Disclosing biome sensitivity to atmospheric changes: Stable C isotope ecophysiological dependences during photosynthetic CO2 uptake in Maritime pine and Scots pine ecosystems from southwestern Europe

• Novel approach can smooth individual variability in tree-ring C isotopic records.
• Compared to Maritime pine, Scots pine wood is significantly 13C enriched.
• Pine forest stand quality affects the tree-ring C isotope composition.
• Tree-ring δ13C can reflect the biome sensitivity to atmospheric changes.
• Nuanced responses of the biosphere to global change shown by isotopic dendrology.

Background:   The late XX century showed a sharp atmospheric δ13CO2 decline mainly ascribed to increased emissions of greenhouse gases (GHG) resulting from fossil fuel combustion. Thus, in the current global-warming scenario, a deep knowledge of biosphere–atmosphere interactions became especially relevant to adopt appropriate guidelines for climate change management.Objective: Although tree-rings can attest long-term atmospheric composition trends, C isotopic variability among individual trees often disturbs the accurate interpretation of 13C atmospheric changes from tree-rings at different timescales. Therefore, the aim of this research is to overcome this intertree variability by applying an isotopic approach that can practically absorb high-frequency climatic irregularities and genetic variabilities from dendrochronological series, hence allowing the accurate deconvolution of past atmospheric composition to improve current models.Methods:   This research is based on original isotopic dendrochronological results obtained by performing tree-by-tree differential studies with intra-tree δ13C shifts to allow interspecies data standardization.Results:   The isotopic composition of dendrochronological series collected from northwestern Spanish coniferous ecosystems clearly reflected the corresponding atmospheric 13C changes but the stringency of the match also depended on some silvicultural parameters, tree-ring isotopic composition being able to exhibit either a magnification or attenuation of atmospheric changes according to specific metabolic differences that modulate photosynthetic 13C discrimination in each ecological context.Conclusion:   Relative isotopic changes revealed from our 25-year-long dendrological research, which properly mirrored the contemporary atmospheric 13CO2 composition (1978–2002), also showed the biome sensitivity to atmospheric changes, pointing towards a notable aptitude to respond to even incipient mitigation strategies and a significant resilience capacity of the Earth system.

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