Hydrothermal conversion of big bluestem for bio-oil production: the effect of ecotype and planting location.

Three ecotypes (CKS, EKS, IL) and one cultivar (KAW) of big bluestem (Andropogon gerardii) that were planted in three locations (Hays, KS; Manhattan, KS; and Carbondale, IL) were converted to bio-oil via hydrothermal conversion. Significant differences were found in the yield and elemental composition of bio-oils produced from big bluestem of different ecotypes and/or planting locations. Generally, the IL ecotype and the Carbondale, IL and Manhattan, KS planting locations gave higher bio-oil yield, which can be attributed to the higher total cellulose and hemicellulose content and/or the higher carbon but lower oxygen contents in these feedstocks. Bio-oil from the IL ecotype also had the highest carbon and lowest oxygen contents, which were not affected by the planting location. Bio-oils from big bluestem had yield, elemental composition, and chemical compounds similar to bio-oils from switchgrass and corncobs, although mass percentages of some of the compounds were slightly different.

Effect of elevated CO2 and drought on soil microbial communities associated with Andropogon gerardii.

Our understanding of the effects of elevated atmospheric CO2, singly and in combination with other environmental changes,on plant-soil interactions is incomplete. Elevated CO2 effects on C4 plants, though smaller than on C3 species, are mediated mostly via decreased stomatal conductance and thus water loss. Therefore, we characterized the interactive effect of elevated CO2 and drought on soil microbial communities associated with a dominant C4 prairie grass, Andropogon gerardii Vitman. Elevated CO2 and drought both affected resources available to the soil microbial community. For example, elevated CO2 increased the soil C:N ratio and water content during drought, whereas drought alone decreased both. Drought significantly decreased soil microbial biomass. In contrast, elevated CO2 increased biomass while ameliorating biomass decreases that were induced under drought. Total and active direct bacterial counts and carbon substrate use (overall use and number of used sources) increased significantly under elevated CO2. Denaturing gradient gel electrophoresis analysis revealed that drought and elevated CO2, singly and combined, did not affect the soil bacteria community structure.We conclude that elevated CO2 alone increased bacterial abundance and microbial activity and carbon use, probably in response to increased root exudation. Elevated CO2 also limited drought-related impacts on microbial activity and biomass,which likely resulted from decreased plant water use under elevated CO2. These are among the first results showing that elevated CO2 and drought work in opposition to modulate plant-associated soil-bacteria responses, which should then influence soil resources and plant and ecosystem function.

Effects of N on plant response to heat-wave: a field study with prairie vegetation.

More intense, more frequent, and longer heat-waves are expected in the future due to global warming, which could have dramatic ecological impacts. Increasing nitrogen (N) availability and its dynamics will likely impact plant responses to heat stress and carbon (C) sequestration in terrestrial ecosystems. This field study examined the effects of N availability on plant response to heat-stress (HS) treatment in naturally-occurring vegetation. HS (5 d at ambient or 40.5 degrees C) and N treatments (+/-N) were applied to 16 1 m(2) plots in restored prairie vegetation dominated by Andropogon gerardii (warm-season C4 grass) and Solidago canadensis (warm-season C3 forb). Before, during, and after HS, air, canopy, and soil temperature were monitored; net CO2 assimilation (P(n)), quantum yield of photosystem II (Phi(PSII)), stomatal conductance (g(s)), and leaf water potential (Psi(w)) of the dominant species and soil respiration (R(soil)) of each plot were measured daily during HS. One week after HS, plots were harvested, and C% and N% were determined for rhizosphere and bulk soil, and above-ground tissue (green/senescent leaf, stem, and flower). Photosynthetic N-use efficiency (PNUE) and N resorption rate (NRR) were calculated. HS decreased P(n), g(s), Psi(w), and PNUE for both species, and +N treatment generally increased these variables (+/-HS), but often slowed their post-HS recovery. Aboveground biomass tended to decrease with HS in both species (and for green leaf mass in S. canadensis), but decrease with +N for A. gerardii and increase with +N for S. canadensis. For A. gerardii, HS tended to decrease N% in green tissues with +N, whereas in S. canadensis, HS increased N% in green leaves. Added N decreased NRR for A. gerardii and HS increased NRR for S. canadensis. These results suggest that heat waves, though transient, could have significant effects on plants, communities, and ecosystem N cycling, and N can influence the effect of heat waves.

Arbuscular mycorrhizal fungi enhance aluminium resistance of broomsedge (Andropogon virginicus L.).

In the eastern United States, broomsedge (Andropogon virginicus L.) is found growing on abandoned coal-mined lands that have extremely acidic soils with high residual aluminium (Al) concentrations. Broomsedge may be inherently metal-resistant and nutrient-efficient or may rely on the arbuscular mycorrhizal (AM) fungal association to overcome limitations on such sites. Broomsedge plants were grown with and without an acidic ecotype AM fungal consortium and exposed to controlled levels of Al in two experiments. The AM fungal consortium conferred Al resistance to broomsedge. Arbuscular mycorrhizal fungi reduced Al uptake and translocation in host plants, potentially reflecting measured reductions in inorganic Al availability in the rhizosphere of mycorrhizal plants. Mycorrhizal plants exhibited lower shoot P concentrations, higher phosphorus use efficiency, and lower root acid phosphatase rates than non-mycorrhizal plants. Aluminium significantly reduced calcium (Ca) and magnesium (Mg) tissue concentrations in both mycorrhizal and non-mycorrhizal plants. However, plant response to any change in nutrient acquisition was substantially less pronounced in mycorrhizal plants. The exclusion of Al and greater stability of tissue biomass accretion-tissue nutrient relationships in mycorrhizal broomsedge plants exposed to Al may be important mechanisms that allow broomsedge to grow on unfavourable acidic soils.