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Natural climate solutions, such as reforestation, are increasingly called for to lower atmospheric CO2 concentrations and prevent further warming of the climate. Predictive modeling of forest stand dynamics provides a quantitative framework that can be used to select the tree species with the highest carbon (C) uptake potential for restoration efforts based upon site-specific and species-specific data. To simulate stand dynamics and compare C uptake and storage potential of three pine species across Florida, I developed individual-based models that combined environmentally-sensitive tree growth models with background mortality taken from the literature. Growth model parameters were estimated using space for time (SFT) substitution and mortality model parameters were estimated from published literature possibly introducing biases into model development. Therefore, to explore these possible biases, parameters of both growth and mortality models were calibrated through a Bayesian inversion technique using forest growth and mortality data. Simulated results of total above-ground biomass (AGB), for both calibrated and SFT models, were compared with Forest Inventory and Analysis (FIA) re-measurement data. Model results demonstrate that SFT substitution adequately predicted growth rate of P. taeda, P. palustris, and P. elliottii, while Bayesian inversion helped to calibrate parameters in mortality functions reported in published literature. The results highlight the possible benefit of using SFT substitution in tree growth models, helping to save time and resources, as this modeling framework can be easily replicated for forests in other states using open-sourced data from FIA and globally gridded raster data of climate and edaphic properties.

To understand the molecular mechanisms that regulate expansion in plants, I analyzed a mutant, rsw4, previously isolated on the basis of temperature-dependent root swelling. Map based cloning had identified RSW4 as At4g22970, which contains a domain homologous to separase, an enzyme demonstrated to be required for sister chromatid disjunction during mitosis in animals and fungi. I confirmed a role for separase in segregation of sister chromatids in plants. However, with defects in chromosome disjunction, I detected no DNA damage. In addition, the non-disjoined chromosomes did not trigger detectable cell cycle arrest, based on the expression of cell cycle marker genes examined by real time qRT-PCR. Interestingly, the degradation of cyclin B1;1 was prevented in rsw4, based on the extensive accumulation of a reporter construct based on GUS. The transverse alignment of cortical microtubules, which are widely believed to define the directionality of expansion, were disrupted in rsw4 . The disorganization of cortical microtubules was concomitant with root swelling. In addition, polarity of cortex cells appeared to be affected in rsw4. The polar targeting of the auxin efflux protein, PIN2, reversed polarity in cortex cells of rsw4. One micro-array run showed a variety of genes with changed expression level in rsw4. By real rime PCR, I confirmed some genes to have altered expression, including enzymes involved in cell wall metabolism, proteins involved in ethylene signaling, and proteins related to calcium signaling. The finding of changes in the expression of these genes provides potential connections between defective mitosis and aberrant expansion. This study not only confirmed the conserved roles of plant separase in chromosome disjunction, but also advanced our understanding of regulation of plant cell cycle and expansion. My results and following research should provide further insight into the relationship between chromosome disjunction, cell cycle regulation, and expansion.

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Rocky Canyon Quarry is a granite mine located in the Santa Lucia Mountains about 5 miles southeast of the city of Atascadero. The Surface Mining and Reclamation Act (SMARA), which passed in 1975, dictates that California mines must rehabilitate lands disturbed by mining operations. Dr. V. L. Holland and his students in the Biological Sciences Department at California Polytechnic State University, San Luis Obispo (Cal Poly) have been working on restoration and revegetation of the Rocky Canyon Quarry since the early 1990’s. Adenostoma fasciculatum (chamise) dominates the chaparral communities (chamisal chaparral) found in Rocky Canyon. Chamise is the most common shrub in much of California’s chaparral and is adapted to recovery after fires by both seed germination and lignotuber sprouting. In laboratory and greenhouse experiments, it has been shown that chamise seeds have an increased germination rate when subjected to fire related stimulates such as heat, smoke, and charate. The goal of my research, which was conducted over a two year period (2002-2004), is to find successful, inexpensive techniques to restore chamisal chaparral on the mined granite slopes of Rocky Canyon Quarry. My study focused on examining and comparing the different techniques that have been shown by other researchers in laboratory and greenhouse situations to increase the germination rate of chamise. I compared the effects of heat, sulfuric acid, powdered charred wood (charate), and smoke on the germination of chamise seeds under the natural field conditions found in the Rocky Canyon Granite Quarry. Seeds were subjected to between one and four of these treatments, to examine possible interactive effects amongst the treatments, and then placed in plots containing the topsoil used to restore the mined hillsides. Plots remained under natural field conditions, and seedlings were counted following emergence. Results of my studies indicate that the smoke related treatments of liquid smoke and chamise smoke have the greatest effect in increasing the seed germination rate of chamise and that there is little to no benefit in subjecting chamise seeds to more than one treatment.

Cool-season grasses are adapted to seasonal decreases in temperature that in some areas reach well below freezing; however, despite being able to acclimate to such conditions, plants may still be susceptible to winter injury. Specifically, direct low temperature kill caused by freezing temperatures has been identified as a major component of winter injury across many plant species including turfgrasses. Although cool-season species are the grasses of choice for Northern climatic regions, a high degree of variability in freezing tolerance exists among cool-season turfgrasses. Tolerance to freezing temperatures is influenced by both the capacity of plants to cold acclimate prior to the onset of winter and the ability to withstand decreases in freezing tolerance (deacclimation) during winter and early spring months. Therefore, the objectives of my dissertation research were to (i) evaluate the physiological and biochemical modifications occurring during the cold acclimation and deacclimation process using cool-season turfgrasses that vary in freezing tolerance and (ii) determine the effects of differences in cold acclimation capacity and deacclimation sensitivity on overall freezing tolerance of cool-season grasses. Differences in freezing tolerance among the cool-season grasses evaluated were associated with variations in cold acclimation capacity and deacclimation resistance. Overall, the accumulation of protective compounds such as carbohydrates along with changes in lipid composition during cold acclimation may represent critical mechanisms to help lower cellular freezing point and improve cellular stability of cool-season grasses at freezing temperatures. In addition, decreases in freezing tolerance in response to mild warming events were minimized in plants that maintained higher levels of specific carbohydrates such as fructans. Additionally, strategies such as wilt-based irrigation may be used as a tool to enhance cold acclimation and maximize freezing tolerance of cool-season grasses. Taken together, the mechanisms identified in these studies may serve as selection criteria for the development of cool-season grasses with enhanced freezing tolerance.