Exploring optimal stomatal control under alternative hypotheses for the regulation of plant sources and sinks

Abstract

Experimental evidence that nonstomatal limitations to photosynthesis (NSLs) correlate with leaf sugar and/or leaf water status suggests the possibility that stomata adjust to maximise photosynthesis through a trade-off between leaf CO 2 supply and NSLs, potentially involving source-sink interactions. However, the mechanisms regulating NSLs and sink strength, as well as their implications for stomatal control, remain uncertain.We used an analytically solvable model to explore optimal stomatal control under alternative hypotheses for source and sink regulation. We assumed that either leaf sugar concentration or leaf water potential regulates NSLs, and that either phloem turgor pressure or phloem sugar concentration regulates sink phloem unloading.All hypotheses led to realistic stomatal responses to light, CO 2 and air humidity, including conservative behaviour for the intercellular-to-atmospheric CO 2 concentration ratio. Sugarregulated and water-regulated NSLs are distinguished by the presence/absence of a stomatal closure response to changing sink strength. Turgor-regulated and sugar-regulated phloem unloading are distinguished by the presence/absence of stomatal closure under drought and avoidance/occurrence of negative phloem turgor. Results from girdling and drought experiments on Pinus sylvestris, Betula pendula, Populus tremula and Picea abies saplings are consistent with optimal stomatal control under sugar-regulated NSLs and turgor-regulated unloading.Our analytical results provide a simple representation of stomatal responses to aboveground and below-ground environmental factors and sink activity.

Do stomata optimize turgor‐driven growth? A new framework for integrating stomata response with whole‐plant hydraulics and carbon balance

“…Under water stress, our GOSM predicts similar results as embolism‐ and conductance‐centric models (Figs 4, S9), though without explicitly minimizing embolism or maximizing conductance. This agreement may not be surprising, considering numerous stomatal strategies inadvertently prevent embolism (Novick et al ., 2016; Dewar et al ., 2022). While plants indeed tend to operate with minimal embolism and constant xylem conductance (Carminati & Javaux, 2020), this phenomenon does not necessitate that stomata strictly close to prevent embolism and conductance loss.…”

“…Nonstomatal limitations should be incorporated into the GOH for these instances and improve predictions when plants cannot grow (Fig. 4g,h) following aspects of AOHs that maximize A n subject to nonstomatal limitations, since these AOHs implicitly assume χ w = 0 (Hölttä et al, 2017;Dewar et al, 2018Dewar et al, , 2022.…”

“…However, these experiments are difficult and rarely performed (Hall & Schulze, 1980; Fites & Teskey, 1988; Thomas et al ., 1999). Overall, AOHs emphasize carbon acquisition, but few AOHs consider how plants actually use carbon once assimilated (Nikinmaa et al ., 2013; Hölttä et al ., 2017; Dewar et al ., 2022). Plant survival, competition, and reproduction should be better reflected by carbon use than by assimilation.…”

Bumblebees sense rootstock-mediated nutrition and fertilization regime in tomato

“…Besides the differences in structural carbohydrates such as cellulose, hemicellulose and lignin, the increases in C concentration under reduced fertilization may be rather due to the accumulation of NSC, such as sucrose, hexoses and starch (Ma et al 2018), which could negatively impact on photosynthesis through non-stomatic feedback inhibition (Dewar et al 2022), but positively on pollinator foraging decisions if assimilates accumulate in the owers. This situation is likely to occur under low-P because of the strong induction of leaf C accumulation (Fig.…”

Intercomparison of methods to estimate gross primary production based on CO2 and COS flux measurements

“…LRU CAP is based on a generic physiological model of stomatal function whose predictions have been successfully tested previously (e.g. Lintunen et al, 2020 ; Salmon et al, 2020 ; Dewar et al, 2021 ; Gimeno et al, 2019 ). The model parameters are all physiologically meaningful and can be measured independently or obtained from the literature.…”