Abstract
The primary function of stomata is to minimize plant water loss while maintaining CO2 assimilation. Stomatal water loss incurs an indirect cost to photosynthesis in the form of non-stomatal limitations (NSL) via reduced carboxylation capacity (CAP) and/or mesophyll conductance (MES). Two optimal formulations for stomatal conductance (gs) arise from the assumption of each type of NSL. In reality, both NSL could coexist, but one may prevail for a given leaf ontogenetic stage or plant functional type, depending on leaf morphology. We tested the suitability of two gs formulations (CAP versus MES) on species from six plant functional types (C4 crop, C3 grass, fern, conifer, evergreen, and deciduous angiosperm trees). MES and CAP parameters (the latter proportional to the marginal water cost to carbon gain) decreased with water availability only in deciduous angiosperm trees, while there were no clear differences between leaf ontogenetic stages. Both CAP and MES formulations fit our data in most cases, particularly under low water availability. For ferns, stomata appeared to operate optimally only when subjected to water stress. Overall, the CAP formulation provided a better fit across all species, suggesting that sub-daily stomatal responses minimize NSL by reducing carboxylation capacity predominantly, regardless of leaf morphology and ontogenetic stage.
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Claims 7
Claim · model-written summary
MES parameters decreased with water availability only in deciduous angiosperm trees.
Verbatim
e0“MES and CAP parameters (the latter proportional to the marginal water cost to carbon gain) decreased with water availability only in deciduous angiosperm trees”
Claim · model-written summary
CAP parameters decreased with water availability only in deciduous angiosperm trees.
Verbatim
e0“MES and CAP parameters (the latter proportional to the marginal water cost to carbon gain) decreased with water availability only in deciduous angiosperm trees”
Claim · model-written summary
There were no clear parameter differences between leaf ontogenetic stages.
Verbatim
e0“there were no clear differences between leaf ontogenetic stages”
Claim · model-written summary
Both CAP and MES formulations fit the data in most cases, particularly under low water availability.
Not reportedTaxonComparatorValue
Verbatim
e0“Both CAP and MES formulations fit our data in most cases, particularly under low water availability”
Claim · model-written summary
Fern stomata appeared to operate optimally only under water stress.
- Taxon
- fernsPolypodiopsidae0
- Outcome
- stomata appeared to operate optimallye0
- Qualifier
- only when subjected to water stresse0
Not reportedDirection
Verbatim
e0“For ferns, stomata appeared to operate optimally only when subjected to water stress”
Claim · model-written summary
The CAP formulation fitted the data better across all species.
Not reportedValue
Verbatim
e0“the CAP formulation provided a better fit across all species”
Claim · model-written summary
The authors infer that sub-daily stomatal responses predominantly minimize limitations through reduced carboxylation capacity.
Verbatim
e0“sub-daily stomatal responses minimize NSL by reducing carboxylation capacity predominantly, regardless of leaf morphology and ontogenetic stage”