Responses of spring leaf phenological and functional traits of two urban tree species to air warming and/or elevated ozone

Climate warming and surface ozone (O-3) pollution are important global environmental issues today. However, the combined impacts of air warming and O-3 on phenology and its functional traits of urban trees are still poorly understood. Here, an experiment was performed to explore the variations of the spring phenological and functional traits in leaves of Populus alba 'Berolinensis' and Forsythia suspensa under ambient air (15.8 degrees C, 35.7 ppb), increased air temperature (IT, ambient air temperature + 2 degrees C, 17.9 degrees C), elevated O-3 (EO, ambient air O-3 concentrations + 40 ppb, 77.4 ppb), and their combined treatments (17.7 degrees C, 74.5 ppb). Our results showed that: IT advanced the beginning of leaf bud expansion phase of P. alba 'Berolinensis' and F. suspensa for 6 d and 5 d, respectively, increased leaf unfolding rate, leaf area and dry weight, and enhanced photosynthesis and anti-oxidative enzyme activities. EO delayed the beginning of leaf bud expansion phase of P. alba 'Berolinensis' for 5 d, decreased leaf area and biomass, and inhibited photosynthesis and caused oxidative damage of plant leaves. Compared to EO, the combined treatment advanced the spring phenophase, increased growth and induced the higher level of photosynthetic rate and antioxidative enzymes activities in plant leaves, which indicated that the positive effects of increased temperature (17.7 degrees C) alleviated the inhibition of growth and photosynthesis induced by ozone. Our findings can provide a theoretical reference for predicting the adaptation of functional traits of the two trees blossomed early under warming and O-3 pollution at spring phenological stage.

Automated summary

This study investigated the combined impacts of air warming and ozone pollution on the phenology and functional traits of urban trees. The results showed that warming promoted growth and photosynthesis, while ozone pollution inhibited these effects. However, the combined treatment of warming and ozone alleviated the inhibition and led to earlier phenological stages, increased growth, and higher photosynthetic rates.