Ryan R. Busby

Soil bacteria and fungi respond on different spatial scales to invasion by the legume Lespedeza cuneata

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 allelopathic 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.

Melilotus officinalis (yellow sweetclover) causes large changes in community and ecosystem processes in both the presence and absence of a cover crop

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.

Native Lespedeza species harbor greater non-rhizobial bacterial diversity in root nodules compared to the coexisting invader, L. cuneata

Background and AimsLespedeza 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.MethodsPlots 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.ResultsNodule 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.ConclusionsSignificant 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.

Invasive Lespedeza cuneata and native Lespedeza virginica experience asymmetrical benefits from rhizobial symbionts.

Background and AimsLespedeza 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.MethodsPlants were grown under nitrogen-limiting conditions in sterilized soil in pairs consisting of two L. cuneata, two L. virginica, or one of each species, and then plants were inoculated with one of seven rhizobial isolates, or with a no-strain control. After 3xa0months, plants were harvested for determination of biomass and nodulation rate.ResultsFive of the assayed stains improved L. cuneata biomass over uninoculated controls, but none of the strains benefited L. virginica. L. cuneata plants had more biomass and root nodules when grown in competition with L. virginica than with a conspecific.ConclusionsAsymmetrical benefits from these symbionts accrued to invasive L. cuneata but not to native L. virginica, and this may provide the invader with a growth advantage in the field. Changes in the availability of effective symbionts in the soils of invaded sites can shape performance of native and invasive plants.

Non-Composted Municipal Solid Waste Processing Byproduct Effect on Soil Reclamation

ABSTRACT A new garbage processing technology has been developed that sterilizes and separates inorganic and organic components of municipal solid waste. The non-composted byproduct of this process, Fluff®, has the potential to be utilized as a soil amendment to improve soil conditions in highly degraded soils. A study was initiated to evaluate Fluff as a soil amendment for establishing native grasses on disturbed US Army training lands. The Fluff was incorporated into a sandy loam soil at Fort Benning Military Reservation, GA on two sites: a moderately degraded and a highly degraded soil. The Fluff was incorporated at rates of 0, 18, 36, 72, and 143 Mg ha− 1 to assess the effects on soil properties for two growing seasons. The addition of Fluff improved available plant nutrients and soil pH levels at both sites. Also, Fluff reduced the level of soil bulk density and increased soil concentration of carbon (C) and nitrogen (N). Because no adverse environmental effects were detected and Fluff improved soil physical and nutrient conditions as well as improving perennial grass establishment with increasing application rates, land application of Fluff to degraded US Army training grounds could be considered a viable and beneficial alternative to current waste management practices.

Flavonoids Differentially Influence Rhizosphere Bacterial Communities from Native and Introduced Lespedeza Roots

Military training can create disturbances that facilitate invasive plant establishment. Introduced plant species’ interactions with soil microbial communities through root exudates often aid plants in colonizing new locales. This study tested the hypothesis that rhizosphere bacterial communities associated with the native legume, Lespedeza virginica, and the non-native legume, Lespedeza cuneata, respond differently to plant-exuded molecules. Bacterial communities collected from coexisting populations of the two species were grown in the presence of four separate flavonoids at four concentrations. Following 96 hours of incubation, DNA was recovered from the enrichment cultures and analyzed using next-generation sequencing. In cultures receiving a flavonoid, L. virginica enrichments were characterized by a greater operational taxonomic unit (OTU) richness and exhibited a dose-response relationship to one of the flavonoids. The L. cuneata enrichments were characterized by a decreased OTU richness. Bacterial genera containing known pathogenic taxa occurred at a significantly greater relative frequency in L. cuneata enrichments than in the L. virginica enrichments. However, calculation of a species diversity index indicated greater OTU diversity in the L. cuneata enrichments across all four flavonoid treatments. These results indicate the rhizosphere microbial communities of co-existing L. cuneata and L. virginica legumes exhibit different responses when exposed to plant communication molecules. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.

Exudate chemical profiles derived from Lespedeza and other tallgrass prairie plant species

Abstract : 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.

Effects of a New Waste-Processing By-product on Soil and Vegetation at Fort Campbell, Tennessee

A garbage‐processing technology has been developed that sterilizes and separates inorganic and organic components of municipal solid waste. A study was initiated to evaluate the uncomposted organic by‐product of this process as a soil amendment for establishing native prairie grasses on disturbed Army training lands. The waste was incorporated into a silt loam soil at Fort Campbell Military Reservation in the central United States. The waste material was applied at rates of 0, 4.5, 9, 18, and 36 Mg ha−1 and seeded with native prairie grasses to assess its effects on vegetation for two growing seasons, with an additional unseeded control treatment for comparison to natural recovery. Treatments receiving the highest rate of application had significantly more native grass basal cover and percent composition than the controls. Plant phosphorus accumulation increased significantly with increasing pulp application. Soil phosphorus and lead concentrations increased in the top 10 cm of the highest application rates where pulp was mixed in the soil. Because minimal environmental effects were detected and the pulp improved perennial grass establishment and nutrition at the 36 Mg ha−1 rate, land application should be considered a viable and beneficial alternative to current waste‐management practices.