Jun 2022, Volume 4 Issue 2

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    Baoyuan Qu
    Fang Wang, Yu Wang, Leilei Xiang, Marc Redmile-Gordon, Chenggang Gu, Xinglun Yang, Xin Jiang, Damià Barceló

    • Microplastics and phthalate acid esters concentrations are positively correlated in soils.

    • Phthalate acid esters levels are greatest in Chinese soils.

    • Microplastics and phthalate acid esters share common sources and sinks.

    • Microplastics and phthalate acid esters are taken up by plants.

    • Microplastics and phthalate acid esters exert confounded influences on soil ecosystems.

    Microplastics (MPs) and Phthalate acid esters (PAEs) co-occur as emerging contaminants of global importance. Their abundance in soil is of increasing concern as plastic-intensive practices continue. Mulching with plastic films, inclusion in fertilizers, composts, sludge application, and wastewater irrigation are all major and common sources of MPs and PAEs in soil. Here, we review studies on the concentration and effects of MPs and PAEs in soil. While there is limited research on the interactions between MPs and PAEs in agroecosystems, there is evidence to suggest they could mutually affect soil ecology and plant growth. Therefore, we propose new research into 1) establishing an efficient, accurate, and simple method to quantify different types of microplastics in soils and plants; 2) exploring the behavior and understanding the mechanisms of co-transfer, transformation, and interactions with soil biota (especially in vegetable production systems); 3) assessing the risk and consequences of combined and discreet impacts of MPs and PAEs on plants and soil biota, and 4) preventing or reducing the transfer of MPs and PAEs into-and within- the food chain.

    Shin Woong Kim, Matthias C. Rillig

    • We collated and synthesized previous studies reporting on impacts of microplastics in soils.

    • We found the most frequently used composition, shapes, size, and concentration.

    • Species sensitivity distribution (SSD) method was used to screen the significant effects.

    • We suggested special considerations are necessary to manage microplastics in soils.

    We collated and synthesized previous studies that reported the impacts of microplastics on soil parameters. The data were classified and integrated to screen for the proportion of significant effects, then we suggest several directions to alleviate the current data limitation in future experiments. We compiled 106 datasets capturing significant effects, which were analyzed in detail. We found that polyethylene and pellets (or powders) were the most frequently used microplastic composition and shape for soil experiments. The significant effects mainly occurred in broad size ranges (0.1–1 mm) at test concentrations of 0.1–10% based on soil dry weight. Polyvinyl chloride and film induced significant effects at lower concentrations compared to other compositions and shapes, respectively. We adopted a species sensitivity distribution (SSD) and soil property effect distribution (SPED) method using available data from soil biota, and for soil properties and enzymes deemed relevant for microplastic management. The predicted-no-effect-concentration (PNEC)-like values needed to protect 95% of soil biota and soil properties was estimated to be between 520 and 655 mg kg-1. This study was the first to screen microplastic levels with a view toward protecting the soil system. Our results should be regularly updated (e.g., quarterly) with additional data as they become available.

    Renjun Zhou, Hao Wang, Dongdong Wei, Shenzheng Zeng, Dongwei Hou, Shaoping Weng, Jianguo He, Zhijian Huang

    • Positive microbial interaction dominating in sedimentary bacterial and eukaryotic communities.

    • Homogeneous selection process governed the assemblage of both bacterial and eukaryotic communities.

    • Bacterial and eukaryotic diversities were in the reverse correlations with microbial positive interaction.

    Sedimentary bacterial and eukaryotic communities are major components of the aquatic ecosystem. Revealing the linkages between their community structure and interactions is crucial to understand the diversity and functions of aquatic and soil ecosystems. However, how their diversity and assembly contribute to their interactions on time scale is unclear. This study examined sedimentary bacterial and eukaryotic communities in shrimp culture ponds at different culture stages. The most abundant bacteria were Proteobacteria (38.27%), whereas the most abundant eukaryotes were Chytridiomycota (27.48%). Bacterial and eukaryotic diversities were correlated (P<0.05), implying the strong interactions between bacteria and eukaryotes. Results showed that the bacterial and eukaryotic communities became increasingly similar on a local scale along with the shrimp culture. Only the eukaryotic community significantly increased in similarity along with the shrimp culture (P<0.05), suggesting that the sedimentary eukaryotic community structure is sensitive under shrimp culture. Co-occurrence network modeling indicated that positive microbial interactions were dominant. The homogeneous selection was the major driver of community assembly. Bacterial diversity negatively correlated with operational taxonomic units and positive links in networks (P<0.05), whereas eukaryotic diversities positively correlated with positive links in networks (P<0.05). This study broadens our knowledge about sedimentary microbial diversity, community assembly, and interaction patterns on time scale, providing a reference for the sustainable management in aquaculture production.

    Yanxia Xu, Junjie Liu, Xuefeng Liu, Hong Li, Zhao Yang, Hongbao Wang, Xinyu Huang, Lan Lan, Yutong An, Lujun Li, Qin Yao, Guanghua Wang

    • 10 years of CC was a cut-off point in separating soil bacterial community structures.

    • Soil pH and P were well associated with changes of diversity and community structures.

    • N fixation bacteria were increased with successive year, but P, K solubilizing bacteria decreased.

    • Monocropped alfalfa simplified the complexity of the cooccurrence networks.

    Alfalfa is a perennial herbaceous forage legume that is remarkably and negatively affected by monocropping. However, the contribution of the changes in bacterial communities to the soil sickness in alfalfa have not been elucidated. Therefore, we investigated bacterial community structures responses to monocropped alfalfa along the chronosequence. Continuous cropping remarkably reduced bacterial alpha diversity and altered community structures, and soil pH, total P and available P were strongly associated with the changes of bacterial diversity and community structures. Intriguingly, 10-year of monocropped alfalfa might be a demarcation point in separating soil bacterial community structures into two obvious groups that containing soil samples collected in less and more than 10-years. The relative abundances of copiotrophic bacteria of Actinobacteria and Gammaproteobacteria were significantly increased with the extension of continuous cropping years, while the oligotrophic bacteria of Armatimonadetes, Chloroflexi, Firmicutes and Gemmatimonadetes showed the opposite changing patterns. Among those altered phyla, Actinobacteria, Chloroflexi, Alphaproteobacteria and Acidobacteria were the most important bacteria which contributed 50.86% of the community variations. Additionally, the relative abundances of nitrogen fixation bacteria of Bradyrhizobium and Mesorhizobium were obviously increased with successive continuous cropping years, while the abundances of Arthrobacter, Bacillus, Burkholderiaceae and Microbacterium with potential functions of solubilizing phosphorus and potassium were remarkably decreased after long-term continuous cropping. Furthermore, bacterial cooccurrence patterns were significantly influenced by continuous cropping years with long-term monocropped alfalfa simplifying the complexity of the cooccurrence networks. These findings enhanced our understandings and provided references for forecasting how soil bacterial communities responses to monocropped alfalfa.

    Dayong Gan, Hui Zeng, Biao Zhu

    • We performed a meta-analysis to synthesize the rhizosphere effect on soil gross nitrogen mineralization rate.

    • It was 81% on average, being significantly higher in woody (than non-woody species) and in ECM associated species (than AM associated species).

    • It was positively correlated with the rhizosphere effects on soil C mineralization rate, microbial biomass nitrogen, phenol oxidase activity and root biomass.

    • Its variations were mainly controlled by soil microbial variables and plant factors rather than climatic factors.

    Rhizosphere effects play crucial roles in determining soil carbon (C) and nitrogen (N) cycling. However, the rhizosphere effect on soil gross nitrogen (N) mineralization (Nmin) has not been quantitatively assessed on the global scale. Here we performed a meta-analysis of compiled data from 24 publications and 37 species to synthesize the rhizosphere effect on soil gross Nmin and its influencing factors. We found that the rhizosphere effect significantly enhanced soil gross Nmin by 81% on average. Such rhizosphere effect was significantly higher in woody species than in non-woody species, and higher in ECM (ectomycorrhizal) associated species than in AM (arbuscular mycorrhizal) associated species. Moreover, the variations of the rhizosphere effect on soil gross Nmin were correlated with those on soil C mineralization, phenol oxidase activity and root biomass rather than with other plant (growth form and mycorrhizal association) and climatic (mean annual temperature and precipitation) factors. These results support the ‘microbial activation’ and ‘microbial N mining’ hypotheses of rhizosphere effects and indicate the coupling of soil C and gross N mineralization in the rhizosphere. Overall, these findings provide novel insights into the rhizosphere effect on soil gross Nmin among plant growth forms and mycorrhizal associations, and improve our mechanistic understanding of soil N dynamics in the rhizosphere.

    Minghe Jiang, Luan Zhang, Ming Liu, Han Qiu, Shungui Zhou

    • We evaluated effects of fungi on N2O emission in Chinese milk vetch-containing soils.

    • Fungi to contributed to soil N2O production in CMV-amended soils.

    • Fungi accounted for 56% of N2O emission in CMV-amended soils.

    • Fungi may be important contributors to N2O production in CMV-amended soils.

    Fungi play an important role in soil nitrous oxide (N2O) emission in many agricultural soil systems. However, the effect of fungi on N2O emission in Chinese milk vetch (CMV)-containing soils has not been examined sufficiently. This study investigated the contribution of bacteria and fungi to soil N2O emission in CMV-amended soils. We compared soils from an experimental field in the Fujian Academy of Agricultural Sciences that had been treated with 30 000 kg of CMV per 667 m2 per year with one that was not treated with CMV. We incubated soil using cycloheximide and streptomycin to differentiate fungal and bacterial N2O emissions, respectively. Quantitative PCR (qPCR) was performed to investigate bacterial and fungal abundances in the two agricultural soil ecosystems. The contribution of fungi to soil N2O emission in CMV-amended soils was greater than that in non-CMV-amended paddy soils, with fungi accounting for more than 56% of the emissions in CMV-amended soils. Quantitative PCR showed that the ratio of the internal transcribed spacer to 16S rDNA was significantly higher in CMV-amended soils than in non-CMV-amended paddy soils. Furthermore, soil properties, such as pH (P<0.05) and NH4+ concentration (P<0.05), significantly and negatively affected N2O emission by fungi in soil, whereas the total organic carbon (P<0.05) and NO3- concentration (P<0.05) showed significant positive effects. Fungi may be important contributors to N2O production in CMV-amended soils, which may create challenges for mitigating N2O production.

    Xiaofeng Luo, Linglong Zhu, Guoliang Xu, Jiaen Zhang, Jianlong Xu, Shiqin Yu, Xiaohua Chen

    • This study discovered the direct responses of soil fauna to acid deposition.

    • Soil fauna showed a certain adaptability of the pH change.

    • There was interaction between pH and exposure term on the avoidance behaviors.

    • Folsomia candida appeared signifcant avoidance behavior at pH<4.5.

    Excessive acid deposition causes soil acidification and changes the soil microhabitat, affecting the survival and reproduction of soil organisms. Folsomia candida (Collembola, Isotomidae) is used internationally as a model organism for assessing chemical toxicity in soil and it is feasible to use its avoidance response as an indicator of environmental changes as well. In this study, we used Folsomia candida avoidance behavior to assess the risks of acid deposition on soil ecosystems. Different pH (3.0, 3.5, 4.0, 4.5, 5.0, and 5.5) treatments were set up in petri dish experiments, and the avoidance behavior of Folsomia candida was measured after 12, 24, and 48 h of exposure to the pH conditions. The results indicated that (1) both the exposure duration and pH level influenced collembolan avoidance behavior. (2) After 12 h exposure, most of the insects showed avoidance behavior but without significant differences among the treatment conditions. (3) After 24 h exposure, significant avoidance behavior was observed at pH 3.0, 3.5, and 4.0. (4) After 48 h exposure, avoidance behavior was seen in all treatment conditions except for pH 5.5. This study described the direct responses of soil fauna to acid deposition and indicated that both pH and length of exposure interacted to influence the avoidance behavior of Folsomia candida. During the experimental period, the insects reacted negatively and show consistent avoidance behavior at pH 3.0, 3.5, and 4.0. Reversed avoidance behavior was apparent between pH 4.5 and 5.0 and not observed at pH 5.5, indicating that the latter was the preferred pH environment.

    Hongwei Xu, Zemin Ai, Qing Qu, Minggang Wang, Guobin Liu, Sha Xue

    •Exotic species cannot obtain more biomass when growing in new areas.

    •The invasion ability of the exotic species decreased following succession.

    •The recovery ability of native species increased following succession.

    •Our study can strengthen our understanding of invasion and restoration ecology.

    Exotic species invasion represent important causes of harming the structure, function, and ecological environment in ecosystems. Yet, knowledge remains limited on the invasibility (invasion advantage of exotic species) and recoverability (recovery ability of native species) of a plant community following invasion depend on its successional stages. We selected three grasses of Setaria viridis, Artemisia gmelinii, and Bothriochloa ischemum representing early (E), middle (M), and late (L) successional species, respectively. Meanwhile, the grasses of Panicum virgatum was selected represent exotic species (invasion species). Three types of soil were collected to treat the three E, M, and L successional species, and one types of soil was collected to treat the exotic species. We compared the performance of the three native plant species and one exotic species grown in their “own” and “other” soils in a 2-year greenhouse experiment. Our study showed that exotic species performed better in soils of E and M successional species than in the soil of L successional species. After exotic species removed, E and M successional species exhibited poor growth in the soil of exotic species, while that of L successional species performed poor in field exotic species soils, but performed better in soils disturbed by exotic species. Our study demonstrated that the invasibility and recoverability of native plant communities changed with vegetation succession.