Eastern gamagrass (EG), Tripsacum dactyloides, is a diverse warm-season, perennial bunchgrass that is widespread in the eastern half of the United States. The objectives of this study were to obtain a large assortment of ecotypes, measure and quantify some of their morphological aspects, and determine ploidy level for many of these ecotypes. Nearly 300 ecotypes were collected from 10 states and planted in a common garden in Temple, TX. Plants were measured throughout the growing season and ploidy was determined using flow cytometry. Plant morphology measurements were variable, though none were statistically significantly correlated when compared pairwise to ploidy levels, origin, landform, precipitation, or temperature. However, multivariate analyses showed that ploidy was significantly correlated with plant volume, plant height, and leaf width. Diploids were more narrowly restricted to drier habitats, while the tetraploids were widespread. Tetraploids have also a higher volume than diploids. Likewise, mean annual precipitation was correlated with plant height and leaf width. Landform (wet vs. dry) for collection sites was significantly correlated with plant volume in the multivariate analysis. Though not statistically significant, the southernmost populations start growing earlier than plants collected further north. This new insight into EG ecology via the collected data is useful to better answer producer questions about climate and management operations as they differ among ecotypes. Morphology of eastern gamagrass was highly variable among 284 ecotypes.Ploidy, origin, landform, precipitation, and temperature were not significantly correlated when compared pairwise.Multivariate analyses show that ploidy was significantly correlated with plant volume, plant height, and leaf width.Tetraploids were more widespread and had larger volume.Mean annual precipitation of the collection sites was correlated with plant height and leaf width.

The goal of this study was to evaluate growth and nutritional characteristics of seven warm season grasses, including several natives, produced under simulated partial shading (50%) typical of loblolly pine silvopastoral systems in the southeastern United States. Forages included ‘Tifton 9’ bahiagrass (Paspalum notatum), ‘Tifton 85’ bermudagrass (Cynodon dactylon), ‘Alamo’ switchgrass (Panicum virgatum), ‘Kaw’ Big Bluestem (Andropogon gerardii), ‘Americus’ Indiangrass (Sorghastrum nutans), ‘Harrison’ Florida paspalum (Paspalum floridanum), and Nacogdoches Eastern gamagrass (Tripsacum dactyloides). Shade affected several quality parameters, including crude protein (CP) (p < 0.0001), acid detergent fiber (ADF) (p = 0.0413), in vitro true digestibility (IVTD) (p < 0.0001), and total digestible nutrients (TDN) (p = 0.0132). Shade affected the parameters differently depending on forage type, but generally improved quality by increasing CP, IVTD, and TDN; however, shade significantly increased ADF (p = 0.0413), though the magnitude was small (344.2 vs. 351.1 g kg−1), and increases were isolated to big bluestem and bahiagrass. Shade reduced dry matter yield (DMY) (p < 0.0001), and there were differences among forage species (p < 0.0001). Bahiagrass and Florida paspalum showed the highest yields, regardless of shade treatment. Gamagrass and Florida paspalum would likely have performed better if harvested by days of rest, instead of by height. These could be viable forage species to a silvopasture system, but further studies should be conducted. Based on overall quality and yield, potential beef cattle gains, and persistence under intensive defoliation, the best forage was bahiagrass (introduced), and the best selections for native grasses were switchgrass and Indiangrass. These results indicate that there is potential for several warm season forages, including native grasses, to maintain productivity and quality under shade, which would increase the site-specific options for forage selections in this system.

Heritable symbionts are often observed at intermediate prevalence within host populations, despite expectations that positive fitness feedbacks should drive beneficial symbionts to fixation. Intermediate prevalence may reflect neutral dynamics of symbionts with weak fitness effects, transient dynamics of symbionts trending towards fixation (or elimination), or a stable intermediate outcome determined by the balance of fitness effects and failed symbiont transmission. Theory suggests that these outcomes should depend on symbiont‐conferred demographic effects and vertical transmission efficiency, which may both depend on environmental context. We established experimental populations of winter bent grass Agrostis hyemalis across a range of prevalence of the heritable fungal endophyte Epichloë amarillans. Using irrigation, we elevated the precipitation for half of the populations, which we hypothesized would weaken the benefits of symbiosis. Across two annual transitions, we assayed 5,485 individuals to determine prevalence and censused 954 individuals for demographic (survival, flowering, reproduction and recruitment) and vertical transmission data. We used hierarchical Bayesian models to infer long‐run equilibria from short‐term changes in symbiont prevalence and estimated demographic vital rates to link individual‐level effects to population‐level outcomes. We found evidence for all three proposed mechanisms for intermediate symbiont prevalence, but the outcome differed qualitatively across years and precipitation treatments. In the first year, symbionts trended towards fixation under drought conditions but drifted neutrally under elevated precipitation. Fixation likely arose from symbiont‐conferred recruitment benefits outweighing reproductive costs under the drought conditions, while elevated precipitation tempered these effects. In the second transition year, we inferred stable intermediate prevalence across both precipitation treatments, which indicated a balance between symbiont conferred recruitment benefits that allowed low‐prevalence populations to increase and imperfect transmission that caused high‐prevalence populations to decrease. Synthesis. We find support for neutral, transient and stable mechanisms underlying symbiont prevalence, indicating that symbiont prevalence is often pushed and pulled in different directions by the composite outcome of symbiont effects on demographic rates and transmission efficiency, and the way in which these processes respond to environmental context.

Plant adaptation plays a critical role in the success of conservation plantings. Commercially produced native plant species used in conservation plantings have a wide range of origin. The USDA-NRCS ETPMC conducted an adaptation trial of switchgrass (Panicum virgatum L.), Indiangrass [Sorghastrum nutans (L.) Nash], big bluestem (Andropogon gerardii Vitman) and little bluestem [Schizachyrium scoparium (Michx.) Nash] cultivars and pre-varietal releases for resource conservation programs in NRCS administrative Zone 4 which is primarily in the Western Coastal Plain’s, Major Land Resource Area (MLRA) 133b. Cultivar and pre-varietal germplasm releases from the USDA-NRCS Plant Materials Program were planted in a randomized complete block design at the East Texas Plant Materials Center (ETPMC) and evaluated for yield, stand persistence, plant height, and disease and insect resistance. Switchgrass cultivars performed well with the lowland types producing yields in excess of 15,000 lb/acre at maturity. Stand survival of Indiangrass remained > 80%. Except for ‘Earl’, big bluestems entries also maintained > 80% stand survival. Little bluestem entries showed a decline in stand except for Coastal Plain Germplasm which increased to 100% from 20132018. Results from this study will be used to update the Texas NRCS planting standards for NRCS administrative Zone 4.

Beneficial inherited symbionts are expected to reach high prevalence in host populations, yet many are observed at intermediate prevalence. Theory predicts that a balance of fitness benefits and efficiency of vertical transmission may interact to stabilize intermediate prevalence. We established populations of grass hosts (Lolium multiflorum) that varied in prevalence of a heritable fungal endophyte (Epichloё occultans), allowing us to infer long-term equilibria by tracking change in prevalence over one generation. We manipulated an environmental stressor (elevated precipitation), which we hypothesized would reduce the fitness benefits of symbiosis, and altered the efficiency of vertical transmission by replacing endophyte-positive seeds with endophyte-free seeds. Endophytes and elevated precipitation both increased host fitness, but symbiont effects were not stronger in the drier treatment, suggesting that benefits of symbiosis were unrelated to drought tolerance. Reduced transmission suppressed the inferred equilibrium prevalence from 42.6% to 11.7%. However, elevated precipitation did not modify prevalence, consistent with the result that it did not modify fitness benefits. Our results demonstrate that failed transmission can influence the prevalence of heritable microbes and that intermediate prevalence can be a stable equilibrium due to forces that allow symbionts to increase (fitness benefits) but prevent them from reaching fixation (failed transmission).

As highly productive perennial grasses are evaluated as bioenergy feedstocks, a major consideration is biomass yield stability. Two experiments were conducted to examine some aspects of yield stability for two biofuel species: switchgrass (Panicum vigratum L.) and Miscanthus x giganteus (Mxg). Biomass yields of these species were evaluated under various environmental conditions across the Southern Great Plains (SGP), including some sites with low soil fertility. In the first experiment, measured yields of four switchgrass ecotypes and Mxg varied among locations. Overall, plants showed optimal growth performance in study sites close to their geographical origins. Lowland switchgrass ecotypes and Mxg yields simulated by the ALMANAC model showed reasonable agreement with the measured yields across all study locations, while the simulated yields of upland switchgrass ecotypes were overestimated in northern locations. In the second experiment, examination of different N fertilizer rates revealed switchgrass yield increases over the range of 0, 80, or 160 kg N ha−1 year−1, while Mxg only showed yield increases between the low and medium N rates. This provides useful insights to crop management of two biofuel species and to enhance the predictive accuracy of process-based models, which are critical for developing bioenergy market systems in the SGP.