Design and performance of micro-zone C diffusion device to explore the importance of distance for soil microorganisms to utilize available exogenous carbon source

Abstract

Soil acts as both a major sink and source of carbon in terrestrial ecosystems. Soil microorganisms play an important role in carbon sequestration as well as carbon mobilization. Either substrate to microbe or microbe to substrate transport are important in barren soil environments. Available external carbon sources can be utilized before some soil organic matter components are activated. In this process, external carbon source availability markedly determines soil microorganism activity (e.g., the distance between the carbon source and soil microorganisms). Here, I investigated the role of space as a factor influencing carbon utilization. I designed a soil incubation device that both separated the carbon source from soil microbes and ensured free carbon movement. Dextran was applied to avoid mass flow and maintain a balanced water potential. An isotope-labeling technique was used to quantitatively study carbon diffusion. The microcosm experiment verified that the carbon source was gradually utilized by the soil microorganisms according to the distance gradient. Soil microorganisms close to the carbon source initially used glucose, whereas more remote microbes waited for glucose to be transported. The microbial biomass carbon (MBC) content was much higher at smaller (0–0.5 cm) distances than they did at larger (0.5–1 or 1–2 cm) ones, which indicated that the higher concentration of available carbon source in the space closer to the glucose was conducive to the rapid acquisition and assimilation of microorganisms. The findings of this study establish a methodology and identify potential applications for further analysis of the spatial effects of carbon source availability on soil microbial activity.