Abstract
BackgroundSince the industrial revolution, the contamination of agricultural soils by polycyclic aromatic hydrocarbons (PAHs) has increasingly become of serious global environmental concern and poses a huge threat to human beings and natural ecosystems. Microbial degradation is a proved technology mostly used to depollute polycyclic aromatic hydrocarbon (PAH) in the environment. However, very limited information is available regarding the interaction of earthworms with rice straw on the soil microbial community and the degradation of phenanthrene. This study was performed to enlighten the rice straw and earthworms’ interaction on soil bacterial abundance and structure and phenanthrene removal.ResultsResult about functional gene information revealed that both rice straw and earthworm enhanced phenanthrene degradation. Subsequently, both Shannon diversity index (r2 = − 0.8807, p < 0.001) and bacterial 16S rRNA genes (r2 = − 0.7795, p < 0.001) negatively correlated with the remaining phenanthrene concentration in soil. The application of both rice straw and earthworms in soil had the lowest ratio of soil remaining phenanthrene concentration (0.16 ± 0.02), the highest Shannon diversity index (6.45 ± 0.2) and the highest bacterial 16S rRNA genes. This implied that both earthworms and rice straw might improve the phenanthrene metabolism by increasing soil bacteria diversity. The abundance of genera Pseudomonas, Luteimonas, Rhodanobacter, Sphingomonas, Gemmatimonas, Flavobacterium, and Leifsonia was significantly increased in the presence of both earthworms and rice straw and was found to negatively correlate with the remaining phenanthrene concentration in soil.ConclusionBased on these results, this study offers clear and strong evidences that the positive interaction between earthworms and rice straw could promote phenanthrene degradation in soil. These finding will improve our understanding on the importance of the natural resources forsaken and how they can interact with the soil macro- and microorganisms to change soil structure and enhance PAH degradation in soil.
Highlights
Since the industrial revolution, the contamination of agricultural soils by polycyclic aromatic hydrocarbons (PAHs) has increasingly become of serious global environmental concern and poses a huge threat to human beings and natural ecosystems
Out of a total of 50 mg/kg of phenanthrene initially added in the soil, 64%, 80% and 83% was removed in rice straw (PS), earthworms (PW) and in earthworms + straw (PSW) treatments, respectively
The results showed that rice straw and earthworms improve the soil structure and phenanthrene degradation, and interacted each other and changed the soil microbial community and structure
Summary
The contamination of agricultural soils by polycyclic aromatic hydrocarbons (PAHs) has increasingly become of serious global environmental concern and poses a huge threat to human beings and natural ecosystems. For efficient and profitable bioremediation of PAHs, both bio-augmentation involving resistant microorganism strains capable of degrading various pollutants in soil [39] and bio-stimulation which attempts to increase exogenous and indigenous soil microbial activity [24] are commonly used. Another low-cost efficient and environmentally friendly remediation technology is the use of earthworms. During the feeding process of earthworms, organic and mineral composites are mingled in their gut and turned down as casts on the soil surface or along burrows [26] This phenomenon might increase the microbial population and improve the connection between soil microorganisms and pollutants [22]. The approach integrating earthworm–soil microbial interaction to remove PAHs in soil appeared to be compromising, most of PAH-removal study such as [3, 4, 7] involved plant system and very limited information is available regarding the integration of rice straw in the microbial community change and the degradation of PAHs
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