Effects of Nitrogen Availability and Cheatgrass Competition on the Establishment of Vavilov Siberian Wheatgrass

Abstract

Cheatgrass (Bromus tectorum L.) is the most widespread invasive weed in sagebrush ecosystems of North America. Restoration of perennial vegetation is difficult and land managers have often used introduced bunchgrasses to restore degraded sagebrush communities. Our objective was to evaluate the potential of 'Vavilov' Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy) to establish on cheatgrass-dominated sites. We examined Vavilov establishment in response to different levels of soil nitrogen availability by adding sucrose to the soil to promote nitrogen (N) immobilization and examined cheatgrass competition by seeding different levels of cheatgrass. We used a blocked split-split plot design with two sucrose levels (0 and 360 g ? m 22), two levels of Vavilov (0 and 300 seeds ? m 22), and five levels of cheatgrass (0, 150, 300, 600, and 1 200 seeds ? m 22). Seeding was conducted in fall 2003 and 2004, and measurements were taken in June 2004, 2005, and 2006. Sucrose addition decreased availability of soil nitrate but not orthophosphate. In the first year after seeding, sucrose reduced cheatgrass density by 35% and decreased both cheatgrass biomass per square meter and seed production per square meter by 67%. These effects were temporary, and by the second year after seeding, there was a sevenfold increase in cheatgrass density. As a result, the effects of sucrose addition were no longer significant. Sucrose affected Vavilov growth, but not density, during the first year after seeding. Vavilov density decreased as cheatgrass seeding density increased. Short-term reductions in N or cheatgrass seed supply did not have long-term effects on cheatgrass and did not increase Vavilov establishment. Longer-term reductions in soil N, higher seeding densities, or more competitive plant materials are necessary to revegetate areas dominated by cheatgrass.

Managing soil nitrogen to restore annual grass-infested plant communities: effective strategy or incomplete framework?

“…In restoration scenarios in which annual and perennial grasses are interacting as seedlings, our analyses indicate that soil N management alone will not directly facilitate establishment of native perennial grasses in terms of growth and initial competitive ability. While this conclusion is supported by a number of studies showing that soil N management failed to facilitate restoration of systems dominated by invasive plants (e.g., Corbin and D'Antonio 2004, Huddleston and Young 2005, Mazzola et al 2008, other studies have demonstrated that soil N management facilitates restoration of systems infested by a range of invasive plants (e.g., Alpert and Maron 2000, Paschke et al 2000, Prober et al 2005. A critical question to answer then is can we use results from this analysis to provide insight into these discrepancies and improve our ability to understand the conditions allowing soil N management to facilitate restoration of annual grass-infested systems?…”

“…While these studies did not identify mechanisms associated with species replacement, these results were attributed largely to an overall lower N requirement of perennial grasses or to changes in competitive relationships among species as N availability declined. On the other hand, carbon addition to coastal and interior grasslands, as well as sagebrush steppe communities in North America, lowered soil N availability but did not facilitate reestablishment of perennial grasses (Corbin and D'Antonio 2004, Huddleston and Young 2005, Mazzola et al 2008. Therefore, while the positive relationship between increased soil N availability and annual grass invasion is well demonstrated, it is not clear that lowering soil N necessarily will allow perennial grasses to reestablish in annual grass-dominated systems.…”

“…These trait differences have led to the suggestion that managing soils for low N availability will facilitate reestablishment of native perennial grasses in annual grass-dominated systems Manuscript (Krueger-Mangold et al 2006, Vasquez et al 2008b, Brunson et al 2010. Although soil N management is increasingly being presented as a key management strategy for large-scale restoration efforts and invasive plant management programs, (e.g., Prober et al 2005, Krueger-Mangold et al 2006, Mazzola et al 2008 there has been no quantitative synthesis evaluating the degree to which soil N management differentially impacts growth and competitive ability of annual and perennial grasses. Such insight is critical to improving prediction of when soil N management will facilitate perennial grass reestablishment in annual grass-dominated ecosystems.…”

Cheatgrass Invasion - The Below-Ground Connection

“…The interactions described above may help to understand the continued success of cheatgrass as well as challenges encountered with rehabilitation projects targeting B. tectorum invaded sites. Approaches to rehabilitate areas invaded by cheatgrass and other invasives have included the addition of carbon in the form of sugar, straw, sawdust, mulch, biochar or activated charcoal (Beckstead & Augspurger, 2004;Kulmatiski, 2011;Mazzola et al, 2008;Ohsowski et al, 2012, Paschke et al, 2000. The idea behind these applications is that added carbon immobilizes nitrogen in soil bacteria by increasing the C/N ratio (Perry et al, 2010).…”

“…The idea behind these applications is that added carbon immobilizes nitrogen in soil bacteria by increasing the C/N ratio (Perry et al, 2010). This approach, though, has not always been successful in long-term restoration of native or non-native perennials and studies using woodchips from masticated pinyon-juniper woodland even resulted in increased B. tectorum cover (Mazzola et al, 2008;Owen et al 2009). The timing of carbon applications is crucial since nitrogen accumulated in soil microbes can be released by freeze-thaw or wet-dry cycles resulting in nutrient flushes that, if superimposed on cheatgrass active growth periods, could foster the growth of this invasive instead of decreasing it.…”