Positive effects of elevated CO2 and its interaction with nitrogen on safflower physiology and growth

Over the last two decades, the impact of elevated CO2 on crops has become a major issue in the context of climate change. Increasing CO2 levels should modify the plant demand for nutrients, but precise effects on plant physiology are poorly known. Here, we studied the effect of ambient CO2 at 400 μmol mol−1 and high CO2 at 1,000 μmol mol−1 on safflower (Carthamus tinctorius L.) at N levels from 25 to 175 kg ha−1. Growth and physiology of safflower were assessed in pots in controlled enclosure chambers in a glasshouse. Overall results show that high CO2 increased assimilation rate by +27 %, leaf area index (LAI) by +28 %, total above-ground dry weight by +51 %, and total above-ground dry weight by +43 % at harvest. High CO2 reduced stomatal conductance by −29 % and transpiration rate by −18 %. At anthesis, results show that high CO2 increases assimilation rate by +13 %, LAI by +2 %, and above-ground dry weight by +34 %. At anthesis, results also show that high CO2 decreases leaf N and chlorophyll content.