Relationships between biodiversity and soil structure and function: Evidence from laboratory and field experiments

Abstract

This paper offers new insights into the structure and carbon dynamics of an upland organo-mineral soil using a range of complementary research methods including soil micromorphology and laser sizing of water-stable aggregates to quantify the development of aggregates and pore space and the spatial location of carbon additions. Examination of soil thin sections revealed that the organic horizons and uppermost organo-mineral horizon are dominated by excrement from meso- and macrofauna, a finding which highlights the importance of soil fauna in reprocessing organic material. Much of this excrement had fused into undifferentiable forms, but some could be associated specifically with enchytraeids and earthworms. The specific objective of the study was to determine the extent to which alterations in soil faunal diversity and activity result in changes to the soil structure. This was done through a series of experiments at different scales in which faunal communities were manipulated by liming to increase soil pH, additions of nitrogen to increase faunal activity and additions of fauna of different sizes. Induced changes in soil fauna did not produce marked and immediate responses in either void space or water-stable aggregation; changes induced by liming and additions of fauna were small and often statistically not significant. When the location of newly photosynthesised C was traced using pulse labelling with 13CO 2 it was found that there was a nucleated distribution with low concentrations of new C found in between 0 and 40% of aggregates derived from faunal excrement. Bacterial numbers on excrement were also not consistently high, although some excrement was colonised more densely, probably a result of more recent formation. This upland grassland soil is very largely the product of faunal activity over the course of its development. However, it is highly resistant to change, as current faunal activity appears to have a relatively small impact on its structure, and thus contains many elements which have functional redundancy.