Integrating leaf gas exchange and chlorophyll fluorescence to reveal the long-term regulation of photosynthesis in situ

Understanding the diurnal and seasonal regulation of photosynthesis is an essential step in quantifying and modeling the impact of the environment on plant function. Although the dynamics of photosynthesis have been widely investigated in terms of CO2 exchange measurements, a more comprehensive view can be obtained when combining gas exchange and chlorophyll fluorescence (ChlF) measurements. However, such integrated measurements have been so far restricted to short term analysis using portable systems that combine IRGA and PAM-ChlF techniques. Here we introduce and demonstrate a new method for integrated, long-term and in situ measurements of leaf gas exchange and ChlF, based on an autonomous gas exchange system and a new miniature PAM- fluorometer. The method is used to simultaneously track the dynamics of the light and carbon reactions of photosynthesis at a 20-minute resolution in leaves of silver birch during summer time. The potential of the method is initially demonstrated using the ratio between electron transport and net assimilation (ETR/ANET). We successfully captured the diurnal patterns in the ETR/ANET during summer time, including a drastic increase in ETR/ANET upon a high-temperature period. We suggest that these measurements can provide valuable data to model and quantify the regulation of leaf photosynthesis in situ. HighlightWe introduce new integrated measurements to help resolve the seasonal and diurnal dynamics of photosynthesis regulation by combining long-term simultaneous measurements of gas exchange and chlorophyll fluorescence in field conditions.