WATER ACQUISITION AND ROOTING CHARACTERISTICS IN NORTHERN AND SOUTHERN-POPULATIONS OF GUTIERREZIA-SAROTHRAE

Seeds from northern (Idaho) and southern (New Mexico and Texas) popula tions of broom snakeweed (Gutierrezia sarothrae) were germinated in a greenhouse and the seedlings grown in a soil mixture in 30-cm deep (19 -1) plastic pots for 50 days. The pots were then fastened onto the top of similar pots and the seedling root systems were allowed to grow in to the lower pots for 4 weeks through punctures in the bottoms of the upper pots. Soil water extraction from four different depths was measu red using time domain reflectometry (TDR) 2 weeks after roots had begu n to grow into the lower pots. The two New Mexico populations (Jornada and Mountainair) and a population from Plains, Texas extracted more w ater from deeper (greater than or equal to 38 cm) soil layers than the Idaho population (P < 0.05). Root length in the deeper soil layers (5 5-60 cm) was greater (P < 0.05) for the Jornada desert population than for the Idaho and Mountainair populations. The Plains population had shorter roots and extracted less water in the upper soil layers than t he other populations (P < 0.05). Specific root length in the Idaho pop ulation was at least 67% greater (P < 0.01) than those in southern pop ulations, indicating smaller root diameters. The patterns of soil wate r extraction and root penetration were correlated with the seasonal di stribution of precipitation in the plants' natural habitats. The Idaho seedlings had roots confined primarily to the topsoil to secure water from spring precipitation. In contrast, some southern seedlings were able to develop an extensive deep root system to avoid spring drought.