Influence of seed size on drought tolerance in Eugenia uniflora L. seedlings

Drought events have become more intense and frequent in tropical ecosystems, which can limit plant growth and development, as well as the germination and recruitment of tree species. The variation in seed size may give plants advantages in the establishment in an environment and greater tolerance to environmental stress. Eugenia uniflora L. is a species found in different Brazilian biomes, such as Atlantic Forest and Pampa, and has high survival capacity in degraded areas and in various environmental conditions. To analyze the effect of seed size on the emergence capacity and drought response of E. uniflora seedlings, seeds were separated into two classes according to size and later analyzed for emergence, growth variables, soluble carbohydrate content, and anatomical changes of plants under drought settings. Analysis of the results showed that seed size and drought affected most growth parameters, in which drought caused a reduction in the number of leaves, fresh leaf mass, fresh stem mass and fresh root mass, and collar diameter. Drought also induces a larger diameter of the central cylinder in the root of plants originating from large seeds and a smaller thickness of the cortical parenchyma of the root of plants originating from small seeds. The content of soluble carbohydrates was reduced in the roots of plants under drought compared to the control, and there was also a blockage in sap transport in plants under drought. The results obtained show that water stress caused by drought reduced the growth and anatomical characteristics of root; however, plants from large seeds had greater leaf mass, fresh stem mass, root dry mass, and total dry mass, and higher shoot/root dry mass ratio. Thus, seed size influenced the performance of E. uniflora seedlings, both under drought and in the control setting.