Global negative effects of nitrogen deposition on soil microbes

Abstract

Soil microbes comprise a large portion of the genetic diversity on Earth and influence a large number of important ecosystem processes. Increasing atmospheric nitrogen (N) deposition represents a major global change driver; however, it is still debated whether the impacts of N deposition on soil microbial biomass and respiration are ecosystem-type dependent. Moreover, the extent of N deposition impacts on microbial composition remains unclear. Here we conduct a global meta-analysis using 1408 paired observations from 151 studies to evaluate the responses of soil microbial biomass, composition, and function to N addition. We show that nitrogen addition reduced total microbial biomass, bacterial biomass, fungal biomass, biomass carbon, and microbial respiration. Importantly, these negative effects increased with N application rate and experimental duration. Nitrogen addition reduced the fungi to bacteria ratio and the relative abundances of arbuscular mycorrhizal fungi and gram-negative bacteria and increased gram-positive bacteria. Our structural equation modeling showed that the negative effects of N application on soil microbial abundance and composition led to reduced microbial respiration. The effects of N addition were consistent across global terrestrial ecosystems. Our results suggest that atmospheric N deposition negatively affects soil microbial growth, composition, and function across all terrestrial ecosystems, with more pronounced effects with increasing N deposition rate and duration.

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

“…We also measured soil phospholipid fatty acid in 2013 and 2014. The results showed a consistent pattern with previous studies that N addition decreased fungi abundance and reduced fungi: bacteria ratio (Figure S5) (Zhang, Chen & Ruan, ). Compared with bacteria, fungi often have lower carbon use efficiency (CUE) and respired more CO 2 to decompose per unit litter mass (Liu, Qiao, Yang, Bai, & Liu, ).…”

Soil GHG fluxes are altered by N deposition: New data indicate lower N stimulation of the N2O flux and greater stimulation of the calculated C pools

“…In addition, soil CO 2 emissions responses decreased as the N enrichment rate increased (Figure S2; Table S1) because the higher amounts of N reduced microbial biomass and soil microbial activity. A global meta‐analysis has reported that atmospheric N deposition negatively affects soil microbial growth, composition and function across all terrestrial ecosystems, with more pronounced effects with increasing N deposition rate and duration (Zhang et al, ). Recent meta‐analyses have shown that total microbial biomass declines with N addition, with global average estimates of the decrease varying from 5.0% to 20.0%, and the extent of the decline increased with the amount of N added and the experimental duration (Liu & Greaver, ; Lu, Yang, et al, ; Treseder, ).…”

Plant diversity loss reduces soil respiration across terrestrial ecosystems

“…Subsequently, we employed structural equation modeling ( SEM ) to examine the simultaneous effects of SR, stand age, and their interaction on the ln RR s of Rs and Rh, both directly and indirectly, via the ln RR of plant litter inputs (litterfall and fine root biomass as a latent variable), while accounting for the effects of mean annual temperature and aridity index. Similar to Garcia‐Palacios et al () and Zhang, Chen, and Ruan (), we assessed direct effects of the ln RR of plant inputs on the ln RR of Rs, direct effects of SR in mixtures (natural log transformed), stand age (natural log transformed), and the direct effects of mean annual temperature, and aridity index on the ln RR of plant inputs and the ln RR of Rs. As recommended (Grace, ), we assessed the conceptual model (full model) vs. reduced models by goodness‐of‐fit statistics and used AIC to select among alternative models.…”