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

Leaf surface wetness, e.g., dewfall, has been shown to have a strong influence on photosynthetic CO2 exchange in native plants. The important influence of trichomes on leaf surface wettability has also been established. We evaluated the effect of leaf surface wetness on photosynthesis and yield in soybeans (Glycine max) for five isolines that varied in trichome density. Artificial misting was used to simulate the influence of natural dewfall as well as spray irrigation. Leaf trichomes had an important influence on droplet formation and the distribution and retention of liquid water on individual leaves, even though trichome densities were low compared with maximum values reported for native species. Greater water droplet formation and, thus, water repulsion occurred for isolines with greatest trichome density. Somewhat surprisingly, these isolines also have the greatest droplet retention. However, all isolines showed relatively low water repellency, along with reductions in CO2 assimilation that averaged about 15%. Isolines subjected to misting during the morning (simulated dewfall) also had lower aboveground(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 reductions in CO2 exchange and growth potential in agricultural species, as reported for native species.