Large variability of soil microbial diversity and functions in an over 20-year old Eucalyptus grandis plantation

The spatial heterogeneity in soil properties as well as in molecular and catabolic diversities of the soil microbial community were investigated by soil analyses, Illumina MiSeq sequencing and MicroResp™ profiling, respectively, in 51 plots of a 20 year-old eucalyptus plantation in south Brazil. The relationships between these parameters were assessed to test whether small scale variation in soil properties and understory vegetation generated heterogeneity in the soil microbial community. The spatial variability of soil microbial community and functioning was shown to be substantial. A greenness index, used as a proxy of the density of the understory biomass, explained very little of the soil microbial parameters. Variability in soil properties (mainly C availability, pH) partly explained shifts in molecular and catabolic parameters of the soil microbial community. Bacterial (and, to a lower extent, fungal) molecular parameters were the main factors explaining the catabolic capabilities of the soil microbial community. But overall, the sequencing data was of little use in explaining C processes in these soils, underlying the difficulty in predicting the contribution of large tree-plantations to the global C cycle. • Understanding how soil heterogeneity relates to microbial functions is critical for predicting C cycle. • Soil and microbial parameters varied to various extents in a 20-years old Eucalyptus plantation. • Bacterial, and (to a lower extent fungal) parameters explained part of the catabolic profiles. • But overall, sequence data little explained the catabolic parameters.