Short- and long-term responses of leaf day respiration to elevated atmospheric CO2

Abstract

Evaluating leaf day respiration rate (RL), which is believed differ from that in the dark (RDk), is essential for predicting global carbon cycles under climate change. Several studies have suggested that atmospheric CO2 impacts RL. However, the magnitude of such an impact and associated mechanisms remain uncertain. To explore the CO2 effect on RL, wheat (Triticum aestivum) and sunflower (Helianthus annuus) plants were grown under ambient (410 ppm) and elevated (820 ppm) CO2 mole fraction ([CO2]). RL was estimated from combined gas exchange and chlorophyll fluorescence measurements using the Kok method, the Kok-Phi method, and a revised Kok method (Kok-Cc method). We found that elevated growth [CO2] led to an 8.4% reduction in RL and a 16.2% reduction in RDk in both species, in parallel to decreased leaf N and chlorophyll contents at elevated growth [CO2]. We also looked at short-term CO2 effects during gas exchange experiments. Increased RL or RL/RDk at elevated measurement [CO2] were found using the Kok and Kok-Phi methods, but not with the Kok-Cc method. This discrepancy was attributed to the unaccounted changes in Cc in the former methods. We found that the Kok and Kok-Phi methods underestimate RL and overestimate the inhibition of respiration under low irradiance conditions of the Kok curve, and the inhibition of RL was only 6%, representing 26% of the apparent Kok effect. We found no significant long-term CO2 effect on RL/RDk, originating from concurrent reduction in RL and RDk at elevated growth [CO2], and likely mediated by acclimation of nitrogen metabolism.

Breath of green life: Reduction in plant day and night respiration under elevated CO2

“…Similar to previous results, including those from free-air CO 2 enrichment studies ( Ainsworth and Long 2005 ), Sun et al (2023) found a reduction in both leaf N and chlorophyl content under elevated (CO 2 ). Thus the concurrent reduction in R l and R d is linked to changes in N metabolism in leaves.…”

“…However, the authors did not identify any significant change in the R l : R d ratio between each treatment. During a short-term change in (CO 2 ) during measurement, Sun et al (2023) found an increase in R l and the R l : R d ratio using the Kok and Kok-Phi method but not the Kok-Cc method, a discrepancy attributed to changes arising from differences in intercellular (CO 2 ). This indicates a tendency to underestimate R l and overestimate light inhibition under low light intensities using the Kok and Kok-Phi methods.…”

“…In this issue of Plant Physiology, Sun et al (2023) explore the short- and long-term responses of leaf day respiration to ambient (410 ppm) and elevated (820 ppm) (CO 2 ) in wheat ( Triticum aestivum ) and sunflower ( Helianthus annuus ). Using the Kok method, the Kok-phi method, and a modified Kok method [termed by the authors as the Kok-Cc method that accounts for changes in chloroplastic (CO 2 )], they identified, on average, an 8.4% reduction in R l and a 16% reduction in R d undergrowth at elevated (CO 2 ) ( Fig.…”

“…Together this indicates a complex relationship between atmospheric CO 2 , C-, and N- cycles. Whilst the modified Kok-Cc method presented by Sun et al (2023) presents a more reliable approach toward the assessment of plant respiration, theoretical difficulties still arise due to measurement under low ambient light intensities. Thus, whilst we are now one step closer to understanding plant function in future environments, further work is needed to determine the response of R l to changes in irradiance.…”

Temperature responses of leaf respiration in light and darkness are similar and modulated by leaf development

“…The Kok method has large uncertainty concerning its two assumptions (Farquhar & Busch, 2017;Tcherkez et al, 2017a;Yin et al, 2020;Yin & Amthor, 2023), namely constant photochemical efficiency of photosystem II (Φ 2 ) and chloroplast CO 2 concentration (C c ) along the A-I inc curve. Both Φ 2 and C c have been shown to decline with increasing irradiance (Yin et al, 2011;Berghuijs et al, 2019;Sun et al, 2023). To address these issues, Yin et al (2011) suggested using measurements of Φ 2 via chlorophyll fluorescence to improve R L estimates (hereafter named 'Yin method').…”