Study on the regulation of earthworm physiological function under cadmium stress based on a compound mathematical model

https://doi.org/10.1016/j.etap.2020.103499Get rights and content

Highlights

  • Study on the function and role of the microbial community in detoxification mechanism.

  • Study on the regulation between oxidative stress and microbes in worm after Cd stress.

  • EW and TOPSIS were synthesized to establish a new analysis model.

  • Under short-term Cd stress, oxidative stress regulated the microbes in worms.

  • Under long-term Cd stress, the microbes were regulated by other factors.

Abstract

A cadmium (Cd) stress test was carried out on Eisenia fetida in artificial soil. Six Cd concentration gradient solutions (0, 50, 100, 125, 250 and 500 mg/kg) were prepared. Two treatment groups, short-term stress and long-term stress, were established. The former lasted for 10 days, and the latter lasted for 30 days. The Biolog ECO-microplate culture method was used to determine the utilization of the 31 carbon sources by the microbes in earthworm homogenate. The total protein content (TP), peroxidase activity (POD), catalase activity (CAT), superoxide dismutase activity (SOD), glutathione peroxidase activity (GPX), glutathione-S-transferase activity (GST), malondialdehyde content (MDA) and acetylcholinesterase activity (AChE) in earthworm were determined in order to investigate the regulation of oxidative stress and the functional diversity of microbial communities in earthworms under Cd stress. By combining the entropy weight method (EW) and the technique for order preference by similarity to an ideal solution model (TOPSIS), the physiological functional indices of earthworms were assessed objectively and scientifically, and the physiological changes under the different stress periods were evaluated. The results showed that a Cd-tolerant dominant population appeared in the microbial community under Cd stress. In the short-term test, oxidative stress were more effective in coping with Cd stress than the microbial community, and oxidative stress regulated the microbial community functional diversity. Under long-term Cd stress, the regulatory effect was weak or non-existent. In this study, a new evaluation model was established to explore the regulation process of earthworm on its oxidation stress and the functional diversity of microbial communities under Cd stress, and provide a theoretical basis for revealing the detoxification mechanism of earthworms.

Introduction

The heavy metal cadmium (Cd) has become one of the most important inorganic pollutants in contaminated soils in China (Yang et al., 2016a, b), the over-standard rate for Cd reached 7% (Ministry of Environmental Protection and Ministry of Land and Resources, 2014). At present, Cd has been detected in a large number of plants and animals (Wang et al., 2013; Chauvin et al., 2015; Sousa et al., 2014; Zhen et al., 2014; Dong et al., 2016; Li et al., 2016a, b, c, Lin et al., 2016; Song et al., 2019). Earthworms are more sensitive to most pollutants than other soil animals. Studies have shown that the antioxidant enzyme system in earthworms can be induced by heavy metals and persistent organic pollutants, and the avoidance reaction and neutral red test can respond to almost all pollution stresses (Anyanwu and Semple, 2016; Wang et al., 2016a, b). The study on the biological toxicity of Cd pollution to earthworms and the detoxification mechanism in worms are the focus of ecotoxicology and agricultural ecology (Shi et al., 2014; Liu et al., 2016; Li et al., 2016a, b, c).

There are many indices involved in the response of earthworms to Cd stress. When conducting research with the traditional bio-statistical methods, it is necessary to include the changes in the individual, tissue, cell, gene and other indices to reach a final conclusion (Zhou et al., 2006; Li et al., 2014; Samal et al., 2017). For the microbial community, the current reports are confined to the speculation and explanation of earthworm physiological changes after stress (Kreps et al., 2002; Ji et al., 2014; Ning et al., 2019), and studies on the function of the microbial community and its role in the detoxification mechanism of earthworm are rare. In addition, the existing mathematical models do not correspond to biological significance (Ning et al., 2018a; Zhou et al., 2019), which makes it inconvenient to use earthworms as biomarkers to monitor soil heavy metal pollution, and the mechanism of worm’s internal toxicity response remains unclear, especially the scientific evaluation of the changes of physiological function indices in worms after stress is restricted, and the determination of the regulatory relationship between the oxidative stress effects and the functional diversity of microbial communities is still in the blank.

This paper attempts to establish a composite evaluation model based on the EW (entropy weight) method and the TOPSIS (technique for order preference by similarity to an ideal solution) method. Through comprehensive weighing, the physiological changes in earthworms under different stress periods were evaluated scientifically and the regulation process between the oxidation stress effects and the functional diversity of microbial communities was explored. In order to provide a theoretical basis and a methodological reference for revealing the detoxification mechanism of earthworms.

Section snippets

Chemicals

Cd in the test was CdCl2·2.5H2O, which was of analytical purity and produced by Tianjin Guangfu Science and Technology Development Co., Ltd. PBS buffer (dry powder) was of analytical purity and produced by Coolaber Science. The buffer was prepared, and deionized water was added to each bag to 1 L.

Artificial soil

The test soil was OECD standard artificial soil consisting of 10 % peat, 20 % kaolin, and 70 % sand (particle size was 0.1−0.3 cm). Calcium carbonate was added to adjust the pH to 6.5 ± 0.5. The peat

Determining the entropy weight of indices based on the EW method

EW method can reflect the implicit informations of data, so as to achieve the purpose of comprehensively reflecting various kinds of information (He et al., 2016; Suo et al., 2018). Based on the idea of weight determination by the EW method, the single weight results of indices of the oxidative stress effect and the microbial community functional diversity in the earthworm after Cd stress are shown in Table 2 (the D + and D- are shown in Schedules Table Schedule 1, Schedule 2, Schedule 3 and

Conclusion

The EW method and the TOPSIS method can improve the objectivity of the weighing process of earthworm physiological function indices, and can scientifically reveal the regulation processes between the oxidative stress effect and the microbial community functional diversity in earthworms under Cd stress. The combination provides theoretical basis and data model reference for the study of earthworm detoxification mechanisms and pollution environment monitoring and evaluation.

In the oxidative

CRediT authorship contribution statement

Haoran Zhou: Date curation, Formal analysis. Tingxiu Zhang: Investigation, Methodology. Jiayun Zhuang: Investigation, Methodology. Mingyuan Xu: Investigation. Xueli Liu: Investigation. Qinghua Shi: Conceptualization, Writing - original draft. Dongxing Zhou: Conceptualization, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was supported by grants from the National Key R&D Plan (2018YFD0300106).

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