Author
|
Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/1/2015 Publication Date: 1/19/2015 Citation: Blank, R.R., Morgan, T.A., Allen, F.L. 2015. Suppression of annual Bromus tectorum by perennial Agropyon cristatum: roles of soil N availability and biological soil space. AoB Plants. 7:plv006. doi: 10.1093/abpia/plv006. Interpretive Summary: Rangelands of the western United States have been and are being degraded through invasion by the annual grass Bromus tectorum. Rehabilitation of degraded rangelands is predicated on establishing healthy and dense perennial grass communities, which suppress B. tectorum. We report on experiments to increase our understanding of soil factors involved in suppression. Established Agropyron cristatum greatly reduced the growth of B. tectorum. Suppression of B. tectorum was lost when soil was separated from growing A. cristatum. Soil that suppressed B. tectorum growth was characterized by low mineral N availability and a high molar ratio of NO2- in the solution-phase pool of NO2- + NO3-. Moreover, resin availability of NO2- + NO3- explained 66 % of the variability in B. tectorum above-ground mass, attesting to the importance of A. cristatum growth in reducing N availability to B. tectorum. Trials in which B. tectorum was suppressed the most were characterized by very high shoot/root mass ratios and roots that have less root hair growth relative to non-suppressed counterparts, suggesting co-opting of biological soil space by the perennial grass as another suppressive mechanism. Greater understanding of the role of biological soil space could be used to breed and select plant materials with traits that are more suppressive to invasive annual grasses. Technical Abstract: Worldwide, exotic invasive grasses have caused numerous ecosystem perturbations. Rangelands of the western United States have experienced increases in the size and frequency of wildfires largely due to invasion by the annual grass Bromus tectorum. Rehabilitation of invaded rangelands is difficult; but long-term success is predicated on establishing healthy and dense perennial grass communities, which suppress B. tectorum. This paper reports on two experiments to increase our understanding of soil factors involved in suppression. Water was not limiting in this study. Growth of B. tectorum in soil conditioned by and competing with the exotic perennial Agropyron cristatum, was far less relative to its growth without competition. When competing with A. cristatum, replacing a portion of conditioned soil with fresh soil before sowing of B. tectorum did not significantly increase its growth. The ability of conditioned soil to suppress B. tectorum was lost when it was separated from growing A. cristatum. Soil that suppressed B. tectorum growth was characterized by low mineral N availability and a high molar ratio of NO2- in the solution-phase pool of NO2- + NO3-. Moreover, resin availability of NO2- + NO3- explained 66 % of the variability in B. tectorum above-ground mass, attesting to the importance of A. cristatum growth in reducing N availability to B. tectorum. Trials in which B. tectorum was suppressed the most were characterized by very high shoot/root mass ratios and roots that have less root hair growth relative to non-suppressed counterparts, suggesting co-opting of biological soil space by the perennial grass as another suppressive mechanism. Greater understanding of the role of biological soil space could be used to breed and select plant materials with traits that are more suppressive to invasive annual grasses. |
