Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

The carbon-sink strength of temperate and boreal forests at midlatitudes of the northern hemisphere is decreased by ozone pollution, but knowledge on subtropical evergreen broadleaved forests is missing. Taking the dataset from Chinese studies covering temperate and subtropical regions, effects of elevated ozone concentration ([O ]) on growth, biomass, and functional leaf traits of different types of woody plants were quantitatively evaluated by meta-analysis. Elevated mean [O ] of 116 ppb reduced total biomass of woody plants by 14% compared with control (mean [O ] of 21 ppb). Temperate species from China were more sensitive to O than those from Europe and North America in terms of photosynthesis and transpiration. Significant reductions in chlorophyll content, chlorophyll fluorescence parameters, and ascorbate peroxidase induced significant injury to photosynthesis and growth (height and diameter). Importantly, subtropical species were significantly less sensitive to O than temperate ones, whereas deciduous broadleaf species were significantly more sensitive than evergreen broadleaf and needle-leaf species. These findings suggest that carbon-sink strength of Chinese forests is reduced by present and future [O ] relative to control (20-40 ppb). Given that (sub)-tropical evergreen broadleaved species dominate in Chinese forests, estimation of the global carbon-sink constraints due to [O ] should be re-evaluated.