Ozone (O3) pollution is accompanied by drought stress, especially at high temperatures. Tree species in cities often face dual stresses from O3 and drought. In this study, Acer rubrum ‘Autumn Blaze’ and A. pictum were used as test plants in open-top-chambers (OTCs) to investigate the trees most tolerant to increasing O3 and drought stresses in urban gardens. The results showed that the dual stresses induced a change in A. rubrum’s leaf coloration from green to red. The leaf representation in A. rubrum was more variable than that of A. pictum. The leaf pigment content affected the plant leaf color difference, and the Chl and Car contents of both species were negatively correlated with L*. Under the dual stresses of O3 and drought, the changes in the net photosynthetic rate (Pn) and transpiration rate (Tr) were less variable in A. rubrum than A. pictum. The stomatal conductance (Gs) was more sensitive to higher O3 stress, the effect of which was enhanced by moderate drought (MD) conditions on Gs. The Tr decreased more significantly under drought stress, which mitigated the effect of O3 stress on the stomatal limit value (Ls). A. rubrum displayed differential color changes, resulting in greater structural heterogeneity within the garden landscape. The saplings adjusted their photosynthetic parameters under the dual stresses, whereas the dual stresses played an antagonistic role in protecting A. rubrum, suggesting that A. rubrum can resist O3 and drought. Our study suggests that A. rubrum is an alternative tree species for inclusion in urban gardens exposed to increasing O3 and drought stresses.

Background and aims The introduced lineage of Phragmites australis (haplotype M) in North America outcompetes the native lineage (haplotype P). Haplotype M situates at the fast-side of trait economic spectrum rather than haplotype P. The present study evaluated the plant traits and associated soil microbiome of the introduced and native Phragmites lineages using a common garden experiment in East China. Methods Four geographic groups including the introduced lineage of North America (NAint, haplotype M), native lineage of North America (NAnat, haplotype P), European group (EU, haplotype M) and Northwestern China group (CHN, haplotype M) were probed for plant traits and associated soil microbiome in two life-history stages – growing period and withering period. Results No significant differences in functional traits were shown among the four groups. The difference existed mainly in the soil microbial structure. The soils derived from the four groups had different bacterial generic structure however similar bacterial functional structure. NAint accumulated more orchid mycorrhizal fungi than the other three groups, while NAnat gathered more plant pathogenic and ectomycorrhizal fungi in the growing period. In the withering period, NAint accumulated more plant pathogenic fungi while NAnat gathered more arbuscular mycorrhizal fungai. NAint, EU and CHN shared different soil microbial structures despite the same haplotype. Conclusion The interaction between plant traits and soil microbiome seemed weak. However, the long-term effects of microbial transition on the introduced and native lineage are unknown and the potential plant-soil interactions need further exploration.

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Background and Aims Plant invasion can modify habitat characteristics for instance soil stoichiometry and microbial pattern. However, few studies concerned the effects of plant invasion on the soil properties in the urban ecosystem. The present study aims to explore the impact of aquatic plant invasion on sediment properties within the urbanization context. Methods First, population density and impervious surface area, were used to construct an urbanization gradient of river wetlands and divide the two rivers of Qingdao City, China – Zhangcun River and Wenquan River into urban and periurban types. Second, sediment samples were collected from the plots invaded by the aquatic plant invader, Alternanthera philoxeroides and its native neighbor, Typha angustifolia in urban and periurban rivers. Lastly, sediment properties were determined and a comparison was performed. Results First, a general similar fertility and stoichiometry was found between the sediment derived from the invasive and that from the native. Second, a higher bacterial diversity was found in the sediment derived from A. philoxeroides merely in the periurban river, while the higher bacterial diversity was merely shown for the Shannon’s diversity index of A. philoxeroides in the urban river. Third, A. philoxeroides shaped a novel soil microbial structure since more microbes relevant with nutrient cycling were accumulated compared to the native. Lastly, urbanization gradient affected the comparison between the invasive and native plants on soil properties. Conclusion The invasion of exotic aquatic plant altered the sediment microbial pattern to some extent and the potential plant-soil feedback needs further investigation.

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