A Gaseous Milieu: Extending the Boundaries of the Rhizosphere.

Plant root activities shape microbial community functioning in the soil, making the rhizosphere the epicenter of soil biogeochemical processes. With this opinion article, we argue to rethink the rhizosphere boundaries: as gases can diffuse several centimeters away from the roots into the soil, the portion of soil influenced by root activities is larger than the strictly root-adhering soil. Indeed, gases are key drivers of biogeochemical processes due to their roles as energy sources or communication molecules, which has the potential to modify microbial community structure and functioning. In order to get a more holistic perspective on this key environment, we advocate for interdisciplinarity in rhizosphere research by combining knowledge of soluble compounds with gas dynamics.

Biological H2 and CO oxidation activities are sensitive to compositional change of soil microbial communities.

Trace gas uptake by microorganisms controls the oxidative capacity of the troposphere, but little is known about how this important function is affected by changes in soil microbial diversity. This article bridges that knowledge gap by examining the response of the microbial community-level physiological profiles (CLPPs), carbon dioxide (CO2) production, and molecular hydrogen (H2) and carbon monoxide (CO) oxidation activities to manipulation of microbial diversity in soil microcosms. Microbial diversity was manipulated by mixing nonsterile and sterile soil with and without the addition of antibiotics. Nonsterile soil without antibiotics was used as a reference. Species composition changed significantly in soil microcosms as a result of dilution and antibiotic treatments, but there was no difference in species richness, according to PCR amplicon sequencing of the bacterial 16S rRNA gene. The CLPP was 15% higher in all dilution and antibiotic treatments than in reference microcosms, but the dilution treatment had no effect on CO2 production. Soil microcosms with dilution treatments had 58%-98% less H2 oxidation and 54%-99% lower CO oxidation, relative to reference microcosms, but did not differ among the antibiotic treatments. These results indicate that H2 and CO oxidation activities respond to compositional changes of microbial community in soil.