Photosynthetic Response of an Alpine Plant, Rhododendron delavayi Franch, to Water Stress and Recovery: The Role of Mesophyll Conductance

Abstract

Rhododendron delavayi Franch is an evergreen shrub or small tree with large scarlet flowers that makes it highly attractive as an ornamental species. The species is native to southwest China and southeast Asia, especially the Himalayan region, showing good adaptability, and tolerance to drought. To understand the water stress coping mechanisms of R. delavayi, we analyzed the plant's photosynthetic performance during water stress and recovery. In particular, we looked at the regulation of stomatal (gs) and mesophyll conductance (gm), and maximum rate of carboxylation (Vcmax). After 4 days of water stress treatment, the net CO2 assimilation rate (AN) declined slightly while gs and gm were not affected and stomatal limitation (SL) was therefore negligible. At this stage mesophyll conductance limitation (MCL) and biochemical limitation (BL) constituted the main limitation factors. After 8 days of water stress treatment, AN, gs, and gm had decreased notably. At this stage SL increased markedly and MCL even more so, while BL remained relatively constant. After re-watering, the recovery of AN, gs, and gm was rapid, although remaining below the levels of the control plants, while Vcmax fully regained control levels after 3 days of re-watering. MCL remained the main limitation factor irrespective of the degree of photosynthetic recovery. In conclusion, in our experiment MCL was the main photosynthetic limitation factor of R. delavayi under water stress and during the recovery phase, with the regulation of gm probably being the result of interactions between the environment and leaf anatomical features.

Thresholds for leaf damage due to dehydration: declines of hydraulic function, stomatal conductance and cellular integrity precede those for photochemistry

“…Several previous studies have suggested that leaf photochemistry is relatively stable under water stress (Shabala & Pang, 2007;Flexas et al, 2009), as declines in PSII photochemistry occur at lower water contents than g s and TLP (Boyer & Potter, 1973;Miyashita et al, 2005). Moreover, significant declines in F v /F m occur after the complete loss of midrib xylem hydraulic function in sunflower plants (Cardoso et al, 2018). We importantly extended these findings showing…”

“…Several studies have shown that stomatal pores reopen after plant rehydration, and reopening is associated with the recovery of K leaf and gas exchange (Miyashita et al, 2005;Blackman et al, 2009;Brodribb & Cochard, 2009;Martorell et al, 2014;Cai et al, 2015;Li et al, 2016;Skelton et al, 2017b). However, in contrast to g s , there may be limited recovery of photochemistry and mesophyll conductance after rehydration, which constrain full recovery of overall photosynthetic rate (Miyashita et al, 2005;Galm es et al, 2007).…”

Photosynthesis and photosynthetic efficiencies along the terrestrial plant’s phylogeny: lessons for improving crop photosynthesis

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How do vascular plants perform photosynthesis in extreme environments? An integrative ecophysiological and biochemical story

“…Correlation between V cmax and J max at 20–25°C modelled from A/C i curves from Arctic/alpine (blue diamond), warm desert (red square) and temperate (orange triangle) species. Data were compiled from Rogers et al (), Albert et al (), Cai et al (), Fan et al (), Shi et al (), Hamerlynck et al (), Huxman and Smith (), Shi et al (), Utsugi et al (), Hinojo‐Hinojo et al () and Kattge and Knorr (). Only statistically significant linear correlations for each group of species are shown.…”