This spring you may have noticed a curious planting in the experimental garden behind the hoop house. Growing in two raised beds was a crop of European broad beans, Vicia faba, more commonly known in our markets as fava or faba beans. UCLA's Professor Eduardo Zeiger was conducting an experiment in the botanical garden, the only convenient on-campus site for controlled outdoor plant studies.
Professor Zeiger came to UCLA's plant biology faculty in 1989 from Stanford, where he was doing pioneering research on the physiology of stomates. He made a major contribution by clearly demonstrating that stomates open when given only blue light, a discovery he made by studying leaves of the fava bean. Whereas other factors cause stomates to open or close, the blue-light response now appears to be the leaf's light sensor, operating much as a light sensor in a camera.
Around the world, a tremendous amount of research is being done on stomates, because the opening and closure of stomates determines how much photosynthesis takes place instantaneously and over the course of the day, how much water vapor is lost to the atmosphere, and how much cooling occurs through water loss. Among the fairly recent findings has been the discovery that stomates tend to open wider, and hence have greater uptake of carbon dioxide and water vapor loss, when the plant is growing under high relative humidity versus a drier atmosphere. Such sophisticated research is most conveniently performed in growth chambers or special growth rooms that can be set for exact environmental conditions. However, Professor Zeiger wanted to determine whether the same stomatal behavior could be observed in an irrigated field.
Westwood is not like UC Davis or UC Riverside, both agricultural institutions that have expanses of acreage for field experiments. Here, open land is at a premium--and a thing of the past. Professor Zeiger and his coworker Dr. Larry Tolbott approached MEMBG to create beds of plants where they could monitor stomatal behavior of outdoor plants, rooted in the soil, for three distinct levels of relative humidity. Maintaining differing levels of relative humidity for adjacent plants is no easy order, because air movement (wind) mixes air. Our combined solution was to grow the beans at three densities, while keeping soil wet, so that the densest crop would be expected to have the highest relative humidity within the still plant canopy. The researchers also used plastic to partially shelter the plants and thereby keep relative humidity artificially high.
These efforts paid off! Measurements taken with an instrument called a diffusion porometer clearly indicated that stomates were opened wider for plants grown under the highest relative humidity. Not only that, these plants--treated with the same water and nutrients and receiving the same level of sunlight--grew substantially taller and were much darker green. The high humidity enabled plants to have a significantly increased uptake of carbon dioxide as compared with the other two groups. In fact, these were the healthiest fava bean plants we have ever seen in the field. Thinking ahead, this result may have some broad applications for crop plants and plants grown in very humid habitats, such as tropical rain forests.
Thumbs up for the garden, for contributing to scientific research!