Carbon turnover in the rhizosphere under continuous plant labeling with 13CO2: Partitioning of root, microbial, and rhizomicrobial respiration

Abstract

The input of labeled C into the pool of soil organic matter, the CO2 fluxes from the soil, and the contribution of root and microbial respiration to the CO2 emission were studied in a greenhouse experiment with continuous labeling of oat plants with 13CO2 using the method of the natural 13C abundance in the air. The carbon of the microbial biomass composed 56 and 39% of the total amounts of 13C photoassimilates in the rhizosphere and in the bulk soil, respectively. The contribution of root respiration to the CO2 emission from the soil reached 61–92%, including 4–23% of the rhizomicrobial respiration. The contribution of the microbial respiration to the total CO2 emission from the soil varied from 8 to 39%. The soil organic matter served as the major carbon-containing substrate for microorganisms in the bulk soil and in the rhizosphere: 81–91% of the total amount of carbon involved in the microbial metabolism was derived from the soil organic matter.