Autumnal leaf abscission of sugar maple is not delayed by atmospheric CO 2 enrichment

To investigate the effects of atmospheric CO 2 enrichment on physiology and autumnal leaf phenology, we exposed 3-year-old sugar maple ( Acer saccharum Marsh.) seedlings to 800 (A8), 600 (A6), and 400 μL(CO 2 ) L –1 (AA) in nine continuous stirred tank reactor (CSTR) chambers during the growing season of 2014. Leaf abscission timing, abscised leaf area percentages, leaf number, light-saturated net photosynthetic rate ( P Nmax ), leaf area, accumulative growth rates, and biomass were determined and assessed. The results suggested the following: ( 1 ) no significant differences were found in the timing of leaf abscission in the three CO 2 -concentration treatments; ( 2 ) P Nmax was continuously stimulated to the greatest extent in A8 at 319% and 160% in A6 until the end of the growing season, respectively; and ( 3 ) leaf number, leaf area, and accumulative height growth all significantly increased by elevated CO 2 , which led to a 323% increase in A8 biomass and 235% in A6 biomass after 156-d fumigation. In summary, the results suggest, the timing of leaf abscission of sugar maple in fall was not modified by CO 2 enrichment, the increased carbon gain by elevated CO 2 was mainly due to increased leaf area, more leaves, and the continuously enhanced high photosynthesis throughout the growing season instead of the leaf life span.