Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystem

Abstract

Summary The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with 13 CO 2 for a 3‐day period. In plots that had been limed (CaCO 3 amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform‐labile C demonstrated lower levels of 13 C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated 13 C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of 13 C in total microbial biomass in limed soils indicated that the half‐life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of 13 C fixed and allocated within the plant–soil system.

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