Anatomia do xilema secundário, crescimento e condutividade hidráulica potencial de clones de Toona ciliata M. Roem var. australis cultivados no campo com condições ambientais contrastantes

Abstract

The water deficit is one of the factors limiting growth and forest productivity and, according to forecasts; it may intensify in the coming years, as a result of climate change. As sessile organisms, plants cannot move to escape environmental tensions and, as they are continuously exposed to stress, they develop adaptation mechanisms in response. Anatomical adjustments in the secondary xylem are one of the strategies adopted by plants to maintain vital physiological processes. Therefore, the aim is to investigate the effect of environmental conditions on the variability of the lume area, hydraulic diameter and frequency of conducting vessels, potential hydraulic conductivity, growth and survival of Toona ciliata (Red cedar) clones. For this purpose, were used wood from four clones (FE, XD, XE, MD) from two T. ciliata multiclonal tests located in the municipality of Campo Belo and district of Cana Brava, both in the state of Minas Gerais. For the anatomical characterization of the secondary xylem, permanent histological slides were made. From the diameter and frequency of the vessels, the potential hydraulic conductivity was evaluated. The average annual increment data was obtained by the width of the growth rings of the individuals sampled. The variables were related to the average precipitation rates for each location. There was no influence of environmental conditions on qualitative anatomy, which is genetically fixed. In Cana Brava, the place with the lowest annual average rainfall, the vessel lume area is 60% less than that found in Campo Belo, as well as the hydraulic diameter (23,67%) and the potential hydraulic conductivity (29%), while the frequency of vessels is 42% higher. Such anatomical adjustments offer greater security in water transport, characteristic of environments under water stress. The clones cultivated in Campo Belo showed the highest mean annual increment (MAI) and the highest survival rates, as a result of the environmental conditions favorable to the development of the trees. The rainfall variations over the years that formed the annual growth rings caused changes in the anatomy of the conducting vessels and in the hydraulic conductivity of the genotypes, with different responses for each clone and planting site. The XD clone, among all the evaluated clones, is characterized as having greater phenotypic plasticity, as it presents anatomical changes capable of maintaining the hydraulic conductivity, growth and survival of individuals, even in limiting conditions. On the other hand, the MD clone is the most susceptible to the risk of mortality due to hydraulic failure, because, despite modifying its anatomical structure, it was the clone that least survived in Cana Brava. The plasticity of the xylem secondary to environmental conditions may have resulted from memory of stress acquired by parenting, which is an important factor for the performance and survival of Toona ciliata in the face of the future climate change scenario.