O3impacts on plant development: a meta‐analysis of root/shoot allocation and growth

Abstract

The mechanism of O 3 action on plants remains poorly characterized. Symptoms include visible lesions on the leaf surface, reduced growth and a hypothesized reduction in allocation of carbohydrate to roots. The generality of this latter phenomenon has not been demonstrated. Here, a meta‐analysis is performed of all available experimental data, to test the hypotheses that O 3 exposure of the shoot inhibits biomass allocation below ground (the root/shoot allometric coefficient,k) and inhibits whole‐plant growth rate [relative growth rate (RGR)]. Both k and RGR were significantly reduced by O 3(5.6 and 8.2%, respectively). Variability in k was greater than in RGR, and both exhibited some positive as well as mostly negative responses. The effects on k were distinct from the effects on RGR. In some cases,k was reduced while RGR was unaffected. Slow‐growing plants (small RGR) exhibited the largest declines in k. These observations may have mechanistic implications regarding O 3 phytotoxicity. There were no effects of type of exposure chamber on sensitivity to O 3. The analyses indicate that the O 3 inhibition of allocation to roots is real and general, but variable. Further experiments are needed for under‐represented plant groups, to characterize exceptions to this generalization and to evaluate O 3–environment interactions.