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Abstract Background and AimsDynamic global vegetation models (DGVMs) are essential for quantifying the role of terrestrial ecosystems in the Earth’s climate system, but struggle with uncertainty and complexity. Eco-evolutionary optimality (EEO) theory provides a promising approach to improve DGVMs based on the premise that leaf carbon gain is optimized with resource costs. However, the timescales at which plant traits can adjust to environmental changes have not yet been systematically incorporated in EEO-based models. Our aims were to identify temporal constraints on key leaf photosynthetic and leaf functional traits, and develop a conceptual framework for incorporation of temporal leaf trait dynamics in EEO-based models. MethodsWe reviewed the scientific literature on temporal responses of leaf traits associated with stomata and hydraulics, photosynthetic biochemistry, and morphology and lifespan. Subsequent response times were categorized from fast to slow considering physiological, phenotypic (acclimation) and evolutionary (adaptation) mechanisms. We constructed a conceptual framework including several key leaf traits identified from the literature review. We considered temporal separation of dynamics in the leaf interior to atmospheric CO2 concentration (ci:ca) from the optimal ci:ca ratio [χ(optimal)] and dynamics in stomatal conductance within the constraint of the anatomical maximum stomatal conductance (gsmax). A proof-of-concept was provided by modelling temporally separated responses in these trait combinations to CO2 and humidity. Key ResultsWe identified 17 leaf traits crucial for EEO-based modelling and determined their response mechanisms and timescales. Physiological and phenotypic response mechanisms were considered most relevant for modelling EEO-based trait dynamics, while evolutionary constraints limit response ranges. Our conceptual framework demonstrated an approach to separate near-instantaneous physiological responses in ci:ca from week-scale phenotypic responses in χ(optimal), and to separate minute-scale physiological responses in stomatal conductance from annual-scale phenotypic responses in gsmax. ConclusionsWe highlight an opportunity to constrain leaf trait dynamics in EEO-based models based on physiological, phenotypic and evolutionary response mechanisms.
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Quantitative critique of leaf‐based paleo‐CO 2 proxies: Consequences for their reliability and applicability
A variety of proxies have been developed to reconstruct paleo-CO2 from fossil leaves. These proxies rely on some combination of stomatal morphology, leaf δ13C, and leaf gas exchange. A common conceptual framework for evaluating these proxies is lacking, which has hampered efforts for inter-comparison. Here we develop such a framework, based on the underlying physics and biochemistry. From this conceptual framework, we find that the more extensively parameterised proxies, such as the optimisation model, are likely to be the most robust. The simpler proxies, such as the stomatal ratio model, tend to under-predict CO2, especially in warm (>15C) and moist (>50% humidity) environments. This identification of a structural underprediction may help to explain the common observation that the simpler proxies often produce estimates of paleo-CO2 that are lower than those from the more complex proxies and other, non-leaf-based CO2 proxies. The use of extensively parameterised models is not always possible, depending on the preservation state of the fossils and the state of knowledge about the fossil's nearest living relative. With this caveat in mind, our analysis highlights the value of using the most complex leafbased model as possible.
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- Award ID(s):
- 1636005
- PAR ID:
- 10197310
- Date Published:
- Journal Name:
- Geological Journal
- ISSN:
- 0072-1050
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/gj.3807
