Abstract:

This study comprehensively investigated the effects of plant extracts on the community structure and functional composition of phytoplankton in aquaculture water. Conducted over a 40-day period at an ecological aquaculture farm in Jinshan District, Shanghai, China, this research aimed to explore the potential of plant extracts as a natural and sustainable addition to regulate aquatic ecosystems and improve water quality in aquaculture ponds. This study aimed to utilize plant extracts composed of a blend of traditional Chinese herbal medicines, including Andrographis paniculata (Burm. F.) Nees, Penthorum chinense Pursh, Vanilla planifolia Andrews, Mollugo lotoides (L.) O. Kuntze, and Cynanchum hancockianum (Maxim.) Iljinski. These plants were chosen based on their rich pharmacological history and known properties, which could potentially influence the aquatic environment. The plant extracts were introduced into the aquaculture ponds at a specific volumetric ratio of 1꞉ (1.20×10⁴-1.44×10⁴) (V_{plant extract}꞉V_{pond water}), with the objective of evaluating their impacts on various water quality parameters, as well as the composition and function of the phytoplankton community. The findings of this study are multifaceted and offer valuable insight into the ecological dynamics of aquaculture systems. The addition of plant extracts significantly improved the water quality indicators. Specifically, the concentrations of chlorophyll a, nitrogen nutrients, and organic matter were notably reduced in the treatment ponds compared to those in the control ponds. This reduction suggests that the plant extracts facilitated the breakdown of organic matter and enhanced nutrient cycling, thereby improving the water quality and reducing the risk of eutrophication. The improved water quality is crucial for the overall health and productivity of aquaculture systems as it provides a more favorable environment for the growth of aquatic organisms. Furthermore, this study revealed that plant extracts had a profound influence on the phytoplankton community structure. Initially, both the control and treatment ponds were dominated by Cyanobacteria, a group of phytoplankton that can sometimes proliferate excessively, leading to harmful algal blooms and degraded water quality. However, over the course of the experiment, a marked shift occurred in the phytoplankton communities in the treatment ponds. The proportion of Cyanobacteria gradually decreased, whereas that of Bacillariophyta, a group of phytoplankton that is often considered beneficial to aquatic ecosystems, significantly increased. This succession from Cyanobacteria to Bacillariophyta is indicative of a healthier and more balanced phytoplankton community, which is essential for maintaining the ecological integrity of aquaculture systems. In addition to altering community structure, plant extracts also had a significant impact on the functional composition of phytoplankton. Metagenomic analysis was used to elucidate the functional roles of the phytoplankton communities in both the control and treatment ponds. The results showed that the top KEGG pathways of phytoplankton during the experiment were related to amino acid metabolism, metabolism of cofactors and vitamins, carbohydrate metabolism, energy metabolism, and replication and repair. These pathways collectively represent the metabolic (L1) and genetic information processing (L1) pathways, which are fundamental to the growth and reproduction of phytoplankton. Notably, the addition of plant extracts led to a reduction in the abundance of genes related to these metabolic pathways in the treatment ponds, indicating a decrease in the metabolic activity of phytoplankton. This finding suggests that plant extracts may inhibit the growth of phytoplankton that rely heavily on these metabolic pathways, thereby promoting the growth of more adapted and resilient species. Conversely, plant extracts enhanced the functions related to genetic information processing pathways. This observation suggests that the extracts may have promoted the growth and reproduction of phytoplankton, which are better equipped to handle environmental stressors and utilize available nutrients. These adapted phytoplankton may have played a crucial role in maintaining the ecological balance of the aquaculture ponds, contributing to improved water quality and enhanced productivity. To gain a deeper understanding of the relationships between phytoplankton communities, their functional roles, and environmental factors, a comprehensive correlation analysis was conducted. The results revealed that Cyanobacteria were positively correlated with factors such as pH, chlorophyll a, total phosphorus, and chemical oxygen demand, but negatively correlated with dissolved oxygen, conductivity, and nitrogen nutrients. In contrast, Bacillariophyta showed the opposite correlation with these environmental factors. Similar patterns were observed for metabolic functions, which were positively correlated with those favoring Cyanobacterial growth and negatively correlated with factors favoring Bacillariophyta. Conversely, the genetic information processing function was negatively correlated with factors favoring Cyanobacteria, but positively correlated with those favoring Bacillariophyta. These correlations provide valuable insights into the environmental conditions that favor the growth and reproduction of different phytoplankton species and functional groups, and highlight the importance of maintaining a balanced and diverse phytoplankton community in aquaculture systems. Moreover, this study investigated the potential active compounds in plant extracts that may have contributed to their effects on the phytoplankton community and functional composition. The analysis revealed the presence of various flavonoids including arbutin, trigonelline, wogonoside, octahydrocurcumin, and propyl gallate. These compounds are known for their diverse biological activities including anticancer, antibacterial, anti-inflammatory, and immunomodulatory effects. In the context of this study, it is plausible that these flavonoids may inhibit the growth of harmful Cyanobacteria by disrupting cellular processes or competing for essential nutrients. Additionally, flavonoids may promote the growth of beneficial Bacillariophyta by providing them with essential nutrients, enhancing their resistance to environmental stressors, or facilitating their interaction with other aquatic organisms. In summary, this study demonstrated the significant potential of plant extracts to improve water quality, regulate the community structure of phytoplankton, and enhance their functional composition in aquaculture systems. Plant extracts promoted the succession of phytoplankton communities from Cyanobacteria to Bacillariophyta, reduced metabolic functions, and enhanced genetic information processing. These findings not only provide a deeper understanding of the mechanisms by which plant extracts can influence aquatic ecosystems but also offer a promising natural and sustainable alternative to chemical treatments for the regulation of phytoplankton in aquaculture systems. Future research should aim to further elucidate the active compounds in plant extracts and their specific modes of action on phytoplankton communities, as well as evaluate the long-term effects of plant extract addition on the overall health, productivity, and sustainability of aquaculture systems.

Key words: aquaculture pond, plant extracts, metagenomics, phytoplankton communities, environmental factors

摘要：

水产养殖水体中的浮游植物群落结构及其功能组成是养殖生态系统的关键组成部分。在上海市金山区某生态养殖农场开展了一项为期40 d的实验，旨在评估植物提取液对水产养殖水体中浮游植物群落演替的影响。所使用的植物提取液主要为中草药提取物，中草药包括穿心莲（Andrographis paniculata）、赶黄草（Penthorum chinense）、香兰草（Vanilla planifolia）、虎咬癀（Mollugo lotoides）和对叶草（Cynanchum hancockianum）。实验中，植物提取液与池塘水的体积比例设定为1꞉（1.20×10⁴-1.44×10⁴）。在实验期间，定期监测水质参数，并运用宏基因组学技术分析植物提取液对环境因子及浮游植物群落结构与功能的影响。结果显示，植物提取液有效降低了水体中叶绿素a、氮营养盐及有机物的浓度，并促进了浮游植物群落由蓝藻门向硅藻门进行演替。此外，植物提取液还降低了浮游植物的代谢功能，增强了与遗传信息处理相关的功能。蓝藻丰度与pH、叶绿素a、总磷及化学需氧量呈正相关，而与溶解氧和氮营养盐呈负相关；反之，硅藻对环境因子的响应与蓝藻相反。研究结果为植物提取液在水产养殖领域针对浮游植物群落调控的潜在应用提供了重要见解。

关键词: 养殖池塘, 植物提取液, 宏基因组学, 浮游植物, 环境因子