Warming enhances old organic carbon decomposition through altering functional microbial communities

Abstract

Soil organic matter (SOM) stocks contain nearly three times as much carbon (C) as the atmosphere and changes in soil C stocks may have a major impact on future atmospheric carbon dioxide concentrations and climate. Over the past two decades, much research has been devoted to examining the influence of warming on SOM decomposition in topsoil. Most SOM, however, is old and stored in subsoil. The fate of subsoil SOM under future warming remains highly uncertain. Here, by combining a long-term field warming experiment and a meta-analysis study, we showed that warming significantly increased SOM decomposition in subsoil. We also showed that a decade of warming promoted decomposition of subsoil SOM with turnover times of decades to millennia in a tall grass prairie and this effect was largely associated with shifts in the functional gene structure of microbial communities. By coupling stable isotope probing with metagenomics, we found that microbial communities in warmed soils possessed a higher relative abundance of key functional genes involved in the degradation of organic materials with varying recalcitrance than those in control soils. These findings suggest warming may considerably alter the stability of the vast pool of old SOM in subsoil, contributing to the long-term positive feedback between the C cycle and climate.

Comment on “The whole-soil carbon flux in response to warming”

“…This method differed from the majority of previous studies, in which soil temperature was elevated through heating surface air and/or topsoil layers to simulate the magnitude of rise in surface air temperature (2,3). Although it is expected that ongoing and future air warming would increase the temperature of the soil profile, the magnitude of temperature elevation likely attenuates with depth.…”

“…They found that a 2-year in situ warming of 4°C significantly enhanced the whole-soil CO 2 production by 34 to 37%, and that all soil layers exhibited similar temperature sensitivity with a mean apparent Q 10 of 2.7 ± 0.3. We argue that although the idea of subsoil carbon dynamics in response to warming is worth testing (2, 3), their conclusions are critically undermined by the experimental approach and analysis.…”

Soil carbon loss with warming: New evidence from carbon‐degrading enzymes

“…Our finding of a warming‐induced increase in ligninase activity relative to cellulase activity indicates soil microbes decompose more chemically complex and recalcitrant C pools (e.g., lignin) to fuel their metabolic processes (Romero‐Olivares et al, ; Sinsabaugh, ). Indeed, several recent studies found that warming favors microbial functional communities degrading old and recalcitrant C pools (Cheng et al, ; Feng et al, ; Woodcroft et al, ; Xue et al, ).…”

Effects of climate warming on carbon fluxes in grasslands— A global meta‐analysis

“…In line with previous meta-analyses across multiple terrestrial ecosystems (Lu et al, 2013;Rustad et al, 2001;Wang et al, 2014), our study also reported that warming-induced changes in ANPP, NPP, NEE and GPP were negatively correlated with MAT (Table 1) Cold grasslands were expected to be generally more limited by temperature than by water compared to semi-arid and temperate grasslands, and should benefit the most from longer snow-free and growing seasons associated with warming (e.g., Price, Waser, Ecology, & Jun, 1998). In addition, warming is likely to increase the microbial decomposition of soil organic matter (e.g., Crowther et al, 2016, Cheng et al, 2017 and N mineralization (e.g., Bai et al, 2013;Liu et al, 2017;Rustad et al, 2001), thus alleviating nutrient limitations and stimulating plant N uptake, particularly for cold grassland soils, which are characterized by the highest SOC contents. Only in cold grasslands did the responses of Rs, ANPP and BNPP significantly increase with warming magnitude (Table S1), suggesting that neither heat stress nor nutrient limitation of plant growth was confounding warming effects in these ecosystems.…”