CR 76:115-130 (2018)  -  DOI: https://doi.org/10.3354/cr01526

ABSTRACT: Understanding the responses of tree growth and intrinsic water-use efficiency (iWUE) to anthropogenic CO₂ increase and climate warming provides important benchmarks for evaluating future forest dynamics under different scenarios of warming and CO₂ changes. Relative to the short period of instrumental data of the past few decades, long-term tree-ring width and stable carbon isotopic (δ¹³C) data are invaluable in fully comprehending their interactions during the entire industrial era, since ~1850. Here, we present a tree-ring width chronology (1856 to 2015) and δ¹³C series (1876-2015) of Pinus massoniana for Yongtai county of Fujian province, in humid subtropical China, a ‘green island’ relative to other dry subtropical areas of the world. Tree growth was limited by precipitation of the hydrological year (previous November to current October) (r = 0.568, p < 0.001), and the stable carbon isotope discrimination (Δ¹³C) was strongly correlated with relative humidity in September-October (r = -0.677, p < 0.001) of the current growing season. We found that the iWUE increased by 40.9% since 1876. Specifically, we found that the c_i:c_a ratio decreased during the study period whereas intercellular CO₂ concentration (c_i) increased. The negative relationship between basal area increment (BAI) and iWUE indicated that increasing iWUE may not lead to long-term enhancement of tree growth. Our results indicated a drought-induced limitation to tree growth in response to rising CO₂, and that trees may mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance.

KEY WORDS: Tree-ring · Stable carbon isotope · Intrinsic water-use efficiency · Pinus massoniana · Humid subtropical China