Correlatos ambientais e análises macroecológicas de sementes e folhas das espécies lenhosas no semiárido tropical

Abstract

The survival and distribution of plant species in the extreme environmental conditions of semiarid environments is strongly dependent on characteristics associated with drought resistance. The weight of the seeds and the size of the leaves can be particularly important, since they are features capable of responding to various environmental conditions, especially in stressful environments, such as those with great water restriction. The aim of our research is to describe functional biogeography and to provide the first biogeographic assessment of the weight of seeds and leaf area in climatic and edaphic conditions of the Caatinga biome in northeastern Brazil. We used seed weight data for 277 woody species and the leaf size of 192 woody plant species in the Caatinga. Structural equation models (SEM) were used to test direct and indirect effects between seed weight and climatic conditions, including temperature, precipitation, climatic seasonality, and soil compaction and associations of soil properties and average leaf size. Species occurrence data were retrieved 510 022 records of occurrence of species of Angiosperms in the Caatinga from the data portals GBIF and SpeciesLink in November 2016. Our results indicate that the highest weights of seeds of woody species in the Caatinga are mainly an adaptation to compacted soil, uneven distribution of rain and high temperatures.The strongest association was between seed weight and soil compaction, with average temperature of the driest quarter and aridity directly influencing soil compaction (indirectly influencing seed weight).We found that 67% of the pH variation of the Caatinga soil is explained by aridity and there is a positive relationship between leaf size and the availability of cationic minerals in the soil.Although the relationship between leaf area and availability of cationic minerals is stronger than the average leaf size and soil pH, this relationship may reflect different drought tolerance strategies. We argue that soil pH can be recognized as an important factor in the distribution of plants in tropical forests. Overall, the sampling effort across the Caatinga showed heterogeneous geographic coverage; as indicated by the large areas of the biome that remain under collection.We conclude that the environmental variables favor the adaptation of larger seeds and that the physical-chemical properties of the soil have a direct influence on leaf size.