Growth inhibition and recovery of Pinus massoniana in Chongqing since the 1980s

Abstract

Over recent decades, the forest ecosystems of southern China have been substantially affected by acid rain, a principal biogeochemical driver. Despite recent efforts to mitigate acid rain, the long-term adaptive responses of trees of varying ages remain insufficiently understood. In this study, we employed the tree-ring basal area increment (BAI), δ13C, δ15N, and δ18O values to identify patterns in growth inhibition and recovery in young and mature Pinus massoniana within acid rain-afflicted zones in China. A marked growth inhibition phase occurred from 1983 to 2010, characterized by a significant decline in BAI, particularly in mature trees. A growth recovery phase occurred from 2011 to 2020, with considerable BAI increases. Throughout the growth-inhibition phase, the intrinsic water-use efficiency (iWUE) increased, whereas δ15N levels were stable, suggesting gradual stomatal closure influenced by both acid rain and elevated CO2 levels. During this phase, mature and young trees exhibited differing strategies in response to environmental stressors. The growth recovery phase was characterized by significant reductions in both iWUE and δ15N, leading to a more closed nitrogen cycle. Structural equation modeling and correlational analyses identified SO42−, NO3−, and precipitation as key determinants of growth variations in both young and mature trees. Our findings underscore the effect of prolonged acid rain exposure on growth suppression across P. massoniana age groups, highlighting iWUE as a reliable predictor of tree growth, although age should be considered. With the ongoing reduction in acidic gas emissions, subtropical P. massoniana forests have exhibited significant resilience, highlighting rapid ecological recovery. We advocate for continued large-scale monitoring and model-based assessments of acid rain effects, emphasizing the need for long-term evaluations to comprehend the ecological resurgence and carbon sequestration potential within these ecosystems.