Efeito da resistencia à cavitação na mortalidade de árvores da Amazônia

Abstract

Extreme weather events are becoming more frequent and intense worldwide. Especially for Amazonia, drought episodes are increasingly frequent, varying in intensity, with an effect of increasing tree mortality in the last decade. Therefore, the interest in recent years is to understand the mechanisms of tree mortality through functional characteristics, which allowed predicting the level of vulnerability of species to these extreme weather events. This research aims to determine the effect of lower cavitation resistance (lower P50) on tree mortality in Central Amazonia. The central hypothesis is that the characteristics of trees' hydraulic architecture affect their mortality rates and that these effects depend on the water environment with which the species is associated. Soil conditions are expected to be determinant factors of this performance through the water availability gradients. The study was developed in the Adolpho Ducke Forestal Reserve, characterized as terra firme forest, with contrasting hydro-edaphic plateau and shoal environments. Twenty-eight species were sampled, and we performed measurements of stem anatomical characteristics (vessel diameter and density, inter vessel wall length, vessel cluster percentage) and leaves (stoma length and density, and venation density). For 18 species with cavitation resistance data, the mortality rates of trees juveniles (<10 cm DBH) were estimated between the periods 2001-2016. We found that the lowest P50 is related to higher mortality of trees juveniles in plateau environments. The anatomical characteristic that best-predicted tree mortality was the highest percentage of vessel grouping. Smaller P50 correlates positively with features of greater vessel grouping and inter-vessel wall length, which are linked to greater efficiency in water conductivity, deteriorating water transport safety. Our result is considered the first record of the effect of lower P50 on the mortality of trees juveniles under natural drought in plateau environments, which suggests the important effect of this environment as a filter on tree survival. The anatomical characteristics of the stem were better predictors of the high tree mortality compared to the leaf. These correlate significantly with lower cavitation resistance, favoring the air seeding hypothesis, which establishes that the greater connectivity between vessels facilitates the propagation of cavitation between membrane scores. We consider these results to be important for understanding the interactions between water and soil conditions, and how these dynamics reflect changes in the structure and composition of forests under conditions of future extreme weather events.