Consequences of elevated temperatures on legume biomass and nitrogen cycling in a field warming and biodiversity experiment in a North American prairie

Increases in global temperature are likely to have effects on the nitrogen cycle, including those mediated through effects on legumes, which have a role in the N cycle by fixing N2. These effects may alter plant functioning and community structure, especially in N-limited ecosystems. We manipulated temperature and plant diversity in the field to investigate the effects of elevated temperature on aboveground biomass, shoot N concentration ([N]), and reliance on N2 fixation of four prairie legumes (Amorpha canescens Pursh., Dalea purpurea Vent., Lespedeza capitata Michx. and Lupinus perennis L.) planted in plots of varying species numbers. We monitored the effect of warming on soil microclimate and net N mineralisation rates, as these variables may mediate the effect of warming on legumes. Warming decreased soil moisture and increased soil temperature, but had no effect on net N mineralisation. Warming increased the aboveground biomass of D. purpurea and L. perennis, but decreased shoot [N] for all species in one year. Though the data were not optimal for quantifying N2 fixation using stable isotopes, they suggest that warming did not affect the reliance on N2 fixation. Species diversity did not have strong effects on the response to warming. These results suggest that legume-mediated effects of temperature on N cycling will arise from changes in biomass and tissue chemistry, not N2 fixation. We observed strong interannual variation between a wet and dry year for N mineralisation, shoot [N] and reliance on N2 fixation, suggesting that these may be more responsive to precipitation changes than elevated temperature.

Vascular Plant Communities of the Green River Lowlands in Northwestern Illinois

A few high-quality prairies still exist in the sand deposits of the Green River Lowlands. The most extensive remnants are in the Green River State Wildlife Area, Lee County, Illinois. Three upland prairie communities were surveyed; a dry sand prairie dominated by Schizachyrium scoparium, Ambrosia psilostachya, and Amorpha canescens; a dry-mesic sand prairie dominated by Sorghastrum nutans, Schizachyrium scoparium, Antennaria plantaginifolia, and Liatris aspera; and a mesic sand prairie where Sorghastrum nutans and Andropogon gerardii were the dominant grasses, and Parthenium integrifolium, Fragaria virginiana, Liatris pycnostachya, and Euthamia gymnospermoides the common forbs. The lowlands, which included approximately 325 ha, were dominated by the exotic Phalaris arundinacea, but high-quality wet sand prairie, sedge meadow, and marsh communities existed. The wet sand prairies were dominated by Spartina pectinata, Helianthus grosseserratus, and Solidago canadensis; the sedge meadows were dominated by Carex haydenii, Calamagrostis canadensis, and Persicaria coccinea; the marsh communities were divided into distinct vegetation zones. These vegetation zones were surveyed in 2002 and subjected to an extensive uncontrolled fire in 2005. Surveys completed in 2006 and 2007 were used to determine successional changes resulting from the fire. These studies suggested that most communities were returning to the species composition found before the 2005 fire.

High Pressure Liquid Chromatographic Separation of Rotenoids from Plant Extracts

The concomitant isolation, identification, and quantitative determination of rotenoids by high pressure liquid chromatography and ultraviolet and mass spectral analyses is presented. Plant samples are extracted with chloroform-methanol, subjected to a combination of solvent partitioning and silica gel open column chromatographic cleanup, and then chromatographed by HPLC reverse phase techniques. Concentrations of rotenone and deguelin are reported for Tephrosia virginiana (L.) Pers. and Amorpha canescens Persh.