Evaluating carbon allocation in Arctic plants photosynthesizing in the subnivean environment

Background/Question/Methods

Plants have evolved numerous strategies for surviving the harsh conditions of the Arctic tundra. A previous study found that common evergreen and semi-evergreen species were photosynthetically active beneath the snow during the spring. As climate change is altering biological and climatic conditions in the Arctic faster than most other locations on the planet there is an enhanced need to study the impact of this unique physiological process on plant survival. This is especially true in the context of earlier snowmelt, which may allow deciduous species to begin photosynthesizing earlier and thus compound changes in tundra plant communities. An understanding of the physiological basis of subnivean photosynthesis will improve modelling of future community dynamics in the context of climate change and associated ecosystem services. In light of this need, we sought to answer the question: How is newly acquired carbon allocated in plants photosynthesizing beneath the snow? To answer this question, we used a continuous flow system over multiple days to deliver isotopically labeled 13CO2 to evergreens, semi-evergreens, and mosses under the snow in the Alaskan tundra. We then collected samples and used elemental analysis and mass spectrometry to determine which metabolic pools (soluble sugars, starch, or lipids) were 13C enriched.

Results/Conclusions

Overall, we found a significant increase in 13C enrichment from our unlabeled control plots providing further evidence for subnivean photosynthesis. Our results provide evidence that tundra evergreens, semi-evergreens, and mosses photosynthesize beneath the snow to recover energy stores depleted over the long winter. Soluble sugars were preferentially 13C enriched over the other metabolites in nearly all the labelled mosses, evergreens, and semi-evergreens, with starches being a close second, and lipids showing little to no 13C enrichment. In addition, leaf tissue was more 13C enriched than stem tissue in woody species. Furthermore, prioritization of soluble sugar synthesis may be evidence for upregulation of anthocyanin synthesis for photoprotection and cold tolerance upon snowmelt. Interestingly, enrichment of metabolic pools did not significantly differ between various growth forms-- woody, graminoid, or moss-- though it did between species. These results shed light on the function of subnivean photosynthesis. By extension, they can inform researchers’ understanding of how changes in snowmelt regime with climate change will affect the survival of mosses, evergreens, and semi-evergreens. In turn, our research will serve to improve predictions of tundra plant community dynamics in the face of climate change.