Litter Mass Loss Rates Research Articles

Litter mass loss and nutrient release influenced by soil fauna of Betula ermanii forest floor of the Changbai Mountains, China

The objective of this study was to examine the litter mass loss of single and mixed plant species, and the nutrient release influenced by soil fauna on the Betula ermanii Cham. (BE) forest floor of the Changbai Mountains, China. A 24 month experiment of litter decomposition was conducted using litterbags with two mesh sizes (0.01 and 2mm), for three litter species incubated separately or in 1:1 and 1:1:1 combinations. Following the 24 month experiment, it was found that the faunal effect on the litter mass loss varied between 8.91 % and 19.9 %. Parasenecio komarovianus (Pojark.) Y.L. Chen (PK) litter decomposed fastest, however, B. ermanii had the highest faunal effect. During the experiment, C loss was found in all litter species and their mixtures, while N accumulation was found in B. ermanii, Rhododendron aureum Georgi (RA), and BE+RA litterbags of both mesh sizes only after 6 months. Soil fauna limited release of C was also found in all litter species and their mixtures after 6 months. By the 24th month of the experiment, soil fauna limited the release of C and N in the R. aureum litterbags, but the C and N release was enhanced in all other litter incubations. Our results illustrate that the mixed–species litter accelerated the mass loss for the low-quality litter, but reduced the soil fauna effect on the mass loss when it was mixed with the high-quality litter. The soil fauna contributed to the C and N release in all litter incubations, both single and mixtures, during the 24 month experiment, with the exception of R. aureum. The rate of litter mass loss, and the nutrient release attributable to the soil fauna, depended on the composition of the litter. The mechanism can be explained by litter heterogeneity, as well as by soil faunal interactions.

Effects of litter traits, soil biota, and soil chemistry on soil carbon stocks at a common garden with 14 tree species

Tree species interact with soil biota to impact soil organic carbon (C) pools, but it is unclear how this interaction is shaped by various ecological factors. We used multiple regression to describe how ~100 variables were related to soil organic C pools in a common garden experiment with 14 temperate tree species. Potential predictor variables included: (i) the abundance, chemical composition, and decomposition rates of leaf litter and fine roots, (ii) species richness and abundance of bacteria, fungi, and invertebrate animals in soil, and (iii) measures of soil acidity and texture. The amount of organic C in the organic horizon and upper 20 cm of mineral soil (i.e. the combined C pool) was strongly negatively correlated with earthworm abundance and strongly positively correlated with the abundance of aluminum, iron, and protons in mineral soils. After accounting for these factors, we identified additional correlations with soil biota and with litter traits. Rates of leaf litter decomposition, measured as litter mass loss, were negatively correlated with size of the combined soil organic C pool. Somewhat paradoxically, the combined soil organic C pool was also negatively related to the ratio of recalcitrant compounds to nitrogen in leaf litter. These apparent effects of litter traits probably arose because two independent components of litter “quality” were controlling different aspects of decomposition. Leaf litter mass loss rates were positively related with leaf litter calcium concentrations, reflecting greater utilization and depolymerization of calcium-rich leaf litter by earthworms and other soil biota, which presumably led to greater proportional losses of litter C as CO2 or dissolved organic C. The fraction of depolymerized and metabolized litter that is ultimately lost as CO2 is an inverse function of microbial C use efficiency, which increases with litter nutrient concentrations but decreases with concentrations of recalcitrant compounds (e.g. lignin); thus, high ratios of recalcitrant compounds to nitrogen in leaf litter likely caused a greater fraction of depolymerized litter to be lost as CO2. Existing conceptual models of soil C stabilization need to reconcile the effects of litter quality on these two potentially counteracting factors: rates of litter depolymerization and microbial C use efficiency.

亚热带常绿阔叶林6个常见树种凋落叶在不同降雨期间的分解特征

PDF HTML阅读 XML下载 导出引用 引用提醒 亚热带常绿阔叶林6个常见树种凋落叶在不同降雨期的分解特征 DOI: 10.5846/stxb201403180470 作者: 作者单位: 四川农业大学生态林业研究所,四川农业大学生态林业研究所,四川农业大学生态林业研究所,四川农业大学生态林业研究所,四川农业大学生态林业研究所,四川农业大学生态林业研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(3117023, 31200474);国家"十二五"科技支撑计划项目(2011BAC09B05);四川省杰出青年学术与技术带头人培育项目(2012JQ0008, 2012JQ0059);中国博士后科学基金项目(7013M540714) Litter decomposition of six common tree species at different rainy periods in the subtropical region Author: Affiliation: Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University,Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University,Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University,Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University,Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University,Key Laboratory of Ecological Forest Engineering of Sichuan Province,Institute of Ecology Forestry,Sichuan Agriculture University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:地处长江上游的四川盆地亚热带常绿阔叶林具有典型雨热同季的气候特点,季节性干湿交替可能显著影响凋落物分解,但迄今缺乏相应的报道.因此,采用凋落物分解袋法,研究了常绿阔叶林区最具代表性的马尾松(Pinus massoniana)、柳杉(Cryptomeria fortunei)、杉木(Cunninghamia lanceolata)、香樟(Cinnamomum camphora)、红椿(Toona ciliata)、麻栎(Quercus acutissima)等6种凋落叶在第1年不同雨热季节的分解特征.结果表明,经历1a的分解,6种凋落叶质量残留率大小顺序依次为: 红椿(27.90%) < 柳杉(41.39%) < 杉木(48.93%) < 麻栎(49.62%) < 马尾松(68.82%) < 香樟(72.23%),6种凋落叶在不同干湿季节质量损失差异显著(P < 0.05).阔叶树种在旱季(MRS、SRS和WRS)的质量损失显著高于针叶树种.雨季(ERS和LRS)对6种凋落叶质量损失的贡献率(69.73%-89.68%)均明显大于旱季(10.32%-30.27%).6种凋落叶在不同时期中质量损失速率差异显著(P < 0.05),且6种凋落叶在雨季的质量损失速率明显高于旱季.相关分析结果表明,凋落叶质量损失及其速率均与降雨量和温度呈极显著(P < 0.01)正相关关系.凋落叶质量损失与初始C、木质素含量及C/N、木质素/N极显著(P < 0.01)负相关,与N含量极显著(P < 0.01)正相关.这些结果表明亚热带地区森林凋落物分解的质量损失主要发生在雨季,雨季温湿度的改变可显著影响凋落物分解过程. Abstract:Litter decomposition is an essential process of material cycling in the terrestrial ecosystem that can be the primary source of nutrients for plant growth, and of both nutrients and energy for soil biota. The present consensus is that climate-related precipitation and temperature patterns determine the rate of litter decomposition at the regional scale, while the substrate quality related to plant species manipulates the process of litter decomposition at the ecosystem level. Consequently, much more attention has been focused on litter decomposition as affected by climate, substrate quality, and soil biota in past decades. Theoretically, precipitation, temperature, biological activity, and their combined effects control the process of litter decomposition at different critical periods. As yet, little information has been available on the process of litter decomposition in different rainy and dry periods. Therefore, in order to understand the process of litter decomposition in seasonal rainy and dry periods, a field litterbag experiment was conducted in the Chongzhou Modern Agricultural Research & Development Base of Sichuan Agricultural University, which is located in the subtropical humid climate zone of Sichuan Basin at the upper reaches of the Yangtze River. Foliar litter was selected from Pinus massoniana, Cryptomeria fortunei, Cunninghamia lanceolata, Cinnamomum camphora, Toona ciliata, and Quercus acutissima, which are widely distributed in the subtropical evergreen broadleaved forest. Litterbags were sampled in the dry season, spring minor rainy season, early rainy season, later rainy season, and winter minor rainy season as litter decomposition proceeding from January 18, 2013 to January 18, 2014. In turn, the mass loss rates of foliar litter were measured, and rainfall and temperature were investigated at the same time. The results indicated that the litter mass loss of all six tree species increased as decomposition proceeded. Over one year's decomposition, the remaining litter mass of six tree species was in the order T. ciliata (27.90%) < C. fortunei (41.39%) < C. lanceolata (48.93%) < Q. acutissima (49.62%) < P. massoniana (68.82%) < C. camphora (72.23%). Seasonal rainfall had significant (P < 0.05) effects on the litter mass loss of the six species. Compared with needle litter, broad-leaved litter had higher mass loss in the dry season (MRS, SRS, and WRS). The mass loss in the rainy season (ERS and LRS) accounted for 69.73%-89.68% of the mass loss of the entire first decomposition year, while that in the dry season accounted for only 10.32%-30.27%. Meanwhile, the rates of foliar litter mass loss in the rainy season were significantly (P < 0.05) higher than those in the dry season regardless of tree species. Pearson correlation analysis results revealed that the litter mass loss rate was significantly (P < 0.01) and positively correlated with precipitation and temperature. In addition, mass loss was significantly (P < 0.01) and negatively related to the initial concentrations of C, lignin, C/N, and lignin/N in foliar litter, but significantly (P < 0.01) and positively related to the initial N concentration in foliar litter. In conclusion, the mass loss of foliar litter occurred mainly in the rainy season in the subtropical humid region, so changes in seasonal rainfall patterns and the corresponding changes in temperature and humidity would significantly affect the process of litter decomposition. 参考文献 相似文献 引证文献

Interaction between decomposing litter and soil fauna of theBetula ermaniiforest floor of the Changbai Mountains, China

Soil fauna play a key role in litter decomposition as they influence the litter mass loss rate in terrestrial ecosystems. However, the interaction between decomposing litter and soil fauna has not been adequately addressed. We examine the interaction between different types of decomposing litter and soil fauna on the Betula ermanii Cham. (BE) forest floor of the Changbai Mountains, China, by measuring the mass loss of six litter species groups using litterbags with two sizes of mesh (4 mm and 0.01 mm) during a yearlong experiment. Soil fauna were identified at the order level. We found that soil fauna have a limited effect on litter mass loss at the initial stage of the experiment. Its positive effect became apparent at month 12 of the experiment. After 1 year, soil fauna increased the litter mass loss rate of the high-quality litter of Parasenecio komarovianus (Pojark.) Y.L. Chen (PK) by 7.02% and of the low-quality litter of Rhododendron aureum Georgi (RA) by 25.26%. BE + PK litter was associated with a significantly higher abundance of soil fauna at months 8 and 10 of the experiment and also with a significantly higher richness of soil fauna at month 10 of the experiment. At the end of the experiment, however, the Shannon–Wiener diversity index of soil fauna was not necessarily higher in mixed-species litter. Litter mixing did promote the abundance, richness, and diversity of soil fauna during the warm season in the high-quality litter substrate of BE + PK. Our results illustrate that the impact of soil fauna on the litter mass loss of both single- and mixed-species litterbags ranges from a limited impact to a positive impact as litter mass loss advances. The soil fauna contribute more to the litter mass loss of the low-quality litter with higher C to N ratios than to those with a low C to N ratio. The promoting effect of litter mixing on the soil faunal community composition is only short term and is dependent on substrate quality.

Litter decomposition rates of green manure as affected by soil erosion, transport and deposition processes, and the implications for the soil carbon balance of a rainfed olive grove under a dry Mediterranean climate

Soil erosion by water promotes the distribution of soil organic carbon (SOC) and nutrients within the landscape. Moreover, soil redistribution may have a large impact on litter decomposition dynamics. There is a current lack of information about the role of soil erosion in the SOC balance of sloping agricultural fields because its magnitude and direction depend on the dominant horizontal and vertical C fluxes at the different landform (eroding, transport and depositional) positions within the hillslope. Therefore, the significance of these lateral fluxes in the local C balance has to be assessed when interactions with vertical C fluxes (e.g., litter decay) are also taken into account. An experiment was designed to increase our understanding of the role of different phases of the soil erosion process in litter decomposition and the resulting impact on the soil C balance of a rain-fed olive grove under a dry Mediterranean climate, in which two or three high intensity-low frequency rainfall events are responsible for the majority of the annual soil erosion. To accomplish this, four replicate plots were installed at three different landform positions, according to erosion criteria (eroding, transport and depositional sites), and two litter types (Avena sativa L. or Vicia sativa L.) with contrasting initial litter chemistry (high C:N, low C:N) were deployed in the middle of the summer season, before the expected occurrence of rainfall events in the experimental area. Two successive rainfall events led to pronounced patterns of erosion and associated processes of soil transport and deposition, accounting for 99% of total soil loss in the experimental area and leading to the burial of most of the litterbags located at the depositional positions. The results indicate that soil erosion (lateral movement and soil mixing) may be an important mechanism of litter decomposition, as litter mass loss rates were related closely to the amount of soil infiltrated/deposited within the litterbags for both litter types, decay rates at depositional sites being about three-fold higher than at eroding and transport sites. Our results also indicate that soil mobilisation by erosion has significant impacts on C dynamics, causing lateral and vertical fluxes of C similar in magnitude to those induced by changes in land use or management. According to our estimates, soil C losses driven by land-use change could be compensated after 20 years of green manure incorporation in this rainfed Mediterranean olive grove.

Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas

The effects of radioactive contamination from Chernobyl on decomposition of plant material still remain unknown. We predicted that decomposition rate would be reduced in the most contaminated sites due to an absence or reduced densities of soil invertebrates. If microorganisms were the main agents responsible for decomposition, exclusion of large soil invertebrates should not affect decomposition. In September 2007 we deposited 572 bags with uncontaminated dry leaf litter from four species of trees in the leaf litter layer at 20 forest sites around Chernobyl that varied in background radiation by more than a factor 2,600. Approximately one quarter of these bags were made of a fine mesh that prevented access to litter by soil invertebrates. These bags were retrieved in June 2008, dried and weighed to estimate litter mass loss. Litter mass loss was 40% lower in the most contaminated sites relative to sites with a normal background radiation level for Ukraine. Similar reductions in litter mass loss were estimated for individual litter bags, litter bags at different sites, and differences between litter bags at pairs of neighboring sites differing in level of radioactive contamination. Litter mass loss was slightly greater in the presence of large soil invertebrates than in their absence. The thickness of the forest floor increased with the level of radiation and decreased with proportional loss of mass from all litter bags. These findings suggest that radioactive contamination has reduced the rate of litter mass loss, increased accumulation of litter, and affected growth conditions for plants.

Priming in the microbial landscape: periphytic algal stimulation of litter-associated microbial decomposers.

Microbial communities associated with submerged detritus in aquatic ecosystems often comprise a diverse mixture of autotrophic and heterotrophic microbes, including algae, bacteria, protozoa, and fungi. Recent studies have documented increased rates of plant litter mass loss when periphytic algae are present. We conducted laboratory and field experiments to assess potential metabolic interactions between natural autotrophic and heterotrophic microbial communities inhabiting submerged decaying plant litter of Typha angustifolia and Schoenoplectus acutus. In the field, submerged plant litter was either exposed to natural sunlight or placed under experimental canopies that manipulated light availability and growth of periphytic algae. Litter was collected and returned to the laboratory, where algal photosynthesis was manipulated (light/dark incubation), while rates of bacterial and fungal growth and productivity were simultaneously quantified. Bacteria and fungi were rapidly stimulated by exposure to light, thus establishing the potential for algal priming of microbial heterotrophic decay activities. Experimental incubations of decaying litter with 14C- and 13C-bicarbonate established that inorganic C fixed by algal photosynthesis was rapidly transferred to and assimilated by heterotrophic microbial decomposers. Periphytic algal stimulation of microbial heterotrophs, especially fungal decomposers, is an important and largely unrecognized interaction within the detrital microbial landscape, which may transform our current conceptual understanding of microbial secondary production and organic matter decomposition in aquatic ecosystems.

Plant diversity does not buffer drought effects on early‐stage litter mass loss rates and microbial properties

Human activities are decreasing biodiversity and changing the climate worldwide. Both global change drivers have been shown to affect ecosystem functioning, but they may also act in concert in a non-additive way. We studied early-stage litter mass loss rates and soil microbial properties (basal respiration and microbial biomass) during the summer season in response to plant species richness and summer drought in a large grassland biodiversity experiment, the Jena Experiment, Germany. In line with our expectations, decreasing plant diversity and summer drought decreased litter mass loss rates and soil microbial properties. In contrast to our hypotheses, however, this was only true for mass loss of standard litter (wheat straw) used in all plots, and not for plant community-specific litter mass loss. We found no interactive effects between global change drivers, that is, drought reduced litter mass loss rates and soil microbial properties irrespective of plant diversity. High mass loss rates of plant community-specific litter and low responsiveness to drought relative to the standard litter indicate that soil microbial communities were adapted to decomposing community-specific plant litter material including lower susceptibility to dry conditions during summer months. Moreover, higher microbial enzymatic diversity at high plant diversity may have caused elevated mass loss of standard litter. Our results indicate that plant diversity loss and summer drought independently impede soil processes. However, soil decomposer communities may be highly adapted to decomposing plant community-specific litter material, even in situations of environmental stress. Results of standard litter mass loss moreover suggest that decomposer communities under diverse plant communities are able to cope with a greater variety of plant inputs possibly making them less responsive to biotic changes.

Macroarthropod-microorganism interactions during the decomposition of Mediterranean shrub litter at different moisture levels

Saprophagous macroarthropods reach high population densities in many Mediterranean terrestrial ecosystems of southern Europe but their impact on decomposition processes remains unclear. We studied the direct and indirect effects of the millipede Ommatoiulus sabulosus on the decomposition of litter from four shrub species (Cistus albidus, Quercus coccifera, Rosmarinus officinalis and Ulex parviflorus) in a 1-month laboratory experiment. Litter mass loss, substrate-induced respiration (SIR) in litter and faecal pellets, and microbial community structure and biomass in litter (using PLFA profiles) were determined under three sets of conditions: (1) litter and microorganisms; (2) litter, microorganisms and millipedes; (3) litter, microorganisms and millipede faecal pellets regularly added to litter. Two watering frequencies were used to study the effects of simulated drought on the measured variables. Millipedes consumed large amounts of shrub litter with low assimilation efficiency. The largest effect was observed for Cistus that showed also the highest rate of microbial-driven decomposition. Conversion of litter into faecal pellets by millipedes did not increase organic matter decomposition and there was no evidence for a stimulation of microbial activity in faecal pellets compared to uningested litter. Faecal pellet deposition on litter, which was maximal in Cistus, did not change mass loss and SIR rates of litter but significantly changed microbial community structure. Bacterial biomass was lower and fungal:bacterial ratio was higher in moist, but not in dry Cistus litter, after 1 month of regular faeces addition. Simulated drought strongly decreased microbial-driven decomposition but not millipede feeding. The resulting sustained production of faecal pellets, however, did not offset the slower microbial-driven decomposition under dry conditions. We conclude that the transformation of large amounts of shrub litter into faeces by macroarthropods and the resultant interactions with microorganisms do not enhance carbon mineralization in the short term, regardless of litter humidity. We however expect that faeces could be incorporated into the soil more easily than intact plant litter, with important consequences for carbon and nutrient cycling in Mediterranean ecosystems under increasing drought.

Exploring relationships between enzyme activities and leaf litter decomposition in a wet tropical forest

The theory of ecological stoichiometry predicts that the microbial biomass should regulate production of extracellular enzymes to target the resource in shortest supply. Therefore, microbial communities on decomposing leaf litter should optimize allocation to C-, N-, and P-degrading enzymes according to the stoichiometry of the foliar substrate. Because extracellular enzymes are the proximate agents of leaf litter decay, shifts in microbial enzyme allocation may influence overall rates of litter mass loss. To test these hypotheses, I measured fungal growth and the activities of acid phosphatase (AP), beta-glucosidase (BG), cellobiohydrolase (CB) and glycine aminopeptidase (GAP) on decaying leaf litter of five plant species over the course of a 394-day decomposition experiment. I used regression and correlation analyses to link to interspecific variation in mass loss rates with enzyme activities and foliar nutrient content. Enzymes explained 35% of the variance in foliar decay rates across plant species, yet fungal abundance and enzyme activities were unrelated to foliar concentrations of N, P, K, or 9 other nutrients. Furthermore, relative activities of C-, N-, and P-acquiring enzymes did not vary across litter types despite wide variance in foliar C:N and C:P ratios. This weak relationship between litter stoichiometry and decomposition rates suggests that nutrients are not the primary control on microbial growth or enzyme allocation in this tropical forest. However, substantial interspecific differences in fungal abundance and enzyme activities imply that differences in litter composition strongly influence microbial communities and the ecosystem processes they mediate.

Impact of Simulated Changes in Water Table Depth on Ex Situ Decomposition of Leaf Litter from a Neotropical Peatland

Although water table depth is commonly regarded as the primary determinant of litter decomposition rate in tropical peatlands, this has rarely been tested experimentally. This study explored the influence of flooding on decomposition of litter from three dominant plant species in a neotropical peatland. The non-flooded treatment reduced the mass remaining after 14 months from 84 to 81 % for Raphia taedigera, 65 to 58 % for Campnosperma panamensis, and 69 to 58 % for Cyperus sp. The proportions of carbon, nitrogen and phosphorus in the labile, semi-labile and recalcitrant carbon pools, did not reliably predict differences among species in the mass loss rate of litter. Phosphorus was rapidly lost from litter, while carbon losses, including soluble carbon, were slower, but significant for all fractions. The non-flooded treatment substantially reduced the quantity of C remaining in the residue fraction of leaf litter after 12 weeks, with 31, 19 and 6 % less remaining in the non-flooded treatment for R. taedigera, C. panamensis and Cyperus sp. This suggests that lower water table depth on litter decay increase degradation of mainly aliphatic and aromatic carbon in the residual fraction. Thus, although lowering the water table increased decomposition, the chemical composition of litter clearly influences peat accumulation.

No tillage and bagasse mulching alter fungal biomass and community structure during decomposition of sugarcane leaf litter in Lampung Province, Sumatra, Indonesia

Soil fungi are the predominant decomposers of soil organic matter (SOM). To manage SOM in tropical agricultural soils, it is important to understand the effects of agricultural management on fungal communities and their decomposition of organic matter. Our study site was located in a sugarcane plantation in Lampung Province, Sumatra, Indonesia. The objectives of this study were to determine the following: (1) the effect of conversion from conventional tillage to no-tillage farming and the application of bagasse mulch on fungal biomass, community structure, and the relative ratio of fungal to bacterial biomass (F:B); (2) the combination effect of no-tillage with bagasse mulch on these fungal parameters; and (3) possible links between these fungal parameters and the decomposition rate of sugarcane leaf litter. We measured fungal biomass and F:B by phospholipid fatty acid (PLFA) analysis, and we evaluated fungal molecular diversity and community structure by modified terminal restriction fragment length polymorphism (T-RFLP) profiling. Fungal biomass was 2-fold greater with no-tillage and 2.5-fold greater with added bagasse mulch relative to conventional (tillage without mulch) plots. On the other hand, no-tillage also increased bacterial biomass and fungal OTU (operational taxonomic unit) richness, whereas bagasse mulch increased the F:B and inhibited a specific fungal OTU. Under a combination of no-tillage and bagasse mulch, the fungal biomass was 1.7-fold greater than in conventional plots, indicating that the combination did not have an additive effect on fungal biomass. The litter mass loss rate was negatively correlated with fungal biomass, and bagasse mulch suppressed the mass loss approximately 20% less than in the conventional plots. However, the mass loss rate in no-tillage plots did not differ from that in conventional plots. Overall, our results indicated that no-tillage and bagasse much increased litter fungal biomass and altered the fungal communities, and these changes were reflected in the litter decomposition and soil C dynamics. Further studies are needed to clarify the relationship between litter decomposition and fungal species identity.

Non-additive effect of species diversity and temperature sensitivity of mixed litter decomposition in the alpine meadow on Tibetan Plateau

Few studies of the effects of litter diversity on the temperature sensitivity of mixed litter mass loss (MLML) are available. We tested the hypothesis that high litter diversity would reduce the magnitude of effects of climate and environmental change on MLML with 0.5/1 mm litter bags and sampling once after 1 yr of decomposition, using 51 combinations of litter mixtures from 25 dominant species at 3200 and 3800 m elevations on the Tibetan Plateau. Generally, our study supported our hypothesis. High temperature (i.e. lower elevation) reduced the dependency of MLML and non-additive effects on species richness. Species composition significantly affected MLML and its Q10 (i.e. the ratio of litter mass loss rate at a temperature T1 that is 10 °C lower than a temperature T2) when species richness was less than 8. Shrubs significantly decreased the Q10 of MLML when the species richness of litter mixture was less than 4. These findings suggest that the influence of future warming on MLML may depend on the balance between the magnitude of the impacts of climate change on shrub invasion and loss of species diversity in alpine region.

PRODUCCIÓN, PÉRDIDA DE PESO Y TASAS DE DESCOMPOSICIÓN DE HOJARASCA EN CAFETALES TRADICIONAL Y RÚSTICO, Y SELVA MEDIANA, EN VERACRUZ, MÉXICO

Se realizó un estudio para analizar la producción, pérdida de masa y tasa de descomposición de hojarasca en parcelas agroforestales con Sistema Tradicional de Café (STC), Sistemas Rústico de Café (SRC) y Selva mediana subperennifolia (Smsp), en San Miguel, Veracruz, México. En cada sistema se establecieron tres cuadrantes al azar (1000 m2). La colecta de hojarasca producida por el dosel se realizó cada 15 días, durante un año calendario. La descomposición de la hojarasca se evaluó en bolsas de polietileno que contenían10 g (peso seco) de las especies dominantes y una mezcla representativa por sistema. Las bolsas se colectaron en siete fechas durante 352 días. La tasa de descomposición (k) fue alta para Piper hispidum y para la hojarasca en SRC, en todas las fechas de muestreo, indicando un posible efecto del microclima o de la calidad de hojarasca. Las k menores se obtuvieron en Robinsonella mirandae/Coffea arabica y Mastichodendron capirii, en STC y Smsp. El resto de hojarascas mostraron tasas medianas de descomposición; R. mirandae no mostró diferencias entre sistemas. El estudio demostró la importancia de la producción y calidad de hojarasca, así como de los factores medioambientales, en la descomposición, en los sistemas de estudio.

Role of arthropod communities in bioenergy crop litter decomposition†

The extensive land use conversion expected to occur to meet demands for bioenergy feedstock production will likely have widespread impacts on agroecosystem biodiversity and ecosystem services, including carbon sequestration. Although arthropod detritivores are known to contribute to litter decomposition and thus energy flow and nutrient cycling in many plant communities, their importance in bioenergy feedstock communities has not yet been assessed. We undertook an experimental study quantifying rates of litter mass loss and nutrient cycling in the presence and absence of these organisms in three bioenergy feedstock crops-miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum), and a planted prairie community. Overall arthropod abundance and litter decomposition rates were similar in all three communities. Despite effective reduction of arthropods in experimental plots via insecticide application, litter decomposition rates, inorganic nitrogen leaching, and carbon-nitrogen ratios did not differ significantly between control (with arthropods) and treatment (without arthropods) plots in any of the three community types. Our findings suggest that changes in arthropod faunal composition associated with widespread adoption of bioenergy feedstock crops may not be associated with profoundly altered arthropod-mediated litter decomposition and nutrient release.

Predator/Prey-Interactions Promote Decomposition of Low-Quality Detritus

Predation on detritivores is expected to decelerate detritivore-mediated decomposition processes. In field mesocosms, we studied whether the decomposition of leaf and needle litter of live oak (Quercus virginiana) and loblolly pine (Pinus taeda), respectively, was affected by saltmarsh detritivores (Gastropoda: Littoraria irrorata and Melampus bidentatus) and predacious omnivores (Decapoda: Armases cinereum) and their interactions. Both crabs and snails alone increased decomposition (mass loss) rates of oak litter, while a combination of both resulted in the same mass loss as in animal-free controls, probably due to crabs feeding on snails rather than litter. Neither crabs nor snails alone affected mass loss of pine litter, but a combination of both significantly increased decomposition rates. Irrespective of the litter type, crabs significantly increased mortality of the snails but gained biomass only on pine litter and only when detritivorous snails were present. Our findings suggest that unidirectional facilitation of omnivorous semi-terrestrial crabs by their detritivorous prey (saltmarsh snails) promotes the decomposition of low-quality (pine) litter. On high-quality (oak) litter, by contrast, negative effects of the predator prevail, resulting in a drop of decomposition rates when crabs were present, probably owing to predation on detritivorous snails. Thus, the effects of predator/prey-interactions on decomposition processes are context-dependent and are controlled by resource quality.

Interactions among lignin, cellulose, and nitrogen drive litter chemistry–decay relationships

Litter decay rates often correlate with the initial ratios of lignin:nitrogen (N) or lignin:cellulose in litter. However, the chemical and microbial mechanisms that give rise to these patterns are still unclear. To identify these mechanisms, we studied the decomposition of a model plant system, Arabidopsis thaliana, in which plants were manipulated to have low levels of lignin, cellulose, or litter N. Nitrogen fertilizer often increases the loss of cellulose, but it suppresses the breakdown of lignin in plant litter. To understand the mechanisms driving these patterns, we decomposed plants in litterbags for one year in control and N-fertilized plots in an Alaskan boreal forest. We found that litter N had a positive effect on total mass loss because it increased the loss of lignin, N, and soluble C. Lignin had a negative effect on rates of total litter mass loss due to decreases in the loss of cellulose and hemicellulose. Cellulose had a positive effect on lignin loss, supporting the concept of a "priming effect" for lignin breakdown. However, the low-cellulose plants also lost more of their original cellulose compared to the other plant types, indicating that decomposers mined the litter for cellulose despite the presence of lignin. Low-lignin litter had higher fungal biomass and N-acetyl glucosaminidase (NAG, a chitinase) activity, suggesting that lignin restricted fungal growth and may have influenced competitive interactions between decomposers. Nitrogen fertilization increased NAG activity in the early stages of decay. In the later stages, N fertilization led to increased cellulase activity on the litters and tended to reduce lignin losses. The transition over time from competition among decomposers to high cellulase activity and suppressed lignin loss under N fertilization suggests that, in N-limited systems, N fertilization may alter decomposer community structure by favoring a shift toward cellulose- and mineral-N users.

Natural variation in immersion and emersion affects breakdown and invertebrate colonization of leaf litter in a temporary river

Flow pulses that alternately immerse and expose benthic habitats are widely recognized as key determinants of biodiversity and ecosystem functioning in rivers. Terrestrial leaf litter input, colonization, and breakdown are also key processes in river ecosystems, but little is known about the effects of alternating immersion and emersion on these processes. We used litterbags to examine breakdown, microbial activity, and colonization of Populus sp. leaves by invertebrates along a natural gradient in immersion and emersion (i.e., submergence and exposure to air) in a temporary river. Rates of leaf litter mass loss, microbial activity and colonization by invertebrates differed among litterbags that were permanently immersed, intermittently immersed and permanently emersed, and breakdown rate coefficients (k) decreased with increasing cumulative emersed duration (the total number of day of emersion during the experiment). In contrast, the frequency of emersed periods had no detectable effects on these variables. k was positively correlated with the density of invertebrate shredders in immersed litterbags, with microbial activity and shredder density in intermittent litterbags, and with microbial activity in emersed litterbags. These correlations suggest that the relative importance of microbial activity on k increases with emersed duration, due to the periodic elimination of aquatic shredders and the scarcity of terrestrial detritivores. The fact that leaf litter breakdown was detectable under permanently emersed conditions indicates that mechanisms other than shredding by invertebrates, such as leaching and photodegradation, are dominant in dry river habitats.

Snail and millipede complementarity in decomposing Mediterranean forest leaf litter mixtures

Summary 1. The projected increase in loss of biodiversity worldwide has prompted the need to understand the role that diversity plays in key ecosystem functions such as litter decomposition and nutrient cycling. Here we asked how two contrasting species of saprophagous macrofauna and four Mediterranean forest leaf litter species interactively affect decomposition in a 6‐week microcosm study. 2. Litter mass loss and macrofauna relative consumption rates (RCR) were measured on treatments with freshly fallen or partially decomposed leaf litter of Alnus glutinosa, Fraxinus angustifolia, Pistacia terebinthus and Quercus ilex as single‐species or mixtures in absence and presence of the gastropod, Pomatias elegans, the diplopod, Glomeris marginata, or both macrofauna species. 3. Macrofauna consumed all litter substrates except freshly fallen P. terebinthus as a single‐species litter that was fatal to both animals, although its presence in litter mixtures increased overall RCR. Consumption was higher in partially decomposed than freshly fallen litter, and higher in litter mixtures than in single‐species litter. Both litter state and mixing interacted significantly with macrofauna treatment where generally, RCR by P. elegans alone was inferior to that of G. marginata alone or in combination with P. elegans. 4. An overall positive complementarity effect on litter RCR between G. marginata and P. elegans was observed in freshly fallen litter. Particularly strong complementarity was observed in two mixtures of freshly fallen litter and also in one mixture of partially decomposed litter. 5. There were no non‐additive effects of litter mixing on litter mass loss in the absence of animals, indicating no interactions among litter substrates during decomposition. However, in the presence of either G. marginata and/or P. elegans, positive and negative interactions among litter substrates occurred and were enhanced or reversed by the addition of the second macrofauna species. 6. We conclude that saprophagous macrofauna play a critical role in the decomposition dynamics of Mediterranean forest litter by interacting with each other and by driving interactions among litter substrates.

Leaf litter decomposition—Estimates of global variability based on Yasso07 model

Litter decomposition is an important process in the global carbon cycle. It accounts for most of the heterotrophic soil respiration and results in formation of more stable soil organic carbon (SOC) which is the largest terrestrial carbon stock. Litter decomposition may induce remarkable feedbacks to climate change because it is a climate-dependent process. To investigate the global patterns of litter decomposition, we developed a description of this process and tested the validity of this description using a large set of foliar litter mass loss measurements (nearly 10,000 data points derived from approximately 70,000 litter bags). We applied the Markov chain Monte Carlo method to estimate uncertainty in the parameter values and results of our model called Yasso07. The model appeared globally applicable. It estimated the effects of litter type (plant species) and climate on mass loss with little systematic error over the first 10 decomposition years, using only initial litter chemistry, air temperature and precipitation as input variables. Illustrative of the global variability in litter mass loss rates, our example calculations showed that a typical conifer litter had 68% of its initial mass still remaining after 2 decomposition years in tundra while a deciduous litter had only 15% remaining in the tropics. Uncertainty in these estimates, a direct result of the uncertainty of the parameter values of the model, varied according to the distribution of the litter bag data among climate conditions and ranged from 2% in tundra to 4% in the tropics. This reliability was adequate to use the model and distinguish the effects of even small differences in litter quality or climate conditions on litter decomposition as statistically significant.