C3 and C4 plants are the two major terrestrial plant groups and they respond differently to temperature, water, and CO2. Much research has focused on the individual effects of warming, water availability, and elevated CO2 on their growth performance and competitive interactions, yet the joint effects of these factors remain underexplored.
In this study, we grew naturally co-occurring C3 (Oplismenus composites) and C4 (Paspalum conjugatum) grass under three temperature warming scenarios (control, +2°C, and +4°C), two water supply intervals (normal 2 days vs. prolonged 7 days [drought]), and two CO2 concentrations (ambient 400 ppm vs. elevated 800 ppm) in growth chambers and measured their above- and below-ground dry biomass in monoculture and mixture to quantify their biomass performances and competitive responses.
We found that warming and elevated CO2 together enhanced the above- and/or below-ground biomass of both C3 and C4 grass. Moreover, temperature, water, and CO2 interacted to increase the below-ground biomass of the C4 grass. Surprisingly, the C3 grass performed worse under interspecific competition relative to intraspecific competition (i.e., the mixture biomass was lower than the monoculture biomass) at elevated CO2 compared to ambient CO2, whereas the reverse is true for the C4 grass—it had higher mixture biomass than monoculture biomass at elevated CO2. Furthermore, the C4 grass was most competitive against the C3 grass under simultaneous 4°C warming, drought, and elevated CO2.
Overall, these results suggest that temperature warming, increased drought frequencies, and rising atmospheric CO2 may benefit C4 plants and the competitive balance could potentially shift towards an increased C4 relative abundance in future plant communities. Changes in C3-C4 community composition can have profound consequences for the functioning of natural and agricultural systems, including primary productivity, nutrient cycling, herbivore nutritional balance, and crop production. Finally, the effects of climate change are multifaceted and often involve complex interactions and feedback over time and space. A promising avenue for future research will be conducting long-term and large-scale field experiments involving more species to scale up our laboratory results to better predict C3-C4 plant dynamics under changing climate.