02199nas a2200133   4500008004100000245009200041210006900133300001300202490000700215520169200222100002001914700001701934856011401951       1995                        eng d00aGas exchange characteristics of Typha latifolia L. from nine sites across North America0 aGas exchange characteristics of Typha latifolia L from nine site  a203 -2150 v493 aGas exchange characteristics were measured in the field for nine populations of Typha latifolia L. from Florida to Minnesota in North America. 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 (gst) in T. latifolia populations, as well as to identify key environmental and plant factors that may affect gst and, potentially, trace gas emissions through stomata. Midday rates of net photosynthesis (A) and gst were measured under full sunlight conditions at each site, and more intensive measurements of diurnal and seasonal variability were made at selected sites. In general, A varied less than gst (1.5 vs. 3 fold) among sites with maximum A (27.4 μmol m−2 s−1) and gst (1076.7 mmol m−2 s−1) measured at the southern sites. We found that A and gst in T. latifolia increased significantly with increasing temperature and light level, and varied diurnally and seasonally. Moreover, stomata closed completely at night, in contrast to some other wetland plants. Both A and gst also increased significantly along the length of leaves from the base of plants to the upper canopy. Finally, although gst was quite variable, A did not appear to be limited by gst 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. latifolia. As a result, because gst may influence trace gas flux in this species, spatial and temporal variations in gst need to be considered when emissions are estimated.1 aKnapp, Alan, K.1 aYavitt, J.B.  uhttp://knz.lternet.edu/content/gas-exchange-characteristics-typha-latifolia-l-nine-sites-across-north-america