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Lespedeza cuneata is a non-native invasive legume that alters the soil bacterial community, associates promiscuously with rhizobia, and benefits more from rhizobial interactions compared to coexisting native Lespedeza in North America. We tested the hypothesis that native congeners differ in their nodule bacteria associations compared to L. cuneata. Plots with high L. cuneata invasion, low L. cuneata invasion with native Lespedeza species present, and uninvaded plots where native Lespedeza species existed without L. cuneata were sampled. Nodules were collected from all Lespedeza species present, and Chamaecrista fasciculata, a common native annual legume. Bacterial DNA from nodules was isolated and sequenced. Nodule bacterial composition differed significantly between hosts. L. cuneata nodules contained high frequencies of rhizobial DNA and low bacterial diversity, while native Lespedeza nodules contained lower rhizobial frequencies and higher non-rhizobial bacterial diversity. Specific non-rhizobial bacterial groups exhibited strong associations with native legumes and uninvaded sites. Significant differences exist in the nodule bacterial composition between native legumes and an introduced congener. The mechanism(s) and ecological importance of these differences remain unknown. These differences in bacterial associations could influence not only the competitive ability of the invader, but recovery of invaded sites as well.

Lespedeza cuneata is an introduced legume that is invasive in the tallgrass prairie system and open woodlands of North America. This system includes native Lespedeza species that coexist with L. cuneata, including L. capitata and L. virginica. Previous research has indicated that L. cuneata exudates have profound influences on soil biological functions. The goal of this current research was to identify and then compare exudate chemicals from L. cuneata, L. capitata, L. virginica, and common tallgrass prairie grasses. Exudates from Lespedeza species were found to be distinct from the grasses. In particular, L. cuneata and, to a lesser extent, a subset of L. virginica could be differentiated based on the presence of five unique compounds. Two low molecular weight compounds were identified via gas chromatography/mass spectrometry (GC/MS) and tentatively identified as benzophenone and 1,4-diacetylbenzene. Three higher molecular weight compounds were identified by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS), with possible relationships to a 3 sterol, phosphatidylglycerol, and the 19-nor analogues of vitamin D. The relative abundance of these compounds were found to be greater in the invasive species, L. cuneata, than in the native noninvasive species, L. virginica. These results are an integral step in further understanding through chemical exudation how L. cuneata can be benefiting from greater rhizobial associations.

Arbuscular mycorrhizal fungi (AMF) have been implicated in non-native plant invasion success and persistence. However, few studies have identified the AMF species associating directly with plant invaders, or how these associations differ from those of native plant species. Identifying changes to the AMF community due to plant invasion could yield key plant-AMF interactions necessary for the restoration of native plant communities. This research compared AMF associating with coexisting Bromus tectorum, an invasive annual grass, and Artemisia tridentata, the dominant native shrub in western North America. At three sites, soil and root samples from Bromus and Artemisia were collected. Sporulation was induced using trap cultures, and spores were identified using morphological characteristics. DNA was extracted from root and soil subsamples and amplified. Sequences obtained were aligned and analyzed to compare diversity, composition, and phylogenetic distance between hosts and sites. Richness of AMF species associated with Artemisia in cultures was higher than AMF species associated with Bromus. Gamma diversity was similar and beta diversity was higher in AMF associated with Bromus compared to Artemisia. AMF community composition differed between hosts in both cultures and roots. Two AMF species (Archaeospora trappei and Viscospora viscosum) associated more frequently with Artemisia than Bromus across multiple sites. AMF communities in Bromus roots were more phylogenetically dispersed than in Artemisia roots, indicating a greater competition for resources within the invasive grass. Bromus associated with an AMF community that differed from Artemisia in a number of ways, and these changes could restrict native plant establishment.

Arbuscular mycorrhizal fungi (AMF) are an important driver of plant community assembly, and as such may be critical for restoring plant communities. Previous work has shown that as plant communities develop, AMF density is a good predictor of what type of plant community is supported. However, interactions between plants, particularly facultative hosts, and AMF are often assumed from plant growth responses and lack concomitant AMF growth response data. We examined both plant and AMF responses in association using early- and mid-seral plant hosts and a homogenous AMF community. The goal was to determine how variable interactions are between facultative plant hosts and an AMF community. Plant responsiveness was measured using field soil with and without AMF. AMF density was measured by observing root colonization by AMF in a bioassay host plant grown in soils trained by the individual host plant species used in the plant responsiveness study. Plant species studied were highly variable in their interactions with AMF, and mutualisms, parasitisms, amensalisms and commensalisms were all prevalent. The presence of certain AMF facilitators may have a strong founder effect on plant communities and, where such feedbacks exist, identifying and utilizing these key interactions might facilitate the restoration of degraded ecosystems.

Non-native species are hypothesized to decrease native species establishment and cover crops are hypothesized to decrease non-native species abundance. Although many studies have compared invaded to non-invaded habitats, relatively few studies have experimentally added non-native species to directly examine their effects. In a greenhouse mesocosm experiment, we tested the effects of non-native forbs (Melilotus officinalis, Verbascum thapsus, and Lespedeza cuneata), a proposed C3 grass cover crop (Pascopyrum smithii), and a commonly seeded non-native C3 grass (Bromus inermis) on the establishment of target native C4 prairie grass species. All treatments contained the same seed density of target C4 species and were begun on bare soil collected from the field. The legume M. officinalis strongly decreased the abundance of all other species, species diversity, and light and soil moisture levels. Surprisingly, M. officinalis took up relatively large amounts of labeled nitrogen (15N) from the soil early in its development, but M. officinalis fixed nitrogen, thus increasing nitrogen in biomass nearly fivefold by the end of the study. We found few effects of either C3 grass species on non-native forbs or C4 target species, but seeded P. smithii did increase species diversity. Non-native plants therefore impeded native C4 grass establishment through long-lasting effects of target species seedbank depletion (death of most target seedlings) and altered nutrient availability. The effects of M. officinalis were not reduced by the presence of a cover crop.

The spatial scale on which microbial communities respond to plant invasions may provide important clues as to the nature of potential invader-microbe interactions. Lespedeza cuneata (Dum. Cours.) G. Don is an invasive legume that may benefit from associations with mycorrhizal fungi; however, it has also been suggested that the plant is allelopathetic and may alter the soil chemistry of invaded sites through secondary metabolites in its root exudates or litter. Thus, L. cuneata invasion may interact with soil microorganisms on a variety of scales. We investigated L. cuneata-related changes to soil bacterial and fungal communities at two spatial scales using multiple sites from across its invaded N. American range. Using whole community DNA fingerprinting, we characterized microbial community variation at the scale of entire invaded sites and at the scale of individual plants. Based on permutational multivariate analysis of variance, soil bacterial communities in heavily invaded sites were significantly different from those of uninvaded sites, but bacteria did not show any evidence of responding at very local scales around individual plants. In contrast, soil fungi did not change significantly at the scale of entire sites, but there were significant differences between fungal communities of native versus exotic plants within particular sites. The differential scaling of bacterial and fungal responses indicates that L. cuneata interacts differently with soil bacteria and soil fungi, and these microorganisms may play very different roles in the invasion process of this plant.

Background and Aims Lespedeza cuneata (Dum. Cours.) G. Don is an invasive legume that displaces populations of native N. American congeners. Our aims are to determine the growth benefits of different rhizobacterial strains for L. cuneata and native Lespedeza virginica (L.) Britton, and to determine if these strains influence competition between these plants.