CHANGES IN PHYSIOLOGICAL GROUPS OF MICROORGANISMS IN SOIL FOLLOWING WILDFIRE

Physiological groups of soil microorganisms were investigated in a for est (Pinus pinaster Sol.) to asses their response to wildfire-induced soil changes. Microbial fluctuations were recorded I month and 1 year after the fin, both in the field and during controlled soil incubation s. In both the burned and the unburned soil, starch-mineralizing micro bes predominated over cellulose-mineralizing microbes; there were a re latively high number of ammonium-producers, whereas nitrite and nitrat e producers were scarce. In the short term, burning produced a decreas ing to nearly undetectable number in cellulase-producers whilst amylas e-producers, and especially, ammonifying microbes increased, and the n itrifying groups did not change. One year after the wildfire, the burn ing effect was slightly overcome by cellulolytic microorganisms and th e amylolytic population was slightly decreased; the improvement of amm onifiers was reduced, ammonium oxidizers were positively affected and nitrite oxidizers continued to be unaffected by the fire. The trends o f populations during soil incubation indicated that, in the long term, the effect of burning will probably be nil on ammonifiers, somewhat n egative on cellulolytic and amylolytic microbes and slightly positive on nitrite- and nitrate-formers.