Effect of elevated CO2, temperature and drought on dry matter partitioning and photosynthesis before and after cutting of nodulated alfalfa

The rising atmospheric CO2 concentration resulting from industrial development may enhance photosynthesis and plant growth. However, there is a lack of research concerning the effect of combined factors such as CO2, temperature and water availability on plant regrowth following cutting or grazing, which represent the usual methods of managing forage legumes like alfalfa. Elevated CO2, temperature and drought can interact with cutting factors (e.g. cutting frequency or height), and source-sink balance differences before and after defoliation can modify photosynthetic behaviour and dry matter accumulation, as well as dry matter partitioning between above- and belowground organs. The aim of our study was to determine the interactive effect of CO2 (ambient, around 350 μmol mol−1 versus 700 μmol mol−1), temperature (ambient versus ambient + 4 °C) and water availability (well-irrigated versus partially irrigated) on dry matter partitioning and photosynthesis in nodulated alfalfa after vegetative normal growth and during regrowth. At the end of vegetative normal growth, CO2 enhanced dry matter accumulation despite photosynthesis being down-regulated at the end of this period. Photosynthesis was stimulated by elevated CO2 and resulted in greater dry matter accumulation during the regrowth period. Aboveground organs were affected more by drought than belowground organs during the entire experiment, particularly during vegetative normal growth. The higher drought tolerance (greater growth) observed during the regrowth period may be related to higher mass and greater reserves accumulated in the roots of plants.