COS 280-3 - Impact of the regulation of non-structural carbohydrate dynamics for ecosystem climate responses: biological insights from mathematical analysis

Background/Question/Methods

In plants, non-structural carbohydrates (NSCs)—that is sugars and starch—form critical components in the ecophysiology of plant resilience. NSCs buffer asynchronies in photosynthesis, respiration, and growth—processes which determine ecosystem responses to climate change. Despite more than 20 years of study, the fundamental question of whether controls on NSC dynamics are passive or active remains unanswered. Observations of NSCs have found complex temporal dynamics, and as a result, elaborate control mechanisms are suspected. In an effort to better explain how variations in NSC supply and demand govern observed NSC time-series, we investigate the possibility that the amount of NSC itself regulates NSC demand. Using a combination of simulation and mathematical analysis, we identify what properties of how NSC demand depends on NSC availability create certain features of NSC time-series such as homeostatic or lagging responses (i.e., “ecological memory”). Describing this relationship provides insight into temporal NSC responses to variations in photosynthesis, respiration, and growth, providing a new perspective on NSC regulation.

Results/Conclusions

Simulations show that the simple regulation of NSC demands by NSC availability alone can create the complex responses observed in time series. Our analysis of NSC dynamics suggests the same qualitative behavior is probable in reality. For instance, time lags between changes in drivers of NSC dynamics and corresponding NSC responses are likely, and we identify factors controlling the degree of lag. Likewise, we identify conditions under which NSC concentrations would be insensitive to large variations in supply and demand (i.e. homeostatic). We identify conditions under which NSC demands are self-regulating (remain bounded). Our approach analyzes NSC responses to arbitrary variations in photosynthesis, respiration, and growth; therefore, our results are not dependent on particular models of these processes and apply to both the analysis of experiments and computer simulations of ecosystems. The ability to analyze experiments and computer models within the same framework facilitates comparison and calibration between the two. Although further experimentation is required, our results suggest that many NSC experiments may have simpler interpretations than previously thought.