Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/1995
Publication Date: N/A
Citation: Interpretive Summary: Broom snakeweed is a woody species that is an invader of semiarid grasslands of the Western United States. It reduces grazing potential and can virtually eliminate desirable species. The snakeweed is adapted to the semiarid climate due to the ability of the root systems to successfully compete for water and avoid drought. This study reports that populations of broom snakeweed indigenous to New Mexico, for example, was able to tolerate drought conditions and grow better than the more southern counterparts due to the enhanced ability to more efficiently utilize available water as a result of differences in root architecture. This observed variation plays a key role in our understanding of adaptation to drought and increased survival of these ecotypes.
Technical Abstract: Root growth and hydraulic conductance were studied in four populations of Gutierrezia sarothrae. Seedlings from Malta, Idaho (ID) seed source had four times higher root/shoot ratio (P < 0.05), but only 17% hydraulic conductance of those from Tahoka, Texas (TA) seed source. Consequently, transpiration surface area of the ID seedlings was only 17% that of the TA seedlings. There was no difference in total root length between the seedlings, but hydraulic conductance per unit root length was 3.8 times greater (P < 0.05) in the TA seedlings, which was accompanied by the lower specific lateral root length (P < 0.05), thus greater lateral root diameters. A parallel experiment with adult plants from New Mexico (NM) and Plains, Texas (PL) and the above two populations showed that whole-plant hydraulic conductance was ordered as NM>TA=PL>ID. The NM population had similar transpiration surface area and total root length as the TA population, but a greater lateral root biomass (P < 0.005) than the latter Because of higher hydraulic conductance in the NM population, its xylem water potential declined more slowly than the Texas populations as soil moisture deficit developed. Stem hydraulic conductance was positively correlated with xylem water potential. Therefore, the NM population was able to maintain a higher stem conductance during drought which was associated with its higher whole-plant hydraulic conductance and greater carbon partitioning in the stems. The drought avoidance mechanism in the NM plants was characterized by an efficient water transport system due to greater lateral root biomass and more stems per unit leaf area.