposition process may apparently be divided into two phases controlled by different factors. In our study, 0.75 years is believed to be the dividing line of the two phases. The fact that decomposition rates of DHS litters were slower than those of local litters may have been resulted from the acclimation of local decomposer communities to extraneous substrate.     

Factors controlling decomposition rates of fine root litter in temperate forests and grasslands

Background and aims

Fine root decomposition contributes significantly to element cycling in terrestrial ecosystems. However, studies on root decomposition rates and on the factors that potentially influence them are fewer than those on leaf litter decomposition. To study the effects of region and land use intensity on fine root decomposition, we established a large scale study in three German regions with different climate regimes and soil properties. Methods In 150 forest and 150 grassland sites we deployed litterbags (100 μm mesh size) with standardized litter consisting of fine roots from European beech in forests and from a lowland mesophilous hay meadow in grasslands. In the central study region, we compared decomposition rates of this standardized litter with root litter collected on-site to separate the effect of litter quality from environmental factors.

Results

Standardized herbaceous roots in grassland soils decomposed on average significantly faster (24?±?6 % mass loss after 12 months, mean ± SD) than beech roots in forest soils (12?±?4 %; p?Conclusions Grasslands, which have higher fine root biomass and root turnover compared to forests, also have higher rates of root decomposition. Our results further show that at the regional scale fine root decomposition is influenced by environmental variables such as soil moisture, soil temperature and soil nutrient content. Additional variation is explained by root litter quality.     

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。     

桂西北喀斯特区原生林与次生林凋落叶降解和养分释放

凋落叶降解及养分释放研究对喀斯特生态脆弱区森林生态系统的恢复与重建具有重要指导意义。本文选取桂西北喀斯特区3种原生林与3种次生林进行比较,研究其凋落叶降解与降解过程中的营养元素释放规律以及降解速率的影响因子。结果表明,原生林凋落叶的降解速率略大于次生林。C、N、K元素在前180天释放速率较快,随后趋于稳定。次生林凋落叶总P含量在降解初始阶段呈净积累,随后净释放,而原生林的凋落叶在降解360天后仍呈现P素净积累。相关分析表明,凋落叶降解速率与凋落叶初始总N、木质素含量及木质素:N比值呈负相关,与C:N比呈正相关。综合比较发现,次生林圆叶乌桕(Sapium rotundifolium Hemsl)凋落叶的降解速率与养分释放速率较快,是喀斯特退化土地及植被恢复过程中潜在的优势种和建群种。