Environmental Effects on Carbon Isotope Discrimination from Assimilation to Respiration in a Coniferous and Broad-Leaved Mixed Forest of Northeast China

Abstract

Carbon (C) isotope discrimination during photosynthetic CO2 assimilation has been extensively studied, but the whole process of fractionation from leaf to soil has been less well investigated. In the present study, we investigated the δ13C signature along the C transfer pathway from air to soil in a coniferous and broad-leaved mixed forest in northeast China and examined the relationship between δ13C of respiratory fluxes (leaf, trunk, soil, and the entire ecosystem) and environmental factors over a full growing season. This study found that the δ13C signal of CO2 from canopy air was strongly imprinted in the organic and respiratory pools throughout C transfer due to the effects of discrimination and isotopic mixing on C assimilation, allocation, and respiration processes. A significant difference in isotopic patterns was found between conifer and broadleaf species in terms of seasonal variations in leaf organic matter. This study also found that δ13C in trunk respiration, compared with that in leaf and soil respiration, was more sensitive to seasonal variations of environmental factors, especially soil temperature and soil moisture. Variation in the δ13C of ecosystem respiration was correlated with air temperature with no time lag and correlated with soil temperature and vapor pressure deficit with a lag time of 10 days, but this correlation was relatively weak, indicating a delayed linkage between above- and belowground processes. The isotopic linkage might be confounded by variations in atmospheric aerodynamic and soil diffusion conditions. These results will help with understanding species differences in isotopic patterns and promoting the incorporation of more influencing factors related to isotopic variation into process-based ecosystem models.

Spatio‐Temporal Variations in Carbon Isotope Discrimination Predicted by the JULES Land Surface Model

“…4.3. The Agreement Between Δ 13 C TR and Δ 13 C predicted Is Weaker at Four Sites Δ 13 C of structural carbohydrates in wood is closely linked to environmental change, therefore changes in environmental variables could have a greater impact on Δ 13 C TR than on leaf-level Δ 13 C (Diao et al, 2020;Loader et al, 2007). However, this is not consistent with Leppä et al (2022) and Rinne et al (2015) who both found a strong climate signal in leaf-sugar δ 13 C variability.…”

“…Δ 13 C of structural carbohydrates in wood is closely linked to environmental change, therefore changes in environmental variables could have a greater impact on Δ 13 C TR than on leaf‐level Δ 13 C (Diao et al., 2020 ; Loader et al., 2007 ). However, this is not consistent with Leppä et al.…”

“…We ran multiple linear regression models for both Δ 13 C TR and Δ 13 C predicted against environmental drivers to determine how much of the variability in measured and modeled Δ 13 C were caused by local climate. Since atmospheric CO 2 concentration ([CO 2 ] atm ), air temperature ( T air ), vapor pressure deficit (VPD), and atmospheric pressure via elevation ( z ) are the main drivers of c i and thus Δ 13 C at interannual timescales (Cernusak et al., 2013 ; Cornwell et al., 2018 ; Diao et al., 2020 ; Körner et al., 1991 ; Wang et al., 2017 ), we considered these variables in the regression models. Both photosynthetically active radiation (PAR) and plant‐available soil water can also impact Δ 13 C (Cernusak et al., 2013 ; Diefendorf et al., 2010 ; Hafner et al., 2014 ; Kohn, 2010 ; G. H. Young et al., 2010 ) but were not directly accounted for in the JULES model Δ 13 C predictions and thus excluded from the regression models.…”

Altitudinal variation of leaf carbon isotope for Dendrosenecio keniensis and Lobelia gregoriana in Mount Kenya alpine zone

“…We put 0.1 to 0.2 mg of the fine powder into a tin capsule for analysis of leaf δ 13 C. We used FlASH 2000 CHNS/O organic elemental analyzer with ConFlo IV, Trace GC ultra and Delta V Advantage stable isotope ratio mass spectrometer for leaf δ 13 C using manufacturers recommended standards. We calculated photosynthetic Carbon Isotope discrimination ∆ 13 C ‰ as done by Körner et al (1988) and Diao et al (2020). …”

Relationship between Forest Ecophysiology and Environment

“…These species differences can result in pronounced differences in plant carbon gain. Differences in carbon pools and fluxes were investigated by Diao et al [3], in pure conifers vs. mixed broadleaves, through continuous monitoring of CO 2 isotopes in situ. Not just the tree species (or forest type) but also the tree size mattered.…”