Assimilation and partitioning of photosynthates into metabolic pools by the Arctic vegetation

Background/Question/Methods

The increasing temperatures in the Arctic are contributing to changes in regional carbon dynamics. This increase in temperature will potentially influence the allocation of newly assimilated photosynthates into metabolic pools (sugars, lipids) by the vegetation. The study was conducted in arctic tundra near Toolik Lake, Alaska, located in the northern foothills of the Brooks Range (68˚38’ N, 149˚34’W, elevation 760 m) to examine the metabolic allocation by the deciduous and evergreens at a moist acidic tundra site. ¹³C labeling consisted in three consecutive injections of 60 ml ¹³C-enriched CO₂ (AP, 99%) during the peak growing season. During labeling, CO₂ concentration inside the chamber was monitored continuously, using an infrared gas analyzer. The vegetation was collected immediately after labelling and subsequently for a year and analysed for ¹³C of foliage organic matter, soluble carbohydrates, starch, and lipids.

Results/Conclusions

Immediately after the labelling, relative to controls the highest level of enrichment were measured in the soluble carbohydrate pool (~400 permil).  Starch had enrichemnts of 50 ‰ while lipids showed the lowest ¹³C enrichments.  There was an exponential decline in the ¹³C of the soluble carbohydrates and starch with time, while lipids ¹³C enrichments showed minimal temporal changes.  Highest ¹³C enrichments of the soluble carbohydrate pools occurred in Betula and Eriophorum.  In comparison the ¹³C enrichments in the soluble carbohydrates for Ledum were lower, consistent with lower photosynthetic rates. Interestingly, the ¹³C label persisted in all metabolic pools in Ledum for over 200 days following the labeling.  In Eriophorum ¹³C label was also detectable in the starch pool for foliage harvested 200 days post labeling. ¹³C labeling provide a valuable tool to examine assimilation of photosynthates and the differential allocation into the metabolic pools and offer an insight into the use of these carbon pools by respiration during the long and prolonged Arctic winter period.