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Purpose: The increasing soil microplastics (MPs) pollution and the dry–wet alternation caused by climate change occur widely. Emerging studies have shown their negative impacts on the structure of soil bacteria and plant physiology. However, there is limited research on the effects of MPs exposure under different water regimes, and the influence processes are inconclusive. Therefore, the impacts of MPs under different water regimes on the antioxidant activity of vegetable and the soil bacterial community were studied. Materials and methods: A continuous water supply and a dry–wet cycle were established to compare the effects of two types of MPs (polypropylene (PP); polyethylene terephthalate (PET)) on lettuce (Lactuca sativa L. var. longifolia) growth and soil bacterial community, determined by antioxidant enzyme activity analysis, and by high-throughput sequencing analysis, respectively. Results: The PET influenced the lettuce growth and bacterial diversity largely compared to PP. The dry–wet cycle enhanced the effects of MPs on the activity of the antioxidant enzymes in lettuce, while it reduced lettuce biomass and root activity. Proteobacteria and Actinobacteria were the dominant soil bacteria under all treatments. The addition of MPs increased the relative abundance of nutrient-related bacteria such as Proteobacteria. MPs addition increased intragroup differences in soil bacterial diversity, and the dry–wet cycle reduced intergroup differences caused by MPs. Conclusion: The polymer type of MPs influenced the antioxidant activity of lettuce roots and leaves. The dry–wet cycle intensified the exposure risk of MPs by enhancing the stimulation of MPs on the antioxidant activity of lettuce. The dry–wet cycle significantly reduced the MPs-induced differences in bacterial communities. In short, the dry–wet cycle might alter the ecological risks in plant-soil ecosystem by shifting soil bacterial lineages related to nutrient cycling and metabolic function under MPs exposure. [ABSTRACT FROM AUTHOR]

Purpose: Elevated CO2 concentration (eCO2) may stimulate plant growth and influence the soil microbial community, but questions remain for whether microbial responses to elevated CO2 would vary by different CO2-responsive plants. We thus attempted to elaborate the changes of soil microbiome to different rice cultivars under the eCO2 condition. Materials and methods: Two rice cultivars, i.e., the CO2-tolerant cultivar, Wuyunjing23 (WYJ23), and the CO2-sensitive one, Yandao 6 (YD6), were grown under eCO2 and ambient CO2 (aCO2) conditions. The contents of dissolved organic carbon (DOC) and nitrogen (DON) in soil were measured. Real-time qualitative PCR (qPCR) and high-throughput sequencing techniques were employed to characterize the bacterial community. Furthermore, co-occurrence network analysis was applied to reveal the ecological interactions among bacterial taxa. Results and discussion: No significant differences were found among all treatments in terms of bacterial population, alpha-diversity indices, and bacterial community structure. However, the topological parameters of ecological networks highlighted the distinct co-occurrence patterns among treatments. YD6 under eCO2 led to more links, lower modularity, and greater centralization degree compared to that under aCO2. Opposite trends of those parameters were observed for WYJ23 under eCO2 compared to that under aCO2. Besides, more Proteobacteria and Acidobacteria served as keystone taxa in the CO2-sensitive cultivar treatments, compared to those in WYJ23, implying the different influences of rice cultivars on the microbial ecological network. Conclusions: Different rice cultivars under eCO2 did not influence the alpha- and beta-diversity of the soil bacterial community, but changed the co-occurrence network of the community. More attention should be paid to the assembly mechanisms of the soil microbial microbiome when evaluating the impacts of productive crops on the soil-plant ecosystem under the eCO2 condition. [ABSTRACT FROM AUTHOR]

Purpose: The extract of Stevia residue is an ideal substitute for cultivation of the purple nonsulfur bacterium, like Rhodopseudomonas palustris ( R. palustris). But the influence of R. palustris grown under residue extract on its downstream application is still not well-characterized. The objective of this study was to assess the effect of foliar spray of R. palustris grown under Stevia residue extract on the plant growth and soil microbial properties. Materials and methods: A pot experiment was carried out under the greenhouse condition, consisting of four treatments varying in the sprayed substances: sterilized water (control), R. palustris grown under the chemical medium supplemented with L-tryptophan (SyT), R. palustris grown under Stevia residue extract supplemented with L-tryptophan (ExT), and R. palustris grown under Stevia residue extract supplemented with NHCl (ExT). The net photosynthesis rate of the uppermost leaves was measured with a portable photosynthesis system. Soil microbial activity was analyzed by microcalorimetry. Soil bacterial community components were determined by real-time quantitative PCR (qPCR) and high-throughput sequencing techniques. Results and discussion: Compared with SyT, the R. palustris grown under Stevia residue extract not only improved the plant biomass and the net photosynthetic rate to a large extent, but also increased soil microbial metabolic activity and altered community compositions as well. The treatments receiving R. palustris, especially ExT and ExN, increased the relative abundances of some functional guilds involved in C turnover and nutrient cycling in soil, including Acidobacteria, Actinobacteria, Proteobacteria, Gemmatimonadaetes, Nitrospirae, and Planctomycetes. Conclusions: R. palustris grown under the Stevia residue extract showed advantages over that under the chemical medium on both plant growth and soil microbial properties. One of the possible reasons could result from the increases in microbial activity and several bacterial keystone guilds involved into C and nutrient cycling, both of which potentially contribute to the improved plant growth. The results would be conducive to the downstream application of R. palustris in an economical way. [ABSTRACT FROM AUTHOR]