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Purpose: Phosphorus (P) is the main factor limiting crop production in red soils. Examining the bacterial community harboring phoD gene under different long-term cropping systems may supply meaningful insights for improving soil P availability. Here, we analyzed how the cropping systems affect community structure of phoD-harboring bacteria by changing physicochemical properties in red soils. Materials and methods: Twenty-four soil samples from eight cropping systems (abandoned farmland, corn continuous cropping, mango continuous cropping, taro continuous cropping, zucchini–corn rotation, pea–corn rotation, canola–tobacco rotation, and walnut–tobacco intercropping for > 10 years) were collected from 0 to 20 cm depth in Miyi County, Sichuan Province, China. The abundance of phoD gene was determined by quantitative PCR, and phoD-harboring bacterial community structure was analyzed by high-throughput sequencing. Results and discussion: Available P concentration and phoD abundance were the highest in pea-corn rotation soil, while alkaline phosphatase (ALP) activity was the lowest in this soil. Available P showed a significant positive relationship with phoD abundance, while a negative relationship with ALP activity. Moreover, the dominant phyla of phoD-harboring bacterial community were Proteobacteria and Actinobacteria, with Cupriavidus and Bradyrhizobium being the dominant genera. The relative abundances of Streptomyces, Pseudomonas, and Amycolatopsis were positively related to soil P concentration (total and available P) and negatively related to ALP activity, indicating that these genera may be essential in the mineralization of soil organic P. Redundancy analysis (RDA) showed that ALP, soil organic carbon (SOC), and N:P ratio were the remarkable factors affecting the structure of phoD-containing bacterial community across all cropping system soils. Meanwhile, structural equation model (SEM) showed that the effects of total N and available P on soil phoD-harboring bacterial community structure were stronger than that of SOC. Further, soil texture was also one of the main factors affecting the phoD-harboring bacterial community structure, which had a notable up-regulation effect on abundance and diversity of phoD gene and indirectly regulate gene composition by affecting available P. Conclusions: The long-term cropping systems can affect the community structure of phoD-containing bacteria and ALP activity by altering physicochemical properties, and thus contribute to regulation of the biogeochemical cycle of P in red soils. The main factors driving the changes in phoD-harboring bacterial community structure were soil texture, SOC, total N, and available P. [ABSTRACT FROM AUTHOR]

Purpose: Phosphorus (P) fertilizer has been applied in regions with red soils to ensure high crop yield. However, the supply of bioavailable P for crop plants is insufficient due to the strong adsorption and fixing behaviors in red soils. In this study, we explored P adsorption and desorption characteristics in red soils under different long-term cropping systems. We also analyzed how the cropping systems affect P adsorption and desorption through changing soil physicochemical properties under the experimental conditions. Materials and methods: Eighteen red soil samples were collected at depths of 0–20 cm from six cropping systems (abandoned farmland, corn continuous cropping, taro continuous cropping, pea–corn rotation, canola–tobacco rotation, and walnut–tobacco intercropping for at least 10 years) in Miyi County, Sichuan Province, China. Soil physicochemical properties, zeta potentials, and P adsorption and desorption characteristics were evaluated. Results and discussion: The P adsorption capacity of soils increased at a decreasing rate with increasing exogenous P concentration, while the P desorption capacity increased constantly; however, the change in the percentage of desorbed P had no clear trend. The soils under pea–corn rotation and taro continuous cropping had lower P adsorption capacities and higher P desorption capacities compared to those under the other cropping systems. The maximum P adsorption capacities (Qm) of pea–corn rotation and taro continuous cropping soils were 16.1% and 32.4% of abandoned farmland soil, while the corresponding desorption coefficients were 6.93 and 1.62 times higher than that of abandoned farmland soil, respectively. Soil available P (AP), cation exchange capacity (CEC), and clay content were positively correlated with a and readily desorbable P (RDP), while they were negatively correlated with Qm (P < 0.05); opposite trends were found in the sand content. In addition, the zeta potential of soil colloids decreased with increasing soil pH. Among the cropping systems, the absolute value of zeta potential was lowest for tobacco–walnut intercropping, while its isoelectric point was the highest, resulting in the highest P adsorption capacity. Conclusions: The long-term cropping systems affect P adsorption and desorption characteristics and P availability in red soils by influencing soil physicochemical properties. The main factors driving the changes in P adsorption behavior were AP, CEC, free Fe oxides, and sand content, while AP, sand, and clay contents were the major factors for the P desorption. [ABSTRACT FROM AUTHOR]

Semi-agricultural ecosystems in peri-urban areas are susceptible to contamination. The spatial distribution and influencing factors of such pollution are unclear and poorly constrained in many areas worldwide. Therefore, studying the problems of soil pollution in peri-urban areas is critical for environmental management and agricultural production. In this paper, with cadmium (Cd) as the target pollutant, the spatiotemporal variations of soil cadmium pollution and the relative importance of the affecting factors were analyzed at a peri-urban area from the Jingyang District, Sichuan, China. Statistical results showed that the farmland in the study area could be considered moderately soil Cd-polluted, under the dual influence of natural factors and human activity. In particular, the soil Cd concentration in Tianyuan and Bajiaojing exceeded 0.5 mg kg, for intensive industrial enterprises are distributed in these areas. Correspondingly, the geoaccumulation index also showed that the contamination of Cd in this area was moderately polluted. Moreover, the ecological risk index was 80% in the study area, indicating that the soil Cd pollution potential risk was moderate to high. High geological background values (soil Cd = 0.29 mg kg), river migration, industrial enterprises, and traffic significantly influenced soil Cd pollution, with natural geological factors playing greater roles. The significant horizontal-spatial effective distances away from Shiting River, Deyang-Aba Highway, and chemical plants were 200, 400, and 100 m, respectively. These results will be useful in guiding farmland cultivation and pollution remediation effectively in the peri-urban areas. [ABSTRACT FROM AUTHOR]