High carbon dioxide concentrations in Aerenchyma of Typha latifolia

Diurnal and seasonal patterns of CO2 concentration ([CO]) in leaf gas spaces were measured to better understand the relationship of sediment-derived CO2 to photosynthesis in the emergent wetland species, Typha latifolia L. (cattail). Leaf [C02] was above 2,000 Al/liter at dawn on all but the first sampling date. At all sampling dates, leaf [CO2] declined to near atmospheric [C02] at midday and rose to well above atmospheric [C02] in the late afternoon. The maximum leaf [C02] varied with sampling date and was over 18 times atmospheric levels (over 6,300 ,ul/liter) in August. Based on measurement ofphoton flux density and temperature, the diurnal pattern in leaf [C02] may be generally controlled by expected photosynthetic rates. It is hypothesized that seasonal variation in leaf [C02] may be a function of variation in microbial (soil) respiration. Using dye and slight pressurization, it was confirmed that gas spaces in rhizomes were interconnected with the gas spaces in leaves through the rhizome-shoot transition. From anatomical measurements, it was also estimated that over 50% of total leaf volume was occupied by gas spaces and that most of the total gas-space volume in plants was in the shoot. Photosynthetic rate in C3 plants, like cattail, can increase with increasing [C02] under natural conditions. For this reason, cattail and other emergent wetland plants possessing continuous gas-space pathways appear to have a significant carbon supplement as compared to other C3 plants growing in well-aerated soils. The purpose of this study was to determine the diurnal and seasonal patterns of CO2 concentration ([C02]) in leaf gas spaces for the common wetland emergent, Typha la