Calcium-magnesium liming of acidified forested catchments: Effects on humus morphology and functioning

To counteract acidification of terrestrial ecosystems due to decades of acid atmospheric depositions, two forested catchments located in the Vosges Mountains (NE France) were limed (2.5 t ha(-1)) in fall 2003. Seven years later, the effects of liming on humus characteristics were investigated in three horizons OL, OF and OH by comparing the two limed catchments with two adjacent acidified control sites. Two geological substrates (sandstone and granite) were compared. In each catchment 21 sampling points were selected along a transect. Effects of liming were globally dependent on the geological substrate. We observed an increase in pH, Ca-Mg contents in the OL horizon, more pronounced for sandstone compared to granite. Neither fungal biomass revealed by ergosterol measurement nor mesofauna abundance significantly different between acid control and limed catchments, but we observed opposite trends for these two biological components in their reaction to liming on both geological substrates. However, the significant effect of liming on humus morphology showed that soil biological activity was affected by CaCO3 amendment, but this effect was no longer significant 7 years after liming. Owing to the thickness of organic layers, humus forms shifted from eumoder to dysmoder on sandstone whereas the opposite was observed on granite. One of the key outcomes is the increase in thickness of the OH horizon on sandstone substrate. (C) 2012 Elsevier B.V. All rights reserved.