Temperature response of C4 species big bluestem (Andropogon gerardii) is modified by growing carbon dioxide concentration

Climate change factors interact to modify plant growth and development. The objective of this study was to evaluate the response to temperature of big bluestem (Andropogon gerardii Vitman) development, growth, reproduction and biomass partitioning under low and high carbon dioxide concentrations ([CO2]) grown in controlled environmental conditions. Ten sunlit soil–plant–atmosphere-research (SPAR) chambers were used to study the effects of two [CO2] of low (360 μL L−1) and high (720 μL L−1), and five different day/night temperatures of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Big bluestem cv. Bonelli seeds were sown in pure, fine sand, in 11 rows at equal spacing and after emergence were thinned to 10 plants per row. At maturity, individual plants were harvested and divided into leaves, stems, panicles and roots. Biomass decreased either above or below the optimum temperature of 30/22 °C. The effect of high [CO2] on biomass accumulation (12–30% increase) was visible at less than optimum temperature (30/22 °C) and absent at two high temperatures. With increase in temperature, irrespective of the [CO2], biomass partitioned to leaves increased (35%) where as that to stems decreased (33%). Panicle weight was 6–7% of biomass at 25/17 °C and fell to 1.6% at 40/32 °C. The biomass partitioned to roots, across the temperatures, was constant for plants grown at low [CO2] but decreased by 7% for those grown at high [CO2]. The decrease in panicle/seed production at two high temperatures (>30/22 °C) might reduce this species population and dominance in tallgrass prairies. The temperature response functions at different [CO2] will be useful to improve the predictive capabilities of dynamic global vegetation models in simulating dynamics of rangelands, where big bluestem is the dominant species.