Rhizosheath Formation Alters the Molecular-Level Characteristics of Soil Organic Matter

Abstract

Rhizosheaths form on grass roots worldwide especially in semiarid grasslands. However, it remains unclear about molecular-level characteristics of soil organic carbon (SOC) in rhizosheaths and their temporal dynamics, which hinders our understanding of root effects on SOC cycling in grasslands. Here, in an Inner Mongolia grassland in China, we compared SOC characteristics between rhizosheath soils and non-rhizosheath soils for eight herbaceous plant species using solid-state ¹³C nuclear magnetic resonance spectroscopy and biomarker analyses. We further examined the temporal dynamics of the SOC characteristics of rhizosheath soils from early, middle, and late plant growth stages. Compared to non-rhizosheath SOC, rhizosheath SOC had more root inputs of both labile substrates (carbohydrates and free alkanoic acids) and relatively recalcitrant lignin and suberin. The labile inputs provide more substrates for microbial degradation of cutin-derived compounds. These signatures of high labile substrate availability also turned out to be increasingly significant from early to late growth stages. Overall, our findings clarify the molecular characteristics of rhizosheath SOC and its temporal dynamics, both of which suggests a critical role of rhizosheath in shaping rhizosphere microenvironment and regulating SOC cycling.

Keywords: biomarker, Carbon cycle, grassland, rhizosheath, soil organic carbon