A global meta-analysis of woody plant responses to elevated CO2: implications on biomass, growth, leaf N content, photosynthesis and water relations

Abstract

Abstract Background Atmospheric CO 2 may double by the year 2100, thereby altering plant growth, photosynthesis, leaf nutrient contents and water relations. Specifically, atmospheric CO 2 is currently 50% higher than pre-industrial levels and is projected to rise as high as 936 μmol mol −1 under worst-case scenario in 2100. The objective of the study was to investigate the effects of elevated CO 2 on woody plant growth, production, photosynthetic characteristics, leaf N and water relations. Methods A meta-analysis of 611 observations from 100 peer-reviewed articles published from 1985 to 2021 was conducted. We selected articles in which elevated CO 2 and ambient CO 2 range from 600–1000 and 300–400 μmol mol −1 , respectively. Elevated CO 2 was categorized into < 700, 700 and > 700 μmol mol −1 concentrations. Results Total biomass increased similarly across the three elevated CO 2 concentrations, with leguminous trees (LTs) investing more biomass to shoot, whereas non-leguminous trees (NLTs) invested to root production. Leaf area index, shoot height, and light-saturated photosynthesis ( A max ) were unresponsive at < 700 μmol mol −1 , but increased significantly at 700 and > 700 μmol mol −1 . However, shoot biomass and A max acclimatized as the duration of woody plants exposure to elevated CO 2 increased. Maximum rate of photosynthetic Rubisco carboxylation ( V cmax ) and apparent maximum rate of photosynthetic electron transport ( J max ) were downregulated. Elevated CO 2 reduced stomatal conductance ( g s ) by 32% on average and increased water use efficiency by 34, 43 and 63% for < 700, 700 and > 700 μmol mol −1 , respectively. Leaf N content decreased two times more in NLTs than LTs growing at elevated CO 2 than ambient CO 2 . Conclusions Our results suggest that woody plants will benefit from elevated CO 2 through increased photosynthetic rate, productivity and improved water status, but the responses will vary by woody plant traits and length of exposure to elevated CO 2 .