Mass loss and nutrient release during the decomposition of sixteen types of plant litter with contrasting quality under three precipitation regimes

Mass loss and nutrient release during litter decomposition drive biogeochemical cycling in terrestrial ecosystems. However, the relationship between the litter decomposition process and the decomposition stage, precipitation, and litter quality has rarely been addressed, precluding our understanding of how litter decomposition regulates nutrient cycling in various ecosystems and their responses to climate change. In this study, we measured mass loss as well as carbon and nutrient releases during the decomposition of 16 types of leaf litter under three precipitation treatments over 12 months in a common garden experiment (i.e., using standardized soil and climatic conditions). Sixteen types of leaves were divided into three functional groups (evergreen, deciduous, and herbaceous). The objectives were to understand the effects of decomposition stages and precipitation regimes on litter decomposition and to examine the relationship between this effect and chemical properties. The mass loss and release of nitrogen and potassium were significantly higher in the 6‐ to 12‐month stage of decomposition (high temperature and humidity) than in the 0‐ to 6‐month stage. Phosphorus was relatively enriched in evergreen leaves after 6 months of decomposition. The rates of mass loss and nutrient release were significantly greater in herbaceous than in deciduous and evergreen leaves. Increasing precipitation from 400 to 800 mm accelerated mass loss and potassium release but decreased phosphorus release in the 0‐ to 6‐month stage of decomposition. These results highlighted the contribution to and complexity of litter chemical properties in litter decomposition.     

Leaf litter diversity alters microbial activity,microbial abundances,and nutrient cycling in a subtropical forest ecosystem

Human activities affect both tree species composition and diversity in forested ecosystems. This in turn alters the species diversity of plant litter and litter quality, which may have cascading effects on soil microbial communities and their functions for decomposition and nutrient cycling. We tested microbial responses to litter species diversity in a leaf litter decomposition experiment including monocultures, 2-, and 4-species mixtures in the subtropical climate zone of southeastern China. Soil microbial community composition was assessed by lipid analysis, and microbial functions were measured using extracellular enzyme activity and gross rates of nitrogen mineralization. We observed a positive relationship between litter species diversity and abundances of mycorrhizal fungi and actinomycetes. Alternatively, enzyme activities involved in carbon and phosphorus acquisition, and enzyme indices of relative carbon limitation, were higher only in the 4-species mixtures. This suggests that the minimum basal substrate level for enzyme production was reached, or that limitation was higher, at the highest diversity level only. Responses to litter diversity also changed over time, where phosphatase responses to litter diversity were strongest early in decomposition and the indices of carbon limitation relative to other nutrients showed stronger responses later in decomposition. Enzyme activities were related to lipid biomarker data and the mass of litter remaining at the third time point, but relationships between enzyme activity and the mass of litter remaining were not consistent across other time points. We conclude that litter species richness will likely only reduce microbial functions at key intervals of diversity loss while microbial growth is more sensitive to incremental diversity loss, with no clear relationships between them or to ecosystem functions. The observed litter diversity effects on soil microbial biomass and enzyme activity indicate interactions of aboveground and belowground communities, and together with environmental conditions they are important for maintaining ecosystem functions.     

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。     

Decomposition and nutrient release patterns of mistletoe litters in a semi‐arid savanna,southwest Zimbabwe

Nutrient loss from litter plays an essential role in carbon and nutrient cycling in nutrient‐constrained environments. However, the decomposition and nutrient dynamics of nutrient‐rich mistletoe litter remains unknown in semi‐arid savanna where productivity is nutrient limited. We studied the decomposition and nutrient dynamics (nitrogen: N, phosphorous; P, carbon: C) of litter of three mistletoe species, Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum and N‐fixing Acacia karroo using the litter‐bag method in a semi‐arid savanna, southwest Zimbabwe. The temporal dynamics of the soil moisture content, microbial populations, and termite activity during decomposition were also assessed. Decay rates were slower for A. karroo litter (k = 0.63), but faster for the high quality mistletoe litters (mean k‐value = 0.79), which supports the premise that mistletoes can substantially influence nutrient availability to other plants. Nitrogen loss was between 1.3 and 3 times greater in E. ngamicum litter than in the other species. The litter of the mistletoes also lost C and P faster than A. karroo litter. However, soil moisture content and bacterial and fungal colony numbers changed in an opposite direction to changes in the decomposition rate. Additionally, there was little evidence of termite activity during the decay of all the species litters. This suggests that other factors such as photodegradation could be important in litter decomposition in semi‐arid savanna. In conclusion, the higher rate of decay and nutrient release of mistletoe than A. karroo litter indicate that mistletoes play an important role in carbon and nutrient fluxes in semi‐arid savanna.     

Leaf litter decomposition rates in degraded and fragmented tropical rain forests of Borneo

Previously extensive tracts of primary rain forest have been degraded by human activities, and we examined how the effects of forest disturbance arising from habitat fragmentation and commercial selective logging affected ecosystem functioning in these habitats by studying leaf litter decomposition rates in litter bags placed on the forest floor. The rain forests of Borneo are dominated by trees from the family Dipterocarpaceae, and we compared leaf litter decomposition rates of three dipterocarp species at eight forest fragment sites (area 3–3529 ha) that had different histories of disturbance pre‐fragmentation: four fragments had been selectively logged prior to fragmentation and four had been formed from previously undisturbed forest. We compared these logged and unlogged forest fragments with sites in continuous forest that had been selectively logged (two sites) and fully protected and undisturbed (two sites). After 120 d, undisturbed continuous forest sites had the fastest rates of decomposition (52% mass loss). Forest fragments formed from unlogged forest (32% mass loss) had faster decomposition rates than logged forest fragments (28% mass loss), but slower rates than continuous logged forest (39% mass loss). Leaves of a light‐demanding species (Parashorea malaanonan) decomposed faster than those of a shade‐tolerant species (Hopea nervosa), but decomposition of all three dipterocarp species that we studied responded similarly to logging and fragmentation effects. Reduced decomposition rates in logged and fragmented forest sites may affect nutrient cycling and thus have detrimental consequences for forest regeneration. Conservation management to improve forest quality should be a priority, particularly in logged forest fragments.     

Response of litter decomposition and related soil enzyme activities to different forms of nitrogen fertilization in a subtropical forest

With the continuing increase in the impact of human activities on ecosystems, ecologists are increasingly becoming interested in understanding the effects of nitrogen deposition on litter decomposition. At present, numerous studies have investigated the effects of single form of nitrogen fertilization on litter decomposition in forest ecosystems. However, forms of N deposition vary, and changes in the relative importance of different forms of N deposition are expected in the future. Thus, identifying the effects of different forms of N deposition on litter decomposition in forest ecosystems is a pressing task. In this study, two dominant litter types were chosen from Zijin Mountain in China: Quercus acutissima leaves from a late succession broad-leaved forest and Pinus massoniana needles from an early succession coniferous forest. The litter samples were incubated in microcosms with original forest soil and treated with four different forms of nitrogen fertilization [NH₄ ⁺, NO₃ ⁻, CO(NH₂)₂, and a mix of all three]. During a 5-month incubation period, litter mass losses, soil pH values, and soil enzyme activities were determined. Results show that all four forms of nitrogen fertilization significantly accelerate litter decomposition rates in the broadleaf forest, while only two forms of nitrogen fertilization [i.e., mixed nitrogen and CO(NH₂)₂] significantly accelerate litter decomposition rates in the coniferous forest. Litter decomposition rates with the mixed nitrogen fertilization were higher than those in any single form of nitrogen fertilization. All forms of nitrogen fertilization enhanced soil enzyme activities (i.e., catalase, cellulase, invertase, polyphenol oxidase, nitrate reductase, urease, and acid phosphatase) during the litter decomposition process for the two forest types. Soil enzyme activities under the mixed nitrogen fertilization were higher than those under any single form of nitrogen fertilization. These results suggest that the type and activity of the major degradative enzymes involved in litter decomposition vary in different forest types under different forms of nitrogen fertilization. They also indicate that a long-term consequence of N deposition-induced acceleration of litter decomposition rates in subtropical forests may be the release of carbon stored belowground to the atmosphere.     

川西高山林线交错带两种地被物分解的木质纤维素酶活性特征

以川西高山林线交错带两种优势地被物锦丝藓和高山冷蕨为对象,对针叶林和林线中锦丝藓植物残体及高山冷蕨凋落叶分解的质量损失和木质纤维素酶活性特征进行研究.结果表明： 锦丝藓和高山冷蕨的质量损失率在雪被期和生长季均表现为林线高于针叶林,而酶活性整体上表现为针叶林显著高于林线.两种地被物不同季节的质量损失有显著差异,雪被期林线和针叶林的锦丝藓质量损失率占全年的69.8%和83.0%;生长季林线和针叶林的高山冷蕨质量损失率分别占全年的82.6%和83.4%.高山冷蕨凋落叶在生长季节快速分解,与其生长季节末较高的纤维素酶活性相吻合,说明纤维素和半纤维素的酶解作用可能是凋落物前期质量损失的主要原因.多元线性回归分析表明,环境因子和凋落叶初始质量能共同解释酶活性变异的45.8%～85.1%,两种地被物分解过程中酶活性主要受到雪被期冻融循环的影响.     

Grazing history effects on above- and below-ground litter decomposition and nutrient cycling in two co-occurring grasses

Large herbivores may alter carbon and nutrient cycling in soil by changing above- and below-ground litter decomposition dynamics. Grazing effects may reflect changes in plant allocation patterns, and thus litter quality, or the site conditions for decomposition, but the relative roles of these broad mechanisms have rarely been tested. We examined plant and soil mediated effects of grazing history on litter mass loss and nutrient release in two grazing-tolerant grasses, Lolium multiflorum and Paspalum dilatatum, in a humid pampa grassland, Argentina. Shoot and root litters produced in a common garden by conspecific plants collected from grazed and ungrazed sites were incubated under both grazing conditions. We found that grazing history effects on litter decomposition were stronger for shoot than for root material. Root mass loss was neither affected by litter origin nor incubation site, although roots from the grazed origin immobilised more nutrients. Plants from the grazed site produced shoots with higher cell soluble contents and lower lignin:N ratios. Grazing effects mediated by shoot litter origin depended on the species, and were less apparent than incubation site effects. Lolium shoots from the grazed site decomposed and released nutrients faster, whereas Paspalum shoots from the grazed site retained more nutrient than their respective counterparts from the ungrazed site. Such divergent, species-specific dynamics did not translate into consistent differences in soil mineral N beneath decomposing litters. Indeed, shoot mass loss and nutrient release were generally faster in the grazed grassland, where soil N availability was higher. Our results show that grazing influenced nutrient cycling by modifying litter breakdown within species as well as the soil environment for decomposition. They also indicate that grazing effects on decomposition are likely to involve aerial litter pools rather than the more recalcitrant root compartment.     

Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in a Tamarix‐invaded riparian ecosystem

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore‐altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetle Diorhabda carinulata was released across several western states as a biological control agent to reduce the extent of the invasive tree Tamarix spp. in highly‐valued riparian ecosystems; however, very little is currently known about the effects of this biocontrol effort on ecosystem nutrient cycling. In this study, we examined alterations to nutrient dynamics resulting from beetle herbivory in a Tamarix‐invaded riparian ecosystem in the Great Basin Desert in northern Nevada, USA, by measuring changes in litter quality and decomposition, as well as changes in litter quantity. Generally, herbivory resulted in improved leaf litter chemical quality, including significantly increased nitrogen (N) and phosphorus (P) concentrations and decreased carbon (C) to nitrogen (C:N), C:P, N:P, and lignin:N ratios. Beetle‐affected litter decomposed 23% faster than control litter, and released 16% more N and 60% more P during six months of decomposition, as compared to control litter. Both litter types showed a net release of N and P during decomposition. In addition, herbivory resulted in significant increases in annual rates of total aboveground litter and leaf litter production of 82% and 71%, respectively, under the Tamarix canopy. Our finding that increased rates of N and P release linked with an increased rate of mass loss during decomposition resulting from herbivore‐induced increases in litter quality provides new support to the nutrient acceleration hypothesis. Moreover, results of this study demonstrate that the introduction of the northern tamarisk beetle as biological control to a Tamarix‐invaded riparian ecosystem has lead to short‐term stimulation of nutrient cycling. Alterations to nutrient dynamics could have implications for future plant community composition, and thus the potential for restoration of Tamarix‐invaded ecosystems.     

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.     

Drought conditions alter litter decomposition and nutrient release of litter types in an agroforestry system of China

Evaluating how decomposition rates and litter nutrient release of different litter types respond to changes in water conditions is crucial for understanding global carbon and nutrient cycling. However, it is unclear how decreasing water affects litter mixture interactions for the maize–poplar system in arid regions. Here, the responses of the litter decomposition process and litter mixture interactions in the agroforestry system to changes in water conditions (control, light drought, and moderate drought) were tested. Moderate drought significantly decreased the decomposition rate for poplar leaf and mixed litters, and decomposition rate was significantly reduced for maize straw litter in light and moderate drought stress. The mass loss rates of maize straw and mixed litters were significantly higher than that of the poplar leaf litter under drought conditions, but there was no significant difference among the three litter types in the control. There was no interaction between mass loss of the mixed litter in the control and light drought conditions, and the litter mixture interaction showed nonadditive synergistic interactions under moderate drought. In terms of nutrient release, there was also no interaction between litter mixture with nitrogen and carbon, but there was antagonistic interaction with potassium release under the light drought condition. Our results demonstrate that drought conditions can lead to decreasing decomposition rate and strong changes in the litter mixture interactions from additive effects to nonadditive synergistic effects in moderate drought. Moreover, light drought changed the mixture interaction from an additive effect to an antagonistic interaction for potassium release.     

Enhanced summer warming reduces fungal decomposer diversity and litter mass loss more strongly in dry than in wet tundra

Many Arctic regions are currently experiencing substantial summer and winter climate changes. Litter decomposition is a fundamental component of ecosystem carbon and nutrient cycles, with fungi being among the primary decomposers. To assess the impacts of seasonal climatic changes on litter fungal communities and their functioning, Betula glandulosa leaf litter was surface‐incubated in two adjacent low Arctic sites with contrasting soil moisture regimes: dry shrub heath and wet sedge tundra at Disko Island, Greenland. At both sites, we investigated the impacts of factorial combinations of enhanced summer warming (using open‐top chambers; OTCs) and deepened snow (using snow fences) on surface litter mass loss, chemistry and fungal decomposer communities after approximately 1 year. Enhanced summer warming significantly restricted litter mass loss by 32% in the dry and 17% in the wet site. Litter moisture content was significantly reduced by summer warming in the dry, but not in the wet site. Likewise, fungal total abundance and diversity were reduced by OTC warming at the dry site, while comparatively modest warming effects were observed in the wet site. These results suggest that increased evapotranspiration in the OTC plots lowered litter moisture content to the point where fungal decomposition activities became inhibited. In contrast, snow addition enhanced fungal abundance in both sites but did not significantly affect litter mass loss rates. Across sites, control plots only shared 15% of their fungal phylotypes, suggesting strong local controls on fungal decomposer community composition. Nevertheless, fungal community functioning (litter decomposition) was negatively affected by warming in both sites. We conclude that although buried soil organic matter decomposition is widely expected to increase with future summer warming, surface litter decay and nutrient turnover rates in both xeric and relatively moist tundra are likely to be significantly restricted by the evaporative drying associated with warmer air temperatures.     

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。     

Insight into the temperature sensitivity of forest litter decomposition and soil enzymes in subtropical forest in China

Aims With the continuing increase in the impact of human activities on ecosystems, ecologists are increasingly interested in understanding the effects of high temperature on litter decomposition since litter decomposition and the accompanying release of nutrients and carbon dioxide are key processes in ecosystem nutrient cycling and carbon flux. This study was conducted to evaluate the temperature sensitivity of forest litter decomposition and soil enzymes during litter decomposition in subtropical forest in China.Methods Two dominant litter types were chosen from Zijin Mountain in China: Quercus acutissima leaves from a broadleaf forest (BF) and Pinus massoniana needles from a coniferous forest (CF). The litter samples were incubated in soil microcosms at ambient control temperature (20°C) and 10°C warmer. During a 5-month incubation, chemical composition of litter samples, litter mass losses, and related soil enzyme activities were determined.Important findings Three main results were found: (i) high temperature accelerated decomposition rates of both litter types, and the temperature sensitivities of litter decomposition for BF leaves and that for CF needles are equivalent basically, (ii) high temperature enhanced soil enzyme activities in the two forest types, and the temperature sensitivities of polyphenol oxidase were significantly higher than those of the other soil enzymes and (iii) the temperature sensitivities of nitrate reductase were significantly higher in the CF soil than in the BF soil, while there was no significant difference in the temperature sensitivities of the other soil enzymes between BF and CF. As a long-term consequence, the high-temperature-induced acceleration of litter decomposition rates in these subtropical forests may cause carbon stored belowground to be transferred in the atmosphere, which may alter the balance between carbon uptake and release, and then alter the global carbon cycle in the coming decades.     

Litter dynamics recover faster than arthropod biodiversity during tropical forest succession

Litterfall and litter decomposition are key elements of nutrient cycling in tropical forests, a process in which decomposer communities such as macro-arthropods play a critical role. Understanding the rate and extent to which ecosystem function and biodiversity recover during succession is useful to managing the growing area of tropical successional forest globally. Using a replicated chronosequence of forest succession (5–15, 15–30, 30–45 years, and primary forest) on abandoned pastures in lowland tropical wet forest, we examined litterfall, litter chemistry, and effects of macro-arthropod exclusion on decomposition of two litter types (primary and 5- to 15-years-old secondary forest). Further, we assessed macro-arthropod diversity and community composition across the chronosequence. Overstory cover, litterfall, and litter nutrients reached levels similar to primary forest within 15–30 years. Young secondary forest litter (5–15 years) had lower initial N and P content, higher C:N, and decayed 60 percent faster than primary forest litter. The presence of macro-arthropods strongly mediated decomposition and nutrient release rates, increasing litter mass loss by 35–44 percent, N released by 53 percent, and P release by 84 percent. Forest age had no effect on soil nutrients, rates of litter decomposition, nutrient release, or macro-arthropod influence. In contrast, abundance and community composition of macro-arthropods remained significantly lower and distinct in all ages of secondary compared with primary forest. Order richness was lower in 5–15 years of secondary compared with primary forest. Our results suggest that in highly productive tropical wet forest, functional recovery of litter dynamics precedes recovery of decomposer community structure and biodiversity.     

氮、磷养分有效性对森林凋落物分解的影响研究进展

通过对相关研究文献的综述结果表明,氮(N)和磷(P)是构成蛋白质和遗传物质的两种重要组成元素,限制森林生产力和其他生态系统过程,对凋落物分解产生深刻影响。大量的凋落物分解试验发现在土壤N有效性较低的温带和北方森林,凋落物分解速率常与底物初始N浓度、木质素/N比等有很好的相关关系,也受外源N输入的影响;而在土壤高度风化的热带亚热带森林生态系统中,P可能是比N更为重要的分解限制因子。然而控制试验表明,N、P添加对凋落物分解速率的影响并不一致,既有促进效应也有抑制效应。为了深入揭示N、P养分有效性对凋落物分解的调控机制,"底物的C、N化学计量学"假说、"微生物的N开采"假说以及养分平衡的理论都常被用于解释凋落物分解速率的变化。由于微生物分解者具有较为稳定的C、N、P等养分需求比例,在不同的养分供应的周围环境中会体现出不同的活性,某种最缺乏的养分可能就是分解的最重要限制因子。未来的凋落物分解研究,应延长实验时间、加强室内和野外不同条件下的N、P等养分添加控制试验,探讨驱动分解进程的微生物群落结构和酶活性的变化。     

Warming and grazing enhance litter decomposition and nutrient release independent of litter quality in an alpine meadow

增温和放牧对高寒草甸凋落物分解及其养分释放的影响不依赖于凋落物品质在放牧生态系统中,增温、放牧和凋落物品质共同决定着凋落物分解和养分释放。然而,在以往的研究中这些因子的效应通常被单独地研究。在本研究中,我们在青藏高原高寒草甸开展了一个昼夜非对称增温和中度放牧两因子的凋落物分解试验。从每个处理中收集了凋落物样品,这些凋落物一部分放在它们的来源处理小区,另一部分放在其他处理小区以此来探究增温、放牧以及凋落物品质对凋落物分解和养分释放的影响。研究结果表明,增温而不是放牧显著增加了凋落物质量的损失、单位面积全碳、全氮以及全磷含量的损失,这主要是因为增温增加了凋落物生物量和分解速率。然而,尽管同时增温放牧处理也加快了凋落物分解速率,但由于降低了凋落物生物量,所以增温放牧处理并没有显著影响单位面积的凋落物碳和养分释放量。相比木质素含量和碳氮比而言,季节性土壤平均温度能够更好地预测凋落物分解速率。增温和放牧对凋落物分解存在交互作用,但它们和凋落物品质对凋落物的影响均不存在交互作用。单位面积的总氮释放的温度敏感性要高于总磷。因此,我们的结果表明,增温对凋落物分解以及养分释放的影响要显著大于凋落物品质变化对其分解的影响。在高寒草甸,氮释放的增加可能会间接导致土壤磷有效性的缺乏。     

Distinct Microbial Limitations in Litter and Underlying Soil Revealed by Carbon and Nutrient Fertilization in a Tropical Rainforest

Human-caused alterations of the carbon and nutrient cycles are expected to impact tropical ecosystems in the near future. Here we evaluated how a combined change in carbon (C), nitrogen (N) and phosphorus (P) availability affects soil and litter microbial respiration and litter decomposition in an undisturbed Amazonian rainforest in French Guiana. In a fully factorial C (as cellulose), N (as urea), and P (as phosphate) fertilization experiment we analyzed a total of 540 litterbag-soil pairs after a 158-day exposure in the field. Rates of substrate-induced respiration (SIR) measured in litter and litter mass loss were similarly affected by fertilization showing the strongest stimulation when N and P were added simultaneously. The stimulating NP effect on litter SIR increased considerably with increasing initial dissolved organic carbon (DOC) concentrations in litter, suggesting that the combined availability of N, P, and a labile C source has a particularly strong effect on microbial activity. Cellulose fertilization, however, did not further stimulate the NP effect. In contrast to litter SIR and litter mass loss, soil SIR was reduced with N fertilization and showed only a positive effect in response to P fertilization that was further enhanced with additional C fertilization. Our data suggest that increased nutrient enrichment in the studied Amazonian rainforest can considerably change microbial activity and litter decomposition, and that these effects differ between the litter layer and the underlying soil. Any resulting change in relative C and nutrient fluxes between the litter layer and the soil can have important consequences for biogeochemical cycles in tropical forest ecosystems.     

Tree Species Effect on Litter Decomposition and Nutrient Release in Mediterranean Oak Forests Changes Over Time

Tree species can affect the decomposition process through the quality of their leaf fall and through the species-specific conditions that they generate in their environment. We compared the relative importance of these effects in a 2-year experiment. Litterbags containing leaf litter of the winter-deciduous Quercus canariensis, the evergreen Q. suber and mixed litter were incubated beneath distinct plant covers. We measured litter carbon loss, 9 macro- and micronutrients and 18 soil chemical, physical and biological parameters of the incubation environment. Tree species affected decay dynamics through their litter quality and, to a lesser extent, through the induced environmental conditions. The deciduous litter showed a faster initial decomposition but left a larger fraction of slow decomposable biomass compared with the perennial litter; in contrast the deciduous environment impeded early decomposition while promoting further carbon loss in the latter decay stages. The interaction of these effects led to a negative litter–environment interaction contradicting the home-field advantage hypothesis. Leaf litter N, Ca and Mn as well as soil N, P and soil moisture were the best predictors for decomposition rates. Litter N and Ca exerted counteractive effects in early versus late decay stages; Mn was the best predictor for the decomposition limit value, that is, the fraction of slowly decomposable biomass at the later stage of decomposition; P and soil moisture showed a constant and positive relation with carbon loss. The deciduous oak litter had a higher initial nutrient content and released its nutrients faster and in a higher proportion than the perennial oak litter, significantly increasing soil fertility beneath its canopy. Our findings provide further insights into the factors that control the early and late stages of the decomposition process and reveal potential mechanisms underlying tree species influence on litter decay rate, carbon accumulation and nutrient cycling.     

Decomposition dynamics in mixed-species leaf litter

Literature on plant leaf litter decomposition is substantial, but only in recent years have potential interactions among leaves of different species during decomposition been examined. We review emerging research on patterns of mass loss, changes in nutrient concentration, and decomposer abundance and activity when leaves of different species are decaying in mixtures. Approximately 30 papers have been published that directly examine decomposition in leaf mixtures as well as in all component species decaying alone. From these litter‐mix experiments, it is clear that decomposition patterns are not always predictable from single‐species dynamics. (Characteristics of decomposition in litter‐mixes that deviate from responses predicted from decomposition of single‐species litters alone are designated "non‐additive"; "additive" responses in mixes are predictable from component species decaying alone.) Non‐additive patterns of mass loss were observed in 67% of tested mixtures; mass loss is often (though not always) increased when litters of different species are mixed. Observed mass loss in some mixtures is as much as 65% more extensive than expected from decomposition of single‐species litter, but more often mass loss in mixtures exceeds expected decay by 20% or less. Nutrient transfer among leaves of different species is striking, with 76% of the mixtures showing non‐additive dynamics of nutrient concentrations. Non‐additive patterns in the abundance and activity of decomposers were observed in 55% and 65% of leaf mixes, respectively. We discuss some methodological details that likely contribute to conflicting results among mixed‐litter studies to date. Enough information is available to begin formulating mechanistic hypotheses to explain patterns in litter‐mix experiments. Emerging patterns in the mixed‐litter decomposition literature have implications for relationships between biodiversity and ecosystem function (in this case, the function being decomposition), and for potential mechanisms through which invasive plant species could alter carbon and nutrient dynamics in ecosystems.