Abstract
Decomposition of litter mixtures generally cannot be predicted from the component species incubated in isolation. Therefore, such non-additive effects of litter mixing on soil C and N dynamics remain poorly understood in terrestrial ecosystems. In this study, litters of Mongolian pine and three dominant understory species and soil were collected from a Mongolian pine plantation in Northeast China. In order to examine the effects of mixed-species litter on soil microbial biomass N, soil net N mineralization and soil respiration, four single litter species and their mixtures consisting of all possible 2-, 3- and 4-species combinations were added to soils, respectively. In most instances, species mixing produced synergistic non-additive effects on soil microbial biomass N and soil respiration, but antagonistic non-additive effects on net N mineralization. Species composition rather than species richness explained the non-additive effects of species mixing on soil microbial biomass N and net N mineralization, due to the interspecific differences in litter chemical composition. Both litter species composition and richness explained non-additive soil respiration responses to mixed-species litter, while litter chemical diversity and chemical composition did not. Our study indicated that litter mixtures promoted soil microbial biomass N and soil respiration, and inhibited net N mineralization. Soil N related processes rather than soil respiration were partly explained by litter chemical composition and chemical diversity, highlighting the importance of functional diversity of litter on soil N cycling.
Highlights
Litter decomposition is an important process regulating greenhouse gas emission, soil organic matter formation and nutrient availability for soil biota and plants, and is an essential component of C and nutrient cycling in soils in most ecosystems [1, 2]
Regarding litter chemical properties, we found that non-additive soil respiration amended by mixed-species litter was not significantly regulated by chemical diversity and chemical composition in this study, different from Meier and Bowman [20], who found that soil respiration tended to be changed when chemically distinct litter species were assembled
We found that loss of the three individual understory species from litter mixtures differentially affected non-additive responses of soil microbial biomass N, N mineralization and respiration, with removal of S. viridis significantly affecting the responses of soil microbial N and respiration, and removal of A. scoparia and P. communis significantly affecting the responses of soil N mineralization
Summary
Litter decomposition is an important process regulating greenhouse gas emission, soil organic matter formation and nutrient availability for soil biota and plants, and is an essential component of C and nutrient cycling in soils in most ecosystems [1, 2]. Mechanisms responsible for non-additive effects of litter mixtures on decomposition include changes in nutrient release and the degradation of organic compounds (e.g. polyphenol, tannin, lignin, cellulose) from different species in litter mixtures. These changes may inhibit or stimulate microbial growth or activity during decomposition of mixed-species litter, and influence soil C and N cycling [1]. Most previous studies investigating non-additive effects of litter mixing focused on litter decomposition, but ignored the effects of species mixing on soil C and N cycling [13,14,15]
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