Seasonal physiological responses and biomass growth in a bioenergy crop (Phalaris arundinacea L.) under elevated temperature and CO₂, subjected to different water regimes in boreal conditions

We investigated the seasonal variability of effects of elevated temperature (+3. 5°C), CO₂ elevation (700 μmol mol^-1) and varying water regimes (high to low water content) on physiological responses and biomass growth of reed canary grass (Phalaris arundinacea L., local field-grown cultivar) grown in a boreal environment. In controlled environment greenhouses, various physiological and growth parameters of grass, i. e., light-saturated net photosynthetic rates (P_nmax), water use efficiency (WUE) and optimal photochemical efficiency of photosystem II (F_v/F_m), and leaf area development and biomass of plant organs (leaf, stem, coarse, and fine root) were measured. During the early measurement periods, elevated temperature enhanced leaf photosynthesis and above-ground biomass of reed canary grass; however, this resulted in earlier senescence and lower biomass at the end of measurement period, compared to ambient temperature. This effect was more pronounced under water limitation. Elevated CO₂ enhanced P_nmax, WUE, and leaf area and total plant biomass (above- and below-ground) over growing season. The explanation for imbalance between stimulated photosynthesis and increase in above-ground biomass was that CO₂ enrichment causes a greater increase in the plant's root system. The combination of elevated temperature and CO₂ slightly increases the growth of plant. Adequate water availability favored photosynthesis and biomass growth of reed canary grass. The temperature- and drought-induced stresses were partially mitigated by elevated CO₂. Other cultivars should be tested in order to identify those that are better adapted to elevated temperatures and CO₂ and variable water levels.