Biodegradation of glyphosate was evaluated in rhizospheric soil cultivated with Glycine max (soybean, var. BRS245-RR), Canavalia ensiformis and Stizolobium aterrimum. After these species were cultivated for 60 days, soil samples were collected, placed in flasks and treated with 14C-glyphosate. After 30 days of incubation, the total release rate of C-CO2 was determined along with microbial biomass (MBC), metabolic quotient (qCO2), and degradation percentage of the radio-labeled glyphosate released as 14C-CO2. A higher mass of rhizosphere-associated microorganisms was verified in the soil samples from pots cultivated with soybean, regardless of glyphosate addition. However, in the presence of the herbicide, this characteristic was the most negatively affected. Microorganisms from the C. ensiformis rhizosphere released a lower amount of 14C-CO2, while for those originated from S. aterrimum, the amount released reached 1.3% more than the total carbon derived from the respiratory activity. The rhizospheric soil from S. aterrimum also presented higher glyphosate degradation efficiency per microbial biomass unit. However, considering qCO2, the microbiota of the rhizospheric soil cultivated with soybean was more efficient in herbicide degradation.
soil microbial activity; leguminous plants; transgenic soybean
