Interactive effects of carbon dioxide, water, and nitrogen on grassland ecosystem processes
Understanding interactions among cycles of CO2, water and other key plant resources is critical to effectively predict future patterns of water, C, and N cycling under global environmental change. By adding water treatments to an ongoing experiment, we are testing several hypotheses about water-CO2-N interactions.
Using the 48 BioCON plots (see above) planted with 16 species (half experiencing rain removal via portable rain shelters), we are examining how inputs of water, CO2 and N interact to influence soil water availability, soil-plant interactions that influence available N, interactions with the belowground community of decomposers and mutualists, and thus net primary production (NPP) and plant and soil C pools.
|(2 x 2 x 2 = 8)||Dry, Ambient+||Ambient, 560 ppm||Ambient, amb +4g/m2/yr|
In addition, by sowing Pinus strobus, Quercus macrocarpa and Q. ellipsoidalis seeds, then measuring seedling survival and growth, soil water, N, and light availability, we are directly assessing effects and interactions among water, CO2, and N on seed germination and seedling establishment, in the critical stages of woody encroachmentin secondary successional grasslands.
Variables measured: net photosynthesis, leaf % N, stomatal conductance, specific leaf area, above- and below-ground biomass, above- and below-ground plant N, root growth and mortality, % cover, light interception, soil pH, soil CO2 flux, N2 fixation in legume species, net N mineralization and others.
Our overarching hypothesis is that water shortage and low N supply are fundamental constraints on the response of net primary production (NPP) to elevated CO2 such that NPP shows little response to eCO2 under either low water or N availability.
This research is supported by the National Institute for Climatic Change Research.