Suprimento de potássio como mitigador dos efeitos do déficit hídrico em espécies florestais amazônicas.

Abstract

The increase in tree mortality due to extreme drought events in the Amazon has caused significant forest degradation and a reduction in carbon stocks. The ability of plants to withstand water stress is primarily linked to the hydraulic characteristics of species, such as water safety margins and phenotypic traits. Additionally, the presence of soil nutrients may play a modulatory role in plant responses to water deficit. Among these nutrients, potassium (K) stands out as a fundamental cation for plants, being one of the most demanded elements by them. K is widely distributed in plant tissues due to its high mobility and plays essential roles, including translocation, energy, and assimilate storage. Furthermore, K plays a key role in maintaining water in plant tissues. Therefore, the objective of this study was to evaluate the morphophysiological responses of plants subjected to potassium fertilization and water restriction. We studied two native Amazon tree species, one fast-growing (fava-orelha) [Enterolobium schomburgkii (Benth.)] and one slow-growing (jatobá) (Hymenaea courbaril L.). The experiment consisted of a completely randomized design in a double factorial scheme (2 x 2), with two water conditions (adequate irrigation and water deficit) and four K doses (0, 50, 100, and 200mg/dm3), totaling 8 treatments with 12 replications each. Two species were evaluated (96 plants per species), totaling 192 plants. Height, stem diameter, number of leaves, and the height/diameter ratio were evaluated. Gas exchange, functional traits, K concentration and accumulation, and K use efficiency in the aerial part of the plants were also analyzed. Height and diameter growth were higher in treatments with higher K concentration, with plants in these treatments being less affected by water stress. Overall, higher K concentrations (100 and 200 mg/dm3) reduced plant transpiration and increased water use efficiency. Fava-orelha plants in treatments with higher K levels (50, 100, and 200mg/dm3) and under water stress showed a significant increase in water use efficiency. K treatments and water deficit significantly affected leaf functional traits, with variation between the studied species. Leaf area was smaller in treatments with higher K doses (100 and 200 mg/dm3) for fava-orelha, with the opposite effect for jatobá. There was a reduction in specific leaf area (SLA) for treatments with higher K doses (100 and 200mg/dm3) for fava-orelha, and an increase in SLA for plants under water deficit for jatobá. Our results indicate an important role of K concentration in the soil on transpiration rate and water use efficiency, especially for fava-orelha, a fast-growing species, indicating that variations in nutrient availability influence tree physiology and their ability to withstand extreme droughts. Advancing knowledge of these processes may help in conservation efforts and management strategies that promote the resilience of tropical forests in the face of climate change.