Abstract
Iron is among the most abundant elements in the soil of paddy fields, and its valence state and partitioning can be transformed by flooding and drainage alternations. However, little is known about the function of soil microbes that interact with Fe(II). In this study, sandy and loamy soils originating from rice fields were treated with Fe(II) at low and high concentrations. The findings demonstrate that additional Fe(II) has various effects on the soil’s microbial community structure and metabolic pathways. We conclude that Fe(II) at high concentrations reduced bacterial abundance and diversity in two textured paddy soils, yet the abundance in loamy soils was higher than it was in sandy soil. Additionally, in environments with high Fe(II) levels, the relative abundance of both anaerobic and chemoautotrophic bacteria increased. The Fe(II) concentration was positively correlated with total reduced substances but negatively correlated with redox potential and pH. Co-occurrence networks revealed that Fe(II) significantly promoted interactions with the most anaerobic and chemoautotrophic bacteria. In addition, adding Fe(II) greatly increased the number of more complex bacterial networks, and an increase in the number of mutually beneficial taxa occurred. We found that Fe(II) promoted the methane pathway, the Calvin cycle, and nitrate reduction to small but significant extents. These pathways involve the growth and interrelation of autotrophic and anaerobic bacteria. These results suggest that changes in the bacterial community structure occur in many dry–wet alternating environments.
Highlights
Rice is one of the world’s three major food crops, and approximately 90% of paddy soil is distributed in Asia, where it is mainly concentrated in the subtropical and tropical regions [1]
The rarefaction curves based on operational taxonomic units (OTUs) were smooth, indicating that the sequence data were reliable for analysis (Figure S1)
We explored the effects of Fe(II) concentration on the bacterial community, co-occurrence network and function of two textured paddy soils
Summary
Rice is one of the world’s three major food crops, and approximately 90% of paddy soil is distributed in Asia, where it is mainly concentrated in the subtropical and tropical regions [1]. Paddy soil is one of the most important soil types in China, with a planting area of 3.07 × 107 hectares in 2017, accounting for 18.5% of the total sown area of crops [2]. The soil changes periodically under oxic and anoxic conditions through repeated flooding and drainage cycles [3]. These involved physical, chemical and biological processes have significantly impact paddy soil [4]. As the fourth most abundant element in the Earth’s crust, iron (Fe) is relatively abundant in many cultivated soils [5], and it is one of the most commonly used redox-active metals.
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