Background/Question/Methods With their ability to add fixed nitrogen (N) to the surrounding community and relatively high N tissues, legumes play a significant role in the nitrogen dynamics of a community.  Despite this importance, little research has focused on the responses of prairie legumes to future climate warming.  This study used both a controlled growth chamber experiment and manipulative field experiment to examine the potential consequences of elevated temperature on the growth, N-fixation, and phenology of four common prairie legumes:  Amorpha canascens, Dalea purpurea, Lespedeza capitata, and Lupinus perennis.  In the growth chamber experiment, these species were grown at 25 or 28^oC.  After 10 weeks of growth, we measured biomass, leaf area, nodule number and weight, and stable N isotopic composition (to estimate N-fixation).  The manipulative field study used overhead infrared heat lamps to warm established plots of perennial prairie species at two levels of warming, +2 and +4 ^oC over ambient.  The phenology of the four legumes in the different treatments was monitored weekly.  Tissue was harvested for biomass and N-fixation measurements. We expected legumes that flower in the spring to show detrimental effects of warming while legumes that flower in the summer to show beneficial effects of elevated temperature.   
Results/Conclusions In the growth chamber experiment, Dalea and Lespedeza plants were 35-65% taller (P-values <0.0001) and Lespedeza plants had 83% more biomass at 28^oC (P-value =0.017) relative to 25^oC.  Amorpha and Lupinus displayed no difference in height or biomass between the two temperatures.  Lupinus plants had 88% fewer nodules at 28^oC (P-value <0.0001), while Lespedeza had 1.5 times more nodules at 28^oC (P-value=0.024).  In the field study, tagged individuals of Amorpha growing at +4 ^oC flowered an average of 5 days earlier than those at ambient temperature (P-value =0.005), but the timing of flowering was not affected by temperature for Lupinus individuals.  Interestingly, plants that responded to elevated temperature in the growth chamber did not respond in the field study and those that responded in the field study did not show much response in the growth chamber experiment.  Collectively, these results reveal that responses are species-specific and lend support to the hypothesis that spring flowering species (Lupinus) will show detrimental effects of elevated temperature while late summer flowering species (Lespedeza) will display beneficial effects of warming.  By altering growth and phenology, climate warming may modify species interactions and the influence of legumes on community dynamics and ecosystem processes.