Influence of orientation, vegetation and season on soil microbial and biochemical characteristics under semiarid conditions

The semiarid climatic conditions of southeast Spain prevent the growth of stable vegetation that would help preserve soil fertility. The aim of this work was to evaluate the effect of orientation, vegetation and season on soil microbial and biochemical properties in a semiarid climate. For this purpose four experimental sites were chosen: two southerly orientated (SO) and two northerly orientated (NO). One of the SO sites had a vegetal cover of shrubs (SOS) and the other of Pinus halepensis (SOP). Similarly, one of the north-facing sites had a cover of shrubs (NOS) and the other of P. halepensis (NOP). The vegetal cover of north-facing sites was about 75% while on the south-facing sites it was less than 25%. Orientation significantly influenced the C fractions, which were higher on north-facing sites than on south-facing sites. Microbial biomass C (MBC) reached 400 mg C kg−1 soil in north-facing sites. Microbial activity was also greater in NO than in SO sites, the NOP site showing basal respiration of 15 mg CO2-C kg−1 soil−1 day−1, while basal respiration did not reach 2 mg CO2-C kg−1 soil−1 day−1 in either SO sites. Urease, β-glucosidase and N-α-benzoyl-l-argininamide (BAA) protease showed higher values in NO sites than in SO sites, being lower in autumn than in summer and spring in NO sites. As regards factor analysis, the biochemical and microbiological parameters measured were able to separate the soils. The effects of vegetation type were orientation-dependent. With a southerly orientation, vegetation type influenced microbial activity sufficiently to generate different grouping in the factor analysis. However, NO soils were more influenced by climatic factors than by vegetation type. The results allow to conclude that orientation plays an important role in the biochemical and microbiological properties of soil, outweighing, even, the effects of vegetation type and season.