Changes in water relations for leaves exposed to a climate-warming manipulation in the Rocky Mountains of Colorado

Relative water content (RWC) and water potential were compared for leaves of several plant species exposed to a warming manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, Colorado, USA, to test the hypothesis that species-specific changes in water relations parameters will occur in response to future increases in planetary air temperatures. Leaves of Artemisia tridentata, Erigeron speciosus, Festuca thurberi, Helianthella quinquinervis, Potentilla fruticosa, Potentilla gracilis and Rhodiola integrifolia were collected from plants growing in situ in control and infrared (IR)-heated (22 W m(-2)) plots in a meadow near the upper elevational distribution limit for A. tridentata. For six of the seven herbaceous species, RWC was not significantly different from that for A. tridentata (0.903+/-0.019 on control plots and 0.846+/-0.031 from heated plots). However, RWC was 0.644+/-0.04 and 0.596+/-0.029 for F. thurberi on control and heated plots, respectively. Water potential (Psi) varied from -1.04 MPa for A. tridentata (control plots) to -4.83 MPa for leaves of F. thurberi (heated plots); Psi for the other species ranged from -1.08 MPa (R. integrifolia on control plots) to -2.62 MPa (P. gracilis on heated plots). To characterize further the responses of water relations parameters to the IR heating treatment, pressure-volume isotherms were generated for A. tridentata and P. gracilis. Both species exhibited effects of the IR heating treatment on saturated osmotic potential and the relative symplastic water content. Based on changes in osmotic potential and relative water content, an increase in osmotically active solutes was exhibited for leaves collected from plants under heaters. Species-specific patterns of RWC and water potential (as well as effects on cellular water relations) may influence the ability of plant species to cope with changes in soil water content that are expected to occur with global warming for montane ecosystems in the western USA. (C) 1997 Elsevier Science B.V.