The leaf anatomical trade-offs associated with plant ecological strategy variation

Plant functioning depends on variation in resource economics traits (acquisition vs. conservation) and the size of plants and their parts (the ‘global spectrum of plant form and function’). The anatomical basis of single traits (e.g., leaf mass per area; LMA) is understood, but little is known regarding the relationship between anatomical trade-offs and ecological strategies (suites of traits). We hypothesised correlations between the relative extent of leaf tissue types and Grime’s Competitor Stress-tolerator Ruderal (CSR) strategies, principally a trade-off between structural (mechanical/fibro-vascular) vs. photosynthetic (chlorenchyma and intercellular airspace; ICAS) tissues, for ecologically-contrasting herbaceous angiosperms in northern Italy. Specifically, that in the lamina portion the trade-off represents the economics spectrum (S-R selection), but in the mid-vein portion it reflects the mechanical constraints inherent to large leaves (varies with C-selection). We used microscopy and image analysis to determine the relative cross-sectional area of tissues from transverse leaf sections (lamina and midvein portions) of angiosperms of contrasting CSR strategies. Principal components analysis (PCA) determined that the main spectrum was that of economics (S-R selection) characterised by a mechanical/ICAS vs. chlorenchyma/epidermis trade-off in the midvein, but contrary to expectations ICAS and chlorenchyma did not trade-off in the lamina. The secondary axis involved a trade-off between larger leaved competitors with extensive mechanical/fibrovascular tissue and small-leaved species (S and R-selected) with proportionally greater ICAS, chlorenchyma and epidermis. Our results confirm the expectation that ecological strategy variation has a basis in underlying trade-offs between tissues with contrasting physiological and structural roles.