Quantifying the variation in foliar physiognomy along altitudinal gradients in Australian tropical rainforests.

摘要

A number of studies have shown relationships between foliar physiognomic characters and climatic gradients are also present with variation in altitude. Few studies have explored these trends in foliar characters over a localized altitudinal gradient and none have repeated such collections on different gradients. This is an analysis of the foliar physiognomic variation seen over three localized altitudinal gradients in an Australian tropical rainforest environment. The study was based upon leaf litter collections and selected foliage samples. A unique aspect is the inclusion of two vine species in the exploration of physiognomic responses to altitude. Analysis of the leaf litter showed no significant variation in the number of species between altitudinal sites on two of the three gradients, or between either the percentage of leaves with entire margins. All three gradients showed significant variation in the percentage of entire margined species with varying altitude. Therefore, this study shows that species numbers are generally equally distributed with varying altitude, as well as leaf margin type measured on an individual specimen level. On a taxon level, it was found that there was a significant variation in entire margined species, but this variation did not have a linear relationship with altitude. Leaf size classes were found to have significant linear relationship with altitude on all three gradients. The smallest size class increased with increasing altitude, while the two larger classes decreased. Analysis of foliage from five selected species showed a wide range of responses between individual species with increasing altitude. Both vine species were found to have similar physiognomic responses to altitude as one of the tree species examined. These results suggest that intraspecific variations and changes in species composition are important factors controlling variation in foliar physiognomy across altitudinal gradients. Stomatal density increased with altiude for two of the three species examined, while the third decreased. This result shows that CO2 concentration may be a factor controlling stomatal density for some species, while for others it may not be important. Finally, experiments aimed to test whether there is correlation between the size of leaves and the distance they travel in rainforest streams showed that there is significant variation. With some exceptions, smaller species were found to travel further than large species. It was also found that fresh, green leaves consistently traveled further than dried leaves that had been rehydrated.