| A descriptive eco-physiological investigation was conducted on Gutierrezia sarothrae, a competitive and poisonous half shrub, to describe the species' position in the ecosystem of southern New Mexico, in the northern regions of the Chihuahuan Desert. Little rudimentary physiological knowledge was available on G. sarothrae growing in southern New Mexico. This research fills this discrepancy by reporting on plant data collected over more than two years. Data were collected on (1) phenological development of G. sarothrae, (2) photosynthetic capacity and carbon gain of the plant, (3) plant-water relations in comparison with Atriplex canescens, and (4) canopy architecture. The highest growth rates and photosynthetic activity in plants was seen in spring, which coincides with early spring regrowth after winter dormancy. Photosynthesis rates approached 13 {dollar}mu{dollar}moles m{dollar}sp{lcub}-2{rcub}{dollar}s{dollar}sp{lcub}-1{rcub}{dollar}in April, which was determined to be high enough to compensate for spring regrowth, within 14 days. Due to this high photosynthetic activity, plants attain rapid seasonal physiological maturity, allowing G. sarothrae to out-compete associated species during this period, monopolizing the already scarce resources such as soil water and nutrients.; Because of its rather shallow, but extensive root system, G. sarothrae is able to use relatively small rainfall events, as evidenced by its highly fluctuating xylem water potential (pre-dawn {dollar}Psi{dollar} ranged from {dollar}-{dollar}0.5 to {dollar}-{dollar}3.5 MPa), compared to A. canescens which had a more stable xylem water potential (pre-dawn {dollar}Psi{dollar} ranged from {dollar}-{dollar}0.6 to {dollar}-{dollar}2.0 MPa).; In order to determine if allelopathy may play a role in G. sarothrae's dominance in many communities, a greenhouse trial was set up to test for phytotoxic properties of fresh leaves, dead leaves from G. sarothrae, and soil from underneath G. sarothrae plants. These residues were added to mature grass plants to determine any growth altering effects before and after clipping (simulated grazing). Grass species used were Sporobolus airoides, Bouteloua gracilis and Bouteloua curtipendula. Residues from G. sarothrae did not have detectible effects on S. airoides, but significantly altered the growth characteristics of the two Bouteloua species. This research offers some insight into the characteristics that allow Gutierrezia sarothrae to dominate some undisturbed native conditions. |
