Demystifying the enigma of soil biodiversity: long-term effects of 14 tree species and underlying mechanisms

Background/Question/Methods

The enormous diversity of soil biota is a great riddle in ecology. We assessed the controls on soil biodiversity, including 13 different groups of soil organisms ranging from bacteria to macrofauna, using ~125 abiotic and biotic variables measured in replicated plantations of 14 tree species.  The plantations were planted in 1970 and 1971 after clear-cutting an even-aged stand of Pinus sylvestris.  The planted species included deciduous angiosperms, evergreen gymnosperms, and one deciduous gymnosperm.

Results/Conclusions

Approximately 70% of the variability in total diversity of these soil organisms was explained by six variables. Soil biodiversity was increased by factors related to habitat and resource availability (fine root production, forest floor depth, and soil phosphorus content) as well as by factors indicating both fine-scale habitat heterogeneity and resource availability (understory light availability and biomass of earthworms). Strong positive effects of light availability on soil biodiversity could be explained in part by changes in soil temperature and herbaceous plant diversity. The 13 groups of soil organisms had highest diversity levels under eleven different tree species, stressing the relevance of tree diversity. These results suggest that a small number of key ecosystem factors strongly regulate soil biodiversity at the local scale.