Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2009
Publication Date: 6/4/2010
Citation: Chimner, R., Welker, J.M., Morgan, J.A., Lecain, D.R., Reeder, J. 2010. Experimental manipulations of winter snow and summer rain influence ecosystem carbon cycling in a mixed grass prairie, Wyoming, USA. Ecohydrology. 3:284-293. Interpretive Summary: One of the important predictions of climate change is that precipitation patterns will be altered throughout much of the world. To understand how such changes will impact the ecology and productivity of native semi-arid grasslands in the western Great Plains, this experiment enhances winter precipitation through the use of snow fences and simulates altered summer precipitation by either augmenting (through irrigation; +50%) or decreasing (-50%) amounts of summer rainfall. Changes in winter precipitation had the greatest effects, with additional snow leading to higher rates of ecosystem carbon dioxide uptake and plant growth, resulting in more soil carbon uptake. Summer rainfall had no significant affect on plant growth or carbon dioxide exchange rates in plots that received additional snowfall. However, in experimental plots without snow additions, plant biomass increased 44% with summer irrigation and decreased 18% in the reduced rain treatment. Our findings indicate the importance of understanding alterations in both winter and summer precipitation patterns in evaluating how these grasslands will function as climate changes. The results suggest that not only will higher winter precipitation lead to greater plant productivity, but it may also encourage the storage of more soil carbon.
Technical Abstract: Water-limited grasslands may be exceeding vulnerable to changes in the timing or amount of precipitation which may result in shifts in the magnitudes and patterns of biogeochemical cycles. Shifts in CO2 exchange may lead to alterations in carbon sequestration or net losses and could accentuate the rising CO2 concentrations in the atmosphere or ameliorate the increases. The objective of our project was to quantify how changes in winter, summer, and combined winter and summer precipitation may alter rates of ecosystem C cycling in the mixed-grass prairie of the US. Three replicated 50 m snow fences were installed to increase winter snow while summer precipitation was manipulated by either increasing (+50%) or decreasing (–50%) precipitation amounts. Measurements of net ecosystem exchange (NEE), gross ecosystem photosynthesis (GEP), and ecosystem respiration (ER) and plant biomass were conducted throughout the snow-free period. Ecosystem C cycling rates and vegetation biomass responded to increases in winter precipitation to a greater degree than changes in summer rainfall (either higher or lower). Deeper snow in winter increased summer ER by an average of 27%, GEP by 45%, NEE by 90% and plant biomass by 50% compared to ambient snow conditions. Average plant biomass increased 44% with the addition of summer rain and decreased by 18% where rainfall was excluded under ambient snow conditions. Average NEE was also lower where rain was excluded. Our findings indicate that seasonality changes of precipitation may be important in regulating the future extent of C sequestration and C cycling in one of the most extensive, intact grasslands of North America.