Immobilizing nitrogen to control plant invasion

Abstract

Increased soil N availability may often facilitate plant invasions. Therefore, lowering N availability might reduce these invasions and favor desired species. Here, we review the potential efficacy of several commonly proposed management approaches for lowering N availability to control invasion, including soil C addition, burning, grazing, topsoil removal, and biomass removal, as well as a less frequently proposed management approach for lowering N availability, establishment of plant species adapted to low N availability. We conclude that many of these approaches may be promising for lowering N availability by stimulating N immobilization, even though most are generally ineffective for removing N from ecosystems (excepting topsoil removal). C addition and topsoil removal are the most reliable approaches for lowering N availability, and often favor desired species over invasive species, but are too expensive or destructive, respectively, for most management applications. Less intensive approaches, such as establishing low-N plant species, burning, grazing and biomass removal, are less expensive than C addition and may lower N availability if they favor plant species that are adapted to low N availability, produce high C:N tissue, and thus stimulate N immobilization. Regardless of the method used, lowering N availability sufficiently to reduce invasion will be difficult, particularly in sites with high atmospheric N deposition or agricultural runoff. Therefore, where feasible, the disturbances that result in high N availability should be limited in order to reduce invasions by nitrophilic weeds.

Post-fire erosion control mulches alter belowground processes and nitrate reductase activity of a perennial forb, heartleaf arnica (Arnica cordifolia)

“…This result may have been due to the low mulch application rate (compared to forest fuel mitigation and agricultural applications) and the long delay (4 years) in measurement following mulch application. Microbial immobilization of N in organic amendments is typically highest at high initial C:N and high C:N substrates such as sugar and sawdust are often used to immobilize soil N as part of ecosystem restoration (Paustian et al 1992;Perry et al 2010). Our wheat straw application rate of 2.2 Mg ha -1 is on the lower range of that remaining after agricultural practices (3 to 10 Mg ha -1 ) shown to immobilize soil N (Mary et al 1996); however, it should be pointed out that, unlike surface aerial mulching, previous research on wheat straw amendments involved physical incorporation into the soil, which would have maximized microbial access to C. Thus, the low application rates of the wheat straw or the lack of wheat straw incorporation could have minimized N immobilization.…”

The role of resource limitation in restoration of sagebrush ecosystems dominated by cheatgrass (Bromus tectorum)

“…Restoration experiments that decreased available nitrogen (N) through topsoil removal (Buisson et al 2006, Perry et al 2010, sucrose or other carbon (C) source addition (Morghan and Seastedt 1999, Blumenthal et al 2003, Suding et al 2004, Prober et al 2005, Mazzola et al 2011, and repeated burning (Ojima et al 1994, Blair 1997) reduced invasive species abundance and, in some cases, increased native species establishment , Blumenthal et al 2003, Prober et al 2005. However, reducing available soil N has not decreased the competitive advantage of invasive species in all studies (Corbin and D'Antonio 2004, Huddleston and Young 2005, James et al 2011.…”

Amending Soil with Mulched European Buckthorn (Rhamnus cathartica) Does Not Reduce Reinvasion

“…High carbon:nitrogen (C:N) ratio soil amendments (e.g. mulch, sawdust, and sucrose) can decrease soil N availability by stimulating soil microbial immobilization of N and in doing so, limit reinvasion by aggressive herbaceous plants (Alpert 2010, Perry et al 2010). Whether or not such amendments limit reinvasion by slowergrowing exotic shrubs is unknown (Alpert 2010).…”