Desenvolvimento inicial da bananeira micorrizada e atividade microbiana em neosolo quartzarenico irrigado com água salina

Abstract

The Northeast of Brazil region meets the soil-climate conditions for a favorable cultivation of the banana plant, which can be demonstrated by the prominent position of the region as a great banana producer in the country. The banana is a fruit consumed all over the world, so being intensively cropped everywhere; its importance involves economic, nutritional and social aspects. The soil salinity represents a fundamental stress factor on the banana yield and such soil salinity is very common in northeast of Brazil (semi-arid climate) soils where the crop is widely grown. Under this conditions, arbuscular mycorhizal fungi (AMF) have been investigated lately with the objective to evaluate the role of the fungus in decreasing the plant salinity stress effects. Thus, the present study had the objective to investigate the effects of different irrigation water salt levels on: (a) the soil salt accumulation, (b) on the fungus (AMF) colonization, and (c) on the banana Musa sp. seedling plant growth colonized with native AMF. An experiment was conducted under greenhouse conditions (belonging to Soil Science Department – Federal University of Ceará State – Campus PICI, Fortaleza city). The statistical design was an entirely randomized blocks, in subdivided plots, with a four harvest periods (40, 60, 80 and 100 days after planting), five level of soil salinity (0,5; 1,5; 2,5; 3,5 and 4,5 dS m-1) and four replicates, summing a total of 80 treatments. The banana seedling plants were subjected to a 40 days period of adaptation for fungus infection (mycorrization) and afterwards being irrigated with saline water. The first harvest was at the 40 days after the planting; the other harvests were done at the 60, 80, and 100 days after the planting. The following variables were evaluated: aerial plant dry matter, plant height, stem diameter, stomatal conductance, transpiration rate, photosynthetic rate, soil pH, soil electrical conductivity, root fungus colonization, estimates of AMF sporous, and soil basic respiration. Increase in the irrigation water salt level caused salt accumulation in the soil which was measured through soil electrical conductivity; the soil pH was not significantly affected. The increasing soil salinity did not cause significant differences in the following varables: stomatal conductance, plant transpiration rate, plant height, and stem diameter, otherwise, it reduced the photosynthetic rate and the plant aerial dry matter yield, notably at the 80th after planting. The increase in the salinity of the irrigation water caused a reduction of N and K plant concentrations, but increased the Na concentration an had no effect on the XIII P. The root fungus colonization and the basic soil respiration were both reduced by the salinity of the irrigation water; AMF fungus sporous formation in the soil was not affected. In general, the responses observed in both soil (chemical and microbiological) and plant, as results of the water salinity, were affected by the time exposure of the system soil/plant to the different salinity irrigation water levels.