MICROBIAL-POPULATIONS IN THE RHIZOSPHERE OF BRACHYPODIUM-RETUSUM AND THEIR RELATIONSHIP WITH STABLE AGGREGATES IN A SEMIARID SOIL OF SOUTHEASTERN SPAIN

The rhizosphere of Brachypodium retusum was surveyed in eight semiarid soils from southeastern Spain. The percentages of stable aggregates. microbial populations, organic matter content, and carbohydrate conten ts were assessed in order to establish correlations between these para meters. The percentages of stable aggregates were highly correlated wi th total hyphal length in soil (R = 0.9444, P < 0.001) and, to a lesse r extent, with total bacteria (R = 0.8714, P < 0.01) and culturable fu ngal propagules (R = 0.7256, P < 0.005). No correlation was found betw een aggregation levels and carbohydrate contents in soils. The estimat ion of total fungi and bacteria was a more accurate method than the as sessment of culturable populations when the relative importance of mic ro-organisms were considered as factors in soil aggregation processes.