Differential responses of structural and functional aspects of soil microbes and nematodes to abiotic and biotic modifications of the soil environment

We evaluated the effect of an abiotic and a biotic modification of soil environment on the structure and function of soil biological communities in a six month experiment established in a recently abandoned wheat field. Evaluations included PLFA and CLPP microbial profile as well as the nematode trophic structure and functional indices in plots that differed in irrigation (abiotic modification) and manure application (biotic modification). Four treatments were created: low water supply-manure fertilization, low water supply-no fertilization, high water supply-manure fertilization and high water supply-no fertilization. Two samplings were carried out: the first after 8 weeks of irrigation (March) and the second after 20 weeks (June). The PLFA groups were mainly affected by the abiotic treatment (water supply), which acted either alone in June or in combination with the biotic treatment in March. In all plots, there was an increase of bacterial and to a lesser extent of fungal biomass from March to June, as well as a shift of the bacterial community towards Gram(+). The microbial catabolic profile was different in the two sampling occasions, whereas the microbial functional diversity (Shannon index) was not affected either by treatment or by sampling time. Nematode abundance was also higher in June in relation to March in all plots, whereas the response of nematode feeding groups to treatments was occasional and related to manure rather than to water supply. (c) 2012 Elsevier B.V. All rights reserved.