Trophic regulation of soil microbial biomass under nitrogen enrichment: A global meta-analysis
Creators: name: Lu, Xiaoming
name: Xing, Wen
name: Chen, Xinli
name: Thakur, Madhav
name: Kardol, Paul
name: Bai, Yongfei
Publisher: name: Zenodo
Year: 2024
Subjects: soil microbial biomass
nematodes
trophic regulation
soil food web
Eutrophication
meta-analysis

description: Eutrophication, including nitrogen (N) enrichment, can affect soil microbial communities through changes in trophic interactions. However, a knowledge gap still exists about how plant resources ('bottom-up effects') and microbial predators ('top-down effects') regulate the impacts of N enrichment on microbial biomass at the global scale.

To address this knowledge gap, we conducted a global meta-analysis using 2885 paired observations from 217 publications to evaluate the regulatory effects of plant biomass and soil nematodes on soil microbial biomass under N enrichment across terrestrial ecosystems.

We found that the effects of N enrichment on soil microbial biomass strongly varied across ecosystems. N enrichment decreased the soil microbial biomass of natural grasslands and forests due to soil acidification and the subsequent losses of predatory and microbivorous nematodes stimulating microbial growth. By contrast, N enrichment increased the microbial biomass of managed croplands mainly via increasing plant biomass production. The short-term of N enrichment (experimental duration ≤ 5 years) could reduce microbial biomass via decreasing nematode abundance across diverse ecosystems, whereas the long-term of N enrichment (experimental duration > 5 years) mainly promoted microbial biomass via increasing plant biomass.

These findings highlight the critical roles of microbial predators and plant input in shaping microbial responses to N enrichment, which are highly dependent on ecosystem type and the period of N enrichment. Earth system models that predict soil microbial biomass and their linkages to soil functioning should consider the variations in plant biomass and soil nematodes under future scenarios of N deposition.
description: We systematically searched all peer-reviewed studies on the effects of N enrichment on plant biomass, microbial biomass, and nematodes, using the Web of Science, Google Scholar, and the China National Knowledge Infrastructure Database (to 1st January, 2023). We used the following search string: (nitrogen addition OR nitrogen application OR nitrogen deposition OR nitrogen enrichment OR nitrogen fertilization OR nitrogen input OR nitrogen amendment) AND (fungi OR bacteria OR microbial biomass OR microbial community) AND (plant OR crop OR plant biomass OR above-ground biomass OR below-ground biomass OR root biomass OR yield OR nematod* OR fungivor* OR bacterivor* OR omnivor* OR predat* OR carnivor* OR nematode community OR nematode feeding groups OR bacterial-feeding nematode OR fungal-feeding nematode OR omnivorous nematode OR carnivorous nematode). The references listed in relevant previously published reviews and meta-analyses were also searched. In total, 207 studies from 217 publications were included in our database. Data were directly extracted from the text and tables of publications or digitized by WebPlotDigitizer 4.1 (https://autom eris.io/WebPlotDigitizer/) if presented in figures. From each study, we extracted data on the experimental duration (years), soil microbial biomass carbon, nematode abundance, plant biomass, and soil environmental factors.To assess the effect size of N enrichment on all response variables, we used the natural log-transformed response ratio (lnRR). And we used the sample sizes of response variables for weighting.