Analysis of the microbial nutrient status in soil microcompartments: earthworm faeces from a basalt–limestone gradient

Abstract

The nutrient status of the microbial community in casts of earthworms ( Octolasion lacteum (Örley)) and in soil from three different beechwood ( Fagus svlvatica L.) sites of a basalt-limestone gradient (basalt, intermediate and limestone site) was investigated by analysing the respiratory response of the microflora to glucose (C) and nutrient (N and P) amendments over a period of about 40 h. Microbial respiration was measured as O 2 consumption by automated microcompensation. Cumulative additional microbial respiration up to the maximum respiration rate was used as a measure of microbial growth ability in C, CN, CP and CNP amended samples. Organic carbon in soil of the limestone site was twice that of the basalt and intermediate site and the initial respiratory response of soil samples from the limestone site exceeded that of samples from the basalt and intermediate site by a factor of about 2. In soils of the basalt and intermediate sites C availability limited microbial growth, whereas in soil of the limestone site microbial growth was limited by the availability of P. In C amended soils of the basalt and intermediate sites microbial growth was enhanced strongly by additional N. The gut passage of the soil reduced microbial N deficiency in soil from the basalt and intermediate sites and reduced P deficiency in limestone soil. In general, microbial growth in earthworm casts was limited by C availability. Microbial biomass was similar in soil and earthworm casts. Soil from the limestone site contained twice the biomass of soils from the basalt and intermediate sites. However, the ratio of C micC org was similar in soil from each of the study sites. A ratio of C micC org close to 0.015 is assumed to be typical for mull beechwood soils.