ALLOMETRY OF CELLS AND TISSUES WITHIN LEAVES

Premise of the study: Allometric relationships among the dimensions of leaf cells, cell walls, and tissues, and whole-leaf thickness and area are likely to have key implications for leaf construction and function, but have remained virtually untested, despite the explosion of interest in allometric analysis of numerous plant properties at larger scales. Methods: Using leaf transverse cross sections and light microscopy, we measured leaf dimensions, tissue thicknesses, mesophyll and xylem cell sizes, and cell wall thicknesses for 14 diverse angiosperm species of wet and dry habitats and tested hypothesized allometric relationships based on geometric scaling due to development and/or function. Key results: We found strong novel allometries relating the dimensions of cells, cell walls, tissues, and gross leaf form. Cell sizes and cell wall thicknesses tended to scale isometrically across mesophyll tissues within the leaf, such that species with large cells or thick cell walls in one tissue had these also in the other tissues; however, leaf vein xylem conduit sizes were independent of those of other cell types. We also found strong geometric scaling of cell wall thicknesses with cell sizes throughout the mesophyll, but not in the leaf vein xylem. Further, leaf thickness scaled with cell sizes, cell wall thicknesses and the thicknesses of component mesophyll tissues, but leaf area was independent of anatomical traits across species. Conclusions: These novel allometries suggest design rules operating at the smallest scales of leaf construction and the possibility of applying these relationships to better characterizing the basis for differences among species in leaf form and functional traits.