Drivers of the microbial metabolic quotient across global grasslands

Abstract

Aim The microbial metabolic quotient (MMQ; mg CO2‐C/mg MBC/h), defined as the amount of microbial CO2 respired (MR; mg CO2‐C/kg soil/h) per unit of microbial biomass C (MBC; mg C/kg soil), is a key parameter for understanding the microbial regulation of the carbon (C) cycle, including soil C sequestration. Here, we experimentally tested hypotheses about the individual and interactive effects of multiple nutrient addition (nitrogen + phosphorus + potassium + micronutrients) and herbivore exclusion on MR, MBC and MMQ across 23 sites (five continents). Our sites encompassed a wide range of edaphoclimatic conditions; thus, we assessed which edaphoclimatic variables affected MMQ the most and how they interacted with our treatments. Location Australia, Asia, Europe, North/South America. Time period 2015–2016. Major taxa Soil microbes. Methods Soils were collected from plots with established experimental treatments. MR was assessed in a 5‐week laboratory incubation without glucose addition, MBC via substrate‐induced respiration. MMQ was calculated as MR/MBC and corrected for soil temperatures (MMQsoil). Using linear mixed effects models (LMMs) and structural equation models (SEMs), we analysed how edaphoclimatic characteristics and treatments interactively affected MMQsoil. Results MMQsoil was higher in locations with higher mean annual temperature, lower water holding capacity and lower soil organic C concentration, but did not respond to our treatments across sites as neither MR nor MBC changed. We attributed this relative homeostasis to our treatments to the modulating influence of edaphoclimatic variables. For example, herbivore exclusion, regardless of fertilization, led to greater MMQsoil only at sites with lower soil organic C (< 1.7%). Main conclusions Our results pinpoint the main variables related to MMQsoil across grasslands and emphasize the importance of the local edaphoclimatic conditions in controlling the response of the C cycle to anthropogenic stressors. By testing hypotheses about MMQsoil across global edaphoclimatic gradients, this work also helps to align the conflicting results of prior studies.

Warming effects on grassland soil microbial communities are amplified in cool months

“…S8D ). Consistently, a positive relationship between microbial metabolic quotient and soil temperature was theoretically predicted and experimentally observed [ 68 ]. Multiple mechanisms contribute to the warming effect because warming accelerates protein turnover and microbial metabolic activity [ 69 ], releases C more rapidly from soil microorganisms by increasing the activity of microbial predators and bacteriophages [ 70 ], and shifts microbial community composition towards fast-growing species as observed in our study ( Fig.…”

Microclimate, an important part of ecology and biogeography

“…Microclimate science is increasingly incorporated into ecological and biogeographical questions at local to regional extents (De Frenne et al, 2021), but questions of continental or global extents are rare (but see e.g. Risch et al, 2023). Incorporating the principles and approaches of microclimate science into studies beyond local extents would call for improved global data integration.…”