CAM‐physiology and carbon gain of the orchid Phalaenopsis in response to light intensity, light integral and CO₂

Abstract

The regulation of photosynthesis and carbon gain of crassulacean acid metabolism (CAM) plants has not yet been disclosed to the extent of C3‐plants. In this study, the tropical epiphyte Phalaenopsis cv. “Sacramento” was subjected to different lighting regimes. Photosynthesis and biochemical measuring techniques were used to address four specific questions: (1) the response of malate decarboxylation to light intensity, (2) the malate carboxylation pathway in phase IV, (3) the response of diel carbon gain to the light integral and (4) the response of diel carbon gain to CO2. The four CAM‐phases were clearly discernable. The length of phase III and the malate decarboxylation rate responded directly to light intensity. In phase IV, CO2 was initially mainly carboxylated via Rubisco. However, at daylength of 16 h, specifically beyond ±12 h, it was mainly phosphoenolpyruvate carboxylase (PEP‐C) carboxylating CO2. Diel carbon gain appeared to be controlled by the light integral during phase III rather than the total daily light integral. Elevated CO2 further enhanced carbon gain both in phase IV and phase I. This establishes that neither malate storage capacity, nor availability of PEP as substrate for nocturnal CO2 carboxylation were limiting factors for carbon gain enhancement. These results advance our understanding of CAM‐plants and are also of practical importance for growers.

Crassulacean acid metabolism species differ in the contribution of C3 and C4 carboxylation to end of day CO2 fixation

“…Exposing Phalaenopsis plants to either narrow‐band red or white light did not affect PEPC activity during phase IV (Zheng et al, 2019). In another recent study on Phalaenopsis ‘Sacramento’, the same cultivar as in the current study, the response for CO 2 uptake during phase IV was similar to ours, though we are using a more dominant red light (Hogewoning et al, 2020, in press). Obviously, growing plants under a narrow‐band light affects photosynthesis and plant growth, regardless of species or photosynthetic type (e.g.…”

Effects of Light Condition on Growth and Physiological Characteristics of the Endangered Species Sedirea japonica under RCP 6.0 Climate Change Scenarios

“…Various types of CAM plants tend to absorb more CO 2 as the atmospheric CO 2 concentration increases [ 10 ]. When the atmospheric CO 2 concentration is doubled, the daily CO 2 uptake of Ananas comosus increased by approximately 15% [ 14 ], that of Agave salmiana increased by approximately 59% [ 15 ], and that of Phalaenopsis increased by approximately 25 to 31% [ 16 ]. This reaction is highly related to the activity of RuBisCo in Phases II and IV, where the stomata open and close.…”

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

“…These data indicate that B. inconspicuum leaves switch their photosynthetic mode from CAM to C 3 while retaining a relatively high amount of malate. It was reported in Phalaenopsis “Sacramento” that the length of phase III and the start of phase IV were adjusted to the moment when malate was depleted, suggesting that the cellular malate content is linked with the transition from phase III to phase IV (Hogewoning et al ., 2021). However, under low light conditions, the Phalaenopsis plants shifted to phase IV even though they retained a high amount of malate.…”