关键词: 酸雨, 内在水分利用效率, 树木生长, 亚热带森林, 树轮生态学, 稳定同位素

Abstract:

Objective: Long-term acid rain deposition poses a severe threat to the stability of subtropical forest ecosystems. Based on dendroecology and stable isotope techniques, this study investigated the radial growth trends and physiological responses to water and nitrogen variations in Pinus massoniana and Castanopsis fargesii under long-term acid rain stress. The aim of this study is to provide a scientific basis for forest management and species selection in acid rain control zones. Method: This study was conducted in Jinyun Mountain National Nature Reserve, Chongqing, and P. massoniana and C. fargesii were selected as the research objects. The tree-ring width, stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in P. massoniana and C. fargesii were measured, with which intrinsic water-use efficiency (iWUE) was calculated. Combined with the deposition of major acid rain components (SO₄^2?, NO₃^?, and NH₄⁺) and climatic data, piecewise regression and multiple linear models were employed to quantify the effects of acid rain on tree growth and physiological indicators. Result: 1) Long-term acid rain stress significantly inhibited the growth rates of both species, yet their response patterns diverged. During the period of severe acid rain stress (1981—2010), the radial growth of P. massoniana significantly declined (P < 0.001), while that of C. fargesii stagnated (P > 0.05). However, as acid rain intensity diminished (2011—2020), both species exhibited a significant recovery trend (P < 0.05), with P. massoniana displaying a faster recovery rate. 2) Regarding water-use strategies, the iWUE of P. massoniana significantly decreased during the acid rain alleviation phase (2011—2020) (P < 0.01), whereas C. fargesii showed no significant change (P > 0.05), highlighting distinct strategies between coniferous and broadleaved species. 3) P. massoniana growth was significantly negatively affected only by SO₄^2? (P < 0.001), and its iWUE was significantly negatively correlated with basal area increment (P < 0.001), indicating that a conservative water-use strategy constrained its radial growth. Conversely, C. fargesii growth was inhibited by both SO₄^2? and NO₃^? (P < 0.001), it showed a significant positive correlation with NH₄⁺ deposition (P < 0.001), and its δ¹⁵N remained stable during the recovery period. Conclusion: P. massoniana and C. fargesii employ distinct growth and physiological adaptation strategies under long-term acid rain stress. P. massoniana exhibits high sensitivity to SO₄^2? stress due to conservative water regulation strategy and failure to effectively utilize nitrogen deposition. In contrast, C. fargesii demonstrates stronger growth recovery potential than P. massoniana, attributed to its efficient utilization of NH₄⁺ and synergistic water-carbon regulation. Therefore, management of subtropical forests should adhere to site-species matching, implement mixed-species planting and zonal configuration, and incorporate long-term acid deposition monitoring and soil amelioration measures to enhance community resilience and stress resistance.

Key words: acid rain, intrinsic water-use efficiency, tree growth, subtropical forests, dendroecology, stable isotopes