Ecofisiologia da germinação de sementes de espécies de caatinga.

Abstract

Ecophysiology of seed germination of caatinga species. Studies of climatic projections for the semiarid, region where caatinga vegetation, predominates foresee a gradual increase in temperature, with a decrease in pluviometric regime in the next century. The knowledge of the appropriate conditions for germination of the seeds is fundamental due to the differentiated responses of the species to environmental factors such as: water, light, temperature. The purpose of the study was to evaluate the influence of environmental factors: temperature, relative air, humidity substrate, field capacity and luminosity, and simulation of stress conditions, on seed germination and growth of Mimosa tenuiflora (Wild.) Poir and Poincianella pyramidalis (Tul) LP Queiroz. The conditions varied from the optimum to those of increasing stress to the seeds, making 13 treatments, with 4 replicates of 25 seeds each. The parameters determined were percentage of germination, dead, hard and abnormal seedlings, germination speed index (IVG), mean germination time (TMG), mean germination velocity (VMG), shoot dry weight, and root dry weight (PSR). The statistical design employed was completely randomized, and the means of the treatments compared by Scott-Knott (p <0.01 and p<0.05). Germination and IVG of Mimosa tenuiflora were reduced gradually even at 300 C, due to the influence of water stress. As the seeds were exposed to thermal stress at temperatures of 350 and 400 C water and low relative humidity, the percentage of germination decays drastically as well as IVG and VMG. Seeds of Poincianella pyramidalis germinated only under conditions of alternating temperature and absence of water stress. At constant temperatures of 30, 35 and 400 C the germination was severely affected, regardless of water stress. The results indicate that, with the advent of climatic changes, the studied species could be affected by the increase in temperature and the scarcity of rainfall in the environment, with Poincianella pyramidalis less tolerant to the factors studied.