Contrasting anatomical and biochemical controls on mesophyll conductance across plant functional types

Abstract

Summary Mesophyll conductance (gm) limits photosynthesis by restricting CO2 diffusion between the substomatal cavities and chloroplasts. Although it is known that gm is determined by both leaf anatomical and biochemical traits, their relative contribution across plant functional types (PFTs) is still unclear. We compiled a dataset of gm measurements and concomitant leaf traits in unstressed plants comprising 563 studies and 617 species from all major PFTs. We investigated to what extent gm limits photosynthesis across PFTs, how gm relates to structural, anatomical, biochemical, and physiological leaf properties, and whether these relationships differ among PFTs. We found that gm imposes a significant limitation to photosynthesis in all C3 PFTs, ranging from 10–30% in most herbaceous annuals to 25–50% in woody evergreens. Anatomical leaf traits explained a significant proportion of the variation in gm (R2 > 0.3) in all PFTs except annual herbs, in which gm is more strongly related to biochemical factors associated with leaf nitrogen and potassium content. Our results underline the need to elucidate mechanisms underlying the global variability of gm. We emphasise the underestimated potential of gm for improving photosynthesis in crops and identify modifications in leaf biochemistry as the most promising pathway for increasing gm in these species.

Photosynthetic plasticity aggravates the susceptibility of magnesium‐deficient leaf to high light in rapeseed plants: the importance of Rubisco and mesophyll conductance

“…However, consistent with the observations across multiple species with contrasting LMA (Tomás et al., 2013), the g m calculated from anatomical data ( g m,anatomy ) tended to be overestimated in Mg‐deficient leaves with high LMA (Figure S3). This may be derived from the limitations of the model which do not take all relevant mechanisms into account, since Mg is known to be involved in the regulation of cellular biochemistry such as aquaporins (Gerbeau et al., 2002; Knauer et al., 2022; Kourghi et al., 2017). Additionally, it may also arise from the deviations of the estimated metrics by using the micro‐ or ultra‐structure of two‐dimensional images and those with actual three‐dimensional structure (Earles et al., 2019; Théroux‐Rancourt et al., 2017).…”

“…Many studies have investigated the effects of leaf features on g m . Leaf mass per leaf area (LMA), cell wall thickness ( T cw ) and chloroplast surface area exposed to intercellular air space per unit leaf area ( S c ) are the most relevant parameters regulating g m (Cousins et al., 2020; Evans, 2021; Knauer et al., 2022; Lu et al., 2016; Tomás et al., 2013). The higher LMA in Mg‐deficient leaf has been extensively reported, and is attributed to the accumulation of carbohydrates in source leaves expressing Mg deficiency chlorosis (Cakmak & Kirkby, 2008; Koch et al., 2019; Mengutay et al., 2013; Tian et al., 2021; Verbruggen & Hermans, 2013).…”

Higher global gross primary productivity under future climate with more advanced representations of photosynthesis

“…Here, the photosynthetic parameters J max25 and V cmax25 , as well as their ratio b JV , were adjusted from a C i -based to a C c -based representation within the photosynthesis module using simulated A n - C i curves as described in full detail by Knauer et al ( 19 ). Since g m25 is correlated with V cmax25 defined on a C i basis ( V cmax25,Ci ), which varies with leaf N content in CABLE-POP ( 63 ), g m25 also varies along with V cmax25,Ci gm25=gm25,ref+sgv.1emfalse(Vcmax25,Ci−Vcmax25,Ci,reffalse)where g m25,ref and V cmax25,Ci,ref are the g m 25 and V cmax25,Ci under average leaf nutrient contents, respectively, and s gv is the slope between g m25 and V cmax25,Ci (table S3) extracted from the dataset presented by Knauer et al ( 69 ).…”

“…where g m25,ref and V cmax25,Ci,ref are the g m25 and V cmax25,Ci under average leaf nutrient contents, respectively, and s gv is the slope between g m25 and V cmax25,Ci (table S3) extracted from the dataset presented by Knauer et al (69).…”

Low internal air space in plants with crassulacean acid metabolism may be an anatomical spandrel

“…Whilst the relationship between % IAS and photosynthetic assimilation in C 3 plants is well accepted, this association is less straightforward in species that do other forms of photosynthesis ( Knauer et al ., 2022 ). Approximately 7 % of all vascular plants do a form of photosynthesis called crassulacean acid metabolism (CAM), which is distinct from the more common C 3 pathway ( Winter, 2019 ; Winter et al ., 2021 ).…”