The Effects Of Litter Quality,Soil Fauna And Dung Addition On Litter Decomposition In A Tibetan Alpine Meadow

Litter decomposition,which converts the products of photosynthesis to inorganic components and soil organic matter,is the main source of greenhouse gases and regulator of global carbon balance.Nutrient cycle of ecosystem is also affected by litter decomposition and nutrient release.Thus,through understanding of litter decomposition will greatly improve our understanding of global carbon and nutrient cycle process.There has been a long history(up to 1000 years)of yak grazing in the Tibetan Plateau,and yak dung is one of another important ways of returning back carbon and nutrient into soil.Thus,the effect of dung deposition on litter decomposition need to be studied,which can help us to improve understanding of the function of alpine meadow ecosystem and to provide theoretical foundation for grassland management.Except for herbivores,how did soil fauna affect litter decomposition,and its interaction with dung addition affect litter decomposition and nutrients release?We selected six common leaf litter species,including Kobresia capillifolia,Elymus nutans,Ligularia virgaurea,Anemone rivularis,Saussurea nigrescens and Thermopisis lanceolata in an alpine meadow,and incubated leaf litter of six species in monocultures and all possible two species combinations in the field using litterbags of different mesh size(3mm and 0.01 mm)with and without dung addition.Our aims were to test the effect of litter quality,soil fauna and dung addition on litter decomposition,nitrogen(N)and phosphorus(P)release.Our results showed that:1)Both initial litter C/N was negatively correlated with litter decomposition rates and nutrient release,respectively,and could be considered as effective predictors of litter decomposition.2)Soil fauna increased the litter mass loss and nutrient release,the strength of which weakened over incubation time.This positive effect was stronger for lowquality species than for high-quality species.In addition,soil fauna decreased the remaining of N and P,the strength of which also weakened over incubation time,but there were not interactions with litter quality.3)Dung addition promoted the mass loss of low-quality species and decreased the remaining of N and P,and significantly interacted with litter quality and incubation time,respectively.4)Additive effects on litter mass loss and N release both occurred in homogeneous litter mixtures(similar C/N and Lignin/N)in all of three incubation times.After 6 months,synergistic interactions appeared in heterogeneous litter mixtures for litter mass loss,and antagonistic interactions for N release.After 12 months,additive effects on both litter mass loss and N release occurred in heterogeneous litter mixtures.After 18 months,synergistic interactions appeared for litter mass loss.For P release,synergistic interactions appeared in all of litter mixtures after 6 months incubation,and additive effects occurred in other cases.5)After 6 months,soil fauna removal could weaken the magnitude of positive non-additive effects on litter mass loss and P release,and enhanced the magnitude of negative non-additive effects on N release.6)After 6 months,dung addition strengthened the magnitude of synergistic interactions and shifted synergistic interactions from additive effects for litter mass loss,shifted additive effects from antagonistic interactions for N release,and enhanced synergistic interactions for some of litter mixtures(contrasting P content);After 12 months,dung addition shifted antagonistic interactions from additive effects for litter mass loss,antagonistic interactions from additive effects for heterogeneous litter mixtures for N release,and synergistic interactions from additive effects for some of litter mixtures(contrasting P content);After 18 months,dung addition shifted antagonistic interactions from additive effects for litter mass loss.