INFLUENCE OF SIMULATED DEWFALL ON PHOTOSYNTHESIS AND YIELD IN SOYBEANISOLINES (GLYCINE-MAX [L] MERR CV WILLIAMS) WITH DIFFERENT TRICHOME DENSITIES

Leaf surface wetness, e.g., dewfall, has been shown to have a strong i nfluence on photosynthetic CO2 exchange in native plants. The importan t influence of trichomes on leaf surface wettability has also been est ablished. We evaluated the effect of leaf surface wetness on photosynt hesis and yield in soybeans (Glycine max) for five isolines that varie d in trichome density. Artificial misting was used to simulate the inf luence of natural dewfall as well as spray irrigation. Leaf trichomes had an important influence on droplet formation and the distribution a nd retention of liquid water on individual leaves, even though trichom e densities were low compared with maximum values reported for native species. Greater water droplet formation and, thus, water repulsion oc curred for isolines with greatest trichome density. Somewhat surprisin gly, these isolines also have the greatest droplet retention. However, all isolines showed relatively low water repellency, along with reduc tions in CO2 assimilation that averaged about 15%. Isolines subjected to misting during the morning (simulated dewfall) also had lower above ground(15%) and seed (19%) biomass, and total leaf area (14%) compared to control plants. Thus, surface wetting, either from natural events (e.g., dewfall) or spray irrigation, may lead to significant reduction s in CO2 exchange and growth potential in agricultural species, as rep orted for native species.