The decline in plant biodiversity slows down soil carbon turnover under increasing nitrogen deposition in a temperate steppe

Abstract

Nitrogen (N) deposition not only alters the physiological processes of individual plant, but also leads to world‐wide biodiversity loss. However, little is known about how the hierarchical responses from individual physiological processes to plant community structure would have cascading effects on soil carbon (C) cycling. Here, we assessed whether changes in plant chemical composition and community composition under increasing N input would affect the turnover rate of litter layer and soil C loss via heterotrophic respiration (Rh) in a temperate grassland. We showed that more than a decade’s N addition significantly decreased plant species richness, litter layer turnover rate and Rh. The 13C‐NMR results showed that, for individual species, N addition either increased the abundance of recalcitrant C groups such as alkyl and methoxyl, or decreased labile C groups such as carbohydrate, resulting in decreases in carbohydrate C‐to‐methoxyl C ratio (CC/MC) for most species. Our data also showed that with the increase in N deposition, the abundance of relatively high degradable dominant species, such as Agropyron cristatum and Artimesia frigida declined rapidly, and the relatively recalcitrant species such as Potentilla bifurca and Leymus chinensis become dominant. Changes in individual species’ chemical composition and plant community composition significantly decreased litter quality at community level, as indicated by the lower community‐level CC/MC at higher N addition rates. The result of step‐AIC model selection further showed that plant diversity loss and the decrease in community‐level CC/MC jointly explained the decrease in Rh after N addition best, and further relative importance partition result showed that these two factors respectively contributed 65.1% and 34.9% of the explained variation. Overall, we demonstrated that changes in plant chemical composition and diversity loss due to N addition reduced the quality of plant C input to soil, which further slowed down litter layer turnover rate and inhibited soil heterotrophic respiration. Our study complements the intermediate links of how shifts in plant community structure regulate soil C cycle under global changes. A plain language summary is available for this article.

Changes in above‐/below‐ground biodiversity and plant functional composition mediate soil respiration response to nitrogen input

“…Furthermore, our results also revealed that the joint effects of plant functional diversity and soil biodiversity loss resulted in the decrease in heterotrophic respiration along the N gradient. This finding expands the biodiversity effects on heterotrophic respiration from above‐ground (Chen & Chen, 2019; Yang et al., 2019) to below‐ground. Given that global change has induced the loss of above‐ and below‐ground biodiversity simultaneously (Bardgett & van der Putten, 2014; Simkin et al., 2016), both of them should be incorporated into Earth system models for better understanding the dynamics of terrestrial C cycle under global N enrichment.…”

“…Recently, N‐induced biodiversity loss has been proposed to affect the response of soil respiration to N input by altering the amount and quality of substrates for microbial decomposition (Yang et al., 2019). Nevertheless, our understanding on this issue is still limited because current studies mainly focus on changes in plant species richness (Wang et al., 2020; Yang et al., 2019). In addition to plant species richness, plant functional diversity (i.e.…”

Nitrogen addition reduces soil respiration but increases the relative contribution of heterotrophic component in an alpine meadow

“…Soil fungi usually have lower C use efficiency than bacteria and driver more CO 2 respired from soils to the atmosphere (Liu et al, ; Manzoni, Taylor, Richter, Porporato, & Ågren, ). In our study, N‐induced changes in soil substrate quality with lower soil C:N ratio under high N inputs (Figure S3) and microbial composition with relatively more abundance of bacteria than fungi (Figure S4) could facilitate microbial C use efficiency (Spohn et al, ; Yang et al, ), partly accounting for the decrease in R h . In all, the changing controlling factors with time could be responsible for the contrasting N response patterns of soil respiration components in varying years and had a potential to explain why distinct responses of R s emerged in different ecosystems.…”

The changes in plant and soil C pools and their C:N stoichiometry control grassland N retention under elevated N inputs

“…Although the meta‐analysis revealed a positive effect of N addition on topsoil C storage (Figure 8b), no significant increase in soil C pool was observed at any depth in our field experiment (Appendix S1: Table S6; Figure 3c). Our previous study at this site found that N addition decreased the turnover rate of the litter layer (Yang et al, 2019), which may reduce the transformation of plant litter C to soil C through decomposition. We also found that N addition decreased litter quality at the community level (Yang et al, 2019).…”