Tree-ring δ¹³C and growth responses of Larix principis-rupprechtii to climate change in the Central-Northern Taihang Mountains.

In the context of global warming and aridification, the Taihang Mountains, recognized as a climate-sensitive transitional zone, necessitate a thorough investigation into the adaptive mechanisms of their forest ecosystems. This study investigates the 60-year variations and climate responses of tree-ring stable carbon isotopes (δ¹³C), intrinsic water-use efficiency (iWUE), and basal area increment (BAI) in Larix principis-rupprechtii from the central-northern Taihang Mountains. The results reveal a phased trend in tree-ring δ¹³C, with an increase from 1964 to 2012 followed by a subsequent decline, suggesting dynamic regulation of the ratio of intercellular to atmospheric CO2 concentrations (Ci/Ca) that may be associated with changes in moisture availability after 2012. iWUE increased significantly during the study period, primarily driven by the combined effects of rising atmospheric CO2 concentrations and stomatal regulation. Carbon isotope discrimination (Δ¹³C) exhibited pronounced seasonal responses to climatic factors. Specifically, water availability was the primary determinant of isotopic fractionation during the April-August growing season, while temperature further intensified water stress by increasing evaporative demand. iWUE demonstrated greater sensitivity to climatic variation than BAI. Although their long-term trends showed general consistency, the interannual coupling remained weak. Commonality analysis indicated that Ca and relative humidity explained 89.62% of iWUE variation, whereas iWUE and relative humidity explained only 20.55% of BAI variation, with the independent contribution of iWUE being minimal. These results suggest that persistent water stress limits the effective conversion of increased iWUE into radial growth, potentially counteracting the effects of CO2 fertilization, and that increases in iWUE do not consistently promote tree growth. This study offers essential insights into the future carbon sequestration potential of central-northern Taihang Mountain forests and adaptive management.