The use of water in the upper 1 m of the soil profile by 3 common herb
aceous species of the southern Great Plains was examined by labeling s
oil water with (H2O)-H-2 and (H2O)-O-18, Uptake of labeled water from
the 15 cm depth was approximately equal for all species, However, wate
r uptake from the 75 cm depth was significantly greater by annual broo
mweed [Amphiachyris dracunculoides (DC.) Nutt] than either sideoats gr
ams [Bouteloua curtipendula (Michx.) Torr] or curlymesquite [Hilaria b
elangeri (Steud.) Nash]. Although both grasses had greater root length
density than annual broomweed at the 75 cm depth, annual broomweed's
rate of water extraction from the 75 cm depth was nearly twice that of
sideoats grams or curlymesquite, Greater access to and more rapid uti
lization of deeper soil water by annual broomweed relative to the gras
s species may partially explain annual broomweed's success at invading
grasslands and reducing grass production in semi-arid rangelands.