In a tree, nonstructural carbohydrates (NSC’s) meaning sugar and starch, are the core assets to assure healthy bloom, flower fecundity and spring growth. The physiological changes in terms of NSC dynamics a tree undergoes in preparation for dormancy especially in warmer climates is still poorly understood. This is especially true due to the negative effects resulting from climate change including the decrease in winter fog, chilling hours, winter drought, and an increase in annual temperatures.
To better understand the seasonal fluctuations of tree NSC’s in response to climate variability at an accelerated rate for trees, a large scale, multi-year study called the Carbohydrate Observatory has been established using a citizen science approach from ~400 sites throughout the Central Valley of California. This large-scale approach and monthly samples allows for the tracking of seasonal trends of starch and sugar levels in response to climate variability, latitude, species and tree age in three major tree species: Juglans regia, Prunus dulcis and Pistacia vera. All samples are analyzed for sugar and starch content using a colorimetric method and all data are made freely available in real time on a web-based interactive map at: https://mzwienie.shinyapps.io/Shiny_test/.
Results/Conclusions
During bloom time in all three species, stored starch is converted to sugar and transported to new blooms resulting in a significant depletion of NSC reserves. This is followed by a temporary increase of reserves prior to resumption of radial growth of stem and vegetative growth. During summer growth, low levels of NSC reserves are consistent reflecting a high demand for NSCs to support yield and tree growth that exceeds or is equal to photosynthetic supply. At harvest, carbohydrate levels begin to recover, which corresponds to the cessation of stem and radial growth. NSC’s are recharged by December. This recovery period is vital as the tree prepares for dormancy. Interestingly, the oscillating NSC levels of Pistacia vera, appear to reflect its habit of alternate bearing.
Levels of NSC’s over the entire season are lower in northern latitudes than southern latitudes most likely reflecting a shorter growing season. Lower levels of NSC’s is also reflected in lower yields. Additionally, NSC levels increase with tree age.