Microbes, memory and moisture: Predicting microbial moisture responses and their impact on carbon cycling

Abstract

Soil moisture is a major driver of microbial activity and thus, of the release of carbon (C) into the Earth's atmosphere. Yet, there is no consensus on the relationship between soil moisture and microbial respiration, and as a result, moisture response functions are a poorly constrained aspect of C models. In addition, models assume that the response of microbial respiration to moisture is the same for all ecosystems, regardless of climate history, an assumption that many empirical studies have challenged. These gaps in understanding of the microbial respiration response to moisture contribute to uncertainty in model predictions. We review our understanding of what drives microbial moisture response, highlighting evidence that historical precipitation can influence both responses to moisture and sensitivity to drought. We present two hypotheses, the ‘climate history hypothesis’, where we predict that baseline moisture response functions change as a function of precipitation history, and the ‘drought legacy hypothesis’, in which we suggest that the intensity and frequency of historical drought have shaped microbial communities in ways that will control moisture responses to contemporary drought. Underlying mechanisms include biological selection and filtering of the microbial community by rainfall regimes, which result in microbial traits and trade‐offs that shape function. We present an integrated modelling and empirical approach for understanding microbial moisture responses and improving models. Standardized measures of moisture response (respiration rate across a range of moistures) and accompanying microbial properties are needed across sites. These data can be incorporated into trait‐based models to produce generalized moisture response functions, which can then be validated and incorporated into conventional and microbially explicit ecosystem models of soil C cycling. Future studies should strive to analyse realistic moisture conditions and consider the role of environmental factors and soil structure in microbial response. Microbes are the engines that drive C storage and are sensitive to changes in rainfall. A greater understanding of the factors that govern this sensitivity could be a key part of improving predictions of soil C dynamics, climate change and C‐climate feedbacks. Read the free Plain Language Summary for this article on the Journal blog.

The activity and functions of soil microbial communities in the Finnish sub-Arctic vary across vegetation types

“…However, the overall greening of the Arctic is more complex, as graminoids instead of shrubs are increasing in colder parts of the region (Elmendorf et al ., 2012). In addition, with increasing temperatures, high latitudes will receive more precipitation as rainfall across the Arctic (Bintanja & Andry 2017), which will likely affect microbial communities which are strongly reliant on soil moisture resources (Evans et al ., 2022). Therefore, the consequences of macroclimatic changes on soil moisture are not straightforward.…”

Emerging relationships among soil microbes, carbon dynamics and climate change

“…(2022), Notthingham et al (2022), Evans et al. (2022) and Wan & Crowther (2022) propose meaningful ways to do so. Lastly, emerging findings and ideas regarding the abiotic control of microbial processes such as the priming effect (Bernard et al., 2022), necromass formation and recycling (Buckeridge et al., 2022) and interactions with the soil mineral matrix (Sokol et al, 2022) should shape how we address soil C turnover and stabilization under climate change.…”

“…To move this forward, Evans et al. (2022) bring us a conceptual framework based on empirically derived moisture response curves that can be used to inform trait‐based microbial models and soil C models.…”

“…From here, the authors discuss potential applications of the Y‐A‐S framework that are highly relevant for this Special Feature. For instance, how drought‐induced shifts and trade‐offs between microbial traits can impact necromass production and determine the stabilization of soil C in the mineral‐associated pool (see Buckeridge et al., 2022 and Sokol et al, 2022 in this Special Feature), or how microbial adaptation to drying–rewetting cycles can result in nonlinear relationships between soil moisture and soil respiration (see Evans et al., 2022 in this Special Feature). As such, the review of Malik et al (2022) integrates some of the most important aspects investigated in this Special Feature, from the abiotic control on microbial processes to variation of microbial‐moisture relationships across spatiotemporal scales.…”

“…Buckeridge et al (2022) and Sokol et al (2022) deal with the new paradigm of plant inputs and microbial necromass interactions with mineral surfaces as mechanisms driving soil C accrual and persistence. Then, two reviews propose new frameworks to address the impacts of changing precipitation patterns on soil microbes and C using moisture response curves (Evans et al, 2022) and microbial traits (Malik & Bouskill, 2022). Lastly, Wan & Crowther (2022) bring us some recent advances merging trait-based and soil C modelling.…”