Seasonal fluctuations and crop influence on microbiota and enzyme activity in fully developed soils of central Spain

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Abstract
Soil biological activity in the Mediterranean region is subject to succession of favorable and unfavorable periods as a consequence of climatic conditions. In fully developed soils (Aquic Haploxerult and Aquultic Haploxeralf) of central Spain and under natural vegetation (evergreen oak) and different degrees of human intervention on vegetal cover (brushwood and cereal crop), the seasonal dynamic of microflora systematic groups and enzyme activities was studied. Total microflora, actinomycetes, fungi, and algae tend to decrease according to the sequence: evergreen oak > brushwood > cereal, spring and autumn being the favorable seasons. Most of enzyme activities show the same sequence of variation as the soil microflora groups: from natural vegetation to cropland. The highest values appear during spring, while the lowest are given in autumn or winter. Factorial analysis establishes a clear difference between natural vegetation, brushwood, and cereal (spatial variation). There is a seasonal grouping subject to that which tends to group the spring and autumn samples on one hand and the summer and winter on the other (seasonal variation). Results show a significant reduction of soil microflora populations and catalytic capacity in cropland, since the brushwood maintains patterns that are closest to that of natural vegetation. On the other hand, the favorable seasons have a different meaning, from our point of view. Spring would correspond to a phase in which the edaphic metabolism produces a significant release of nutrients (there is a greater intensity of enzymatic processes), while autumn would correspond to a phase in which an opportunistic exploitation of resources (proliferation of r‐strategy organisms) predominates.