Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/1997
Publication Date: N/A
Interpretive Summary: Broom snakeweed (Gutierrezia sarothrae) is a perennial shrub species occurring in arid and semiarid rangelands of the western U.S., northern Mexico, and southern Canada. It is a common neighbor of grasses and reduces grass production through competition for water and nutrients. Studies were conducted to determine if genetic differences in water use and root development between plants native to northern (Idaho) and southern (Texas) climates were environmentally controlled. The results indicated that when the environmental demand was increased (more stressful environment), the Texas populations grew longer and more lateral roots and water use increased indicating that the southern populations were better adapted to environmental stress than the northern populations. These differences may help to explain the aggressive encroachment of these plants onto the southwestern rangelands.
Technical Abstract: We hypothesize that genotypic differences in transpiration and root growth in the southern and northern populations of Gutierrezia sarothrae are driven by growing season vapor pressure deficit (VPD), and these ecotypic differentiations are linked to corresponding variations in tissue- and leaf-water relations. Seedlings from Idaho (ID) and Texas (TX) seed sources were grown either in an open nursery or under a shade. There were no population differences in transpiration, root growth and tissue water relation parameters when the plants were grown under the shade. However, significant population differences were observed in the plants grown in the open where VPD was substantially higher. Transpiration in the TX population increased twice as rapidly as the ID population in response to rising potential evapotranspiration (PET). Total root length and root/shoot ratio were greater (P<0.05) in the plants grown in the open than those grown under the shade in both populations. In addition, the TX plants grew longer and larger lateral roots than the ID plants when both populations were grown in the open. Moreover, the TX plants had more elastic cell walls (lower bulk cell elastic modulus, E), and were able to maintain leaf turgor at lower relative water content than the ID plants when grown in the open. Higher photosynthetic water use efficiency (WUE) and higher apoplastic water fraction in the ID population reflected conservative water use at the leaf and tissue levels, which was consistent with the water use pattern at the canopy level.