Carbon accumulation in soils constitutes a significant sink for carbon. How the climate change with increasing temperatures will affect the soil carbon storage represents uncertainty of the predictions in the climate change ecosystem feedback mechanisms. In this study the temperature impact on the decomposition of the large carbon pools in peatlands was investigated. Peat cores from different microtopographic units in a boreal oligotrophic minerogenic mire in northern Sweden were collected from in three depths (5-10, 10-15 and 15-20 centimeters below the surface). The samples were incubated at four temperatures: 4, 9, 14 and 19°C and the heterotrophic respiration (CO2- production) was measured hourly or 37 days. Unexpectedly, basal respiration did not show any correlation with temperature. However, the exponential increase in respiration (µ) was correlated with temperature: i.e.  giving Q10 values between 2 (SE +/- 0.36) and 5 (SE +/-1.05). Soil depth or vegetation covers did not affect temperature response (Q10) of µ. The substrate induced respiration (SIR) did not occour but for a few of the samples. The conclusion from this study is that degradation of peat seams not be affected by a temperature increase. The addition of glucose, nitrogen and phosphorus increased with increasing temperature with a Q10 value as expected.

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.

Climate change poses a significant threat to bioenergy production, impacting plant’s phenology and physiological performance. Investigating the adaptation of bioenergy crops like Populus is crucial for sustaining production. Populus, known for its genetic variation and ease of study, offers insights into tree responses to climate change. My research, part of the Advancing Populus Pathways in the Southeast (APPS) project, focuses on various Populus genotypes across multiple growing seasons, exploring phenology under different management strategies. Planting Populus across two sites, namely Monroe and Pontotoc, allows for the examination of genotype responses to climate change factors, particularly in terms of phenology and productivity. Factors like parentage provenance and temperature fluctuations influence budburst timing. Additionally, management practices, such as coppicing, significantly affect budburst, with coppiced trees showing delayed timing (five to ten days) compared to non-coppiced ones. Cold spell damage during budbreak reveals vulnerability, with northern provenances exhibiting greater resilience. Understanding such events is vital for tailored management. Cold spells not only impact initial budbreak but also alter leaf phenology and canopy dynamics, affecting overall productivity. Genotypes exhibit varied responses to rising temperatures and CO2 levels, influenced by their parentage. Trees with northern provenance, for instance, display higher photosynthetic capacity, but may face thermal stress under certain temperature increases. Conversely, southern genotypes demonstrate moderate photosynthetic capacity, but showcase better adaptation to heat, offering potential for breeding resilient varieties. Leaf traits serve as proxies for biomass production and water use efficiency prediction, aiding in genotype screening. Mechanisms like self-shading and leaf movability influence responses to environmental changes. For instance, self-shading helps regulate leaf temperature, thereby enhancing photosynthetic performance, albeit with some trade-offs. Elevated CO2 levels enhance water use efficiency, but determining whole-tree water use efficiency requires integration of various methods. While leaf-level measurements correlate with whole-tree water use efficiency, an integrated approach, combining leaf-level gas exchange and isotopic measurements, shows promise. In conclusion, understanding Populus responses to climate change is crucial for sustainable bioenergy production in the southeastern United States. Insights into phenology, productivity, and adaptation mechanisms offer avenues for management and breeding strategies, ensuring resilience amidst shifting climates.

Invasive non-indigenous species are among the principle drivers of global change, altering nutrient cycles, changing disturbance regimes, and generally threatening biodiversity. Climate change is widely expected to exacerbate invasions by relaxing abiotic barriers, such as low temperature, but the mechanistic evidence supporting this is limited. Here, I evaluate the hypothesis that low temperatures determine the northern range limit of kudzu (Pueraria montana var. lobata), an invasive Asiatic vine in North America, by assessing freezing and chilling tolerance of kudzu plants in winter, spring, summer, and fall. Kudzu was widely planted throughout the southeastern U.S. in the early 20th Century to prevent erosion. It is winter-deciduous and reproduces primarily from buds on stem nodes. In the last 40 years, kudzu has migrated northward in concert with a northward shift in the -20oC minimum winter temperature isocline, indicating that less severe winter cold is permitting northward migration. Freezing mortality during winter does not explain this correlation. Electrolyte leakage assays demonstrate that above- and belowground kudzu stems can survive to -27oC and -17oC. Insulation provided by soil and snow protects belowground stems from lethal temperatures to well north of kudzu's current range limit. Severe spring chill stops growth and photosynthesis and causes some shoot mortality, but both growth and photosynthesis recover quickly following the chill. Summer growth rates are rapid (up to 22 cm/d), responding within hours to temperature changes, and are unimpaired by nighttime lows. Photosynthesis is reduced at cool temperatures, but on cool days, kudzu leaves tend to be warmer than air temperature, so photosynthesis rates generally remain close to optimal values. In autumn, growth stops below 15oC, but leaves are retained and maintain modest photosynthetic competence until killed by frost in November. In colder climates that occur far north of kudzu's current range, reductions in the length and quality of the growing season could accumulate over time to reduce kudzu's success. There is, however, no strong evidence that low temperatures in any season will prevent kudzu from migrating throughout southern Ontario, making kudzu a good candidate for invasive species regulations.

Invasive non-indigenous species are among the principle drivers of global change, altering nutrient cycles, changing disturbance regimes, and generally threatening biodiversity. Climate change is widely expected to exacerbate invasions by relaxing abiotic barriers, such as low temperature, but the mechanistic evidence supporting this is limited. Here, I evaluate the hypothesis that low temperatures determine the northern range limit of kudzu (Pueraria montana var. lobata), an invasive Asiatic vine in North America, by assessing freezing and chilling tolerance of kudzu plants in winter, spring, summer, and fall. Kudzu was widely planted throughout the southeastern U.S. in the early 20th Century to prevent erosion. It is winter-deciduous and reproduces primarily from buds on stem nodes. In the last 40 years, kudzu has migrated northward in concert with a northward shift in the -20oC minimum winter temperature isocline, indicating that less severe winter cold is permitting northward migration. Freezing mortality during winter does not explain this correlation. Electrolyte leakage assays demonstrate that above- and belowground kudzu stems can survive to -27oC and -17oC. Insulation provided by soil and snow protects belowground stems from lethal temperatures to well north of kudzu's current range limit. Severe spring chill stops growth and photosynthesis and causes some shoot mortality, but both growth and photosynthesis recover quickly following the chill. Summer growth rates are rapid (up to 22 cm/d), responding within hours to temperature changes, and are unimpaired by nighttime lows. Photosynthesis is reduced at cool temperatures, but on cool days, kudzu leaves tend to be warmer than air temperature, so photosynthesis rates generally remain close to optimal values. In autumn, growth stops below 15oC, but leaves are retained and maintain modest photosynthetic competence until killed by frost in November. In colder climates that occur far north of kudzu's current range, reductions in the length and quality of the growing season could accumulate over time to reduce kudzu's success. There is, however, no strong evidence that low temperatures in any season will prevent kudzu from migrating throughout southern Ontario, making kudzu a good candidate for invasive species regulations.

The intensification of aridity due to anthropogenic climate change is likely to have a large impact on the growth and survival of plant species in the southwestern U.S. where species are already vulnerable to high temperatures and limited precipitation. Global climate change impacts plants through a rising temperature effect, CO2 effect, and land management. In order to forecast the impacts of global climate change, it is necessary to know the current conditions and create a baseline for future comparisons and to understand the factors and players that will affect what happens in the future. The objective of Chapter 1 is to create the very first high resolution, accurate, park-wide map that shows the distribution of dominant plants on the Colorado Plateau and serves as a baseline for future comparisons of species distribution. If we are going to forecast what species have already been impacted by global change or will likely be impacted in the future, we need to know their physiology. Chapter 2 surveys the physiology of the twelve most abundant non-tree species on the Colorado Plateau to help us forecast what climate change might do and to understand what has likely already occurred. Chapter 1. Our objective was to create an accurate species-level classification map using a combination of multispectral data from the World View-3 satellite and hyperspectral data from a handheld radiometer to compare pixel-based and object-based classification. We found that overall, both methods were successful in creating an accurate landscape map. Different functional types could be classified with fairly good accuracy in a pixel-based classification but to get more accurate species-level classification, object-based methods were more effective (0.915, kappa coefficient=0.905) than pixel-based classification (0.79, kappa coefficient=0.766). Although spectral reflectance values were important in classification, the addition of other features such as brightness, texture, number of pixels, size, shape, compactness, and asymmetry improved classification accuracy.Chapter 2. We sought to understand if patterns of gas exchange to changes in temperature and CO2 can explain why C3 shrubs are increasing, and C3 and C4 grasses are decreasing in the southwestern U.S. We conducted seasonal, leaf-level gas exchange surveys, and measured temperature response curves and A-Ci response curves of common shrub, forb, and grass species in perennial grassland ecosystems over the year. We found that the functional trait of being evergreen is increasingly more successful in climate changing conditions with warmer winter months. Grass species in our study did not differentiate by photosynthetic pathway; they were physiologically the same in all of our measurements. Increasing shrub species, Ephedra viridis and Coleogyne ramosissima displayed functional similarities in response to increasing temperature and CO2.

The intensification of aridity due to anthropogenic climate change is likely to have a large impact on the growth and survival of plant species in the southwestern U.S. where species are already vulnerable to high temperatures and limited precipitation. Global climate change impacts plants through a rising temperature effect, CO2 effect, and land management. In order to forecast the impacts of global climate change, it is necessary to know the current conditions and create a baseline for future comparisons and to understand the factors and players that will affect what happens in the future. The objective of Chapter 1 is to create the very first high resolution, accurate, park-wide map that shows the distribution of dominant plants on the Colorado Plateau and serves as a baseline for future comparisons of species distribution. If we are going to forecast what species have already been impacted by global change or will likely be impacted in the future, we need to know their physiology. Chapter 2 surveys the physiology of the twelve most abundant non-tree species on the Colorado Plateau to help us forecast what climate change might do and to understand what has likely already occurred. Chapter 1. Our objective was to create an accurate species-level classification map using a combination of multispectral data from the World View-3 satellite and hyperspectral data from a handheld radiometer to compare pixel-based and object-based classification. We found that overall, both methods were successful in creating an accurate landscape map. Different functional types could be classified with fairly good accuracy in a pixel-based classification but to get more accurate species-level classification, object-based methods were more effective (0.915, kappa coefficient=0.905) than pixel-based classification (0.79, kappa coefficient=0.766). Although spectral reflectance values were important in classification, the addition of other features such as brightness, texture, number of pixels, size, shape, compactness, and asymmetry improved classification accuracy.Chapter 2. We sought to understand if patterns of gas exchange to changes in temperature and CO2 can explain why C3 shrubs are increasing, and C3 and C4 grasses are decreasing in the southwestern U.S. We conducted seasonal, leaf-level gas exchange surveys, and measured temperature response curves and A-Ci response curves of common shrub, forb, and grass species in perennial grassland ecosystems over the year. We found that the functional trait of being evergreen is increasingly more successful in climate changing conditions with warmer winter months. Grass species in our study did not differentiate by photosynthetic pathway; they were physiologically the same in all of our measurements. Increasing shrub species, Ephedra viridis and Coleogyne ramosissima displayed functional similarities in response to increasing temperature and CO2.