The world\'s highest yielding crops are C4 plants due to their higher water use efficiency, nitrogen use efficiency, and productivity compared with C3 plants.  With an increasing demand for renewable resources as a result of the decreasing global supplies of fossil fuels, we need to improve our understanding of the limitations of biomass fuel feedstock to improve yields and better satisfy energy requirements.  The ability to attain the goal feedstock production in the US is limited by available arable land and cool temperatures.  This study investigates the effects of cool temperatures on the productivity and photosynthesis of the two species with the highest potential for feedstock production in the US: switchgrass (Panicum virgatum) cv. Alamo and miscanthus (Miscanthus × giganteus).  At 14/12"C and a 14/10 hour light/dark photoperiod, switchgrass showed lower productivity and light saturated photosynthetic rates (Amax=10.3 "mol m-2s-1) compared with 28/25"C and the same photoperiod (Amax=18.8 "mol m-2s-1).  Miscanthus has demonstrated cold tolerance in previous studies, and here showed no significant decrease in the productivity or photosynthetic rates in cool, compared with warm, growing conditions (Amax=8.2 "mol m-2s-1 and 7.0 "mol m-2s-1 for warm and cool conditions, respectively). Also, this study examines the potential limitations of C4 photosynthesis by the enzyme pyruvate phosphate dikinase (PPDK) under the same cool conditions, transgenic switchgrass cv. Alamo were created with the insertion of the miscanthus PPDK gene. Productivity and photosynthetic responses of the transgenic plants were evaluated in cool and warm growth temperatures.  Of the two transgenic events tested here, line S(1) displayed cold tolerance, as seen in no loss of both carboxylation efficiency and the ratio of CO2 assimilation to electron transport (Asat/Jmax).  These results indicate that PPDK may pose a significant limitation to C4 photosynthesis in cool conditions and there is a possibility that cold season photosynthesis of switchgrass cv. Alamo could be improved. / Master of Science

Interest in renewable energy and governmental mandates has motivated land managers to consider cellulosic feedstocks for bioenergy. I investigated plant community response to a system including switchgrass (Panicum virgatum) as a feedstock intercropped with loblolly pine (Pinus taeda). I estimated plant species evenness, richness, and diversity and biomass production, with emphasis on white-tailed deer (Odocoileus virginianus) forages. I detected 225 species in 2,220 1-m2 quadrats, and 7,495 biomass samples (96.4 kg dry weight) from 960 quadrats. Intercropping reduced plant species diversity, total non-pine tree biomass, and biomass of deer forages during switchgrass establishment. These effects were no longer apparent at treatment level two years after switchgrass establishment, except that deer browse and total deer forage biomass remained less in intercropped interbeds. Intercropping in managed pines may temporarily effect plant communities but further studies are needed to examine longer term effects and to quantify effects on nutritional carrying capacity for deer.

An experiment was conducted to determine temperature effects on switchgrass seed germination, a native species with feedstock potential for the biofuel industry. Stratified seeds were germinated at constant temperatures, 15 to 45°C with 5°C interval. Maximum seed germination (MSG) and germination rate (GR), estimated by fitting sigmoid function to germination-time series data, varied among genotypes. Quadratic and bilinear models best described the MSG and GR responses to temperature, respectively. The mean cardinal temperatures, minimum, optimum and maximum, were 8.1, 26.6 and 45.1ºC for MSG and 11.1, 33.1 and 46.0ºC for GR, respectively, varied among genotypes. Genotypes were classified for temperature tolerance based on cumulative temperature response index: ‘Summer’ and ‘Expresso’ were identified as the most heat- and cold-tolerant genotypes, respectively. The functional algorithms and identified tolerant genotypes may be used to improve switchgrass models for field applications and breeding programs to develop new genotypes with enhanced tolerance for niche environments.

No description available.

Switchgrass (Panicum virgatum), a high-yielding perennial C4 prairie grass species, is a top candidate as a bioenergy feedstock for cellulosic ethanol production. Seedling establishment is a primary concern given the inherent variability in switchgrass seed dormancy. Determining current states of seed quality in terms of emergence percentage is crucial for a successful stand establishment. A practical seed vigor test was conducted under greenhouse conditions to determine current emergence percentage. Three depths and three media types were conditions evaluated in the vigor test. To find correlation between emergence percentage in greenhouse test conditions and that in field conditions, results from the vigor test were applied in two separate field evaluations. Field evaluations showed that vigor test conditions of field soil at 1-cm depth yielded below the target, suggesting that this condition did not put enough stress on seedling emergence in the greenhouse vigor test. A 20% increase of vigor test results in the field soil/1 cm condition could accurately predict field emergence. Field results suggested that coarse sand at 5-cm accurately predicted field emergence of highly vigorous varieties and that coarse sand at 1-cm and fine sand at 3-cm predicted field emergence in moderately to least vigorous varieties.

No description available.

To decrease dependency of fossil fuels and avoid direct competition with food crops, massive research efforts are investigating next-generation cellulose biofuel crops such as switchgrass (Panicum virgatum). A low-input, sustainable switchgrass production could be achieved by reducing traditional management practices though applying plant growth promoting rhizobacteria (PGPR), of which our understanding is still rather limited. To elucidate physiological mechanisms behind PGPR's beneficial effects, we inoculated switchgrass seedlings with Burkholderia phytofirmans strain PsJN. Two experiments were conducted to determine the initial and long-term responses of switchgrass to PsJN inoculation by tracking growth and leaf physiology. In a third experiments, we tested the effects of PsJN on growth and leaf-level physiology of switchgrass under a moderate pre-drought conditioning and a successive severe drought stress. PsJN inoculation increased biomass and promoted elongation of shoots within 17 days following inoculation. The enhanced root growth in PsJN inoculated plants lagged behind the shoot response, resulting in greater allocation to aboveground growth (p=0.0041). Lower specific root length (p=0.0158) and higher specific leaf weight (p=0.0029) were also observed in PsJN inoculated seedlings, indicating advanced development. Photosynthetic rates (Ps) were higher in PsJN inoculated seedlings after 17 days (54%, p=0.0016), which were related to higher stomatal conductance, greater water use efficiency, and lower non-stomatal limitation of Ps. These rapid changes in leaf physiology are at least partially responsible for switchgrass growth enhancement from PsJN treatment. The early growth enhancement in PsJN inoculated switchgrass linearly decreased with plant age. PsJN inoculation increased Ps of upper canopy leaves by 13.6% but reduced Ps of lower canopy leaves by 8.2%. Accelerated leaf senescence and early flowering were observed in PsJN-inoculated switchgrass, which might contribute to slightly lower aboveground biomass at final harvesting. Drought preconditioning increased Ps of PsJN-inoculated switchgrass during a later severe drought; whereas, control switchgrass only benefited from drought preconditioning when leaf water potential dropped below -1 MPa. This study verified early growth enhancement and accelerated development of switchgrass due to PsJN inoculation. Rapid improvement in leaf physiology is related to enhanced productivity. PsJN inoculation also improve drought tolerance of switchgrass. / Ph. D.

Switchgrass (Panicum virgatum L.) has potential as a biofuels feedstock. Major management questions include cultivar selection, cutting management, and optimizing N fertilization. Four cultivars of switchgrass were evaluated under two cutting regimes at eight locations within KY, NC, TN, VA, and WV in 2000 and 2001. Harvests were made once (in early November) or twice (midsummer and early November). Biomass yields averaged 15 Mg ha-1 and ranged from 10 to 22 Mg ha-1 across locations and years. There was no yield advantage to taking two harvests of the lowland cultivars ("Alamo" and "Kanlow"). If harvested twice, the upland cultivars ("Cave-in-Rock" and "Shelter") provided yields equivalent to the lowland ecotypes. A closer look at Alamo revealed much higher N removal in the midsummer harvests, late-season N translocation out of tillers, and fewer tillers developing under one-cut management. Switchgrass appears to be capable of truly perennial productivity in the upper Southeast USA with 50 kg N ha-1 yr-1 and a single harvest. A second field study was conducted on "Cave-in-Rock" switchgrass at Orange and Blacksburg, VA to examine N dynamics. For the 3-yr study, N fertilizer was applied once in May 2001 at 0, 90, 180, or 270 kg N ha-1. Switchgrass was harvested once (early November) in 2001 and twice (early July and early November) in 2002 and 2003. Tissue, root, and soil samples were collected in May, July, September, and November each year. Nitrogen fertilization had no effect on yield in 2001 and small residual effects in 2002 and 2003. Higher N removal was observed with two-cut management, where a high-yielding July cut had high shoot N concentrations. The amount of N removed as biomass from the 0 N treatments over 3 yr was 227 kg N ha-1; obviously significant amounts of N can be made available by these soils without any fertilizer applied. During the growing season, higher mineral N in soil was observed in July and September, when warmer temperatures increase microbial activity and N mineralization. Nitrogen use efficiency declined with increasing N rates. The low N response could be due to "native" N, to microbiological interactions, and/or to the ability of the plants to create internal N reserves. Proper N management of switchgrass must take into account the dynamics of several N pools. Greenhouse studies were conducted to establish switchgrass' responses to N and P under well-defined, soilless conditions and to examine two N sources. Shoot biomass increased with N fertilization with an observed inflection point at 210 kg N ha-1. In these pot studies, root biomass increased with N only to 115 kg N ha-1. No significant effect of P above 30 kg ha-1 was observed in shoot or root biomass. Biomass yield and tiller number were highly correlated. Biomass production was two times greater with ammonium sulfate than with urea when each was applied at equivalent N rates. Taken together, these findings suggest soils in the upper Southeast USA can supply significant amounts of the N needs of switchgrass, especially when harvested once at the end of the season. / Ph. D.

Switchgrass (Panicum virgatum L.) is a cellulosic feedstock for alternative energy production that could grow well between planted pines (Pinus spp.). Southeastern planted pine occupies 15.8 million hectares and thus, switchgrass intercropping could affect biodiversity if broadly implemented. Therefore, I evaluated effects of intercropping switchgrass in loblolly pine (P. taeda L.) plantations on plant community diversity, plant biomass production, and white-tailed deer (Odocoileus virginianus Zimmerman) nutritional carrying capacity. In a randomized complete block design, I assigned three treatments (switchgrass intercropped, switchgrass monoculture, and a “control” of traditional pine management) to 4 replicates of 10-ha experimental units in Kemper County, Mississippi during 2014-2015. I detected 246 different plant species. Switchgrass intercropping reduced plant species richness and diversity but maintained evenness. I observed reduced forb and high-use deer forage biomass but only in intercropped alleys (interbeds). Soil micronutrient interactions affected forage protein of deer plants. White-tailed deer nutritional carrying capacity remained unaffected.

No description available.