Title: A reduced order model to analytically infer atmospheric CO₂ concentration from stomatal and climate data

Abstract

To address questions related to the acceleration or deceleration of the global hydrological cycle or links between the carbon and water cycles over land, reliable data for past climatic conditions based on proxies are required. In particular, the reconstruction of palaeoatmospheric CO₂ content (C_a) is needed to assist the separation of natural from anthropogenic C_a variability and to explore phase relations between C_a and air temperature T_a time series. Both T_a and C_a are needed to fingerprint anthropogenic signatures in vapor pressure deficit, a major driver used to explain acceleration or deceleration phases in the global hydrological cycle. Current approaches to C_a reconstruction rely on a robust inverse correlation between measured stomatal density in leaves (ν) of many plant taxa and C_a. There are two methods that exploit this correlation: The first uses calibration curves obtained from extant species assumed to represent the fossil taxa, thereby restricting the suitable taxa to those existing today. The second is a hybrid eco-hydrological/physiological approach that determines C_a with the aid of systems of equations based on quasi-instantaneous leaf-gas exchange theories and fossil stomatal data collected along with other measured leaf anatomical traits and parameters. In this contribution, a reduced order model (ROM) ismore » proposed that derives C_a from a single equation incorporating the aforementioned stomatal data, basic climate (e.g. temperature), estimated biochemical parameters of assimilation and isotope data. The usage of the ROM is then illustrated by applying it to isotopic and anatomical measurements from three extant species. The ROM derivation is based on a balance between the biochemical demand and atmospheric supply of CO₂ that leads to an explicit expression linking stomatal conductance to internal CO₂ concentration (C_i) and C_a. The resulting expression of stomatal conductance from the carbon economy of the leaf is then equated to another expression derived from water vapor gas diffusion that includes anatomical traits. When combined with isotopic measurements for long-term C_i/C_a, C_a can be analytically determined and is interpreted as the time-averaged C_a that existed over the life-span of the leaf. Key advantages of the proposed ROM are: 1) the usage of isotopic data provides constraints on the reconstructed atmospheric CO₂ concentration from ν, 2) the analytical form of this approach permits direct links between parameter uncertainties and reconstructed C_a, and 3) the time-scale mismatch between the application of instantaneous leaf-gas exchange expressions constrained with longer-term isotopic data is reconciled through averaging rules and sensitivity analysis. The latter point was rarely considered in prior reconstruction studies that combined models of leaf-gas exchange and isotopic data to reconstruct C_a from ν. The proposed ROM is not without its limitations given the need to a priori assume a parameter related to the control on photosynthetic rate. Our work here further explores immanent constraints for the aforementioned photosynthetic parameter.« less

Authors:

Konrad, Wilfried ^[1]; Katul, Gabriel ^[2]; Roth-Nebelsick, Anita ^[3]; Grein, Michaela ^[3]

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+ Show Author Affiliations

1. University of Tubingen (Germany); Technische Universität Dresden (Germany)
2. Duke University, Durham, NC (United States)
3. State Museum of Natural History, Stuttgart (Germany)

Publication Date:

Sat Mar 25 00:00:00 EDT 2017

Research Org.:

Duke Univ., Durham, NC (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); Volkswagen Foundation; National Science Foundation (NSF)

OSTI Identifier:

1533486

Alternate Identifier(s):

OSTI ID: 1416382

Grant/Contract Number:  

SC0006967; SC0011461; Az 87139; EAR-1344703

Resource Type:

Accepted Manuscript

Journal Name:

Advances in Water Resources

Additional Journal Information:

Journal Volume: 104; Journal Issue: C; Journal ID: ISSN 0309-1708

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; carbon isotope composition; eco-hydrology; leaf gas exchange; paleoclimate; photosynthesis; stomatal density; time-average