Organic matter cycling in grassland soils of the Swiss Jura mountains: biodiversity and strategies of the living communities

Several characteristics of the soils of three nutrient-poor grasslands, per taining to their biological activity, have been measured three times during the vegetation cycle of 1994 in the Swiss Jura. Properties measured were: abundances of the faunal groups Collembola (Insecta), Oribatida, Gamasida a nd Actinedida (Acarina); PLFA richness, abundance and diversity (indicating microbial diversity); ATP content (an index of soil biomass), soil respira tion (CO2 production); and alkaline phosphatase, urease, chitinase, xylanas e and laminarinase activities, as biochemical tracers of biotic activity. M ost of these variables showed significant differences from site to site. In particular, the biochemical descriptors ATP content and phosphatase and ur ease activities varied in accordance with the amount of the clay-humic comp lex. The soils showed two strategies of litter degradation: (a) an enzymati c strategy, prevailing at the end of winter, when the edaphic climate is un favourable; (b) a biotic strategy, based upon the work of the whole living community (fauna and microflora), at its maximum at the end of summer. Dive rsity of the microbial communities (as estimated by the PLFA richness) was highest in spring, when the carbon sources are complex (young litter), and subsequently decreased in inverse relationship with the specific activity o f the biomass (viz, CO2 production-to-ATP ratio). This behaviour is attribu ted to an increase of the amount of simple organic compounds resulting from enzymatic activity and also to the activity of microphytophagous microarth ropods. (C) 1999 Elsevier Science Ltd. All rights reserved.