Introduction
The Alaskan arctic appears to be under going substantial warming. In order to understand how these changes will effect tundra plant communities we are examining the leaf level gas exchange and morphological responses of tundra species to long term (12 year) warming and snow addition designed to simulate components of climatic change at Toolik Lake, Alaska (http://www.uaf.edu/toolik/). In the first year 2007 we used two species that have shown differential responses to experimental warming and to fertilization in these nutrient limited systems. Betula nana has shown a positive response while Salix pulchra has shown a negative response. In addition we recently established a new set of snow manipulations to attempt to differentiate the multifaceted effects of snow- including warming soil temperatures in winter, added snow melt water in the spring, plus a shortening of the growing season.
These efforts are part of the larger International Polar Year (IPY), International Tundra Experiment (http://www.geog.ubc.ca/itex/research/) and include collaborators thorough the world. Another focus of our efforts is working with other ITEX collaborators to understand how warming impacts leaf carbon, nitrogen and stable isotope ratios. These measurements are in conjunction with other researchers who are focusing their efforts on other impacts of warming e.g., secondary compounds, available nitrogen, plant community composition.
Figure 1. Snow fence with ITEX chambers at
Toolik Lake , Alaska .
Figure 2. Measuring leaf level gas exchange of tundra species.
Results
Fig. 3. Betula nana and Salix pulchra in ambient and 12 year snow addition treatments with and without 12 year increased air temperatures. Measurements were also made in a naturally occurring shrub patch. * refers to significant difference between species within a treatment at P<0.05.
Fig. 4. A.
Mean stem height of tallest stems of
B. nana in permanent plots in the ambient and long-term snow addition treatments.
Fig. 4. B. Mean leaf area index of all plants in permanent plots in the ambient and long-term snow addition treatments.
Discussion
Long-term snow and air temperature manipulation results: There were no differences in photosynthetic rates between B. nana and S. pulchra for any of the combinations of long-term snow addition and/or increased air temperatures or at the shrub patch. These results are consistent with long term fertilization and warming studies1. Both species showed positive photosynthetic responses to both warming and snow addition. However the increases were not additive. Betula tended to have lower d13C and d15N than Salix across treatments however there were few differences between treatments.
Morphological response of Betula nana to long-term snow addition: Betula nana stems were taller in the long-term snow addition treatment than in ambient snow (Fig.3). Plots in the long-term snow addition treatment also had higher LAI’s than those in the ambient treatment. These results are consistent with other studies1,2 and suggest that long-term snow addition alters plant biomass allocation strategies with potential implications for competitive interactions. Further research is needed to understand both of these processes and their interactions with snow accumulation
Acknowledgements: This work was supported by the National Science Foundation Office of Polar Programs, Arctic Systems. We thank the staff of ENRI and Toolik
Lake for their assistance.
References:
- Bret-Harte et al. (2001) Developmental plasticity allows Betula nana to dominate tundra subjected to an altered environment. Ecology 82:18-32.
- Hobbie et al. (2005) Species compositional differences on different-aged glacial landscapes drive contrasting responses of tundra to nutrient addition. J. Ecology. 93:770-782.
