CALORESPIROMETRY OF SOILS TREATED WITH EXTRACTS OF Brachiaria platyphylla

SESTO CABRAL MARIA EUGENIA; E. ELIZABETH SIGSTAD

Jornada; JORNADAS DE LA ASOCIACION DE BIOLOGIA TUCUMAN; 2009

Brachiaria platyphylla (Munro ex C. Wright) Nash has invaded cultivated fields in Tucumán province, Argentina, with the consequent economic damage to producers. To understand its invasivity EtOAc and MeOH extracts of its aerial parts were incubated with soil to further investigate chemical, microbiological and calorimetric modifications. Also, soil samples from invaded (IS) and non invaded (NIS) areas were studied. An isothermal heat conduction calorimeter was used to obtain the curves of microbial growth. Invaded soil had higher values of organic carbon (OC), extractable phosphorus (P), pH and microbial biomass (MB) than the non invaded one. This coincided with the lower evolution of CO2 g-1 MB for the invaded soil, indicating a more efficient metabolism. A concentration of 250 mg kg-1 of the EtOAc extract selectively inhibited microbial activity reflected by the lowest MB together with a lower mineralization of organic matter. The same concentration of MeOH extract activated microorganisms with poor efficiency to convert substrate into biomass with respect to the control soil. Thus, both extracts have a negative effect on the soil microbial activity so that the improvement in soil quality observed in IS with respect to NIS is probably due to root exudates that will be studied further.