Tree physiological processes greatly influence the movement of carbon through ecosystems. Through photosynthesis, trees absorb, transform, and store energy in reduced carbon form, especially sugars and starch. To survive, trees expend this energy to grow and reproduce. A thorough understanding of how and when trees allocate this energy is key to predicting changes in the residence time and movement of carbon through ecosystems. Previous research suggests that incentivize allocation to storage and that allocation could shift in response to environmental variation. We hypothesized that chronic soil moisture differences result in different phase and amplitudes in seasonal oscillation of starch concentrations. To test this hypothesis, we compared annual storage dynamics in xeric and mesic sites for two tree species exhibiting contrasting leaf habits. We measured sugar and starch concentrations in the canopy branches, stem, and coarse roots of five Pinus palustris L. and five Quercus spp. individuals (an evergreen conifer and winter-deciduous angiosperm, respectively).
Results/Conclusions
Our results partially support our hypothesis that chronic soil moisture differences result in different phases and amplitudes of seasonal starch oscillations; however, the responses depended on the organ and the storage molecule. For both species, we observed little seasonal oscillation in sugar concentrations or in stem and canopy branch starch. The seasonal oscillation of root starch differed between xeric and mesic sites, with root starch peaking approximately one month later at the xeric site. This delay in seasonal depletion of root starch in the xeric site could indicate an extended period of allocation to storage and therefore a delay in allocation to growth relative to the mesic site. These observations suggest that carbon allocation, especially allocation to storage, responds to chronic differences in soil resources. These results further the description of tree carbon allocation, its response to environmental variation, and the corresponding predictions of ecosystem and global carbon fluxes.