Numerical abundance and biodiversity of below-ground taxocenes along a pH gradient across the Netherlands

Aim: Taxocenes are regulated by different kinds of predictors, but can broad-scale patterns of prokaryotes (bacteria) and eukaryotes (such as fungi and invertebrates) be ascribed to soil acidity? We sought to test for relationships between the numerical abundances of bacteria, microfungi, nematodes and arthropods along a pH gradient. Location: 284 agro-ecosystems on Pleistocene sand across the Netherlands. Methods: Generalized Linear Models (GLM) and stepwise regressions were applied, using soil- and leaf-litter organisms sampled from a land-cover network. Results: The major variation in the numerical abundance of the organisms belonging to the investigated taxocenes could be ascribed to soil acidity. Contrary to expectations, the effects of temperature on numerical abundance were significant only for Fungi and Nematoda (P < 0.0001). Geographical co-ordinates always play a minor role. The often-suggested close correlation between the numerical abundance of eukaryotes and their local taxonomic diversity applied only to Arthropoda and Fungi (P < 0.00001). Only the number of bacterial DNA bands seemed to reflect the taxa-area relationship (F-value = 22.45, P < 0.0001). Main conclusions: There were strong relationships between the numerical abundances of all the investigated taxocenes and the field-measured soil acidity (P < 0.0001). The largest effects were detected in the Fungi, which tended to be much more acid-tolerant than Bacteria. These patterns imply ecological shifts in the detrital soil food web and deserve further investigation. © 2005 Blackwell Publishing Ltd.