LEAF ANATOMY, SPECIFIC MASS AND WATER-CONTENT IN CONGENERIC ANNUAL AND PERENNIAL GRASS SPECIES

Previous experiments have shown that leaf specific mass (LSM: the rati o of leaf dry mass to area) was lower and leaf water content (LWC) was higher in annuals than in perennials, differences that are more gener ally found between fast- and slow-growing species. Leaf transverse sec tions of seven annual-perennial pairs of grass species grown in the la boratory were analyzed to elucidate the anatomical bases of these diff erences. Leaf thickness was similar in annuals and perennials, but lea f density was significantly higher in perennials. The proportion of th e leaf volume occupied by mesophyll was higher in annuals, at the expe nse of the three other tissues (i.e. epidermis, sclerenchyma and vascu lar tissues). The cross-sectional area of mesophyll cells was higher i n annuals than in perennials, but epidermal cell size was similar for both life-forms. The ranges of LSM (23.1-49.5 g m(-2)) and LWC (0.70-0 .86 g g(-1)) displayed by the 14 species were large enough to examine the general relationships between these two parameters and various ana tomical characters. LSM was significantly correlated with leaf density , but not with leaf thickness. The anatomical character that best expl ained interspecific differences in LSM was the volume of cell walls pe r unit leaf area (approximated by the sum: sclerechyma + vascular tiss ues (including its living component) + cell wall components of mesophy ll and epidermis). LWC was found to depend on leaf density, and inters pecific differences in this parameter were best explained by the propo rtion of mesophyll protoplast (i.e. proportion of mesophyll minus prop ortion of mesophyll occupied by cell walls) in the transverse sections . The physiological and ecological implications of these findings are discussed in terms of a trade-off between leaf productivity and persis tence.