The Effects of Different Lead Pollution Levels on Soil Microbial Quantities and Metabolic Function with/without Salix integra Thunb. Planting

Abstract

Background and Objectives: Salix integra Thunb., a fast-growing woody species, has been used in phytoremediation in recent years. It has the potential to accumulate high amounts of lead (Pb) in its growth, however, its effects on soil microbial community structure and function during its phytoextraction processes are not well understood, especially at different pollution levels. Materials and Methods: In our study, we set unplanted and planted Salix integra in areas with four levels of Pb treatments (0, 500, 1000, and 1500 mg/kg). After six months of planting, the rhizospheric soil, bulk soil, and unplanted soil were collected. Soil properties and microbes participating in nitrogen and phosphorus cycling were measured, following standard methods. Microbial metabolic functions were assessed using a Biolog-ECO microplate. Results: The bacteria (nitrogen-fixing bacteria, ammonifying bacteria, inorganic phosphorus-solubilizing bacteria, and nitrosobacteria) all increased in the 500 mg/kg treatment and decreased in the 1500 mg/kg treatment compared with the 0 mg/kg treatment, especially in rhizospheric soil. The microbial metabolisms decreased along with the increase of Pb levels, with the exception of the rhizospheric soil with a 500 mg/kg treatment. The metabolic patterns were relative to the pollution levels. The utilization of carbohydrates was decreased, and of amino acids or fatty acids was increased, in the 500 mg/kg treatment, while the opposite occurred in the 1500 mg/kg treatment. The values of soil properties, microbial quantities, and metabolic activities were higher in rhizospheric than bulk soil, while the differences between bulk and unplanted soil were different among the different Pb treatments. The soil properties had little effect on the microbial quantities and metabolic activities. Conclusions: S. integra planting and Pb levels had an interactive effect on the microbial community. In general, S. integra planting promoted microbial quantities and metabolic activity in rhizospheric soil. Lower Pb pollution increased microbial quantities and promoted the utilization of amino acids or fatty acids, while higher Pb concentrations decreased microbial quantities and metabolic activities, and promoted the utilization of carbohydrates.

Indigenous Bacteria Have High Potential for Promoting Salix integra Thunb. Remediation of Lead-Contaminated Soil by Adjusting Soil Properties

“…The initial soil properties were as follows: "organic carbon 2,780 mg kg −1 , total nitrogen 240 mg kg −1 , available nitrogen 22.28 mg kg −1 , total phosphorus 510 mg kg −1 , available phosphorus 10.54 mg kg −1 , total potassium 8,080 mg kg −1 , available potassium 278.4 mg kg −1 , cation exchange capacity 8.46 cmol kg −1 , and pH 8.14" (Niu et al, 2019). The Pb concentrations were as follows: total Pb concentrations were 14.21 mg kg −1 , 510.28 mg kg −1 , 1513.45 mg kg −1 and the acid-soluble Pb concentrations were 0.42 mg kg −1 , 15.32 mg kg −1 , 81.52 mg kg −1 in CK, LT and HT, respectively.…”

“…After the soil drying and passing through a 10 mesh sieve, the soil properties were measured, such as available nitrogen (AN), available phosphorus (AP), available potassium (AK), pH, and cation exchange capacity (CEC), following the methods of Niu et al (2019).…”

“…Salix integra Thunb., is a fast-growing woody species, with a large biomass and deep root system (Kuzovkina and Volk, 2009;Niu et al, 2019). It is a well-known Pb/Zn/Cd co-accumulator native to China (Liu et al, 2011).…”

Inoculation With Indigenous Rhizosphere Microbes Enhances Aboveground Accumulation of Lead in Salix integra Thunb. by Improving Transport Coefficients

“…Pb is a widespread heavy metal in soil, and its accumulation causes severe harm to humans, particularly children. Many strategies have been developed to reduce the effects of Pb on ecosystems and humans, although most have high costs and can cause secondary pollution ( Niu et al, 2019 ). Phytoremediation offers a low-cost approach without secondary contamination; however, its lower remediation efficiency hinders its large-scale application ( Ye et al, 2019 ).…”

“…Salix integra Thunb. is a fast-growing woody species, producing a large amount of biomass and a deep root system ( Kuzovkina and Volk, 2009 ; Niu et al, 2019 ). It is a well-known co-accumulator of Pb/Zn/Cd and is native to China ( Liu et al, 2011 ).…”