The Antarctic Peninsula is experiencing some of the most profound climate change on the planet, resulting in increased temperatures, alterations in precipitation patterns and changes in nutrient availability.  These changes have had major effects on tundra ecosystems on the Peninsula, ranging from soil and microbial processes to performance of the two vascular plant species Deschampsia antarctica and Colobanthus quitensis.  Alterations in temperature and precipitation may influence the concentrations and stable isotope ratios of C and N in soils, decomposing plant litter and plants.  We examined the effects of 1 and 2°C warming of air and soil temperatures, respectively, and 25% supplemental precipitation on C:N and δ¹³C and δ¹⁵N in soils, litter and plants in tundra microcosm cores in a 2x2 complete factorial experiment.  Treatments were applied to microcosm cores for two consecutive growing seasons near Palmer Station.

Results/Conclusions

Total dissolved nitrogen, nitrate and ammonia content in leachate collected from cores were 79, 42 and 31% lower, respectively, under warming treatments than ambient controls.  Treatments had few effects on δ¹⁵N of the pools we assessed, although there was a tendency for δ¹⁵N to be lower under warming in the litter layer and live aboveground tissue in D. antarctica.  The δ¹³C of live aboveground tissue in C. quitensis was 1.2‰ higher under warming than ambient treatments.  Most of the analyzed constituents expressed lower δ¹³C signatures after 15 months of treatments relative to initial samples that were not exposed to treatments.  There were no treatment effects on C:N  except for dead aboveground plant biomass, which was higher with warming. The lower total nitrogen, nitrate and ammonia content in leachate under warming treatments did not suggest nitrogen limitation in these microcosms because the δ¹⁵N signatures of plants did not reflect the nitrogen isotopic signature of the sources.  The lower δ¹³C of C. quitensis plants under warming may be attributed to alterations in stomatal conductance and water use efficiency, which may alter carbon fractionation during photosynthesis.  More differences in δ¹³C and δ¹⁵N isotopic signatures would be expected with increased duration of the experiment or temperature treatments.