Gas exchange of four Viburnum species

In the natural environment, a plant\u27s gas exchange and water use efficiency characteristics in response to environmental stresses such as vapor pressure deficit, temperature, light intensity, and water potential may vary according to physiological and morphological species differences, leaf types (deciduous or evergreen), and habitat types (northern and southern). In the field, laboratory, and growth chamber, the effect of vapor pressure deficit, temperature, and light intensity on gas exchange characteristics was investigated for four woody shrub species from the genus Viburnum. The species under investigation include: y. rhytidophyllum (northern evergreen), y. awabuki (southern evergreen), y. dentatum (northern deciduous), and y. integrifolium (southern deciduous). Previous scanning electron microscopy studies showed that y. awabuki had a distinctive leaf anatomy, while the other three species were similar to each other. Field studies were conducted on sunny days in August and September, 1989, using a closed, steady state gas exchange system. Gas exchange measurements were recorded for three leaves per species at ambient conditions from 0600 to 1800 hours, and leaf water potential was determined with a pressure chamber at each sampling time. In the laboratory, gas exchange parameters were measured for three leaves per species using well watered greenhouse grown plants as light intensity, leaf-to-air vapor pressure deficit, or leaf temperature was varied. Growth chamber studies were conducted using greenhouse grown plants, and stomatal conductance was measured for six leaves per species using a steady state porometer at four water potential ranges at high and low vapor pressure deficits. Under drought conditions in the field and well watered conditions in the laboratory, the evergreen species, especially y. awabuki, typically showed lower conductance, net photosynthesis, and intercellular CO2 than did the deciduous species, but not to the degree expected. Growth chamber studies showed that vapor pressure deficit and water potential were both important in effecting declines in conductance for all species. Water use efficiency varied little between species in the field or in the laboratory. Gas exchange responses of the plants to environmental variables were associated with deciduous or evergreen leaf types, but more strongly with leaf anatomy