Relationship between fluorescence yield and photochemical yield under water stress and intermediate light conditions

The dynamics between fluorescence (F(s)) yield and photochemical (P) yield in a changing environment are essential for understanding the relationship between photosynthesis and fluorescence. The ratio of F(s) yield and P yield tends to be constant under high light intensity, but the relationship between these two yields, and its response to environmental conditions, need to be explored further under intermediate and low light. In this study, we performed leaf-scale measurements of fluorescence parameters by pulse-amplitude modulation (PAM) technology in summer maize (Zea mays L.) plants grown under intermediate light conditions in a climate chamber. Plants were treated as moderately water stressed and non-water stressed. Results showed that a decrease in P yield was accompanied by increases in F(s) yield and non-photochemical quenching (NPQ) yield in response to moderate water stress under intermediate and low light conditions. F(s) yield was negatively correlated with P yield under intermediate and low light conditions when there was sufficient soil water in the root zone. Under water stress, the correlation between F(s) yield and P yield was negative in low light, but became positive under higher light levels. F(s) yield was negatively related to P yield when NPQ yield was low; however, they were synergistically and positively associated when excessive light dissipation was dominated by NPQ.