Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

David J. Longstreth


This study examined the importance of the leaf aerenchyma gas space as a CO$\sb2$ source for photosynthesis in Typha latifolia L. (broadleaf cattail). In the field there was a distinct diurnal pattern of CO$\sb2$ concentration ( (CO$\sb2$)) in the aerenchyma gas space. At dawn the aerenchyma (CO$\sb2$) was 4 to 18 times above atmospheric levels. By midday the aerenchyma (CO$\sb2$) declined to near atmospheric levels and increased again in the late afternoon. It is hypothesized that this diurnal pattern may be controlled by photosynthetic demand for CO$\sb2$. Aerenchyma gas space was estimated as $>$50% of leaf volume, and the continuity of the aerenchyma gas space through the rhizome-shoot transition was confirmed using tracer dyes. Anatomical examination revealed that the aerenchyma gas space separates the anatomically similar adaxial and abaxial palisades. Each palisade was exposed to two CO$\sb2$ sources: (1) atmospheric CO$\sb2$ diffusing through the epidermal stomata along a gaseous pathway; and (2) aerenchyma gas space CO$\sb2$ diffusing through the cells of the internal surface along an aqueous pathway. Using gas exchange measurements, net photosynthetic CO$\sb2$ uptake rate (P$\sb{\rm N}$) of isolated adaxial and abaxial palisades of intact leaves was 6.0 and 4.0 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, and saturated at a photosynthetic photon flux density of 900 and 700 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, respectively. P$\sb{\rm N}$ response to (CO$\sb2$) was similar for intact leaves and dissected leaves when (CO$\sb2$) in aerenchyma gas space was held constant. At a constant epidermal (CO$\sb2$) of about 350 $\mu$L$\cdot$L$\sp{-1}$, internal P$\sb{\rm N}$ from the aerenchyma gas space increased linearly with (CO$\sb2$) to 1.92 $\mu$mol$\cdot$m$\sp{-2}{\cdot}$s$\sp{-1}$, at about 900 $\mu$L$\cdot$L$\sp{-1}$, the highest (CO$\sb2$) used. Over the same range of aerenchyma gas space (CO$\sb2$) epidermal P$\sb{\rm N}$ declined 69%. These results indicate that CO$\sb2$ can be assimilated from both the atmospheric and aerenchyma gas space CO$\sb2$ sources and that these sources of CO$\sb2$ could be "competitive." Although internal P$\sb{\rm N}$ measured in the laboratory is low, at aerenchyma gas space (CO$\sb2$) s found in the field, internal P$\sb{\rm N}$ could represent a significant carbon source for cattail.