Centre for Environmental Studies, Department of Civil Engineering, College of Engineering Guindy, Anna University, Chennai, Tamil Nadu, 600 025, India.
Environ Sci Pollut Res Int. 2024 Nov;31(54):63343-63359. doi: 10.1007/s11356-024-35441-w. Epub 2024 Nov 1.
Microplastics have polluted agricultural soils, posing a substantial risk to crop productivity. Moreover, the presence of microplastic pollution has caused a disturbance in the composition of the microbial community in the soil surrounding plant roots, therefore impacting the growth of beneficial bacteria. A study was conducted to examine if humic acid (HA) can counteract the harmful effects of microplastics (MPs) on the growth of black gram crops and the composition of the rhizosphere soil microbial community, to reduce the negative impacts of microplastics on these microorganisms and crops. The research was carried out using mud pots and the plastic utilized for the experiment consisted of 60% high-density polyethylene (HDPE) and 40% polypropylene (PP). The soil was enriched with lignite-based potassium humate, which had a pH range of 8.0-9.5 and with 65% humic acid. The experiment consisted of six treatments: T1, which served as the control without HA and MP; T2, which involved the use of HA at a concentration of 0.15% w/w; T3, which involved the use of MP at a concentration of 0.2% w/w; T4, which involved the use of MP at a concentration of 0.4% w/w; T5, which involved the combination of HA at a concentration of 0.15% w/w and MP at a concentration of 0.2% w/w; and T6, which involved the combination of HA at a concentration of 0.15% w/w and MP at a concentration of 0.4% w/w. The plant growth characteristics, including germination percentage, nodule number, and chlorophyll content, were measured. In addition, the DNA obtained from the rhizosphere soil was analyzed using metagenomics techniques to investigate the organization of the microbial population. Seedlings in soil polluted with MP exhibited delayed germination compared to seedlings in uncontaminated soil. Following 60 days of growth, the soil samples treated with T5 (0.2% MP and 0.15% HA w/w) had the highest population of bacteria and rhizobium, with counts 5.58 ± 0.02 and 4.90 ± 0.02 CFU g soil. The plants cultivated in T5 had the most elevated chlorophyll-a concentration (1.340 ± 0.06 mg g), and chlorophyll-b concentration (0.62 ± 0.02 mg g) while those cultivated in T3 displayed the lowest concentration of chlorophyll-a (0.59 ± 0.02 mg g) and chlorophyll-b (0.21 ± 0.04 mg g). Within the phylum, Proteobacteria had the highest prevalence in all treatments. However, when the soil was polluted with MPs, its relative abundance was reduced by 8.4% compared to the control treatment (T1). Conversely, treatment T5 had a 3.76% rise in relative abundance when compared to treatment T3. The predominant taxa found in soil polluted with MP were Sphingomonas and Bacillus, accounting for 19.3% of the total. Sphingomonas was the predominant genus (21.2%) in soil polluted with MP and supplemented with humic acid. Humic acid can be used as a soil amendment to mitigate the negative effects of MPs and enhance their positive advantages. Research has demonstrated that incorporating humic acid into soil is a viable method for maintaining the long-term integrity of soil's physical, chemical, and biological characteristics.
微塑料已经污染了农业土壤，对作物生产力构成了重大威胁。此外，微塑料污染已经导致了植物根际土壤微生物群落的组成发生了干扰，从而影响了有益细菌的生长。一项研究旨在检验腐殖酸（HA）是否可以抵消微塑料（MPs）对黑绿豆作物生长和根际土壤微生物群落组成的有害影响，从而减少微塑料对这些微生物和作物的负面影响。该研究使用 Mud Pots 进行，实验中使用的塑料由 60%高密度聚乙烯（HDPE）和 40%聚丙烯（PP）组成。土壤中添加了基于褐煤的腐殖酸钾，其 pH 值范围为 8.0-9.5，腐殖酸含量为 65%。实验包括六种处理：T1 作为对照，不添加 HA 和 MP；T2 添加浓度为 0.15% w/w 的 HA；T3 添加浓度为 0.2% w/w 的 MP；T4 添加浓度为 0.4% w/w 的 MP；T5 添加浓度为 0.15% w/w 的 HA 和 0.2% w/w 的 MP；T6 添加浓度为 0.15% w/w 的 HA 和 0.4% w/w 的 MP。测量了植物生长特性，包括发芽率、根瘤数和叶绿素含量。此外，使用宏基因组学技术从根际土壤中提取的 DNA 进行分析，以研究微生物种群的组织。与未受污染土壤中的幼苗相比，受 MP 污染的土壤中的幼苗发芽时间延迟。经过 60 天的生长，用 T5（0.2% MP 和 0.15% HA w/w）处理的土壤样本中细菌和根瘤菌的数量最高，分别为 5.58 ± 0.02 和 4.90 ± 0.02 CFU g 土壤。在 T5 中培养的植物具有最高的叶绿素-a 浓度（1.340 ± 0.06 mg g）和叶绿素-b 浓度（0.62 ± 0.02 mg g），而在 T3 中培养的植物具有最低的叶绿素-a 浓度（0.59 ± 0.02 mg g）和叶绿素-b 浓度（0.21 ± 0.04 mg g）。在门水平上，变形菌在所有处理中均有最高的丰度。然而，当土壤受到 MPs 污染时，与对照处理（T1）相比，其相对丰度降低了 8.4%。相比之下，与 T3 相比，T5 处理的相对丰度增加了 3.76%。在受 MP 污染的土壤中，主要的分类群是鞘氨醇单胞菌和芽孢杆菌，占总数的 19.3%。在受 MP 污染并添加腐殖酸的土壤中，鞘氨醇单胞菌是主要的属（21.2%）。腐殖酸可用作土壤改良剂，以减轻 MPs 的负面影响并发挥其积极优势。研究表明，将腐殖酸融入土壤是维持土壤物理、化学和生物特性长期完整性的一种可行方法。
