Lower Soil Carbon Loss Due to Persistent Microbial Adaptation to Climate Warming

Abstract

40Soil microbial respiration is an important source of uncertainty in projecting future climate and 41 carbon (C) cycle feedbacks. Despite intensive studies for two decades, the magnitude, direction, 42 and duration of such feedbacks are uncertain, and their underlying microbial mechanisms are still 43 poorly understood. Here we examined the responses of soil respiration and microbial community 44 structure to long-term experimental warming in a temperate grassland ecosystem. Our results 45 indicated that the temperature sensitivity of soil microbial respiration (i.e., Q10) persistently 46 decreased by 12.0±3.7% across 7 years of warming. Integrated metagenomic and functional 47 analyses showed that microbial community adaptation played critical roles in regulating 48 respiratory acclimation. Incorporating microbial functional gene abundance data into a 49 microbially-enabled ecosystem model significantly improved the modeling performance of soil 50 microbial respiration by 5-19%, compared to the traditional non-microbial model. Model 51 parametric uncertainty was also reduced by 55-71% when gene abundances were used. In addition, 52 our modeling analyses suggested that decreased temperature sensitivity could lead to considerably 53 less heterotrophic respiration (11.6±7.5%), and hence less soil C loss. If such microbially mediated 54 dampening effects occur generally across different spatial and temporal scales, the potential 55 positive feedback of soil microbial respiration in response to climate warming may be less than 56 previously predicted. 57 Introduction 58 59Soil stores large quantities of organic carbon (C), about three times more C than the Earth's 60 atmosphere 1,2 . Soil respiration is the largest single source of carbon dioxide (CO2) from terrestrial 61 ecosystems to the atmosphere, whose magnitude is about ten times larger than anthropogenic 62 emissions 3 . Soil total respiration (Rt) includes both autotrophic respiration (Ra) from plant root 63 growth and root biomass maintenance, and heterotrophic respiration (Rh) from microbial 64 decomposition of litter and soil organic matter (SOM). Various short-term experiments show that 65 soil respiration increases exponentially with temperature 4 , which has been used as a general 66 relationship to parameterize ecosystem and Earth System Models (ESMs) 5 . If the near-exponential 67 short-term relationship of soil respiration and temperature holds for the long-term (years to 68 decades), climate warming will trigger a sharp increase in ecosystem respiration. Such an increase 69 could then result in a strong positive feedback to the global C cycle 6 , which is dependent on the 70 responses of Rh and the dynamics of detrital inputs under warming 7 . Therefore, it is particularly 71 important to accurately evaluate soil Rh and its response to climate warming. However, partitioning 72 Rt into Ra and Rh is one of the main challenges in both experiment-and model-based global change 73 research 8 . Consequently, soil respiration is a poorly understood key ...

The elevational patterns and key drivers of soil microbial communities strongly depend on soil layer and season

“…Soil microorganisms play critical roles in soil organic matter turnover and nutrient cycling (García-Palacios et al, 2021;Guo et al, 2020;Rousk et al, 2016;Schimel & Schaeffer, 2012). Changes in soil microbial community composition strongly influence various critical soil processes, which in turn affect ecosystem functions (Bardgett et al, 2008;Bardgett & Van Der Putten, 2014;Van Der Heijden et al, 2008).…”