Schoenoplectus hallii (A.Gray) S.G. Smith is a sedge in the family Cyperaceae that has become a species of concern throughout its range. An obligate of wetland habitats characterized by fluctuating water levels, S. hallii has been described as having a narrow niche. Due to changes in hydrology, areas that once contained populations of the species may no longer offer suitable habitat. Conservation officials agree that a management strategy for S. hallii may be necessary to ensure its continued survival; however, little is known of its physiology, ecology or life history requirements. The primary objective of the current study was to elucidate some of the physiological and environmental factors responsible for the difficulty researchers have encountered in successfully transplanting the species and growing it under controlled conditions. An infra red gas analysis system was used to measure photosynthesis, stomatal conductance and transpiration in response to light and relative humidity. Results indicated that S. hallii has no effective stomatal control in response to vapor pressure deficit; thus, any disturbance of hydraulic conductivity between soil, root and stem during transplantation may result in mortality from excessive water loss.

Key words: photosynthesis, Schoenoplectus hallii, transpiration, wetland species