PNNL

Abstract

Soil microbes play an essential role in maintaining soil functions and services, but the dynamics of soil microbial biomass carbon (MBC) under global climate change remain unclear 1. Recently, Patoine et al. 2 combined a global MBC data set with Random Forest modeling and reported that global MBC decreased over 1992–2013, mainly driven by increasing temperatures. Here, we contend their finding with field observations across the globe from soil warming manipulation experiments and from in-situ long-term MBC measurements, datasets which are independent of those used by Patoine et al. 2. We found that MBC showed no significant changes under warming compared to the control (Figure 1a and 1b). In-situ long-term MBC measurements showed no significant changes either with annual temperature changes (Figure 1a and 1c). Furthermore, global MBC no longer significantly decreasing over 1992–2013 when using a bootstrapping sampling of 100 times that repeated the method of Patoine et al. 2 (Figure 2a, see Methods); and the change rate reduced to close to zero when our new observations were included (Figure 2b). We argue that caution should be exercised when using machine learning approaches to evaluate MBC temporal changes. Our findings suggest that soil MBC is unlikely to have significantly decreased due to the global warming of 0.28ºC over 1992–2013, and that more mechanistic studies are needed to understand potential changes in MBC under global climate change.