Tallgrass prairie is widely restored throughout the Midwest, USA; however, there are uncertainties about the sustainability of restoration success under shifts in precipitation.  Because native C₄ grasses account for the majority of productivity in restored grasslands, understanding dominant prairie grass response to precipitation change is needed to identify which ecotypes should be used in restoration under different climate scenarios. We tested whether source populations of a dominant prairie grass, Sorghastrum nutans (Indiangrass), collected from across the precipitation gradient of tallgrass prairie respond differentially to watering treatments in a common soil and under controlled conditions in a greenhouse.  Source populations or “ecotypes” of S. nutans originated from Illinois, Konza Prairie, and Hays, Kansas.  We also created a “mixed ecotype” treatment using a combination of all 3 source populations.  Three plants were grown in each pot and exposed to three watering levels (approximately 300, 600, and 900 mm) over a 12 week period.  Each source × watering treatment was replicated 5 times (n=60).  Photosynthesis was measured with a Li-Cor 6400.   At the end of the 12 weeks, we quantified aboveground, belowground, and total net primary production (ANPP, BNPP and NPP) in each pot.  

Results/Conclusions

Ecotypic variation in physiological performance and productivity of Sorghastrum nutans from the different source populations occurred in the common soil and controlled environment.  Net photosynthesis varied among the source populations regardless of watering treatment (P = 0.009).  Both Kansas sources of S. nutans exhibited higher rates of photosynthesis than Illinois plants. All productivity measurements revealed an interaction between source and watering treatment. Differences in ANPP among the sources were greatest in the 600 mm watering treatment, whereas there were  no differences in ANPP in the 900 mm water treatment (P = 0.033).  Greatest variation in BNPP and NPP among the ecotypes occurred in the 300 and 600 mm watering treatments (P < 0.03).  Both BNPP and NPP were similar among all sources in the 900 mm watering treatment.  Overall production did not increase with an increase in water supply as predicted.  Interestingly, the “mixed ecotype” pots showed no variation productivity across the varying watering regimes.  These results suggest that combining ecotypes of a dominant grass may stabilize productivity under a wider range of precipitation regimes, but field tests that include more inter-specific interactions are needed to predict whole ecosystem response.