title: A meta-analysis of elevated CO2effects on woody plant mass, form, and physiology.
abstract: Quantitative integration of the literature on the effect of elevated CO2on woody plants is important to aid our understanding of forest health in coming decades and to better predict terrestrial feedbacks on the global carbon cycle. We used meta-analytic methods to summarize and interpret more than 500 reports of effects of elevated CO2on woody plant biomass accumulation and partitioning, gas exchange, and leaf nitrogen and starch content. The CO2effect size metric we used was the log-transformed ratio of elevated compared to ambient response means weighted by the inverse of the variance of the log ratio. Variation in effect size among studies was partitioned according to the presence of interacting stress factors, length of CO2exposure, functional group status, pot size, and type of CO2exposure facility. Both total biomass (WT) and net CO2assimilation (A) increased significantly at about twice ambient CO2, regardless of growth conditions. Low soil nutrient availability reduced the CO2stimulation of WTby half, from +31% under optimal conditions to +16%, while low light increased the response to +52%. We found no significant shifts in biomass allocation under high CO2. Interacting stress factors had no effect on the magnitude of responses of A to CO2, although plants grown in growth chambers had significantly lower responses (+19%) than those grown in greenhouses or in open-top chambers (+54%). We found no consistent evidence for photosynthetic acclimation to CO2enrichment except in trees grown in pots <0.5 l (-36%) and no significant CO2effect on stomatal conductance. Both leaf dark respiration and leaf nitrogen were significantly reduced under elevated CO2(-18% and -16% respectively, data expressed on a leaf mass basis), while leaf starch content increased significantly except in low nutrient grown gymnosperms. Our results provide robust, statistically defensible estimates of elevated CO2effect sizes against which new results may be compared or for use in forest and climate model parameterization.
authors.affiliation: Dept. of Plant Biology, The Ohio State University, 1735 Neil Ave., Columbus, OH 43210, USA, , , , , , US.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Curtis
authors.affiliation: Dept. of Plant Biology, The Ohio State University, 1735 Neil Ave., Columbus, OH 43210, USA, , , , , , US.
authors.forename: Xianzhong
authors.initials: X
authors.lastname: Wang
keywords: Key words Elevated CO2; Meta-analysis; Woody plants