Dick L. Gebhart

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.

Arbuscular mycorrhizal fungal community differs between a coexisting native shrub and introduced annual grass

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.

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.

Grassland Plant Composition Alters Vehicular Disturbance Effects in Kansas, USA

Many “natural” areas are exposed to military or recreational off-road vehicles. The interactive effects of different types of vehicular disturbance on vegetation have rarely been examined, and it has been proposed that some vegetation types are less susceptible to vehicular disturbance than others. At Fort Riley, Kansas, we experimentally tested how different plant community types changed after disturbance from an M1A1 Abrams tank driven at different speeds and turning angles during different seasons. The greatest vegetation change was observed because of driving in the spring in wet soils and the interaction of turning while driving fast (vegetation change was measured with Bray-Curtis dissimilarity). We found that less vegetation change occurred in communities with high amounts of native prairie vegetation than in communities with high amounts of introduced C3 grasses, which is the first experimental evidence we are aware of that suggests plant communities dominated by introduced C3 grasses changed more because of vehicular disturbance than communities dominated by native prairie grasses. We also found that vegetation changed linearly with vehicular disturbance intensity, suggesting that at least initially there was no catastrophic shift in vegetation beyond a certain disturbance intensity threshold. Overall, the intensity of vehicular disturbance appeared to play the greatest role in vegetation change, but the plant community type also played a strong role and this should be considered in land use planning. The reasons for greater vegetation change in introduced C3 grass dominated areas deserve further study.

Seasonal Variation in Arbuscular Mycorrhizal Fungi Root Colonization of Cheatgrass ( Bromus tectorum ), an Invasive Winter Annual

Cheatgrass is a highly invasive winter annual grass that is most aggressive in the semi-arid steppe region of western North America. In this region, cheatgrass invasion becomes so severe that virtual monocultures can result. Due to its strategy for growth from autumn to spring, cheatgrass remains active during winter months when most native vegetation is dormant. This shift in host activity could be important for beneficial soil microbes, particularly the arbuscular mycorrhizal fungi (AMF), as they are adapted for coincidental growth with host plants. Many native plant species that are utilized for restoring areas invaded by cheatgrass associate with AMF, so any reduction in these symbiotic fungi could reduce the successful establishment of desirable plant species. Although cheatgrass is recognized as a facultative associate of AMF, its associations with AMF across seasons and throughout its lifespan are not known. We measured AMF colonization of cheatgrass roots from soon after germination through senescence. We found that cheatgrass remains colonized throughout its life. Colonization drops dramatically once soil temperatures approach freezing, but was highest late in the growth cycle of cheatgrass during flowering and seed set. Colonization by AMF never attained levels comparable to highly mycorrhizal plant species. This indicates that cheatgrass is a poor host for AMF throughout its life, and long-term dominance by cheatgrass could alter AMF in soils. Restoring highly invaded sites quickly following invasion might reduce the negative effects of cheatgrass on this important soil microbial community.

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.

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.

Estimating resistance and resilience of military lands using vegetation indices

Military training inevitably leads to land degradation; however, some ecosystems have higher resistance and resilience to training based on the functional traits of existing vegetation, making them preferred for longterm use. This work estimated resistance and resilience for the continental United States using dominant plant species for numerous plant communities, resistance and resilience values for plant functional groups, and national community vegetation maps. Two datasets were combined to obtain greater detail and values for all land area. Results indicate that graminoid communities have the highest resistance values, and shrublands the lowest; and that eastern deciduous forests and prairies have the highest resilience values, and evergreen forests and shrublands the lowest. This lists the resistance and resilience values of a selection of Army installations using both datasets and a new combined metric. This new method will help the Army determine the portfolio of installations that will best meet its future training land requirements. 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. ERDC/CERL TR-17-12 iii

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.

Unpaved Road Fugitive Dust Control and Road Stabilization using Processed Installation Solid Waste

Fugitive dust generated from military vehicle maneuvers is a serious issue that affects military readiness, human health and safety, and environmental quality. In landing zones and on unpaved roads and trails, excessive amounts of fugitive dust particles generated by helicopters, airplanes, wheeled vehicles, and tracked vehicles reduce operator visibility and safety, allow for enemy remote identification of tactical positions and impair operating performance of ground support teams and equipment. These factors increase the likelihood of accidents and injury. Additionally, dust acts as a respiratory irritant and is considered a health, safety, and air quality hazard that affects the soldiers and civilians that work and live nearby. Furthermore, dust migration from unpaved roads to nearby surfaces impairs plant growth, degrades stream quality and decreases road stability throughout unpaved road corridors. Recently, a study was conducted that evaluated the effectiveness of processed installation solid waste (ISW) for dust suppression and road stabilization on unpaved roads. Initially, laboratory investigations using sand and Drummer soil were utilized to determine the physical characteristics of the processed installation solid waste and to identify the appropriate treatment additives for dust suppression. Three treatment plots replicated at three sites were installed at an orchard near McMinnville, Tennessee. Additionally, a control plot within the study site received no treatment and was typical of unpaved roads in the area. On the basis of the laboratory results the three treatment plots consisted of 1) processed ISW 2) processed ISW plus calcium chloride 3) processed ISW plus vegetable oil. The sites were then subjected to multiple vehicle passes while dust emission measurements were recorded. Results from the study and fugitive dust measurements at the site over several months are discussed..