GAS-EXCHANGE CHARACTERISTICS OF TYPHA-LATIFOLIA L FROM 9 SITES ACROSSNORTH-AMERICA

Gas exchange characteristics were measured in the field for nine popul ations of Typha latifolia L. from Florida to Minnesota in North Americ a. These populations spanned a substantial gradient in growing season length and environmental conditions. The purpose of this study was to assess geographic variability in stomatal conductance (g(st)) in T. la tifolia populations, as well as to identify key environmental and plan t factors that may affect g(st) and, potentially, trace gas emissions through stomata. Midday rates of net photosynthesis (A) and g(st) were measured under full sunlight conditions at each site, and more intens ive measurements of diurnal and seasonal variability were made at sele cted sites. In general, A varied less than g(st) (1.5 vs. 3 fold) amon g sites with maximum A (27.4 mu mol m(-2) s(-1)) and g(st) (1076.7 mmo l m(-2) s(-1)) measured at the southern sites. We found that A and g(s t) in T. latifolia increased significantly with increasing temperature and light level, and varied diurnally and seasonally. Moreover, stoma ta closed completely at night, in contrast to some other wetland plant s. Both A and g(st) also increased significantly along the length of l eaves from the base of plants to the upper canopy. Finally, although g (st) was quite variable, A did not appear to be limited by g(st) under typical field conditions. It was concluded that generalizations that stomata in wetland plants are relatively unresponsive to environmental factors are not consistent with field responses measured in T. latifo lia. As a result, because g(st) may influence trace gas flux in this s pecies, spatial and temporal variations in g(st) need to be considered when emissions are estimated.