Seasonal responses of photosynthesis and growth of a bioenergy crop (Phalaris arundinacea L.) to climatic change under varying water regimes

Abstract

The aim of this study was to investigate how the elevated temperature and CO2 and varying water regimes affected the physiological characteristics (leaf photosynthesis, chlorophyll fluorescence and pigment) and growth of a bioenergy crop, reed canary grass (Phalaris arundinacea L.). For this purpose, the plants (with peat monoliths) was grown in an auto-controlled environment chamber system (Paper I) over two growing seasons (2009–2010) under elevated temperature (ambient + 3.5C) and CO2 (700μmol mol). The plants were also treated as three levels of soil moisture, ranging from high (100% volumetric content), to normal (~50%) and low (~30%). The elevated temperature stimulated the leaf photosynthesis and carbon storage in the biomass during the early growth periods compared to the ambient temperature, while it might result in earlier senescence and lower photosynthesis and biomass during the later periods (Paper II & V). The maximum rate of photosynthesis (Pmax), the maximum rate of ribulose-1,5-bisphosphate carboxylase-oxygenase activity (Vcmax) and the potential rate of electron transport (Jmax) at gradient measurement temperature (5–30°C) showed also significant seasonal variations regardless of climate treatment (Paper IV). At the early stages of growing season, the elevated temperature decreased Vcmax and Jmax compared to the ambient temperature at the lower measurement temperatures (5–15°C), opposite to the higher measurement temperatures (20–30°C). Later in the growing period, Vcmax and Jmax were under the elevated temperature consistently lower across the measurement temperatures. The CO2 enrichment significantly increased the photosynthesis and slightly decreased Vcmax and Jmax compared to the ambient CO2 across the measurement temperatures. The CO2 enrichment led also to a slight down-regulation in the leaf nitrogen, chlorophyll content and fluorescence characters (Paper III). Low soil moisture decreased clearly the photosynthesis performance and chlorophyll fluorescence, which eventually also decreased the carbon storage in plant biomass, particularly under the elevated temperature (Paper II, III & V). Furthermore, Vcmax and Jmax decreased significantly under low soil moisture (Paper IV). This provided further evidence that not only diffusive conductance but also photosynthetic capacity would be reduced in the plants subjected to long-term drought. Nevertheless, the temperatureand drought-induced stresses were partially mitigated by the elevation of CO2. To conclude, the seasonal estimation of the physiological and growth parameters for reed canary grass makes it possible to simulate its photosynthesis and carbon storage in biomass over the whole growing season under varying environmental conditions. The growth of plants on organic soils could also be expected to be favored under warming climate if the water availability is high.