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Soil animals and their interactions exert strong effects on ecosystem processes, such as leaf litter decomposition and nitrogen (N) cycling, thereby contributing to ecosystem functioning and stability. The understanding of how and why certain species interact is important to predict the effect of soil animal communities on ecosystem processes. Species interactions are discussed as being facilitative, antagonistic or neutral. We investigated interactions between two earthworm ( Lumbricus terrestris , Aporrectodea caliginosa ) and two Collembola species ( Heteromurus nitidus and Protaphorura armata ), representing major soil decomposer taxa. The two earthworm species are representatives of the soil macrofauna, with L. terrestris living in permanent vertical burrows and feeding on leaf litter, and A. caliginosa living in non-permanent horizontal burrows and feeding predominantly on resources in organo-mineral soil. The Collembola species are representatives of the soil mesofauna, with H. nitidus predominantly colonizing the soil litter interface and feeding on litter associated resources, whereas P. armata colonizes deeper soil layers and mainly feeds on resources in organo-mineral soil. Therefore, the species were assumed to differ in two major traits, i.e. body size (macrofauna vs. mesofauna) and food microhabitat association (“litter-associated” vs. “soil-associated”). Mesocosms with natural forest floor containing one beech ( Fagus sylvatica ) sapling were set up and incubated in the laboratory for three months. 15 N labeled beech litter was added to follow the effect of detritivore animals on N cycling and N uptake by beech saplings. We hypothesized antagonistic interactions to dominate in species with similar body size or food microhabitat association via hampering the performance (biomass, abundance) of each other thereby reducing effects on leaf litter decomposition and N cycling. On the contrary, we expected species of different body size or food microhabitat association to facilitate each other's effects on ecosystem processes. In contrast to our expectation there was no clear relationship between similarity of body size or food microhabitat association and soil fauna effects on each other. Interactions between detritivores were not consensual with L. terrestris facilitating biomass gain of A. caliginosa , while its own biomass was reduced in presence of A. caliginosa . Additionally, 15 N incorporation into A. caliginosa and the two Collembola species decreased in presence of L. terrestris, irrespective of similarity of body size or food microhabitat association. Leaf litter decomposition was increased by L. terrestris , while none of the other species affected litter decomposition. Generally, 15 N incorporation into beech saplings was significantly increased in presence of L. terrestris or H. nitidus , but reduced in two species treatments due to antagonistic interactions. Interestingly, it was increased if L. terrestris , A. caliginosa and P. armata were present together, indicating facilitative interactions between these species. The results suggest that soil fauna interactions mainly vary with the identity of species and community composition rather than with similarity of traits. This highlights the complexity of soil fauna interactions and the difficulty to predict their effects on ecosystem processes, such as litter decomposition and N cycling, in species rich communities. [ABSTRACT FROM AUTHOR]

In a litterbag study in a tropical montane rainforest in Ecuador we assessed the impact of leaf litter species identity and richness on decomposition. We incubated leaf litter of six native tree species in monocultures and all possible two and four species combinations and analysed mass loss over a period of 24 months. Mass loss in monocultures averaged 30.7% after 6 month and differed significantly between species with variations being closely related to initial concentrations of lignin, Mg and P. At later harvests mass loss in monocultures averaged 54.5% but did not vary among leaf litter species and, unexpectedly, did not increase between 12 and 24 months suggesting that litter converged towards an extremely poor common quality retarding decomposition. After 6 months mass loss of leaf litter species was significantly faster in mixtures than in monocultures, resulting in synergistic non-additive mixture effects on decomposition, whereas at later harvests mass loss of component litter species was more variable and leaf litter mixture effects differed with species richness. Mass loss in the two species mixtures did not deviate from those predicted from monocultures, while we found antagonistic non-additive mixture effects in the four species mixtures. This suggests that litter species shared a poor common quality but different chemistry resulting in negative interactions in chemically diverse litter mixtures at later stages of decomposition. Overall, the results suggest that interspecific variations in diversity and composition of structural and secondary litter compounds rather than concentrations of individual litter compounds per se, control long term leaf litter decomposition in tropical montane rainforests. Plant species diversity thus appears to act as a major driver for decomposition processes in tropical montane rainforest ecosystems, highlighting the need for increasing plant conservation efforts to protect ecosystem functioning of this threatened biodiversity hotspot. [ABSTRACT FROM AUTHOR]

Increasing infestation by insect herbivores and pathogenic fungi in response to climate change will inevitably impact the amount and quality of leaf litter inputs into the soil. However, little is known on the interactive effect of infestation severity and climate change on litter decomposition, and no such study has been published for deciduous forests in Central Europe. We assessed changes in initial chemical quality of beech ( Fagus sylvatica L.) and maple litter ( Acer platanoides L.) in response to infestation by the gall midge Mikiola fagi Hart. and the pathogenic fungus Sawadaea tulasnei Fuckel, respectively, and investigated interactive effects of infestation severity, changes in temperature and soil moisture on carbon mineralization in a short-term laboratory study. We found that infestation by the gall midge M. fagi and the pathogenic fungus S. tulasnei significantly changed the chemical quality of beech and maple litter. Changes in element concentrations were generally positive and more pronounced, and if negative less pronounced for maple than beech litter most likely due to high quality fungal tissue remaining on litter after abscission. More importantly, alterations in litter chemical quality did not translate to distinct patterns of carbon mineralization at ambient conditions, but even low amounts of infested litter accelerated carbon mineralization at moderately increased soil moisture and in particular at higher temperature. Our results indicate that insect herbivores and fungal pathogens can markedly alter initial litter chemical quality, but that afterlife effects on carbon mineralization depend on soil moisture and temperature, suggesting that increased infestation severity under projected climate change potentially increases soil carbon release in deciduous forests in Central Europe. [ABSTRACT FROM AUTHOR]