PARENT SESSION
Symposium #33: The ecology and evolution of coupled energy and material flows: integration of multiple scales and multiple biota.

Organized by: JD Schade, T Markow, and S Hobbie
Friday, August 9. 9:00 AM to 12:00 PM. Crystal Ballroom, TCC.

Water, nutrients and the carbon-nitrogen stoichiometry of grassland ecosystems.

RITCHIE, MARK^*,1, OLFF, HAN², ¹ Syracuse University, Syracuse, NY² University of Groningen, Groningen, Netherlands

ABSTRACT- The comparative ratio of carbon (C) to nitrogen (N) in plant and herbivore tissue is thought to structure trophic relationships and ecosystem processes in grasslands, just as it does for C, N, and P in aquatic ecosystems. Here we hypothesize that the availability of water to plants indirectly controls the supply of C and the standing leaf concentration of N in plants. Higher water availability allows plants to uptake greater CO₂, thereby increasing the relative supply of C to N for plants and hence plant tissue C:N ratio. Therefore, plants experiencing lower water availability, through either lower rainfall or higher evapotranspiration, should have higher tissue N than those experiencing high water availability. We test this prediction by comparing tissue N and water-use efficiency values (as judged from C13) for different species within a community and for the dominant species found in different communities across geographical soil fertility and water availability gradients. We also review literature that compares tissue N for plants experiencing different water availability in different years. The water-related stoichiometry of C and N in plant tissue has dramatic implications for the structure of terrestrial grassland food webs, as it explains variation in the abundance, diversity, and impact of large herbivores across major environmental gradients. Thus, C and N stoichiometry in terrestrial systems has the same potential to structure food webs and ecosystem function as C, N, and P stoichiometries do in aquatic ecosystems.

KEY WORDS: plant, herbivore, stoichiometry, water