UC Davis

With the growing energy demand and global warming crisis, the world is in need of a more renewable and sustainable source of energy. Among the possible options, bioenergy is gaining more attention recently, as it can both act as a cleaner substitute for fossil fuels and sequester carbon from atmospheric CO2. Poplar (Populus trichocarpa) is a highly advantageous bioenergy crop, but since the production of bioenergy crops should minimize the diversion of cropland from food crop production, the marginal lands with greater susceptibility to drought are the main production sites for poplars. To increase the yield on marginal lands, the drought tolerance of poplars needs to be better quantified to determine their potential as an environmentally sustainable source of energy.In this experiment, we measured the leaf-level physiological and developmental traits from 1869 poplar trees of 471 unique genotypes. The genotypes originated from the western part of North America, covering latitudes with diverse rainfall conditions across most of the species’ range (38.9-54.3°N, 116-128.7°W). The leaf’s stomatal density, stomatal size, fresh weight, dry weight, relative water content, contact angle, spectral reflectance, leaf area, leaf perimeter, and compactness were measured to quantify the effect of drought during poplar’s early growth stage on different genotypes. Results indicated that most of the measured traits are significantly affected by drought, while the severity and duration of drought alter the drought response. The measurements of most traits decrease with drought, and genotype affects most traits significantly. Only a few traits show a significant interaction between genotype and treatment. Furthermore, many traits are affected by the latitude and precipitation of the warmest quarter of the genotype’s origin, and few are also affected by the precipitation of the coldest quarter. Several correlations have been noted among traits, such as a negative correlation between stomatal density and stomatal size, a negative correlation between dry weight and compactness, a positive correlation between adaxial and abaxial contact angle, and a positive correlation between NDVI and PRI. Overall, this thesis provides a quantitative assessment of how drought and geographical location impact the physiological and developmental traits of poplar. The findings have practical implications for identifying genotypes that are better suited for commercial cultivation in varying environmental conditions.