树叶凋落物在受酸性矿山废水污染溪流中的分解

为了解华南地区酸性矿山废水对溪流中树叶分解的影响,在广东省大宝山矿区附近的1条受酸性矿山废水污染（pH值为2．7—3．4且富含多种重金属元素）的3级溪流中,利用2种孔径（5ram的网袋和0．1ram的布袋）的分解网袋对2种树叶（人面子和蒲桃）进行了为期101d的树叶分解研究。结果表明,人面子树叶网袋和布袋中的树叶干重剩余率分别为39％和48％,而蒲桃树叶网袋和布袋中的干重剩余率仍保持较高的水平,分别为61％和70％。根据指数衰减模型计算出树叶分解的半衰期,人面子树叶在网袋和布袋中的分解半衰期分别为57d和69d,而蒲桃树叶则分别为14-4d和217d。蒲桃树叶的分解速率明显比人面子树叶慢。在网袋中定殖的底栖动物主要是集食者,其中优势类群为摇蚊幼虫,占底栖动物个体总数的99％。摇蚊种群在网袋中的数量波动对2种树叶分解速率的影响并不明显。结果表明,受酸性矿山废水的影响,底栖动物群落的多样性大为减少。同时由于各种金属氧化物在树叶表面的不断沉淀,使树叶处于缺氧状态,抑制了微生物的活动,导致树叶分解速率大为降低。     

Stronger effects of litter origin on the processing of conifer than broadleaf leaves: A test of home‐field advantage of stream litter breakdown

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Invertebrate colonization and processing of maple leaf litter in a forested and an agricultural reach of a stream

Processing of maple leaf (Acer saccharum Marsh) packs, their colonization by invertebrates and nutrient dynamics in leaves were investigated in a forested reach and agricultural reach of Canagagigue Creek, Ontario. Shredders, Pycnopsyche, and collectors, Ephemerella subvaria, Stenonema vicarium and Baetis were significantly more numerous in packs at the forest site than in packs at the agricultural site, whereas filter feeders, especially blackflies, were significantly more numerous in packs at the agricultural site. Weight loss of litter packs was nearly equivalent at the two sites. However, there were major differences in the mechanism of processing between the sites. Physical abrasion and microbial activity governed weight loss of maple leaf packs at the agricultural site, whereas processing was governed mainly by microbial and invertebrate activity and, to a much lesser extent, by physical abrasion at the forest site. Both shredders and collector species played an important role in the processing of leaf material at the forest site. Greater uptake of N and P (P<0.05 in spring) and higher C concentrations were observed in leaf packs at the forest site than the agricultural site. Therefore, the results support the concept of retention of nutrients in forested areas and their export in deforested (agricultural) areas. Findings also indicated that the processing of leaf litter is not an efficient means of monitoring changes in stream ecosystems since leaf processing is affected by many factors, particularly physical abrasion.     

Leaf litter decomposition of sweet chestnut is affected more by oomycte infection of trees than by water temperature

Riparian forests are subjected to multiple disturbances, such as tree diseases caused by invasive pathogens, whose consequences on stream functioning are unknown. We assessed the impact of Phytophthora cinnamomi infection, and interactions with temperature, on microbial decomposition of Castanea sativa leaves. Leaves from healthy, symptomatic and highly symptomatic trees were incubated in the laboratory at 13 and 18 °C for 64 d. Infection significantly increased polyphenolic concentration and leaf toughness, reducing leaf decomposition and microbial respiration rates irrespective of temperature. Aquatic hyphomycete communities differed significantly in leaves from highly symptomatic trees. Fungal biomass was highest at 18 °C, irrespective of tree health status. None of the parameters were influenced by the tree health status × temperature interaction, suggesting that temperature rise may not synergistically increase the cross-ecosystem effects caused by P. cinnamomi in streams where litter decomposition is microbial-driven. Infection by P. cinnamomi alters the nutritional quality of leaves affecting the functioning of aquatic ecosystems.     

Leaf‐litter colonisation and breakdown in relation to stream typology: insights from Mediterranean low‐order streams

1. Scant information is available on leaf breakdown in streams of arid and semiarid regions, including the Mediterranean, where environmental heterogeneity can be high and the relationship between stream characteristics and leaf breakdown is poorly known. We tested the hypotheses that differences in leaf breakdown metrics would be substantially higher between mountain and lowland Mediterranean streams than among streams within each subregion and that variability among streams would be substantially higher in the lowlands, because permanent reaches in the semiarid lowland streams are rare and isolated. 2. We compared leaf breakdown and associated dynamics of nutrients, fungi and invertebrates in low‐order Mediterranean streams draining sub‐humid forests in the Sierra Nevada Mountains and nearby semiarid lowlands of south‐eastern Spain. Streams differed between the two subregions mainly in water ion content, temperature and riparian tree cover. We detected higher environmental heterogeneity among streams within the lowlands compared to the Sierra Nevada mountain range. In the lowlands, breakdown coefficients (k) of alder leaves spanned almost the entire range reported for this species from temperate streams, overlapping with less variable breakdown coefficients in the Sierra Nevada. 3. The high variability of k values among the lowland sites appeared to be caused primarily by variability in the composition and abundance of a few leaf‐consuming invertebrate taxa, particularly the snail Melanopsis praemorsa. Fungal and nutrient dynamics were less variable among sites within each subregion. 4. These results indicate that the critical condition for stream functional assessment of well‐constrained breakdown rates, or related metrics, could be met at reference sites within homogenous bio‐geo‐climatic regions such as the Sierra Nevada. By contrast, in heterogeneous areas such as the semiarid lowland streams, natural variability of breakdown rates can greatly exceed the magnitude of effects expected in response to anthropogenic disturbances.     

Non‐symbiotic nitrogen fixation during leaf litter decomposition in an old‐growth temperate rain forest of Chiloé Island,southern Chile: Effects of single versus mixed species litter

Heterotrophic nitrogen fixation is a key ecosystem process in unpolluted, temperate old‐growth forests of southern South America as a source of new nitrogen to ecosystems. Decomposing leaf litter is an energy‐rich substrate that favours the occurrence of this energy demanding process. Following the niche ‘complementarity hypothesis’, we expected that decomposing leaf litter of a single tree species would support lower rates of non‐symbiotic N fixation than mixed species litter taken from the forest floor. To test this hypothesis we measured acetylene reduction activity in the decomposing monospecific litter of three evergreen tree species (litter C/N ratios, 50–79) in an old‐growth rain forest of Chiloé Island, southern Chile. Results showed a significant effect of species and month (anova , Tukey's test, P < 0.05) on decomposition and acetylene reduction rates (ARR), and a species effect on C/N ratios and initial % N of decomposing leaf litter. The lowest litter quality was that of Nothofagus nitida (C/N ratio = 78.7, lignin % = 59.27 ± 4.09), which resulted in higher rates of acetylene reduction activity (mean = 34.09 ± SE = 10.34 nmol h^?1 g^?1) and a higher decomposition rate (k = 0.47) than Podocarpus nubigena (C/N = 54.4, lignin % = 40.31 ± 6.86, Mean ARR = 4.11 ± 0.71 nmol h^?1 g^?1, k = 0.29), and Drimys winteri (C/N = 50.6, lignin % = 45.49 ± 6.28, ARR = 10.2 ± 4.01 nmol h^?1 g^?1, k = 0.29), and mixed species litter (C/N = 60.7, ARR = 8.89 ± 2.13 nmol h^?1g^?1). We interpret these results as follows: in N‐poor litter and high lignin content of leaves (e.g. N. nitida) free‐living N fixers would be at competitive advantage over non‐fixers, thereby becoming more active. Lower ARR in mixed litter can be a consequence of a lower litter C/N ratio compared with single species litter. We also found a strong coupling between in situ acetylene reduction and net N mineralization in surface soils, suggesting that as soon N is fixed by diazotroph bacteria it may be immediately incorporated into mineral soil by N mineralizers, thus reducing N immobilization.     

长白山地区溪流冻结初期凋落叶分解与底栖动物定殖的关系

长白山森林源头溪流每年11月至次年4月有约70%的河面被冰覆盖,季节性冻融过程特征明显.为了揭示溪流冻结初期凋落叶分解与底栖动物定殖的关系,在长白山地区1条源头溪流中,利用2种孔径(5和0.3 mm)的尼龙分解袋对色木槭、紫椴、蒙古栎的单一及混合凋落叶进行了为期35 d的分解研究.结果表明: 凋落叶质量损失率在单一树种间差异显著,表现为:色木槭＞紫椴＞蒙古栎,而在4种混合凋落叶间差异不显著;除紫椴和3树种混合凋落叶外,粗、细分解袋间凋落叶质量损失率差异不显著;凋落叶混合效应仅出现在紫椴-蒙古栎混合的粗分解袋内;定殖在不同凋落叶分解袋内的底栖动物群落结构差异较大,但撕食者密度在3种凋落叶间差异不显著,撕食者对凋落叶混合效应的响应也不显著.由结果可知,溪流冻结初期微生物是凋落叶的主要分解者,底栖动物的贡献率较低.虽然撕食者密度较低,但撕食者的活动是凋落叶混合效应出现的必要条件.底栖动物对食物和栖息地有一定的选择性,但由于定殖时间较短,凋落叶对撕食者定殖的影响不显著.本研究对源头溪流生态系统的冬季生态过程研究及生态系统管理具有一定的理论意义.     

Processing of leaf litter in a northern jarrah forest stream,Western Australia: I. Seasonal differences

Seasonal differences in the processing of jarrah (Eucalyptus marginata) leaves were examined in a small forest stream of the Darling Range, Western Australia. Processing rates in both summer and winter were very low, placing this species in the slow category (k < 0.005) of Petersen & Cummins (1974).Macroinvertebrates did not contribute to the processing of jarrah leaves during summer and autumn, coincident with the period of peak litter fall. The low quality of detritus entering the streams, and possibly some adverse interactions with the physical and chemical environment, inhibits processing during the summer months. As a consequence, a significant proportion of the coarse-particle detritus entering these streams may be exported unprocessed at the onset of high winter flows.In contrast with previous studies, jarrah leaves were processed at a faster rate during winter than summer. This seasonal difference can, in part, be attributed to the increased density and proportion of shredders at this time. Despite this, the processing of jarrah leaves during winter was very slow and must reflect the poor quality of this detritus as food for invertebrate consumers.     

A meta‐analysis of the effects of nutrient enrichment on litter decomposition in streams

The trophic state of many streams is likely to deteriorate in the future due to the continuing increase in human‐induced nutrient availability. Therefore, it is of fundamental importance to understand how nutrient enrichment affects plant litter decomposition, a key ecosystem‐level process in forest streams. Here, we present a meta‐analysis of 99 studies published between 1970 and 2012 that reported the effects of nutrient enrichment on litter decomposition in running waters. When considering the entire database, which consisted of 840 case studies, nutrient enrichment stimulated litter decomposition rate by approximately 50%. The stimulation was higher when the background nutrient concentrations were low and the magnitude of the nutrient enrichment was high, suggesting that oligotrophic streams are most vulnerable to nutrient enrichment. The magnitude of the nutrient‐enrichment effect on litter decomposition was higher in the laboratory than in the field experiments, suggesting that laboratory experiments overestimate the effect and their results should be interpreted with caution. Among field experiments, effects of nutrient enrichment were smaller in the correlative than in the manipulative experiments since in the former the effects of nutrient enrichment on litter decomposition were likely confounded by other environmental factors, e.g. pollutants other than nutrients commonly found in streams impacted by human activity. However, primary studies addressing the effect of multiple stressors on litter decomposition are still few and thus it was not possible to consider the interaction between factors in this review. In field manipulative experiments, the effect of nutrient enrichment on litter decomposition depended on the scale at which the nutrients were added: stream reach > streamside channel > litter bag. This may have resulted from a more uniform and continuous exposure of microbes and detritivores to nutrient enrichment at the stream‐reach scale. By contrast, nutrient enrichment at the litter‐bag scale, often by using diffusing substrates, does not provide uniform controllable nutrient release at either temporal or spatial scales, suggesting that this approach should be abandoned. In field manipulative experiments, the addition of both nitrogen (N) and phosphorus (P) resulted in stronger stimulation of litter decomposition than the addition of N or P alone, suggesting that there might be nutrient co‐limitation of decomposition in streams. The magnitude of the nutrient‐enrichment effect on litter decomposition was higher for wood than for leaves, and for low‐quality than for high‐quality leaves. The effect of nutrient enrichment on litter decomposition may also depend on climate. The tendency for larger effect size in colder regions suggests that patterns of biogeography of invertebrate decomposers may be modulating the effect of nutrient enrichment on litter decomposition. Although studies in temperate environments were overrepresented in our database, our meta‐analysis suggests that the effect of nutrient enrichment might be strongest in cold oligotrophic streams that depend on low‐quality plant litter inputs.     

Simple three‐pool model accurately describes patterns of long‐term litter decomposition in diverse climates

As atmospheric CO₂ increases, ecosystem carbon sequestration will largely depend on how global changes in climate will alter the balance between net primary production and decomposition. The response of primary production to climatic change has been examined using well‐validated mechanistic models, but the same is not true for decomposition, a primary source of atmospheric CO₂. We used the Long‐term Intersite Decomposition Experiment Team (LIDET) dataset and model‐selection techniques to choose and parameterize a model that describes global patterns of litter decomposition. Mass loss was best represented by a three‐pool negative exponential model, with a rapidly decomposing labile pool, an intermediate pool representing cellulose, and a recalcitrant pool. The initial litter lignin/nitrogen ratio defined the size of labile and intermediate pools. Lignin content determined the size of the recalcitrant pool. The decomposition rate of all pools was modified by climate, but the intermediate pool's decomposition rate was also controlled by relative amounts of litter cellulose and lignin (indicative of lignin‐encrusted cellulose). The effect of climate on decomposition was best represented by a composite variable that multiplied a water‐stress function by the Lloyd and Taylor variable Q₁₀ temperature function. Although our model explained nearly 70% of the variation in LIDET data, we observed systematic deviations from model predictions. Below‐ and aboveground material decomposed at notably different rates, depending on the decomposition stage. Decomposition in certain ecosystem‐specific environmental conditions was not well represented by our model; this included roots in very wet and cold soils, and aboveground litter in N‐rich and arid sites. Despite these limitations, our model may still be extremely useful for global modeling efforts, because it accurately (R²=0.6804) described general patterns of long‐term global decomposition for a wide array of litter types, using relatively minimal climatic and litter quality data.     

Influence of Colophospermum mopane canopy cover on litter decomposition and nutrient dynamics in a semi‐arid African savannah

The objective of this study was to investigate the influence of mopane canopy cover on litter decomposition in a semi‐arid African savannah. We used a randomized block design with five blocks of 100 × 100 m demarcated in a 10‐ha pocket of open mopane woodland. Litterbags were placed beneath large (8.3 m crown diameter) and small mopane trees (2.7 m crown diameter) and in the intercanopy area. Decomposition was fastest in the intercanopy area exposed to solar radiation (k = 0.35 year^?1), intermediate beneath small trees (k = 0.28 year^?1) and slowest beneath large trees (k = 0.23 year^?1). Soil temperatures beneath small and large trees were 3–5 and 6–9°C lower than in the intercanopy area, respectively. Bacterial and fungal counts were significantly higher (P < 0.05) beneath large than small trees and in the intercanopy area. The amount of N and P released did not vary significantly among sampling sites. Soil moisture in the dry season was similar among sampling sites but rainy‐season soil moisture was significantly greater (P < 0.05) beneath large than small trees and in the intecanopy area. Mopane canopy cover retarded litter decomposition suggesting that photodegradation could be an important factor controlling carbon turnover in semi‐arid African savannahs.     

Disentangling direct and indirect effects of water table drawdown on above‐ and belowground plant litter decomposition: consequences for accumulation of organic matter in boreal peatlands

Pristine peatlands are carbon (C)‐accumulating wetland ecosystems sustained by a high water table (WT) and consequent anoxia that slows down decomposition. Persistent WT drawdown as a response to climate and/or land‐use change affects decomposition either directly through environmental factors such as increased oxygenation, or indirectly through changes in plant community composition. This study attempts to disentangle the direct and indirect effects of WT drawdown by measuring the relative importance of environmental parameters (WT depth, temperature, soil chemistry) and litter type and/or litter chemical quality on the 2‐year decomposition rates of above‐ and belowground litter (altogether 39 litter types). Consequences for organic matter accumulation were estimated based on the annual litter production. The study sites were chosen to form a three‐stage chronosequence from pristine (undrained) to short‐term (years) and long‐term (decades) WT drawdown conditions at three nutrient regimes. The direct effects of WT drawdown were overruled by the indirect effects through changes in litter type composition and production. Short‐term responses to WT drawdown were small. In long‐term, dramatically increased litter inputs resulted in large accumulation of organic matter in spite of increased decomposition rates. Furthermore, the quality of the accumulated matter greatly changed from that accumulated in pristine conditions. Our results show that the shift in vegetation composition as a response to climate and/or land‐use change is the main factor affecting peatland ecosystem C cycle, and thus dynamic vegetation is a necessity in any model applied for estimating responses of C fluxes to changing environment. We provide possible grouping of litter types into plant functional types that the models could utilize. Furthermore, our results clearly show a drop in soil summer temperature as a response to WT drawdown when an initially open peatland converts into a forest ecosystem, which has not yet been considered in the existing models.     

Long‐term responses of leaf litter decomposition to temperature,litter quality and litter mixing in plateau wetlands

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Solar UV-B decreases decomposition in herbaceous plant litter in Tierra del Fuego, Argentina: potential role of an altered decomposer community

Tierra del Fuego, Argentina (55°S), receives increased solar ultraviolet‐B radiation (UV‐B) as a result of Antarctic stratospheric ozone depletion. We conducted a field study to examine direct and indirect effects of solar UV‐B radiation on decomposition of Gunnera magellanica, a native perennial herb, and on the native community of decomposer organisms. In general, indirect effects of UV‐B mostly occur due to changes in the chemical composition of litter, whereas direct effects during decomposition result from changes in decomposer organisms and/or differences in the photochemical breakdown of litter. We designed a full‐factorial experiment using senescent leaves that had received either near‐ambient or attenuated UV‐B during growth. The leaves were distributed in litterbags and allowed to decompose under near‐ambient or reduced solar UV‐B during the growing season. We evaluated initial litter quality, mass loss, and nutrient release of decomposing litter, and microbial colonization of both initial litter and decomposed litter. We found that litter that decomposed under near‐ambient UV‐B had significantly less mass loss than litter that decomposed under reduced UV‐B. The UV‐B conditions received by plants during growth, which did not affect mass loss and nutrient composition of litter, affected fungal species composition but in different ways throughout the decomposition period. Before the decomposition trial, Beauveria bassiana and Penicillium frequentans were higher under reduced UV‐B, whereas Cladosporium herbarum and pigmented bacteria were more common under the near‐ambient compared to the reduced UV‐B treatment. After the decomposition period, leaves that had grown under reduced UV‐B showed higher frequency of Penicillium thomii and lower frequency of Trichoderma polysporum than leaves that had grown under near‐ambient conditions. The UV‐B condition received during decomposition also affected fungal colonization, with Penicillium chrysogenum being more frequent in leaves that had decomposed under reduced UV‐B, while the other species were not affected. Our results demonstrate that, in this ecosystem, the effects of UV‐B radiation on decomposition apparently occurred mostly through changes in the fungal community, while changes in photochemical breakdown appeared to be less important.     

Ecological parameters of the leaf‐litter frog community of an Atlantic Rainforest area at Ilha Grande,Rio de Janeiro state,Brazil

Abstract The Atlantic Rainforest originally covered much of the Brazilian coast and is now reduced to approximately only 7% of its original area. Data on abundance distribution and microhabitat characteristics of anuran amphibians living on the forest floor leaf litter in the Atlantic Rainforest are scarce. In this study, we analysed the effect of litter depth and structure on the abundance and species richness of leaf‐litter frogs in an area of Atlantic Rainforest at Ilha Grande, Rio de Janeiro State, south‐eastern Brazil. We performed monthly samples (nocturnal and diurnal) from August 1996 to October 1997 using small (2 m × 1 m) plots. We sampled 234 plots, totalling 468 m² of forest leaf litter. We estimated leaf‐litter depth and the proportion of leaves in the plot and tested their effect on the total abundance of frogs and species richness using multiple regression analysis. We found 185 frogs from eight species: Brachycephalus (=Psyllophryne) didactylus (Izecksohn, 1971) (Brachycephalidae), Dendrophryniscus brevipollicatus Jiménez de la Espada 1871 (Bufonidae), Adenomera marmorata Steindachner 1867, Eleutherodactylus parvus (Girard 1853), Eleutherodactylus guentheri (Steindachner 1864), Eleutherodactylus binotatus (Spix 1824) and Zachaenus parvulus (Girard 1853) (Leptodactylidae), and Chiasmocleis sp. (Microhylidae). Brachycephalus didactylus was the most abundant species, with 91 individuals, whereas Dendrophryniscus brevipollicatus was the rarest, with two individuals. Mean litter depth and the proportion of leaves in the leaf litter were significantly related to frog abundance (R² = 0.17; F_2,107 = 10.779; P = 0.0001) and species richness (R² = 0.11; F_2,107 = 6.375; P = 0.002) indicating that microhabitat characteristics may affect local distribution and abundance of frogs in the forest floor.     

Effects of heterogeneous habitat use by cattle on nutrient availability and litter decomposition in soils of an Alpine pasture

Grazing by free-ranging cattle on Alpine pastures in southern Switzerland creates sharp contrasts in plant species composition between small camp areas, which are grazed intensely and receive most cattle excreta, and surrounding pasture dominated by Nardus stricta, which is only lightly grazed. We hypothesised that these contrasts are maintained by positive feedbacks related to nutrient availability in soil, in that (a) plant material with rapid decomposition and nutrient release decomposes in camp areas and (b) litter decomposition is further stimulated by enhanced nutrient availability in soil. We compared nutrient availability at three camp areas with that in surrounding Nardus vegetation and investigated how the decomposition of plant material from both vegetation types responds to nutrient availability in soil, both in the field (during 14 weeks) and in the laboratory (during 4, 10, and 16 weeks). At all three field sites P availability was significantly enhanced in camp areas, whereas differences in N availability were inconsistent among the three sites. Laboratory incubations indicated that microbial activity after the addition of labile C (cellulose) was limited by P availability in the Nardus vegetation but not in camp areas. The camp-area plant substrate decomposed much faster (81.5% vs. 27.1% ash-free dry mass loss in the field) and released more N and P than the Nardus substrate, which tended to immobilise soil nutrients. However, the decomposition rate of neither substrate was influenced by nutrient availability in soil, both in the field (comparing camp areas and Nardus vegetation) and in the laboratory (comparing incubations with and without N or P fertilisation). We conclude that the contrasting quality of plant substrates contributes to the greater nutrient availability in camp areas (feedback a) but that the latter does not influence the decomposition of in situ plant material (feedback b) because the latter is not nutrient-limited.     

川西高山林线交错带土壤动物对岷江冷杉和高山杜鹃凋落物分解的贡献

土壤动物是调控凋落物分解的重要生物因素.为了探究川西高山林线交错带土壤动物对两个优势物种岷江冷杉和高山杜鹃凋落物分解的贡献,在3个海拔梯度(针叶林-林线-高山草甸)采用凋落物分解袋试验,通过不同孔径的网袋(0.04 mm,基本排除土壤动物;3 mm,允许土壤动物通过),研究了分解554 d(2013年5月—2014年11月)土壤动物对凋落物的影响.结果表明: 在整个林线交错带上,岷江冷杉的分解速率(k)为0.209～0.243,高山杜鹃的k为0.173～0.189,岷江冷杉的k大于高山杜鹃.土壤动物的参与显著加速了两种凋落叶分解,同时土壤动物对两种凋落物分解的作用和贡献随海拔升高而降低.自针叶林、高山林线至高山草甸,土壤动物对岷江冷杉分解的质量损失率为15.2%、13.2%、9.8%,对高山杜鹃分解的质量损失率为20.1%、17.5%、12.4%;土壤动物对岷江冷杉分解的平均日贡献率为0.17%、0.13%、0.12%,对高山杜鹃分解的平均日贡献率为0.26%、0.25%、0.23%,土壤动物对高山杜鹃的分解影响相对较大.海拔、凋落物自身性质及其交互作用对土壤动物作用下凋落物的质量损失率和贡献率均表现出显著影响.土壤动物的作用于岷江冷杉和高山杜鹃分解的平均日贡献率在当年生长季(0.25%和0.44%)和次年生长季(0.10%和0.19%)均高于雪被期(0.07%和0.12%).回归分析表明,环境因子(日平均气温、冻融循环次数以及雪被厚度)可以解释土壤动物作用于岷江冷杉和高山杜鹃质量损失率的42.7%和50.9%,贡献率的43.2%和55.6%,这对了解土壤动物在凋落物分解中的作用和深入认识高山生态系统物质循环具有重要意义.     

Decoupling the direct and indirect effects of climate on plant litter decomposition: Accounting for stress‐induced modifications in plant chemistry

Decomposition of plant litter is a fundamental ecosystem process that can act as a feedback to climate change by simultaneously influencing both the productivity of ecosystems and the flux of carbon dioxide from the soil. The influence of climate on decomposition from a postsenescence perspective is relatively well known; in particular, climate is known to regulate the rate of litter decomposition via its direct influence on the reaction kinetics and microbial physiology on processes downstream of tissue senescence. Climate can alter plant metabolism during the formative stage of tissues and could shape the final chemical composition of plant litter that is available for decomposition, and thus indirectly influence decomposition; however, these indirect effects are relatively poorly understood. Climatic stress disrupts cellular homeostasis in plants and results in the reprogramming of primary and secondary metabolic pathways, which leads to changes in the quantity, composition, and organization of small molecules and recalcitrant heteropolymers, including lignins, tannins, suberins, and cuticle within the plant tissue matrix. Furthermore, by regulating metabolism during tissue senescence, climate influences the resorption of nutrients from senescing tissues. Thus, the final chemical composition of plant litter that forms the substrate of decomposition is a combined product of presenescence physiological processes through the production and resorption of metabolites. The changes in quantity, composition, and localization of the molecular construct of the litter could enhance or hinder tissue decomposition and soil nutrient cycling by altering the recalcitrance of the lignocellulose matrix, the composition of microbial communities, and the activity of microbial exo‐enzymes via various complexation reactions. Also, the climate‐induced changes in the molecular composition of litter could differentially influence litter decomposition and soil nutrient cycling. Compared with temperate ecosystems, the indirect effects of climate on litter decomposition in the tropics are not well understood, which underscores the need to conduct additional studies in tropical biomes. We also emphasize the need to focus on how climatic stress affects the root chemistry as roots contribute significantly to biogeochemical cycling, and on utilizing more robust analytical approaches to capture the molecular composition of tissue matrix that fuel microbial metabolism.