Drought adaptation and recovery in Scots pine: δ13C evidence from laser ablation and CSIA

Understanding drought-induced changes in tree carbon dynamics is crucial, as forests play a significant role in regulating the global carbon cycle. Tree-rings can serve as detailed archives of intra-seasonal environmental changes, such as intrinsic water-use efficiency (iWUE) in their stable carbon isotope composition (δ¹³C_Ring). However, it remains unclear how multiple, simultaneous physiological responses to drought affect these records. We traced drought and recovery-associated physiological responses from leaves to phloem, roots, and tree-rings in seven-year-old Pinus sylvestris using δ¹³C analysis of sucrose, high-resolution δ¹³C_Ring analysis by laser ablation and leaf gas exchange. Although sucrose captured leaf-level processes, intra-annual δ¹³C_Ring was intermittently uncoupled from leaf-level processes over time. When scaled to the conventional approach in δ¹³C_Ring research—analysing whole annual rings or distinguishing between earlywood and latewood sections—the drought event was not detectable. This study emphasises the need for cautious interpretation when using conventional δ¹³C_Ring analysis to study plant stress responses, while demonstrating the potential of high-resolution intra-annual δ¹³C_Ring for uncovering tree adaptation mechanisms in the context of climate change.