Date Published: July 7, 2017
Publisher: Public Library of Science
Author(s): Bing Mao, Rong Mao, De-Hui Zeng, Riikka Rinnan.
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.
Litter decomposition is an important process regulating greenhouse gas emission, soil organic matter formation and nutrient availability for soil biota and plants, and thus is an essential component of C and nutrient cycling in soils in most ecosystems [1, 2]. In both natural and managed ecosystems, because of the species diversity, plant litters with different initial chemical composition generally become mixed and influence the degradation process of organic matter in the soil [3, 4]. Generally, litter decomposition and nutrient release are controlled by chemical traits of substrate and litter mixing effect in terrestrial ecosystems. Examining the effects of litter mixtures’ chemical traits and litter species interactions on soil C and N cycling is therefore of considerable importance in understanding mechanisms of plant-soil interactions.
In this study, non-additive effect on soil C and N cycling was more common than additive effect. Moreover, we observed a prevalence of synergistic non-additive effects on soil respiration and soil microbial N over antagonistic non-additive effects, and a prevalence of antagonistic non-additive effects on soil net N mineralization. Our results were in line with the majority of limited studies regarding the effect of litter mixtures on C and N dynamics in soils [13, 23, 52], further confirming that litter mixture-induced changes in soil C and N cycling could not be predicted by the values derived from single species litters.
Mixed-species litter produced a prevalence of synergistic non-additive effects on soil N immobilization, soil microbial biomass N and soil respiration. Chemical properties (chemical diversity and chemical composition) rather than species richness per se regulated the non-additive effects of mixed-species litter on soil N immobilization and microbial biomass N, while the influence of mixed-species litter on soil respiration depended on species diversity (species composition and species richness) rather than litter chemical properties. Additionally, loss of understory species had important effects on non-additive soil N immobilization, soil microbial biomass N and soil respiration amended by mixed-species litter, and different chemical compositions of litter might explain the effects of understory species loss. This study found that litter chemical properties showed more important effects on soil N cycling than species richness in the Mongolian pine plantations, and provided an opportunity to understand the understory species loss on belowground soil ecological processes.