The effects of intrinsic water-use efficiency and climate on wood anatomy.

Climate warming may induce growth decline in warm-temperate areas subjected to seasonal soil moisture deficit, whereas increasing atmospheric CO 2 concentration (C a ) is expected to enhance tree growth. An accurate understanding of tree growth and physiological processes responding to climate warming and increasing C a is critical. Here, we analyzed tree-ring stable carbon isotope and wood anatomical traits of Pinus tabuliformis from Qinling Mountains in China to understand how lumen diameter (LD) determining potential hydraulic conductivity and cell-wall thickness (CWT) determining carbon storage responded to climate and C a . The effects of climate and C a on intrinsic water-use efficiency (iWUE) were isolated, and iWUE values due to only-climate (iWUE Clim ) and only-CO 2 effects (iWUE CO2 ) were obtained. During a low-iWUE period, the influences of climate on earlywood (EW) LD and latewood (LW) CWT prevailed. During a high-iWUE period, CO 2 fertilization promoted cell enlargement and carbon storage but this was counteracted by a negative influence of climate warming. The limiting direct effects of iWUE Clim and indirect effects of climate on EW LD were greater than on LW CWT. P. tabuliformis in temperate forests will face a decline of growth and carbon fixation, but will produce embolism-resistant tracheids with narrow lumen responding to future hotter droughts.