Water Content Variation Patterns of Fruits During Development and Their Effects on Fleshiness or Dryness for Fruits at Maturity

The ecological origins of diverse fruit types remain unresolved due to lack of knowledge about variation patterns in fruit water content during fruit development and after fruit maturity. We hypothesized that distinctive water content variation patterns during fruit development mainly determine fleshiness or dryness of fruits at maturity. Controlled water evaporation experiment of fruits of 188 species (belonging to 144 genera and 72 families) was conducted to measure fruit drying days and water content. A phylogenetic tree was built for 29,760 seed plants of China using the R package V.PhyloMaker2 and phylogenetic generalized linear models and Pearson correlation analysis were used to explore the variation patterns of drying days of various fruit types and their mechanism. Water content in dry fruits decreases gradually during fruit development (i.e., prior to maturity, and before dehiscent fruits split), while water content in fleshy fruits (berries, at least the pericarp of drupes and rosehips) increases slightly or remains constant during fruit development. Significant correlations were found between fruit drying period and fruit height, surface area and fruit size. In general, the development of dryness for dry fruits at maturity is primarily attributed to declining fruit water content due to pericarp lignification and consequent fast water loss. Also, possible water imbalance between supply and loss especially for elongated or flaky dry fruits due to allometric growth between pedicel diameter (or fruit mass) and fruit surface area helps account for fruit dryness. Development of dry fruits may be induced by cold, dry and open habitats with strong light. Conversely, fleshiness of mature fleshy fruits is attributed to slow pericarp water loss rate due to low cuticle permeability and high fruit thickness, combined with stable high-water content maintained during fruit development. The evolution of fleshy fruits was induced by warm and humid habitats with weak or possibly strong light.