Carbon assimilation and allocation (13C labeling) in a boreal perennial grass (Phalaris arundinacea) subjected to elevated temperature and CO2 through a growing season

The responses of carbon assimilation and allocation in different plant organs to changed environment depend on the species, their phenology and growth conditions. An integrated experiment was conducted over an entire growing season to understand the effects of elevated growth temperature (ambient + 3.5 °C) and CO2 (700 μmol mol−1) on the seasonal photosynthetic capacity, carbon accumulation and allocation (four 21-day periods of 13C pulse labeling-to-harvest) in a boreal perennial grass (Phalaris arundinacea) using controlled environmental chambers. Elevated temperature was found to significantly enhance leaf photosynthesis and total carbon accumulation in biomass during the early stages of the growing season, while it also resulted in earlier senescence and lower carbon storage at the final harvest. CO2 enrichment significantly stimulated photosynthesis and total carbon accumulation over the growing season. The combination of elevated temperature and CO2 caused a lower total carbon accumulation in biomass at maturity compared to elevated CO2 alone, indicating that this boreal crop grown under increased temperature could not take advantage of CO2 enrichment. Elevated temperature significantly increased 13C assimilation and allocation to the leaves and the stems during the first labeling period, and resulted in 5–6% higher percentage of carbon allocation in the roots during the final two labeling periods. This did not result in increased carbon storage in the roots, but much less carbon accumulation in the shoots during the latter growing periods. Elevated CO2 caused a higher 13C assimilation in the roots, but did not significantly increase the below-ground 13C allocation percentage. This was because of the higher growth of the shoots under high nitrogen availability and CO2 enrichment. The response of carbon allocation pattern to the combined elevation of temperature and CO2 was similar to the responses to elevated temperature alone. We conclude that plant growth and carbon assimilation are clearly controlled by phenology in this boreal crop under the climatic treatments, however, seasonal carbon allocation pattern within the plants was not significantly changed by the treatments.

► Carbon accumulation and allocation in plants would be modified by climatic treatments. ► Elevated temperature resulted in earlier senescence and lower carbon storage. ► CO2 enrichment stimulated photosynthesis and carbon accumulation over growing season. ► Both climatic treatments increased carbon allocation percentage in roots. ► Seasonal carbon allocation pattern within-plant was not significantly changed.