Diversidade e eficiência de bactérias fixadoras de nitrogênio nodulíferas de gliciridia, leucena e sombreiro no Maranhão

Abstract

Legume trees are recommended in agroforestry systems and degraded land restoration for their ability to fix nitrogen in symbiosis with rhizobia. This study evaluated the occurrence, diversity and efficiency of a native rhizobia community for the legumes Gliricidia sepium, Leucaena leucocephala and Clitoria fairchildiana in a soil from center-north Maranhão (Brazil). To evaluate efficiency, the response of these legume trees to commercial inoculants was evaluated with and without the native community. Two greenhouse experiments were settled in a complete random design. The experiment 1 with sterile substrate had 4 treatments and 6 repetitions: 1- inoculation with commercial inoculants; 2- inoculation with soil suspension; 3- control with mineral nitrogen; 4- control without nitrogen and nor inoculation. The experiment 2 with non-sterile soil had 4 treatments and 5 repetitions: 1- inoculation with inoculants BR 825, BR 8003 and BR 8801 for L. leucocephala, C. fairchildiana and Gliricidia sepium, respectively; 2- inoculation with inoculants BR 827, BR 8007 e BR 8003 for the same legumes; 3- control with mineral nitrogen; 4- control without nitrogen and nor inoculation. Main results were: a) the native community had rizobia efficient to nodulate and enhance G. sepium and L. leucocephala growt; but, low ability and efficiency to nodulate C. fairchildiana; b) low competitiveness of commercial inoculants for C. fairchildiana nodulation suggests that efficient inoculants have to be further searched in the native community; c) isolates from native communities studied tolerates better extreme temperature and salinity; d) most of isolates tolerated high pH (12) but not low pH (4); e) local community showed great genetic diversity compared with commercial inoculants, suggesting the occurrence of new rizobia genotypes in the region. These results reinforce the need to further study indigenous communities of rhizobia in Maranhão. The search for strains efficient and adapted to the state climate is essential to maximize the BNF with legumes L.leucocephala, G. sepium and C. fairchildiana.