STRUCTURED INTERSPECIFIC DETERMINANTS OF SPECIFIC LEAF-AREA IN 34 SPECIES OF HERBACEOUS ANGIOSPERMS

1. Specific leaf area is a variable implicated in a number of function al aspects of plant ecology, including gas exchange, relative growth r ate and palatability. 2. Six leaf attributes (water content, lamina th ickness, protruding vein thickness, dry weight, lamina area and specif ic leaf area) were determined on a collection of 572 leaves. The data set was derived from 194 individual plants, 34 species, 32 genera, 18 families and both classes of angiosperms. All species except one (a sh rub) were herbaceous. All species were from sunny habitats. 3. Structu red relationships between these six variables were obtained. These rel ationships consisted of path analyses, multiple regressions and major axis (allometric) regressions. 4. There was an interspecific allometri c trend for leaf dry weight to increase more rapidly than leaf surface area, resulting in larger leaves naving a lower specific leaf area. T his trend did not exist at an intraspecific level. 5. Path analysis sh owed that the most important direct effect on specific leaf area was t he water content of the leaf. Increasing water content resulted in a l arger specific leaf area. The direct effect of lamina thickness was to decrease specific leaf area but lamina thickness itself was affected by leaf water content. 6. These effects on specific leaf area were med iated through variation in leaf dry weight. Leaf surface area appeared to be independent of the other five variables. 7. These results help to explain two unresolved general patterns in plant comparative ecolog y: (1) why net photosynthetic rate is not positively correlated with m aximum relative growth rates and (2) why there is a negative correlati on between maximum relative growth rate and seed size.