Non-structural carbohydrate concentrations in Quercus stellata along the Oklahoma precipitation gradient

Background/Question/Methods

A large part of the United States is experiencing some degree of drought. Drought events can be short (few months) to long-term (several years). In the event of long term drought, plants rely heavily on stored carbohydrates. Non-structural carbohydrates (NSC) are mobile carbohydrates that are able to travel throughout the plant in the forms of sugars and starch. They aid in growth, defense, and completion of phenological developments without the benefit of current photosynthesis. Soluble sugars are also critical for osmotic adjustments and for dehydration tolerance. Since photosynthesis is reduced to minimize water loss during drought, NSC are not able to accumulate, therefore depleting current storage. Oklahoma lies on a distinct precipitation gradient with eastern Oklahoma receiving nearly twice as much rain as western Oklahoma. Three sites were set up along this gradient and stem, root, and leaf samples of Quercus stellatawere taken monthly and analyzed for NSC using colorimetry. The aim of this research was to explore seasonal changes in NSC concentrations and how much they vary within the same species under different water availability conditions. We expected that simple sugar concentrations would accumulate during the dormant season, while starch concentrations would diminish during the dormant season.  

Results/Conclusions

We found that summer and winter starch concentrations seem to follow a trend of accumulating starch during the active growing season, and depleted during the dormant season (p-value <0.001). This suggests that while the trees are actively photosynthesizing during the growing season, starch can be stored for use during the dormant season when the tree is not photosynthesizing. Although there are differences in starch concentration across the precipitation gradient (p-value<0.001), preliminary results suggest that these differences may not be entirely related to water availability. These patterns could be due to different starch accumulation or usage rates.  By following starch concentrations throughout the years, we are able to assess which component of NSC is being used first under water stress. Ultimately, this allows us to more accurately predict the resilience of forests to climate change, including reduced water availability.