Metabolic capabilities mute positive response to direct and indirect impacts of warming throughout the soil profile

Nicholas C Dove,Neslihan Taş,Stephen C Hart,Margaret S Torn

doi:10.1038/s41467-021-22408-5

Abstract

Increasing global temperatures are predicted to stimulate soil microbial respiration. The direct and indirect impacts of warming on soil microbes, nevertheless, remain unclear. This is particularly true for understudied subsoil microbes. Here, we show that 4.5 years of whole-profile soil warming in a temperate mixed forest results in altered microbial community composition and metabolism in surface soils, partly due to carbon limitation. However, microbial communities in the subsoil responded differently to warming than in the surface. Throughout the soil profile—but to a greater extent in the subsoil—physiologic and genomic measurements show that phylogenetically different microbes could utilize complex organic compounds, dampening the effect of altered resource availability induced by warming. We find subsoil microbes had 20% lower carbon use efficiencies and 47% lower growth rates compared to surface soils, which constrain microbial communities. Collectively, our results show that unlike in surface soils, elevated microbial respiration in subsoils may continue without microbial community change in the near-term.

Highlights

Increasing global temperatures are predicted to stimulate soil microbial respiration
We evaluated the impact of altered resource availability on microbial respiration by incubating heated and unheated soils with C and nutrient (N and phosphorus [P]) amendments for 30 days (Fig. 1B)
The “proximate” resource limitation is defined as resource that stimulates an ecosystem process[25]

Summary

Introduction

Increasing global temperatures are predicted to stimulate soil microbial respiration. Besides the direct effects of increased temperature, in situ soil warming can decrease C availability[11,12], alter organic matter composition[13], and increase nutrient availability[11] in surface soils. These impacts are likely to affect rates of respiration through indirect effects on the soil microbial community. Long-term soil warming has been shown to alter surface soil microbial community structure and metabolism[17,18], but it is unclear to what extent this is caused by increased temperatures or in combination with altered availability of resources for microbial growth such as organic substrates and nutrients[19]. Laboratory rates of C and N mineralization of added substrates were as fast in the subsoils as in surface soils in an old-growth forest, suggesting that microbial competition and demand for C and N resources does not decrease with depth[21]

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Conclusion