Drought mitigates the adverse effects of O3 on plant photosynthesis rather than growth: A global meta-analysis considering plant functional types

Tropospheric ozone (O3 ) is a phytotoxic air pollutant adversely affecting plant growth. High O3 exposures are often concurrent with summer drought. The effects of both stresses on plants are complex, and their interactions are not yet well understood. Here, we investigate whether drought can mitigate the negative effects of O3 on plant physiology and growth based on a meta-analysis. We found that drought mitigated the negative effects of O3 on plant photosynthesis, but the modification of the O3 effect on the whole-plant biomass by drought was not significant. This is explained by a compensatory response of water-deficient plants that leads to increased metabolic costs. Relative to water control condition, reduced water treatment decreased the effects of O3 on photosynthetic traits, and leaf and root biomass in deciduous broadleaf species, while all traits in evergreen coniferous species showed no significant response. This suggested that the mitigating effects of drought on the negative impacts of O3 on the deciduous broadleaf species were more extensive than on the evergreen coniferous ones. Therefore, to avoid over- or underestimations when assessing the impact of O3 on vegetation growth, soil moisture should be considered. These results contribute to a better understanding of terrestrial ecosystem responses under global change.

The effects of exogenous malic acid in relieving aluminum toxicity in Pinus massoniana

Two different genotypes of Pinus massoniana seedlings (aluminum-resistant FJ5 and aluminum-sensitive GD20) were used, the effects of different exogenous malic acid (0.00, 0.01, 0.02, 0.04, 0.08, 0.16 mmol·L^-1) on the growth attributes of P. massoniana seedlings treated by the Al³⁺ concentration of 0.8 mmol·L^-1 were studied, to provide a basis for the growth in acidified soil. In our experiment, the seedling growth was inhibited by Al³⁺ treatment. After treatment with a low concentration of exogenous malic acid, the activities of antioxidant enzymes in leaves were enhanced, the concentrations of hydrogen peroxide (H₂O₂), superoxide (O₂^-·), malondialdehyde (MDA) and osmotic adjustment substances were reduced accordingly. GD20 exhibited more severe changes compared with FJ5. The larger ones of the contribution rates of the indices in principal component analysis were H₂O₂, Glutathione Reductase (GR). These results indicated that Al³⁺ with high concentration inhibits the growth of P. massoniana. Malic acid could effectively alleviate the toxicity, and the mitigation effect on the aluminum-sensitive species, which genotype is more sensitive to the response of Al³⁺ toxicity, was more effective than that on the aluminum-resistant. How to select and cultivate more resistant species, by using the main parameter (H₂O₂ and GR), is worthy in further study.