TReSpire – a biophysical TRee Stem respiration model

Abstract

Summary Mechanistic models of plant respiration remain poorly developed, especially in stems and woody tissues where measurements of CO2 efflux do not necessarily reflect local respiratory activity. We built a process‐based model of stem respiration that couples water and carbon fluxes at the organ level (TReSpire). To this end, sap flow, stem diameter variations, xylem and soil water potential, stem temperature, stem CO2 efflux and nonstructural carbohydrates were measured in a maple tree, while xylem CO2 concentration and additional stem and xylem diameter variations were monitored in an ancillary tree for model validation. TReSpire realistically described: (1) turgor pressure to differentiate growing from nongrowing metabolism; (2) maintenance expenditures in xylem and outer tissues based on Arrhenius kinetics and nitrogen content; and (3) radial CO2 diffusivity and CO2 solubility and transport in the sap solution. Collinearity issues with phloem unloading rates and sugar–starch interconversion rates suggest parallel submodelling to close the stem carbon balance. TReSpire brings a breakthrough in the modelling of stem water and carbon fluxes at a detailed (hourly) temporal resolution. TReSpire is calibrated from a sink‐driven perspective, and has potential to advance our understanding on stem growth dynamics, CO2 fluxes and underlying respiratory physiology across different species and phenological stages.

Woody tissue photosynthesis reduces stem CO2 efflux by half and remains unaffected by drought stress in young Populus tremula trees

“…For methodological simplicity, E A is often used as a proxy of stem respiration (R S ). However, E A does not necessarily reflect respiration rates of underlying tissues (Hilman et al, 2019;Salomón, De Roo, Oleksyn, De Pauw, & Steppe, 2019;Steppe et al, 2015;Teskey et al, 2008;Trumbore, Angert, Kunert, Muhr, & Chambers, 2013). The most important pathway of respired CO 2 confounding the interpretation of E A measurements seems to be the transport of CO 2 through the xylem (F T ; Teskey et al, 2008;Teskey, McGuire, Bloemen, Aubrey, & Steppe, 2017).…”

The Impact of a Simple Representation of Non-Structural Carbohydrates on the Simulated Response of Tropical Forests to Drought

“…Some optimised modelling studies have been conducted that explore models of NSC storage and the substrate limitation of respiration and growth (Thornley, 1970(Thornley, , 1971(Thornley, , 1972a(Thornley, , b, 1977(Thornley, , 1991(Thornley, , 1997(Thornley, , 2011Thornley and Cannell, 2000;Dewar et al, 1999). These provide a theoretical framework to develop mechanistic models of NSC storage and utilisation (Hemming et al, 2001;Fritts et al, 2000;Salomón et al, 2019) 15 that allow detailed simulations of plant function. However, there have been few attempts to develop such models in a manner that would be compatible with large scale LSMs (De Kauwe et al, 2014).…”

Respiration in wood: integrating across tissues, functions and scales

“…Advanced models of xylem and phloem function and of cambial growth have existed for a few years (e.g. Hölttä et al , , ; De Schepper & Steppe, ; Mencuccini et al , ), but Salomón et al 's article, in this issue of New Phytologist (; pp. 2214–2230) takes a notable step forward integrating and advancing these approaches.…”

“…through cortical photosynthesis or phosphoenolpyruvate (PEP)‐carboxylase metabolism (Angert et al , ), and by diffusion constraints imposed by tissue properties and stem size (Steppe et al , ). Salomón et al have formalized much of this complexity for the first time in a combined model that fuses bark and xylem hydraulics with two additional sub‐models that quantify carbohydrate use in respiratory metabolism and growth, together with the dynamics of phloem unloading and consequent carbon balance.…”

“…The determination of respiration in Salomón et al 's model is anchored in the classical growth–maintenance paradigm (Thornley, ; Amthor, ). This assumes a constant construction respiration cost for biomass of a given elemental composition, and uses live tissue nitrogen content and temperature to drive short‐term responses in maintenance respiration (Cannell & Thornley, ).…”