12 Jun 2023
 | 12 Jun 2023
Status: a revised version of this preprint is currently under review for the journal BG.

Leaf carbon and nitrogen stoichiometric variation along environmental gradients

Huiying Xu, Han Wang, I. Colin Prentice, and Sandy P. Harrison

Abstract. Leaf stoichiometric traits are central to ecosystem function and biogeochemical cycling, yet no accepted theory predicts their variation along environmental gradients. Using data in the China Plant Trait Database version 2, we aimed to characterize variation in leaf carbon and nitrogen per unit mass (Cmass, Nmass) and their ratio, and to test an eco-evolutionary optimality model for Nmass. Community-mean trait values were related to climate variables by multiple linear regression. Climatic optima and tolerances of major genera were estimated; Pagel’s λ was used to quantify phylogenetic controls, and Bayesian phylogenetic linear mixed models to assess the contributions of climate, species identity and phylogeny. Optimality-based predictions of community-mean Nmass were compared to observed values. All traits showed strong phylogenetic signals. Climate explained only 18 % of C : N ratio variation among species but 45 % among communities, highlighting the role of taxonomic replacement in mediating community-level responses. Geographic distributions of deciduous taxa separated primarily by moisture, evergreens by temperature. Cmass increased with irradiance, but decreased with moisture and temperature. Nmass declined with all three variables. C : N ratio variations were dominated by Nmass. The coefficients relating Nmass to the ratio of maximum carboxylation capacity at 25 °C (Vcmax25) and leaf mass per area (Ma) were influenced by leaf area index. The optimality model captured 68 % and 53 % of variation between communities for Vcmax25 and Ma respectively, and 30 % for Nmass. We conclude that stoichiometric variations along climate gradients are achieved largely by environmental selection among species and clades with different characteristic trait values. Variations in leaf C : N ratio are mainly determined by Nmass, and optimality-based modelling shows useful predictive ability for community-mean Nmass. These findings should help to improve the representation of C : N coupling in ecosystem models.

Huiying Xu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-87', Anonymous Referee #1, 03 Jul 2023
    • AC1: 'Reply on RC1', Huiying Xu, 12 Sep 2023
  • RC2: 'Comment on bg-2023-87', Anonymous Referee #2, 22 Aug 2023
    • AC2: 'Reply on RC2', Huiying Xu, 12 Sep 2023

Huiying Xu et al.

Huiying Xu et al.


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Short summary
Leaf carbon (C) and nitrogen (N) are crucial elements in leaf construction and physiological processes. This study reconciled the roles of phylogeny, species identity and climate in stoichiometric traits at individual and community levels. The variations in community-level leaf N and C : N ratio were captured by optimality-based models using climate data. Our results provide another approach to improve the representation of leaf stoichiometry in vegetation models to better couple N with C cycling.