Efeitos da restrição hídrica sobre aspectos fisiológicos e anatômicos em soja

Abstract

The main frontier for global expansion of soy cultivation is in Brazil, including part of the state of Maranhão. This region includes areas of the National Cerrado, which in turn are subject to rainfall irregularities. It is well established for culture, that water restriction in the reproductive development stage significantly affects productivity, while in the same sense, and about the physiological and anatomical effects in the vegetative stage, there are few reports in the literature. In this sense, the present study aimed to identify changes in the physiological and anatomical responses, as well as possible implications on the hydraulic conductivity of the root in soybean plants submitted to different levels of water restriction. The experiment was carried out in a greenhouse, with plants from cv. conventional brs tracajá, grown in field capacity (CC), and the experimental units were subdivided in stage V3, in treatments T25 (25% of water application from CC), T50 (50% of water application from CC), T75 (75% of DC water application) and T100 (CC). A completely randomized design was applied, with 20 repetitions. Among the aspects evaluated were growth in height and stem diameter, total leaf area, accumulation of dry mass of organs and nodules, leaf water potential, gas exchange, chlorophyll fluorescence, SPAD index, root volume, hydraulic conductivity of root and anatomy of leaves, stem and root. According to the results, the plant height and stem diameter reduced significantly according to the severity of the applied restriction. The same occurred for the dry masses of leaf, stem and root, however, the proportion of the mass of the organs did not differ with this reduction. The T75 treatment kept the values of vegetative development (MSF, MSN and AFT) close to the values of T100. Likewise, T75 achieved the best performance in gas exchange measurements when compared to other treatments in relation to T100. As for the use of water, T75 was the most efficient treatment in the use of this resource. Therefore, this result added with the maintenance of the vegetative development of the T75 close to the T100, point out that the application of 75% of water in the field capacity as an important alternative to planting the variety under study aiming at saving water use. The chlorophyll fluorescence and SPAD index were not altered by the application of the treatments, in the same way as the measures of root hydraulic conductivity (CHR) at 32 days after restriction (DAR). Regarding the organization in the composition of the tissues of the central leaf and stem, no distinctions between treatments were identified. Anatomical analysis showed adaptations at T25, defined by the greater thickness of the sclerenchyma in the stem and the smaller mean diameter of the vessels of the root xylem.