Long-term effects of mineral amendments on soil fauna and humus in an acid beech forest floor

Mineral amendments (lime as CaCO3, N as ammonitrate and NPKCa) were applied in 1973 to the floor of some plots located in an acidic beech forest (Fougères state forest, eastern Brittany, France). Resulting modifications to humus structure and soil fauna composition were observed 22 years after amendment by comparison with control plots without amendment. Abundance and diversity of pedofauna (micro-, meso- and macrofauna) were estimated by Berlese funnel and formaldehyde methods. Micromorphological description of humus profiles and comparative quantification of their structure were achieved by digital image analysis. Humus structure in limed and NPKCa-treated plots had evolved from moder to mull-moder, whereas in N-treated plots it was unchanged and similar to the moder-type humus of control plots. Modifications in soil fauna were also observed, especially an increase in the lumbricid population. The observed changes in abundance and diversity differed between edaphic groups. Some effects of liming, like increase in numbers, were still present in NPKCa or limed plots, for example in pseudoscorpions (long-term effects). Lumbricid numbers (epigeic species) increased and remained higher in limed and NPKCa-treated plots than in N and control plots. Conversely, nitrogenous amendment did not induce similar changes, probably because of its soil acidifying effect. Nitrogenous amendment decreased numbers of oribatid mites and Collembola. These numbers are not different for limed and NPKCa plots in comparison with control ones.