Condições edáficas influenciam a tolerância de Myracrodruon urundeuva Allemão (Anacardiaceae) ao déficit hídrico e sua posterior recuperação

Abstract

Myracrodruon urundeuva Allemão is a tree species native to the seasonally dry tropical forest. It is important in the recovery plans of degraded areas and it is a key species for the maintenance of the biodiversity of this biome, despite being threatened with extinction. In semiarid regions, the water regime is pointed out as the variable with the greatest influence on the distribution of plant species. However, some studies suggest that the type of soil can affect the tolerance of plants to water stress. This study evaluates the influence of the soil type on the physiological changes triggered by water deficit in M. urundeuva species. Its relevance is related to the risk of changes in the distribution pattern of M. urundeuva as a result of climate changes. The experimente was carried out in a greenhouse in a completely randomized design and in a 2x2 factorial scheme. ANOVA test was used to assess the effects of two types of soil (sandy clay loam and sandy), and two water regimes (irrigated and water deficit with subsequent recovery) on gas exchange, maximum and effective quantum efficiency of PSII (Fv/Fm and ΦPSII), water status (Ψwleaf), relative chlorophyll content (SPAD index) and concentration of organic compounds (proteins, amino acids, proline and sugars). Our findings support that the soil characteristics can influence the response pattern of M. urundeuva to stress by water deficit and its subsequent recovery in regards to instantaneous water use efficiency, water status and accumulation of osmorregulators. Contrary to expectations, plants in sandy clay loam soil reached photosynthetic rates close to zero faster and required more time to recover than plants in sandy soil. This can be attributed to the higher concentration of solutes in this soil. Despite this, their stomatal response to moderate water deficit is more efficient, which is recognized by the inability of plants to increase their water use efficiency in sandy soil under moderate stress situations. On the other hand, presumably M. urundeuva in sandy soil adopts a different strategy: to maintain its stomata open for longer periods during the water deficit. It aims to ensure the necessary CO2 input to maintain growth rates, despite the greater risk of hydraulic failure. Even with photosynthetic rates close to zero, M. urundeuva did not suffer with reductions in the maximum quantum efficiency of PSII, regardless of the soil type. Also, plants in sandy clay loam soil accumulate amino acids in addition to proline for osmoregulation and had better water status. This revealed that osmoregulation, combined with the reduction of stomatal opening is an eficiente strategy to save water when growing on this substrate. The large accumulation of proline in plants in both soil types may have also played an important role in the rapid recovery of plants after the water deficit, given its role as an osmoprotective and as a carbon and nitrogen stock after rehydration. This study shows that M. urundeuva communities in sandy soil regions have a stomatal response with a high degree of anisohydrism, meaning that they keep their stomata open during most of the water deficit period. However, this strategy represents a considerable increase in the chances of death of these plants due to hydraulic failure and, thus, the extinction of these communities in a scenario where drought events become progressively longer and more severe.