LB 8-67 - Allocation of biomass and nutrients in above- and below-ground growth vary across populations of Quercus lobata.

Oaks, genus Quercus, are long-lived species that define ecosystems throughout the Northern Hemisphere and dominate many plant communities in California. Oaks provide ecological and economic services, human health benefits through their effects on air quality and hydrology, and have long been culturally important to Indigenous Peoples. Valley oak, Quercus lobata, is an endemic California species found in oak-savanna and riparian woodland habitats with significant gradients in temperature, precipitation, and seasonality. Previous studies have provided evidence of local adaptation to climate environments. Our goal was to test if allocation strategies to below- and above-ground biomass will be locally adapted. We hypothesize that families native to arid climates would have a higher root:shoot ratio and a higher nitrogen concentration in roots and shoots to enable more rapid photosynthesis when water is available at both sites, while mesic species will have lower root:shoot ratios. In this study, we analyzed nearly 1000 9-year-old Q. lobata juveniles, grown in two common gardens in the northern part of its species distribution (Chico and Placerville, CA). These individuals represent 235 families at the Chico site and 165 families at the Placerville site. Sampled trees were cut at the base while roots were excavated and washed. Shoots and roots were dried in order to take a final mass. Welch’s t-tests revealed that the traits, root:shoot and total biomass, differed significantly across gardens. Root:shoot ratios were significantly larger at Placerville (M = 1.09, SD = 0.93) than at Chico (M = 0.91 mean, SD = 0.57); (t(218.87)=-2.0027, p=0.046) while total biomass was significantly larger at Chico (M=8.71, SD=9.14) than Placerville (M=2.88, SD=3.12); (t(6.72)= 148.54, P < < 0.0001). Moreover, in support of the hypothesis, root:shoot ratio was significant associated at Chico (Regression, df =529, R2=0.00697.p=0.0302) and Placerville (Regression, df =390, R2=0.00778, p=0.04442). Nutrient samples are being analyzed. Collectively, this work seeks to address mechanisms of drought tolerance. Determining how climate conditions have shaped the adaptive capacity of oaks is crucial for protecting oaks and potentially other long-lived tree species.