Responses of chlorophyll fluorescence to CO2elimination as an indicator of Crassulacean acid metabolism photosynthesis

Abstract

AbstractCrassulacean acid metabolism (CAM) is found in a wide variety of vascular plant species, mainly those inhabiting water-limited environments. Identifying and characterizing diverse CAM species enhances our understanding of the physiological, ecological, and evolutionary significance of CAM photosynthesis. In this study, we examined the effect of CO2elimination on chlorophyll fluorescence-based photosynthetic parameters in two constitutive CAMKalanchoespecies and six orchids. In CAM-performingKalanchoespecies, the effective quantum yield of photosystem II showed no change in response to CO2elimination during the daytime but decreased with CO2elimination at dusk. We applied this method to reveal the photosynthetic mode of epiphytic orchids and found thatGastrochilus japonicus,Oberonia japonica, andBulbophyllum inconspicuum, but notBulbophyllum drymoglossum, are constitutive CAM. AlthoughB. drymoglossumhad relatively high malate content in leaves, they did not depend on it to perform photosynthesis even under water deficient or high light conditions. Anatomical comparisons revealed a notable difference in the leaf structure betweenB. drymoglossumandB. inconspicuum;B. drymoglossumleaves possess the large water storage tissue internally, unlikeB. inconspicuumleaves, which develop pseudobulbs. Our data propose a novel approach to identify and characterize CAM plants without labor-intensive experimental procedures.HighlightResponses of chlorophyll fluorescence-based photosynthetic parameters to CO2elimination differ between Crassulacean acid metabolism (CAM) and C3metabolism, proposing a novel approach to identify and characterize CAM plants.