PARENT SESSION
Oral Session #39: Invasions: Effects of invaders -- Aquatic, marsh, riparian. Presiding: C. Kolar.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Madison Ballroom C.

Seasonal water-use and gas exchange patterns of an invasive exotic tree in a saline environment.

Ewe, Sharon¹, Sternberg, Leonel¹, ¹

ABSTRACT- Plant water uptake and gas exchange were measured in two coastal plant communities of southwest Florida to determine any physiological differences between the invasive exotic, Schinus terebinthifolius (hereafter Schinus), and native species within a brackish transition zone and an upland pineland. We measured groundwater salinity, soilwater content, predawn water potentials (PDWP), stemwater Na:K ratios, leaf-level gas exchange, stem and soilwater oxygen stable isotope ratios (¹⁸O), and leaf carbon stable isotopes (¹³C) at the end of the wet and dry seasons. Belowground salinity and unsaturated soilwater content at the transition zone site was spatially and seasonally heterogeneous. At both sites, PDWP of Schinus was not seasonally different, unlike that of native species. During the dry season, Schinus Na:K ratios were comparable to that of the mangrove species; however, Schinus gas exchange in the transition zone was the most severely curtailed of all species measured during this period. Unfortunately, stemwater ¹⁸O values could not be used to determine each species' precise source of water. Integrated water-use efficiency of Schinus, based on ¹³C, was not significantly different over season or site compared to that of native species. The presence of Schinus in the coastal communities of south Florida is probably in part due to its ability to persist in saline environments, despite limited gas exchange.

KEY WORDS: invasive, salinity, water-use, assimilation