Spatial variability of mobile carbohydrates within Pinus cembra trees at the alpine treeline

The size of mobile carbohydrate pools in treeline trees may hold the answer to the carbon limitation hypothesis of tree growth at high elevation. However, a major limitation for the use of such a chemical marker is its potentially large spatial and temporal variability at very small scales. Here we explore this variability in Pinus cembra L. at the alpine treeline in the Swiss Central Alps. To our surprise, neither slope exposure (south vs. north) nor position within the tree crown (compass directions and upper, middle and lower part of crown) had a significant influence on the concentration of total non- structural carbohydrates (TNC) in tissues. However, different- aged tissues (noodles and branch segments) showed a significant difference in TNC concentration, maybe due to their different tissue dry matter density and activity. There is no indication that these patterns change across the season, despite significant seasonal variation in tissue specific TNC. Hence, any broad assessment of the carbon supply status of trees at the alpine treeline needs to carefully select tissue samples for equal age, but does not require a lot of spatial replication within individual trees.