The influences of seasonal precipitation on root and canopy development of broom snakeweed (gutierrezia sarothrae)



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Texas Tech University


Broom snakeweed (Gutierrezia sarothrae) is a widespread suffrutescent shrub in large areas of the semiarid rangeland of the western U. S., southern Canada, and northern Mexico. It is considered a major weed problem in the southwestern U.S. It causes poisoning to grazing and browsing animals and competes with desirable species, especially warm season grasses, essentially eliminating them from the plant community. Its population fluctuates according to localized or regional weather patterns. If soil water is adequate in the fall and winter, snakeweed will remain evergreen and use much of the available soil water during the period when warm season grasses are dormant. In the early spring when grasses start growing, snakeweed has a distinct competitive advantage over grasses because of its above- and below-ground biomass.

A field experiment was conducted over two years to study the effect of seasonal precipitation on shallow and deep roots, and canopy development of snakeweed. Plant roots and canopy development were measured in the summer, fall, and spring. Soil water conditions during the spring-summer and fall-winter seasons significantly affected root growth of snakeweed in both shallow and deep soil. While wet springs and summers enhanced both shallow and deep root growth, dry conditions during the spring and summer resulted in the least amount of root growth in both shallow and deep soil. A dry fall and winter following a wet spring and summer reduced root growth and resulted in suberization of other roots. A wet fall and winter following a dry spring and summer enhanced root growth in both shallow and deep soil, but root growth in the deep soil was enhanced more than root growth in shallow soil. Plants irrigated during the fall and winter had the greatest root length density in the deeper soil (30-90 cm) at the end of winter.