Does tree environment in agro-forestry ecosystems influence the population of N2 fixing soil bacteria?

Resumen

The present study aimed to monitor the rhizobial population present in four montado ecosystems from two different locations, Vaiamonte and Estremoz in the South of Portugal, with natural and sown pastures. The influence of tree canopy of Quercus suber was evaluated in relation to rhizobial population abundance, symbiotic effectiveness and genetic diversity. Results showed that the size of natural rhizobial population in the two older improved pastures analyzed, having more than 30 and 12 years, had the highest values outside the influence of cork tree canopy. However, under the canopy, the population size in these two improved pastures decreased. Also, rhizobial abundance in the youngest sown pastures (>5-years-old) had high values, either beneath the tree canopy or outside its influence. Concerning the effectiveness of symbiotic fixation, results revealed the existence of N2 fixing strains in the four pastures, the highest values being observed in the youngest improved pasture and under the tree canopy. A high genetic diversity of rhizobial population was also found in all pastures, especially outside the influence of the tree canopy.