Plants rely on stored carbohydrates for growth, defense, and completion of phenological developments when current photosynthate supplies are not adequate. These non-structural carbohydrates (NSC) are mobile carbohydrates that can be transported throughout the plant in the form of sugar and starch, and can also be critical for osmotic adjustments and dehydration tolerance. For these reasons, it may be expected that NSCs concentrations would increase with decreasing precipitation, as greater storage is necessary in more stressful environments. Oklahoma lies on a distinct precipitation gradient with eastern Oklahoma receiving nearly twice as much precipitation as western Oklahoma. A total of ten sites were set up along this gradient with stem, root, and leaf samples of Quercus stellata being taken monthly and analyzed for NSC using colorimetry. The aim of this research was to determine how precipitation impacts 1) whole plant NSC concentrations, 2) seasonality of NSC concentrations, 3) NSC concentrations of different plant organs, and 4) the proportion of simple sugars, sucrose, and starch making up the NSC pool. Secondly, deviations in annual precipitation during the study period (compared to long term averages) allowed us to ask whether NSC concentrations correspond more strongly to long or short-term (current year) precipitation patterns.
Results/Conclusions
As expected, leaves had the highest NSCs of the different tissues types. Additionally there were significant site and seasonal variations in average NSC concentration across whole plants, and in stems, roots, and leaves separately (p< 0. 005 for all). Finally, NSC concentrations (for whole plant or separate plant organs) were weakly, but significantly correlated with long- and short-term rainfall averages (all r2 < 0.500 and r2 < 0.105, respectively; all p-values < 0.05). Average whole plant NSC had positive correlation with both short-term and long-term precipitation (all p-values < 0.005 and r2 = 0.164 and r2 = 0.233, respectively). Correlations of each sugar type within each plant component with precipitation were also similar for short-term and long-term precipitation. Notably, sucrose and simple sugars were positively correlated with precipitation, while starch was negatively correlated. Ultimately these results suggest that trees in dry locations with low photosynthesis may not be able to build up the expected NSC reserves. This study will allow us to more accurately predict how the resilience of species to climate change, including reduced water availability, may vary across the range of a species.