Nitrogen uptake and preference in a forest understory following invasion by an exotic grass

Abstract

Plant-soil interactions have been proposed as a causative mechanism explaining how invasive plant species impact ecosystem processes. We evaluate whether an invasive plant influences plant and soil-microbe acquisition of nitrogen to elucidate the mechanistic pathways by which invaders might alter N availability. Using a (15)N tracer, we quantify differences in nitrogen uptake and allocation in communities with and without Microstegium vimineum, a shade-tolerant, C(4) grass that is rapidly invading the understories of eastern US deciduous forests. We further investigate if plants or the microbial biomass exhibit preferences for certain nitrogen forms (glycine, nitrate, and ammonium) to gain insight into nitrogen partitioning in invaded communities. Understory native plants and M. vimineum took up similar amounts of added nitrogen but allocated it differently, with native plants allocating primarily to roots and M. vimineum allocating most nitrogen to shoots. Plant nitrogen uptake was higher in invaded communities due primarily to the increase in understory biomass when M. vimineum was present, but for the microbial biomass, nitrogen uptake did not vary with invasion status. This translated to a significant reduction (P < 0.001) in the ratio of microbial biomass to plant biomass nitrogen uptake, which suggests that, although the demand for nitrogen has intensified, microbes continue to be effective nitrogen competitors. The microbial biomass exhibited a strong preference for ammonium over glycine and nitrate, regardless of invasion status. By comparison, native plants showed no nitrogen preferences and M. vimineum preferred inorganic nitrogen species. We interpret our findings as evidence that invasion by M. vimineum leads to changes in the partitioning of nitrogen above and belowground in forest understories, and to decreases in the microbial biomass, but it does not affect the outcome of plant-microbe-nitrogen interactions, possibly due to functional shifts in the microbial community as a result of invasion.

Grass invasion effects on forest soil carbon depend on landscape‐level land use patterns

“…However, like others (Strickland et al 2010, Kramer et al 2012, we found that microbial biomass (but not microbial activity) was lower under M. vimineum. Previous work suggests that M. vimineum can enhance plot-level N demand by sequestering N in aboveground biomass (Fraterrigo et al 2011). Previous work suggests that M. vimineum can enhance plot-level N demand by sequestering N in aboveground biomass (Fraterrigo et al 2011).…”

Local‐scale biotic interactions embedded in macroscale climate drivers suggest Eltonian noise hypothesis distribution patterns for an invasive grass

“…; Fraterrigo et al . ), and evidence suggests that other plants can benefit from this increased N availability (Fraterrigo et al . ).…”

Predicting Microstegium vimineum invasion in natural plant communities of the southern Blue Ridge Mountains, USA

“…At broader scales, such as examined in this study (plots C100 m 2 ), the high levels of resource heterogeneity due to topography, vegetation, light, and edaphic conditions should be conducive for a shade-tolerant invasive . Indeed, when M. vimineum invades and is able to achieve dominance, it may reduce native richness (Adams and Engelhardt 2009;Flory and Clay 2010;Hejda et al 2009), and alter soil chemistry and arthropod communities (Fraterrigo et al 2011;McGrath and Binkley 2009;Simao et al 2010). Consequently, some high diversity plant communities in this region could be jeopardized by detrimental impacts of M. vimineum invasions (Barden 1987;Brewer 2011;Cole and Weltzin 2004;Ehrenfeld et al 2001).…”

“…M. vimineum is highly shade tolerant (Winter et al 1982) but can establish in both sunny and shady areas (Cheplick 2010) and both disturbed and undisturbed habitats (Huebner 2010a;Martin et al 2009). Once established, it can become the dominant herbaceous species in invaded areas (Barden 1987;Cole and Weltzin 2005;Redman 2008), altering community composition (Barden 1987;Fairbrothers and Gray 1972), suppressing forest succession Clay 2006, 2010), and changing ecosystem processes (Ehrenfeld et al 2001;Fraterrigo et al 2011;Kourtev et al 1998;Strickland et al 2011). M. vimineum is a prolific seeder (Cheplick and Fox 2011), but seed production is reduced in deep shade relative to high-light environments (Huebner 2010a).…”