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Irrigation of farmlands in xeric areas can increase soil salinity, reducing their suitability for food and fiber crops. One way to repurpose these lands is to convert them for use in grazing. To choose the best forage species, it is important to understand the impact of soil salinity on the growth and nutritional quality of potential forage grasses. Here, we grew four perennial C4 grasses: blue grama (Bouteloua gracilis), sideoats grama (Bouteloua curtipendula), little bluestem (Schizachyrium scoparium), and bermudagrass (Cynodon dactylon) in soil treated with four different concentrations (0, 8, 16, and 24 dS/m) of sodium chloride salt (NaCl). We then determined the effects of soil salinity on germination, biomass production, and plant tissue nitrogen content (an indicator of nutritional quality). We found a high degree of variability in salinity responses among species. S. scoparium performed poorly relative to the other species across all metrics. C. dactylon showed high biomass and low sensitivity to soil salinity for each index but had the lowest shoot nitrogen concentration of all species tested. This indicated a tradeoff of tissue quality for quantity. On the other hand, the two Bouteloua species showed opposite results, falling on the shoot quality end of the quantity-quality spectrum and even showing increased nitrogen concentration with increasing soil salinity. Given their complimentary traits, C. dactylon and Bouteloua spp. may be good candidates for interseeding on saline lands. These results indicate that species choice can help mitigate negative impacts of soil salinity on forage production and quality and should be carefully considered by land managers.

Soil microorganisms play crucial roles in nutrient cycling and provisioning ecosystem services. However, little is known about how soil microbial communities are affected by soil management and landscape position in silvopastures. The current study aimed to understand effects of forage species [non-native, cool season orchardgrass (Dactylis glomerata L.) and a warm-season native grass mix (Andropogon gerardii L. and Schizachyrium scoparium L.) planted in strips between hedgerows], soil fertility (poultry litter and a control), and soil moisture regimes (aquic and udic) on soil bacterial communities to evaluate linkages between terrain attributes and soil bacterial assemblages. Thirteen terrain attributes representing topographic variability were clustered into four topographic functional units (TFUs) using the k-means method, and their impact on soil microbial diversity was evaluated. Illumina sequencing results identified a soil moisture regime × forage species interaction, with native grass species under wet (aquic) conditions resulting in the most diverse microbial assemblages relative to dry (udic) and wet soil conditions for the non-native forage (orchardgrass). These results suggest an enhanced soil microbial diversity under native grasses with greater available soil water. Overall, microbial diversity was negatively correlated with elevation, suggesting niche differentiation and microbial preference for lower elevations. Overall, TFUs and selected terrain attributes may be useful for predicting microbiota dynamics in integrated tree-livestock systems.

Most grasslands world-wide have been converted into various row crops for agriculture and pasture for livestock foraging. This conversion has likely disrupted arthropod communities, including pollinating bee communities. Pollinating native bees have been in decline in recent decades and much of this decline has been attributed to intensive agricultural practices. Native warm-season grasses have been promoted as alternatives to non-native grasses [e.g., bermudagrass (Cynodon dactylon)] in beef production systems. Reestablishing native grasses may provide an opportunity for land-sharing where agricultural production can enable conservation practices that potentially enhance bee biodiversity. Therefore, agricultural practices such as growing native perennial grasses for livestock forage that may minimize pollinating bee community disruption should be considered. We used colored pan traps to collect bees in four treatments of perennial grass plantings associated with operational livestock pastures during 2011−2012. The four treatments were: (1) mix of Bermuda and tall fescue (Schedonorus arundinaceus) grass grazed with cattle; (2) monocultures of Indiangrass (Sorghastrum nutans) grazed with cattle; (3) native grass polyculture [(Indiangrass, little bluestem (Schizachyrium scoparium), and big bluestem (Andropogon gerardii)] grazed with cattle; and (4) native grass polyculture without cattle. We generally documented greater abundances and richness of bees in native grass treatments compared to exotic grass treatments; however, treatment-level differences were bee genera- or species-dependent. Lack of grazing in the native grass mixture treatment did result in higher bee abundance and taxa richness compared to the native grass mixture treatment with cattle. Our results support the conception that perennial native grasses have the potential to attract numerous, beneficial bee species and may provide some pollen rewards and suitable nesting substrate for bees. Therefore, using native perennial grasses as livestock forage may be a more ecologically friendly surrogate to non-native forage used for livestock production to promote pollination services and native bee diversity in agricultural lands.

Atmospheric deposition of nitrogen (N) has been reported to reduce the diversity of plant species in N-limited soil. The sand dunes along the southern shore of Lake Michigan have been N-limited historically but receive substantial amount of N from the atmosphere currently. We investigated the effect of N-addition to soil on seed germination rates and species composition of nine native plants. In the greenhouse, the ambient addition (15 kg N ha− 1 yr− 1) enhanced the germination of Elymus canadensis and Echinacea purpurea, while the 9 × ambient N addition reduced seed germination of Dalea purpurea and Elymus. However, regardless the results from greenhouse, these species exhibited no or poor emergence in the field plots. Panicum virgatum was the only species whose germination was promoted significantly by the ambient addition in the greenhouse and also emerged in the field plots in the early years (2010 − 2012), but its dominance diminished during 2013–2014. The decline of Panicum suggests a failure of establishment and reproduction after germination. Such failure has likely led to reduction or exhaustion of viable seeds in soil. Meanwhile, the species that showed relatively low germination rates (

Grasslands are among the most imperiled ecosystems in the world, and establishment of exotic forage grasses and management for uniform utilization may have contributed to population declines of many obligate grassland bird species in North America. Native warm-season grasses (NWSG) are increasingly promoted as viable alternatives to exotic forages currently in production such as bermudagrass (Cynodon dactylon) and tall fescue (Schedonorus arundinaceus), but structure of native bunchgrasses also may offer nesting habitat for birds such as the dickcissel (Spiza americana). Establishing NWSG pastures may thereby create an opportunity for land-sharing, where agriculture incorporates biodiversity-friendly practices. We investigated dickcissel responses to NWSG and grazing at the Prairie Research Unit in Monroe Co., Mississippi (USA), where we established a gradient of management intensity among four treatments in small, operational-scale pastures (6.4–10.5 ha). Treatments included grazed exotic forages, two grazed NWSG treatments including Indian grass (Sorghastrum nutans) monoculture and grazed mixed NWSG polyculture of Indian grass, little bluestem (Schizachyrium scoparium), and big bluestem (Andropogon gerardii), and a non-grazed NWSG polyculture treatment. We applied a multi-state capture-recapture model in a Bayesian framework to estimate dickcissel nest density and productivity while accounting for nest stage-specific variation in survival and detection. Nest density and productivity were consistently greater in non-grazed NWSG than grazed exotic pasture, whereas productivity in grazed NWSG treatments was intermediate but declined between years. We also found that variation in survival and density did not always correspond with estimated productivity, and thus solely relying on either parameter may be misleading when making inferences on habitat quality. These results suggest a positive response to NWSG among dickcissels in this system, but grazing may reduce nest site abundance, and consequently productivity. Native warm-season forages may be a viable land-sharing alternative by increasing productivity of tall structure specialists such as dickcissels compared with exotic grass pastures currently in production, but grazing should be managed to ensure abundance of tall vegetation structure for nest sites.

Switchgrass (Panicum virgatum) monocultures are a leading feedstock choice for producing cellulosic biofuels. However, in natural stands, switchgrass is only dominant in a narrow ecological niche of the Tallgrass Prairie. This suggests that strategically selected monocultures or binary mixtures of species, adapted to particular ecological niches, might outyield switchgrass monocultures while increasing biodiversity at the field and landscape scales. To test this hypothesis, we planted monocultures of switchgrass and three alternative species at each of three landscape positions (shoulderslope, midslope, and footslope). Alternative species were also mixed with switchgrass such that they composed 33 or 67% of the total number of plants in each plot. Alternative species at each position included a C3 grass, a C4 grass, and a forb. Biomass data were collected in autumn during each of the two consecutive years following the establishment year. At the shoulderslope, the highest-yielding treatments were those containing little bluestem (Schizachyrium scoparium; 12.0 Mg ha−1) and those dominated by switchgrass (10.4 Mg ha−1). At the midslope and footslope, there were interactions of year × treatment (p

Many prairie plant habitats have similarities to the harsh and stressful growing environments of green roofs. In the Mid-Continent Region of the USA under a hot summer climate, little research has been done to study prairie plant communities and their performance with different substrates on green roofs. To explore more sustainable, diverse green roof ecosystems, this research assessed the first-year growth (June to October 2018) on an experimental green roof in the Flint Hills Ecoregion, which has some of the most extensive coverage of intact tallgrass prairie in North America. A mixture of plants (four native prairie grasses and two sedums) were grown on two substrates—a commercial substrate (rooflite® extensive 800) and a regionally mixed substrate (Kansas BuildEx)—placed at two depths: 6.0–13.0 cm (called the “shallow depth”) and 16.5–25.5 cm (called the “deep depth”). Plant height, coverage, survival, visual appearance, leaf stomatal resistance, and volumetric substrate water content were measured. Supplemental irrigation was provided equally to each experimental plot during the growing season. It was shown that the regionally mixed substrate had greater effect on plant height at the shallow depth and on coverage at the deep depth. However, volumetric water content was usually higher in the commercial substrate. Substrate type did not affect visual appearance and leaf stomatal resistance. Substrate moisture was inversely related to leaf stomatal resistance at low soil moisture levels. All prairie species survived, while Sedum reflexum had poor survival and coverage. Bouteloua curtipendula, Bouteloua gracilis, Schizachyrium scoparium, and Sedum rupestre performed well in a green roof community. Bouteloua dactyloides grew very well, but may be too aggressive when planted with sedums. The findings of this study will be of practical value for the design of mixed-species green roof systems in similar mid-continental regions with hot summers.

This paper discusses the physics and fire behavior of grassland fuel using experimental and modeling results. Experimental characterization included intermediate-scale tests to determine the mass loss rates, heat release rates (HRRs), and flame heat fluxes of burning little bluestem (Schizachyrium scoparium) grass plants at various fuel moisture contents and external flow conditions. The experiments included single-plant tests, multiple-plant tests with no forced flow/wind, and multiple-plant tests in which a forced flow was directed over the plants to simulate wind. The burning characteristics of single plants and fire spread between multiple plants under various conditions are discussed. The computational tool, Wildland–Urban Interface Fire Dynamics Simulator (WFDS), was then used to model the experiments using both a prescribed HRR and the particle-based fuel element model (predicted HRR). Comparisons are made between the experimentally measured quantities and the results predicted by WFDS. The results of the WFDS simulations with a prescribed HRR are in good agreement with the measured heat fluxes for the multiple-plant tests with no wind. The results of the particle-based WFDS fuel element model are in good agreement with the experimentally measured mass loss rates and HRRs of the single-plant tests. The WFDS fuel element model effectively captures the different stages of burning of the little bluestem plant. For the prediction of heat fluxes in the wind tests, there are limitations in the use of the prescribed HRR model.

Arbuscular mycorrhizal fungi (AMF) and N2-fixing legumes can alter the community structure of grasses. However, the effect of AMF, N2-fixing legumes, and their interaction on the dynamics of prairie grass communities remains unclear. The aim of this study was to clarify the influence of two AMF (Glomus cubense and Glomus sp.) and two legumes (Medicago sativa and Dalea purpurea) on the competitive relationship between three native cool-season (Elymus canadensis, Elymus trachycaulus ssp. subsecundus, and Elymus lanceolatus ssp. lanceolatus) and two native warm-season species of grasses (Schizachyrium scoparium and Bouteloua gracilis). Results show that AMF and legumes altered the community structure of the grasses. G. cubense favoured the productivity of warm-season B. gracilis when growing with M. sativa. This might be related to a negative impact of G. cubense on the nitrogen-fixing activity of M. sativa and to a lower N-use efficiency of E. canadensis and E. lanceolatus ssp. lanceolatus under competition. This suggested an increased ability of B. gracilis to use the available N resource as affected by more competitive species, whereas Glomus sp. reduced the competitive ability of this grass when associated with M. sativa. The decrease in B. gracilis biomass was thus likely caused by enhancement of P uptake by M. sativa over this grass. Glomus sp. was beneficial to S. scoparium, another warm-season species, in the absence of legumes, and this may be attributed to improved P-use efficiency of this grass under competition with cool season-grasses. In contrast, AMF and legumes were not beneficial for the cool season grasses. G. cubense depressed the growth of E. trachycaulus ssp. subsecundus, and M. sativa decreased nutrient uptake by cool-season native grasses. This study shows that beneficial effect of the arbuscular mycorrhizal symbiosis on the coexistence of warm-season grasses with more competitive cool-season grasses depends on the identity of the AMF symbiont, the presence of legume species, and nitrogen resource availability that was affected by the most competitive species or P-use efficiency of warm season species.

Plant–soil feedbacks are important to productivity and plant community dynamics in both natural and managed ecosystems. Among soil bacteria, the Streptomyces possess particularly strong antagonistic activities and inhibit diverse plant pathogens, offering a clear pathway to involvement in plant–soil feedbacks. We hypothesized that feedback effects and the ability of individual host plant species to foster antagonistic Streptomyces populations may be modified by the richness of the surrounding plant community. To test this, we collected soil associated with four different plant species (two C4 grasses: Andropogon gerardii , Schizachyrium scoparium ; and two legumes: Lespedeza capitata , Lupinus perennis ), grown in communities that spanned a gradient of plant species richness (1, 4, 8, 16, or 32 species). For each of these soils, we characterized the potential of soil Streptomyces to antagonize plant pathogens, using an in vitro plate assay with indicator strains to reveal inhibition. We cultivated each plant species in each conditioned soil to assess feedback effects on subsequent plant growth performance. Surrounding plant richness modified the impacts of particular plant species on Streptomyces antagonistic activity; A. gerardii supported a higher proportion of antagonistic Streptomyces when grown in monoculture than when grown in 32-spp plant communities, and L. capitata supported more strongly antagonistic Streptomyces when grown in 4- or 32-spp plant communities than in 8-spp plant communities. Similarly, the feedback effects of particular plant species sometimes varied with surrounding plant richness; aboveground biomass production varied with plant species richness for A. gerardii in L. perennis -trained soil, for L. capitata in A. gerardii -trained soil, and for L. perennis in L. capitata -trained soil. Streptomyces antagonist density increased with overall Streptomyces density under low but not under high plant richness, suggesting that plant diversity modifies selection for antagonistic phenotypes among soil Streptomyces . This work highlights the complexity of feedback dynamics among plant species, and of plant–microbiome interactions in soil.

We examined the effect of fire on vegetation composition with the use of an experiment with four different fire frequencies (annual, 2-yr interval, 4-yr interval, and an intended control with no burning) over a 27-yr period in an infertile, old-field grassland at the Cedar Creek Ecosystem Science Reserve, located in Minnesota, United States. We measured the plant species’ aboveground biomass in permanent plots in 1983, 1987, 1991, 2000, and 2010. None of these fire frequencies, even after 27 yr, had a large impact on the vegetation composition. The plant functional groups’ responses to fire frequency were consistent with their respective dominant species. The most abundant C4 grass, little bluestem (Schizachyrium scoparium Michx.), did not change in biomass with fire frequency over time. The biomass of the introduced, invasive grass, Kentucky bluegrass (Poa pratensis L.) decreased significantly with increasing fire frequency, but this decrease did not result in change to the rate and trajectory of vegetation change. Bush clover (Lespedeza capitata Michx.), the only legume in the community, strongly increased with more frequent fire, but only after 20 yr. Species richness and litter mass decreased significantly with increasing fire frequency. These small fire-induced vegetation changes contrast with large fire-induced vegetation changes in fertile grasslands. Management strategies using fire in infertile grasslands can lower Poa abundance; however, increased fire also decreased overall plant diversity.

In many terrestrial ecosystems plant productivity is limited by the availability of mineral nitrogen, which is produced by soil microbial transformations of organic N in soil organic matter (SOM-N). Mineral N availability results from two opposing processes, 1) gross mineral N production (gross ammonification/ gross nitrification) and 2) microbial N immobilization. These processes can be influenced by the availability of plant-derived C (PDC) inputs to the microbes, SOM-N pool size, and the size of the microbial community (microbial biomass). We considered how changes in PDC inputs and SOM-N pool size together may alter microbial biomass, mineral N availability, and feedbacks on plant productivity. In areas dominated by one of six tallgrass prairie species along a natural gradient of PDC inputs and SOM-N pool size, we conducted a field survey of microbial biomass and gross ammonification. We also performed greenhouse manipulations of SOM-N pool size and PDC inputs on two species in our study area (Poa pratensis and Schizachyrium scoparium). Structural equation modeling of the field data showed that gross ammonification was both positively and directly related to microbial biomass and SOM-N pool size. Gross ammonification was positively and indirectly related to SOM-N pool size and belowground PDC inputs, via microbial biomass. In the short-term greenhouse study, PDC inputs and SOM-N pool size positively affected gross mineral N production, although only at high SOM-N pool size. If the patterns in the greenhouse can be applied to field conditions, this suggests that SOM-N pool size may constrain plant driven feedbacks on plant productivity by limiting gross mineral N production. Published by Elsevier Ltd.

Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that often improve plant nutrient and water relations in exchange for photosynthetic carbon. During times of stress; however, plants may divert resources away from the AMF, eventually causing a reduction in mycorrhization rates. In short and mixed grass regions, where inter-annual precipitation varies widely, water availability may be the most influential limiting factor for plant growth and nutrient uptake. It may also impact plant relationships with AMF, further influencing nutrient, water, and carbon relations. To investigate the effect of precipitation rates on AMF relations, we manipulated moisture inputs in a southern mixed grass prairie and quantified mycorrhization rates of two common grasses: Bouteloua hirsuta and Schizachyrium scoparium . A multivariate analysis of variance confirmed differences in mycorrhization rates between years and differences between species responses within years; however, precipitation treatment was not a significant factor in the model. Trends in means pointed to a general reduction in mycorrhization with increasing precipitation, especially for the finer rooted B. hirsuta , but these trends were not significant. Independent variables (growing season phosphate, nitrate and ammonium mineralization, volumetric soil moisture) did not meaningfully correlate to mycorrhization rates of either species. Our results indicate that absolute precipitation and nutrient availability do not alone act upon mycorrhization rates. Our results further support the idea that broad generalization regarding plant–AMF relationships and responses to abiotic forces must be supported by long-term datasets; plant–AMF relationships appear to be too vulnerable to inter-annual variability to make conclusions based on short-term datasets.

We examined how the occurrence and structure of grasses and woody plants changed after 12 yr of a fire season manipulation and removal of livestock herbivores. Applying high intensity fires in the summer preserved the structural integrity of this semiarid live oak ( Quercus virginiana Mill.) savanna while decreasing or eliminating numerous problematic plants in the understory and overstory, such as prickly pear cactus ( Opuntia spp.), sacahuista ( Nolina texana S. Watson), Ashe juniper ( Juniperus ashei J. Buchholz), Pinchot's juniper ( J. pinchotii Sudw.), and honey mesquite ( Prosopis glandulosa Torr.). In the less intense repeat winter burning treatments, undesirable woody plants were generally maintained at pretreatment levels in the overstory but all woody plants except Ashe juniper increased in the understory. Alternatively, areas excluded from fire in the control treatment rapidly transitioned from a grass-tree codominated savanna environment to one that is heavily dominated by woody plants. In the grass community, the most frequently occurring grass species in the winter burn treatment differed from summer burn and control treatments, whereas the summer burn treatment was not different from the control. Of the herbaceous plants, only little bluestem ( Schizachyrium scoparium lMichx.] Nash) responded to fire treatments. Little bluestem increased in the winter burn treatment, remained fairly constant in the summer burn treatment, and decreased in the control. Other grasses varied largely as a function of annual weather variability, the removal of livestock, and legacy effects resulting from pre-existing variability. These findings suggest that fire can reduce or eliminate woody plant species that threaten the stability of live oak savannas while having little long-term effect on grasses desired by rangeland managers.

In grassland ecosystems, spatial and temporal variability in precipitation is a key driver of species distributions and population dynamics. We experimentally manipulated precipitation to understand the physiological basis for differences in responses of species to water availability in a southern mixed grass prairie. We focused on the performance of two dominant C 4 grasses, Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash, in treatments that received ambient rainfall, half of ambient rainfall (“drought” treatment), or approximately double ambient rainfall (“irrigated” treatment). Water potentials of S. scoparium were lower than A. gerardii , suggesting superior ability to adjust to water deficit in S. scoparium . Additionally, drought reduced photosynthesis to a greater extent in A. gerardii compared to S. scoparium . Leaf-level photosynthesis rates were similar in ambient and irrigated treatments, but were significantly lower in the drought treatment. Although stomatal conductance was reduced by drought, this was not limiting for photosynthesis. Leaf δ 13 C values were decreased by drought, caused by an increase in C i / C a . Chlorophyll fluorescence measures indicated light-harvesting rates were highest in irrigated treatments, and were lower in ambient and drought treatments. Moreover, drought resulted in a greater proportion of absorbed photon energy being lost via thermal pathways. Reductions in photosynthesis came as a result of non-stomatal limitations in the C 4 cycle. Our results provide mechanistic support for the hypothesis that S. scoparium is more drought tolerant than A. gerardii .

Inter- (between years) and intra- (within year) annual variability of precipitation are high on rangelands. We used replicated rainout shelters in a southern tallgrass prairie ecosystem to decrease precipitation variability for 3 yr (1999–2001). We removed interannual variability in total precipitation plus either 1) interannual variability in the seasonal distribution of precipitation (seasonal distribution) or 2) all additional variability in precipitation, including within-year differences in precipitation (even distribution). Our objective was to determine if decreasing variability in precipitation elicits aboveground biomass and plant diversity responses. Aboveground biomass was harvested in June (peak biomass) and December (end of growing season). Plant species diversity, richness, and evenness were determined each June. Reducing precipitation variability had limited effects on total aboveground biomass, grass and forb biomass, and biomass of key species across the 3 yr of investigation. Species richness, species diversity, species evenness, and functional group richness and diversity all were similar across the precipitation treatments across years. Total aboveground biomass and biomass of the dominant C4 perennial grasses little bluestem (Schizachyrium scoparium) and Indiangrass (Sorghastrum nutans) generally were not responsive to the precipitation treatments. However, one species-specific response did occur with the annual forb firewheel (Gaillardia pulchella Foug.) displaying consistent increases in biomass in the seasonal distribution precipitation treatment across all 3 yr. This suggests that increased predictability of precipitation at a given stage of this species’s growth can elicit changes in productivity of a single species that are not manifest at the community level due to constraints of the dominant species. These findings indicate that the southern tallgrass prairie ecosystem is adaptable to changes in precipitation to result in relatively stable production that facilitates simpler predictions in response to altered precipitation regimes.

In March 2006 the East Amarillo Complex (EAC) wildfires burned over 367 000 ha of short and mixed grass prairie of the southern High Plains, USA. We studied EAC wildfire effects on perennial grass mortality and peak standing crop on Deep Hardland and Mixedland Slopes ecological sites. Deep Hardlands were dominated by blue grama ( Bouteloua gracilis H.B.K. [Griffiths]) and buffalograss ( Buchloe dactyloides [Nutt.] Engelm.); common species on Mixedland Slopes were little bluestem ( Schizachyrium scoparium [Michx.] Nash.) and sideoats grama ( Bouteloua curtipendula [Michx.] Torr.) with scattered sand sagebrush ( Artemisia filifolia Torr.) sometimes present. We hypothesized that perennial grass mortality would increase and standing crop would decrease following severe wildfire, and that these responses would be greater than documented prescribed fire effects. Frequency of perennial grass mortality was higher on both sites in burned areas than nonburned areas through three growing seasons following wildfire; however, standing crop was minimally affected. Results suggest that post-wildfire management to ameliorate wildfire effects is not necessary, and that wildfire effects in this area of the southern High Plains are similar to prescribed fire effects.

Historically, fire occurred throughout the year in the Great Plains, but current fire prescriptions are generally limited to the dormant season because of concerns for potential damage to fire-sensitive herbaceous plant species deemed economically and ecologically important. We coupled a field-based study and a controlled greenhouse study to quantify the effects of fire season and herbivory on plant species composition, along with survival and productivity of little bluestem (Schizachyrium scoparium [Michx.] Nash). We investigated the effects of both dormant and growing-season fire interacting spatially with grazing on plant community composition in a 10-yr field study. We also examined the influence of both growing-season fire and clipping on survival and aboveground and belowground production of potted little bluestem plants at multiple ages in a controlled greenhouse experiment. Plants were grown to 6 wk, 10 wk, or 18 wk, then either burned or clipped, followed by as many as two successive clipping events. Plant community composition and canopy cover of little bluestem were unaffected by season-of-burning in the field study. Survival of individual little bluestem seedlings in the greenhouse study was dependent primarily on plant age, with nearly 100% survival among all burning and clipping treatments at 18 wk old. Burning or clipping once did not decrease survival compared to seedlings that were not burned or not clipped, and burning followed by clipping did not decrease survival over multiple clipping events among 6-wk-, 10-wk-, or 18-wk-old plants. Both aboveground regrowth and belowground biomass increased with burning, but clipping reduced regrowth. Based on both field and greenhouse experiments, we conclude that little bluestem is well adapted to growing-season disturbance. Moreover, little bluestem responds more positively to growing-season fire than to clipping. Our results provide no evidence that little bluestem should be deferred from grazing after burning as part of a rangeland management strategy.

Warm-season grasses have shown great potential for biomass production. However, their productivity under irrigated conditions has not been thoroughly documented. This study evaluated the biomass production potential and production stability of a number of warm- and cool-season grasses across an irrigation gradient. Under the multiple-harvest management strategy, the cool-season grasses were most productive across the entire growing season. Nevertheless, when considering only the summer harvests, the switchgrass and big bluestem entries were the most productive, although the lowland cultivar Alamo did not perform well under the conditions. Overall, cool-season grasses were clearly the most productive for total biomass production across the growing season. However, based on the high biomass production of switchgrass, this species may have potential as a high-producing option for animal feed during the summer months when the cool-season grasses are unproductive.

A greenhouse experiment was conducted to evaluate the competitive abilities of Schizachyrium scoparium (little bluestem) and Buchloe dactyloides (buffalo grass) in low and high nutrient soil. These species have overlapping ranges and co-occur in semi-arid North American grasslands. Both species showed increases of approximately 2 g plant −1 in aboveground dry mass when soil nutrients were added. Aboveground dry mass of S. scoparium was slightly higher in mixture than in monoculture in low nutrient soil; however, in high nutrient soil, aboveground dry mass in mixture was significantly less than in monoculture. Buchloe dactyloides aboveground dry mass was the same in mixture and monoculture in low nutrient soil; in high nutrient soil, aboveground dry mass was significantly higher in mixture than monoculture. The competitive abilities of these species in shallow soils are dependent upon soil resource levels. At low soil resources, competitive intensity is not great and the two species appear to be equal competitors. At high soil resources, competitive intensity is greater and B. dactyloides reduced the growth of S. scoparium in mixtures. Differences in competitive abilities suggest that during the establishment phase, B. dactyloides would dominate in shallow-high nutrient soils and that coexistence would occur in low nutrient soils.

Big bluestem ( Andropogon gerardii Vitman) and little bluestem [ Schizachyrium scoparium (Michaux) Nash.] are native to the North America and are important forage grasses and ornamental grasses. Both grasses are proposed as ideal biomass producers for cellulosic ethanol production. To apply genetic transformation, which is an important tool for incorporating desirable agronomic traits into plants to both species, however requires an efficient and reproducible regeneration protocol. We used mature caryopses from big and little bluestem as explants and tested the effect of various combinations of 2, 4-dichlorophenoxyacetic acid (2, 4-D) (1, 2, 3, 4 or 5 mg l −1 ) and kinetin (KT) (0, 0.1 or 0.2 mg l −1 ) on embryogenic callus induction with LS as the basal medium. The highest percentage of embryogenic calli induction occurred on medium containing 2, 4-D alone at 2 mg l −1 for ‘Bison’ and on medium containing 4 mg l −1 2, 4-D alone for ‘Bonilla’ big bluestem. For little bluestem, the highest percentage of embryogenic callus induction occurred on medium containing 3 mg l −1 2, 4-D plus 0.1 mg l −1 kinetin, suggesting that addition of KT is beneficial. Shoot regeneration took place on LS basal medium without any plant growth regulator for both species, although the addition of KT increased both regeneration frequency and the number of shoots produced per callus. Rooting of shoots reaching about 2 cm long occurred readily with or without α-naphthaleneacetic acid (NAA). Rooted plantlets were all successfully established in the soil.

Two main hypotheses have been posed to explain the role of phenotypic plasticity in the invasive success of exotic plants: (1) invasive species may be more plastic than resident species in the introduced range, and (2) invasive populations of an exotic species may be more plastic relative to native populations due to evolutionary changes after introduction. To test the first hypothesis, we conducted a greenhouse pot experiment in which seedlings of invasive Sapium sebiferum competed against native Schizachyrium scoparium grasses under different light and water conditions. To test the second hypothesis, we performed an additional greenhouse pot experiment in which seedlings from native and invasive populations of S. sebiferum were grown under environmental treatments analogous to those in the first greenhouse experiment. Compared to native S. scoparium grasses, or to S. sebiferum seedlings from native populations, growth rates of S. sebiferum seedlings from invasive populations were generally higher. When they were competing with S. scoparium grasses, the greater response of S. sebiferum to light and water conditions reflected different patterns: S. sebiferum seedlings were better able to respond with increased growth in unflooded soils, whereas S. sebiferum had more robust growth in the shaded conditions. No difference in responses to change in water conditions, but a significant difference in responses to variation in light conditions was found between two population types of S. sebiferum. The results of this study suggest that relative to S. scoparium, the greater plasticity of S. sebiferum to variation in light conditions is evolved in the introduced range, while that to variation in water conditions reflects an innate property.

We assessed the total length of external arbuscular mycorrhizal hyphae as a function of plant species and functional form richness in restored northern tallgrass prairies. Total hyphal length increased with species and functional form richness. Hyphal length also increased when plant communities were dominated by species with high root density, high root to shoot ratios, and high nitrogen use efficiency. Hyphal length was positively correlated with the biomass of late successional C4 grasses (Andropogon gerardi Vitman, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash-Gould, and Sorghastrum nutans L.), which are obligately mycorrhizal and characterized by high root to shoot ratios, and high root surface area per unit of root biomass. We thus conclude that in order to recover extraradical arbuscular mycorrhizal hyphal length in restored northern tallgrass prairies, at least three factors need to be given priority: 1) achieving high levels of species and functional form richness; 2) making sure that late successional C4 grasses are present; and 3) making sure that the seed mixture includes species that are characterized by high root to shoot ratio, high root density, and high nitrogen-use efficiency.

Two complementary studies were performed to examine (1) the effect of 18 years of nitrogen (N) fertilization, and (2) the effects of N fertilization during one growing season on soil microbial community composition and soil resource availability in a grassland ecosystem. N was added at three different rates: 0, 5.44, and 27.2 g N m−2 y−1. In both studies, Schizachyrium scoparium was the dominant plant species before N treatments were applied. Soil microbial communities from each experiment were characterized using fatty acid methyl ester (FAME) analysis. Discriminant analysis of the FAMEs separated the three N fertilizer treatments in both experiments, indicating shifts in the composition of the microbial communities. In general, plots that received N fertilizer at low or high application rates for 18 years showed increased proportions of bacterial FAMEs and decreased fungal FAMEs. In particular, control plots contained a significantly higher proportion of fungal FAMEs C18:1(cis9) and C18:2(cis9,12) and of the arbuscular mycorrhizal fungal (AMF) FAME, C16:1(cis11), than both of the N addition treatment plots. A significant negative effect of N fertilization on the AMF FAME, C16:1(cis11), was measured in the short-term experiment. Our results indicate that high rates of anthropogenic N deposition can lead to significant changes in the composition of soil microbial communities over short periods and can even disrupt the relationship between AMF and plants.

Sericea lespedeza (Lespedeza cuneata cv. Interstate 76) and little bluestem (Schizachyrium scoparium cv. Aldous) were raised from seed in a glasshouse, transplanted into 5.7-l pots and placed into open-top chambers (OTC) on 6 June 1999. Following a 7-day adjustment period, each of six OTCs (duplicate OTCs per treatment) was ventilated with either air that had been carbon-filtered (CF) to remove ambient ozone (O3); non-filtered (NF), representative of ambient air; or enriched to twice-ambient O3 concentration (2X). Primary-growth forage was harvested on days 7, 32, 46, 59 and 72 following the start of fumigation, and regrowth forage from the first primary-growth harvest was harvested on days 36, 54 and 72 following the start of fumigation. Dry matter (DM) yield of either forage species did not differ among treatments except in the final regrowth period when yield of sericea lespedeza was greater for the NF than 2X O3 treatment. In vitro DM digestibility (IVDMD) and concentrations of crude protein (CP), soluble phenolics (SP) and condensed tannins (CT) in primary-growth sericea lespedeza did not differ between treatments, but NF primary-growth forage had higher concentration of protein-precipitating tannins (PPT) than did 2X primary-growth forage. Concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were higher in NF and 2X than in CF primary-growth sericea lespedeza. Similarly, concentrations of NDF and ADL were higher, and IVDMD was lower for NF and 2X than for CF regrowth sericea lespedeza. Concentrations of ADF and ADL were lower, whereas IVDMD, in vitro NDF digestibility (IVNDFD) and concentrations of CP and SP were greater, in CF than in NF and 2X primary-growth little bluestem. Percentages IVDMD and IVNDFD and concentrations of CP and SP in NF primary-growth little bluestem were greater than those in forage exposed to 2X O3 treatment. No significant differences were observed among treatments in percentages IVDMD and IVNDFD, or concentrations of cell wall constituents or SP in little bluestem regrowth. Nutritive quality of little bluestem was decreased by < 2%, and that of sericea lespedeza by approximately 7% as a result of increased concentrations of cell wall constituents and decreased in vitro digestibility of NF and 2X compared with CF forages. Results indicate that existing and projected O3 levels can drive alterations in forage quality of select warm-season forages sufficient to have nutritional and economic implications for their utilization by ruminant herbivores.

Year-round measurements of surface energy fluxes, supporting meteorological parameters, soil moisture, and leaf foliage area were made at a tallgrass prairie site in north-central Oklahoma. Here we present the results of the first year (August 1996 to early September 1997) of the study. Non-limiting soil moisture and generally moderate atmospheric conditions throughout the measurement period provided a unique opportunity to observe the role of the prairie canopy in influencing energy fluxes. The periods of vegetation activity are determined by employing two approaches: the conventional approach using green foliage area, and a modified approach using photosynthetically active radiation (PAR) albedo in conjunction with the green foliage area. Performance of the two approaches is examined in explaining the seasonal variation in energy fluxes. The conventional approach failed to detect several periods of vegetation activity (e.g., the end of peak growth in 1996, the entire pre-growth and post-burn periods in 1997). Use of the modified approach, on the other hand, allowed us to determine such periods more accurately and in greater detail. Within each of eight periods determined via the modified approach, energy fluxes varied in a manner consistent with the vegetation activity. On an annual basis, evapotranspiration was the main sink of the energy, consuming about 58% of the net radiation. Evapotranspiration was largest during the peak growth period of 1997 (late May to late August: 388 mm, 37% of the annual ET of 1040 mm). Energy fluxes during other periods (e.g., senescence, post-senescence, pre-growth, early growth) were smaller, but still substantial in magnitude as well as in their relative contributions to the annual energy budget.

The Bowen ratio/energy balance (BREB) method was used to measure 30 min water vapor and carbon dioxide (CO 2 ) fluxes over three fields dominated by different C 4 grasses (bermudagrass, tallgrass native prairie, and sorghum) at the Blackland Research Center, Temple, TX. Fluxes were related to biotic and abiotic phenomena. Carbon accumulation rates calculated from BREB measurements were compared with those determined from plant biomass measurements. Thirty min CO 2 fluxes were measured continuously from 22 February to 22 November (days 53–326) in 1993 and from 3 March to 22 November (days 62–326) in 1994. Soil CO 2 fluxes were measured periodically in each field and from a bare soil. In all fields, average daily evapotranspiration varied from less than 1 mm day −1 in March and November to about 5 mm day −1 in June and July. The CO 2 fluxes, which were affected by leaf area, radiation, and soil water content, were near zero in each field in the fall and spring and were maximum in the summer (positive toward surface). Total annual CO 2 flux in the bermudagrass, which was sprigged (planted with grass stolons) in April 1993, was −0.4 and 2.8 kg of CO 2 m −2 year −1 (which are equivalent to −0.1 and 0.8 kg of carbon (C) m −2 year −1 ) in 1993 and 1994, respectively. The larger flux in the second year was due to greater bermudagrass leaf area. Corresponding annual CO 2 fluxes were 0.2 and 0.3 kg m −2 year −1 (0.05 and 0.08 kg C m −2 year −1 ) for the prairie, and 0.9 and −0.3 kg m −2 year −1 (0.2 and −0.09 kg C m −2 year −1 ) for the sorghum. Bare soil CO 2 flux was a small fraction of soil CO 2 flux from all fields, suggesting that a considerable amount of soil CO 2 flux was due to root respiration. The dry matter accumulation rate calculated for each year and field from CO 2 flux measurements was within 20% of the rate calculated from gravimetric biomass measurements. The prairie and sorghum fields were in approximate equilibrium for C storage because estimated annual CO 2 fluxes were near zero. By contrast, the bermudagrass field was a large C sink, primarily in the roots, during the second year. This substantiates other evidence that conversion from continuously cultivated cropland to grassland could create a short-term C sink.

Fallen pine straw (needles) is a renewable biological resource valued as a mulch in horticul- ture and for landscaping. However, its harvesting may have detrimental long-term effects on forest soils and vegetation. To compare current pine straw harvesting practices, a randomized complete block split- plot study was established during 1990 in a 34-year-old stand of direct-seeded longleaf pine (Pinus &usrris Mill.) that had been prescribed burned every 3 years since establishment. Practices included no fertilizer or atmlications of 50 ke ha-' N and 56 kr ha-' P in both 1991 and 1997 as the main olot treatment. Thk' subplot management practices were prescribed burning and the mechanical baling and removal of straw. Pine straw harvesting eventually removed the forest floor and increased soil bulk den- sity by 1993. The growth of longleaf pine was not significantly affected by treatments over a 5-year period from early 1991 to early 1996. Herbaceous plant productivity was determined in July 1997, and there were shifts in plant dominance associated with treatments. Fertilization increased current-year herbaceous plant biomass by 59% on an oven-dried weight basis. Among management practices, pre- scribed burning in early 1991, 1994, and 1997, with two annual straw harvests in early 1992 and 1993, resulted in the greatest herbaceous plant yields by July 1997. The lowest yields in 1997 were on plots that were either annually harvested six times or had been left untreated for over 6 years. Burning every 3 years favored pinehill bluestem (Schizachyrium sq~arium var. divrrgens (Hack.) Gould), which is often the dominant grass on longleaf uplands in the West Gulf Coastal Plain of the U.S.A. Raking straw shifts herbaceous plant dominance to other grasses, principally the panicums (Dicanthelium spp. and Panicum spp.). The cessation of management favored bracken fern (Pteridium aqui linum var. pseu- docaudutum (Clute) Heller). Published by Elsevier Science Ltd.

The aerial parts of Chrysoma pauciflosculosa (syn. Solidago pauciflosculosa ) gave the known diterpenes, 17-oxygrindelic acid, 17-oxogrindelic acid and 17-carboxygrindelic acid, as well as the new diterpene, 17-hydroxy-7α,8α-epoxygrindelic acid. 17-Oxogrindelic acid decomposes in the presence of air giving three products. The structural data of the diterpenes as well as those of degradation products and derivatives were elucidated by chemical and spectroscopic methods. 17-Oxygrindelic acid and 17-oxogrindelic acid were tested for their effect on the germination and radicle growth of three Florida sandhill species and Lactuca sativa . At concentrations of 12 to 48 ppm, 17-oxogrindelic acid reduced the germination and radicle growth of Schizachyrium scoparium and Leptochloa dubia , two native sandhill grasses, but had no significant effects on germination and only a slight stimulatory effect on radicle growth of Rudbeckia hirta and Lactuca sativa . Mixtures of 17-oxogrindelic acid with an equimolar mixture of three C. pauciflosculosa sesquiterpenes, (+)-curlone, (+)-sesquiphellandrene and (−)-α- trans -bergamontene, did not enhance activity. 17-Oxygrindelic acid was in general less active in reducing germination and growth than 17-oxogrindelic acid.

Host-mycorrhizal preference was examined between native prairie grasses, Schizachyrium scoparium, Andropogon gerardii and Sporobolus heterolepis , and isolates of indigenous vesicular-arbuscular mycorrhizal fungal species, Glomus sp. (undescribed), G. geosporum and G. fasciculatum . For most grass-mycorrhizal combinations the percent of root length colonized either increased or remained unchanged with the increase in age of the plants. Glomus sp. was the most highly invasive mycorrhizal fungus, having the highest percent of root length colonized for all three grasses. The other fungal isolates exhibited preferential colonization of the three native grasses. The results demonstrate that the indigenous mycorrhizal fungal isolates tested showed a considerable amount of host preference.

Investigation of the roots of Chrysoma pauciflosculosa (syn. Solidago pauciflosculosa) resulted in the isolation of the known polyacetylenes, cis,cis- and cis,trans-matricaria esters, and their epoxide derivatives. In addition, the triterpene epifriedelinol was obtained, and its molecular structure determined by single crystal X-ray diffraction. The structures of the four polyacetylenes were elucidated by spectroscopic methods and by comparison with reported spectral data. The cis,cis- and cis, trans-matricaria esters were tested for their effects on the germination and radicle growth of the two sandhill grasses Schizachyrium scoparium and Leptochloa dubia, commercial lettuce and commercial radish. They were highly active against three of four test species, completely inhibiting germination at 106 and 92 ppm, respectively. A saturated aqueous solution of the triterpene epifriedelinol showed no activity.

From the aerial parts of Calamintha ashei the new menthofuran, calaminthone, as well as the known terpenoids (+)-evodone, caryophyllene oxide and ursolic acid were isolated and identified by spectroscopic methods (NMR and MS). Menthofuran and 2,3-dihydroevodone were present in the volatiles as determined by GC-MS analyses. Evodone and calaminthone volatiles exhibited strong germination inhibitory activities towards Schizachyrium scoparium seeds. The aqueous solution of a fraction containing calaminthone, evodone and caryophyllene oxide totally inhibited germination of S. scoparium seeds but had no significant effects on Lactuca sativa seed germination. A saturated aqueous solution of pure evodone exhibited stimulatory effects on S. scoparium but inhibitory effects were observed when evodone was administered in a saturated aqueous solution of ursolic acid. The possible role of ursolic acid in the release and transport of allelopathic lipids from the source plant into the soil through rain leachates is discussed.

A study to investigate polynuclear aromatic hydrocarbons (PAH) on leaves of Little Bluestem (Schizachyrium scoparium ( Michx.) nash ) and Post Oak (Quercus stellata wagenh.) was conducted from October 1967 to February 1969. By means of thin-layer and gas-liquid chromatography, five PAH were identified and quantified: anthracene, fluoranthene, pyrene, benz(a)anthracene and benzo(a)pyrene. A sixth compound, 3-methylpyrene, was not detected. Individual PAH contents ranged from 5 to 110 μ kg−1 dry plant material. In most instances, higher levels were obtained from Post Oak leaves than from Little Bluestem. Samples from the control area in most instances had higher concentrations than samples from the railroad right-of-way. Individual and total PAH concentrations were highest on dormant plants and lowest during periods of active plant growth. A comparison of pyrene to benzo(a)pyrene ratios suggested that most of the PAH found on the leaves were products of plant biochemical synthesis and not products of locomotive exhaust.