Hysteresis response of photosynthetic parameters in different plants to external CO2 concentration

Global warming caused by increasing CO ₂ concentration has caused deviations in the original patterns of plant photosynthesis and transpiration in response to CO ₂ . Additionally, it has exacerbated agricultural water shortages, making the requirement to improve water use efficiency (WUE) more urgent than ever. To solve this problem, this study used a rectangular hyperbolic-modified model with two successive periods in reverse order to analyze the hysteresis responses of the net photosynthetic rate ( P _N ), transpiration rate ( E ) and WUE of Triticum aestivum , Rumex crispus , and Taraxacum officinale to CO ₂ concentration. The results show that different plant species follow obvious hysteresis laws: If hysteresis occurs between periods of different plants, P _N and E exhibit hysteresis with a positive main effect, and WUE shows hysteresis with a negative main effect. During the same period of P _N and E , hysteresis occurring in the forward and negative periods shows a positive effect; However, for WUE, the hysteresis effect is opposite to that of P _N and E . This result provides deeper insights into the response of plant photosynthesis, transpiration, and WUE values to changes in CO ₂ concentration. It helps enhance our understanding of the relationship between plant growth and climate change, offering scientific evidence to support maintaining agricultural production and ensuring food security.