Spenders versus Savers: Carbon Allocation Strategies In Relation to Frost Exposure in Tamarix
Randall Long1*, Carla D’Antonio1, Tom L. Dudley2, Kevin C. Grady3, Susan E. Bush4, Kevin R. Hultine4
1Ecology, Evolution & Marine Biology, University of California, Santa Barbara, CA, USA
2Marine Science Institute, University of California, Santa Barbara, CA, USA
3School of Forestry, Northern Arizona University, Flagstaff, AZ, USA
4Department of Research, Conservation, and Collections, Desert Botanical Garden, Phoenix, AZ, USA
Carbon storage is an important functional trait in woody plants. When carbon fixation is interrupted, such as when deciduous species have dropped their leaves, soluble sugars and starch reserves within the plant –referred to as nonstructural carbohydrates (NSCs) - act as a source to meet carbon demands. Plant populations that are regularly subjected to episodic stress such as freezing, fire and herbivory may be under selection for enhanced allocation to NSC storage, the potential tradeoff being reduced allocation to growth or reproduction. The ability for NSC storage to respond to climatic selection pressures may be critical to invasion by a non-native species across a wide climate gradient. To investigate variation in allocation patterns in the widespread invasive tree, Tamarix sp, we constructed a common garden using genotypes of Tamarix, collected across an altitudinal gradient where mid-high elevation populations are exposed to freezing temperatures. Radial growth, biomass accumulation, flower output and NSC concentrations were analyzed to test our hypothesis that carbon should be allocated preferentially to NSC storage in populations from colder sites.
We found significant differences in NSC concentrations throughout the year (F(2,224) = 9.241, P 0.001), with higher elevation populations accumulating higher levels of NSCs. NSC concentrations could be predicted based on the number of freeze-thaw events in the spring at provenance sites (F (1,6) = 24.28, p = .003, R2 = 0.80). With respect to carbon demands for growth and reproduction, low elevation populations had significantly more flowers (F(2,8032) = 138.7, p0.001), and greater total leaf:basal area (F (2,26) = 7.386, p = 0.003). These data, in combination with the lower starch values suggest allocation to growth and reproduction occurs at the expense of storage. Thus, cold temperatures appear to have selected for genotypes that allocate greater carbon to storage as a hedge against stress-related tissue damage.