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Invasive plants decrease soil microbial activity compared to native grassland communities

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Chelsea J. Carey*, Joseph C. Blankinship, Valerie T. Eviner, Carolyn M. Malmstrom, Stephen C. Hart. Invasive plants decrease microbial capacity to nitrify and denitrify compared to native California grassland communities.  Biol Invasions DOI 10.1007/s10530-017-1497-y Accepted: 26 June 2017

*Dr. Carey is a Point Blue Senior Soil Scientist

Abstract: Exotic plant invasions are a major driver of global environmental change that can signicantly alter the availability of limiting nutrients such as nitrogen (N). Beginning with European colonization of California, native grasslands were replaced almost entirely by annual exotic grasses, many of which are now so ubiquitous that they are considered part of the regional ora (‘‘naturalized’’). A new wave of invasive plants, such as Aegilops triuncialis (Barb goatgrass) and Elymus caputmedusae (Med usahead), continue to spread throughout the state today. To determine whether these new-wave invasive plants alter soil N dynamics, we measured inorganic N pools , nitrication and deni trication potentials, and possible mediating factors such as microbial biomass and soil pH in experimental grasslands comprised of A. triuncialis and E. caput medusae. We compared these measure-
ments with those from experimental grasslands containing: (1) native annuals and perennials and (2) naturalized exotic annuals. We found that A. triuncialis and E. caputmedusae signicantly reduced ion-exchange resin estimates of nitrate (NO3) availability as well as nitrication and denitrication potentials compared to native communities. Active microbial biomass was also lower in invaded soils. In contrast, potential measurements of nitrication and denitrication were similar between invaded and naturalized communities. These results suggest that invasion by A. triuncialis and E. caputmedusae may signicantly alter the capacity for soil microbial communities to nitrify or denitrify, and by extension alter soil N availability and rates of N transformations during
invasion of remnant native-dominated sites.

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