Mitigation of drought stress effects on soybean gas exchanges induced by Azospirillum brasilense and plant regulators

Abstract

ABSTRACT Drought stress is a limitation for the agricultural production, having as a primary effect the reduction of plant gas exchanges, and the continuity of its incidence results in a lower yield. This study aimed to evaluate the photosynthetic responses and the soybean yield, concerning the seed inoculation and foliar spray with Azospirillum brasilense and plant regulator containing auxin, gibberellin and cytokinin. A randomized complete block design was used under greenhouse conditions, with five treatments: four under drought stress (control, seed inoculation and foliar spray with A. brasilense and plant regulator) and one irrigated treatment. The soil gravimetric moisture, relative water content, CO2 net assimilation rate, apparent quantum efficiency, light compensation point and grain yield were evaluated. The water deficiency reduced the relative water content by 76.96 % and the soybean gas exchanges by 860.43 %, in the drought stress control. However, when using A. brasilense or plant regulator, the reduction of these values was mitigated, with maximum reductions of 52.40 % in the relative water content and 361.99 % in the gas exchanges. Thus, the mitigation of these effects was directly correlated with the grains yielded by plants, where the use of foliar spray with A. brasilense or plant regulator presented averages 19 % higher than the drought stress control. The applications of foliar spray with A. brasilense and plant regulator mitigate the effects of drought stress on the soybean photosynthesis and culminate in lower yield losses.