Ecophysiological comparison of 50-year-old longleaf pine, slash pine and loblolly pine

Abstract

Longleaf pine (Pinus palustris Mill.), a species that once dominated the southeastern USA, is considered to be more drought tolerant than the principle plantation species in the South, loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.), and so is predicted to better cope with increases in drought frequency associated with climate change. To determine if longleaf pine displays a more conservative water use strategy than the other two southern pine species, we examined diurnal patterns in leaf light-saturated photosynthesis, stomatal conductance, water use efficiency and leaf water potential (ΨL) over one growing season in a 50-year-old replicated field experiment. Short-term photosynthetic response to temperature was examined in August. No consistent differences among species in leaf gas exchange rates were observed, but ΨL was higher in longleaf pine compared to loblolly and slash pine across the growing season. Foliar δ13C measured at the end of the growing season was higher in longleaf pine than in loblolly pine but not slash pine. No temperature optimum of photosynthesis was observed in any species and photosynthesis did not respond to changing temperature. Based on leaf physiological traits, these results do not support the contention that longleaf pine has a more conservative leaf water use strategy than the other two pine species. The results do suggest that differences in hydraulic architecture or hydraulic efficiency may account for higher ΨL and perhaps greater drought tolerance in longleaf pine.