Tigmomorfogênese na rustificação e sobrevivência em mudas de Pinus taeda L.

Abstract

Thigmomorphogenesis is the adopted term to describe the growth response of plants to mechanical stimuli, naturally triggered by abiotic factors or artificially, by agroclimatic adverse event simulation. In the implantation of forest stands, such adversities limit of the seedlings establishment, and condition it to the recognize the limiting factor is the role in the hardening. It is speculated that the thigmomorphogenesis induced by stem bending become's more tolerant by forces exerted by the wind through the activation of mechanisms that alter the growth and accumulation of organic compounds. However, little is known if the employment of mechanical perturbations during seedlings hardening phase results in greater success in the implantation of forest stands. This present work aimed to evaluate morphophysiological alterations in Pinus taeda L. seedlings resulting from thigmomorphogenesis induced and its reflections about establishing in the field. For both, three experiments were conducted with the intention of quantify morphophysiological alterations resulting from stem bending and its reflections about establishing in the field; the partition and the buildup dry weight and carbon; and the correlation between lignin contente with field survival. P. taeda seedlings were produced by the nursery belonging to the company Sbaraini Agropecuária S.A., in Cascavel, PR. When reached the target size, were submitted to different intensities of stem bending during 60 days. At the end, were quantified morphophysiologic attributes, nutritionals, the dry weight and carbon partition between components, and lignin content. Additionally, the seedlings quality was measured by the root electrolyte leakage (REL). Posteriorly, part of the seedlings was planted in a commercial área of Pine monocropping in Cascavel, PR. Was quantitated by the survival, and increases of growth shoot at 90 and 360 days after planting. The increased intensity of the stem bendings reduced linearly of the stem height growth, the leaf area, resulting in the reduction in absolute growth rate and in the phosphorus content. Moderate intensities with up to 20 stem bending increased the secondary growth, the stem volume and the lignin content both in the root system how much aerial. The alteration in the primary and secondary growth was resulting of the carbon redistribution and of the dry weight accumulation in stem and in the root system, mostly in lateral roots, to the detriment of the leaf area reduction in terms of surface and dry matter. On the field, seedlings stimulated with that intensity showed higher survival and growth velocity, observed at 90 days after planting. After this period, he difference in growth velocity between seedlings stimulated or not has reduced, indicating acclimation of the seedlings unstimulated at the environment condition. There was correlation between the lignin content of the root system with the survival percentage at the 90 days, as well as the seedling quality measured by REL test proved to be predictive of field performance. Therefore, the application of 20 stem bendings applied during hardening of the P. taeda seedlings promoted greater success in implanting of the population in the experimental conditions analyzed.