Impacts of elevated temperature and CO₂ with varying groundwater levels on seasonality of height and biomass growth of a boreal bioenergy crop (Phalaris arundinacea) - a modeling study

The boreal aquatic crop reed canary grass (Phalaris arundinacea L., hereafter RCG) is widely cultivated for bioenergy production in northern Europe, where climate change is likely to modify the growing conditions for this species substantially. In this context, we analyzed and modeled the effects of elevated temperature and CO₂ together with variable groundwater levels on the seasonal development of height and the accumulation of the aboveground biomass in RCG. For this purpose, RCG plants were grown in autocontrolled environmental chambers over two growing seasons applying a factorial design, including two temperature regimes (ambient and ambient + approximately 3 °C), two carbon dioxide concentrations (ambient and approximately 700 μmol·mol-1), and three groundwater levels (0, 20, and 40 cm below the soil surface). The results showed that elevated temperature was the dominant variable controlling the seasonal course of height development and biomass accumulation, and soil water levels could accelerate or delay these processes. Compared with ambient conditions, elevated temperatures did not accelerate the onset of RCG but made growth cessation occur earlier. This made the growing period shorter and reduced final height and biomass accumulation than other climatic treatments. Elevated CO₂ significantly increased height development and biomass accumulation throughout the growing period relative to ambient conditions, whereas no differences occurred regarding the onset, cessation, and duration of growing season. A higher groundwater level increased RCG growth, mainly because of the delay in the timing of the peak growth rate and of the cessation with prolonged duration of growing season compared with low groundwater level. However, the enhanced growth of RCG caused by elevated CO₂ may be partly lost due to increasing temperature, which may reduce the availability of soil water and make senescence occur earlier. This will potentially inhibit the growth of RCG under drought conditions. Our results suggested that management of soil water and maintenance of high groundwater levels are key problems with respect to optimizing RCG biomass production under climate change in the boreal conditions.