To arrive at a better understanding of variation in specific leaf mass (SLM, leaf weight per unit leaf area), we investigated the chemical composition and anatomical structure of the leaves of 14 grass species varying in potential relative growth rate. Expressed on a dry weight basis, the fast-growing grass species with low SLM contained relatively more minerals and organic N-compounds, whereas slow-growing species with high SLM contained more (hemi)cellulose and lignin. However, when expressed per unit leaf area, organic N-compounds, (hemi)cellulose, total structural carbohydrates and organic acids increased with increasing SLM.
For the 14 grasses, no trend with SLM was found for the leaf volume per unit leaf area. Leaf density was positively correlated with SLM. Variation in density was not caused by variation in the proportion of intercellular spaces. The proportion of the total volume occupied by mesophyll and veins did not differ either. A high SLM was caused, at least partly, by a high proportion of non-veinal sclerenchymatic cells per cross-section. The epidermal cell area was negatively correlated with SLM.
We conclude that the differences in SLM and in the relative growth rate (RGR) between fast- and slow-growing grass species are based partly on variation in anatomical differentiation and partly on chemical differences within cell types.