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Batch experiments were designed to characterize a multiple metal resistant bacterium Burkholderia sp. D54 isolated from metal contaminated soils in the Dabaoshan Mine in South China, and a follow-up experiment was conducted to investigate the effects of inoculating the isolate on plant growth and metal uptake by Sedum alfredii Hance grown on soils collected from a heavily contaminated paddy field in Daxing County, Guangxi Zhuang Automounous Region, Southwest China. Our experiments showed that strain D54 produced indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and solubilizing inorganic phosphate and solubilized insoluble metal bearing minerals. Bacterial inoculation significantly enhanced S. alfredii biomass production, and increased both shoot and root Cd concentration, but induced little variation in root/shoot Pb concentration and shoot Zn concentration. Despite this, the total shoot and root uptake of Cd, Pb and Zn in S. alfredii inoculated with D54 increased greatly compared to the non-inoculated controls. It was concluded that inoculation with strain D54 could help S. alfredii grow better on metal contaminated soils, produce more biomass, and remove more metals from soil, which implies improved efficiency of phytoextraction from metal contaminated soil. The knowledge gained from the present experiments constitutes an important advancement in understanding of the interaction between plant growth-promoting bacteria and hyperaccumulators with regard to plant ability to grow and remove the multiple heavy metals from soils.

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Considerable nitrogen (N) losses from intensive vegetable systems have become an important source of environmental damage. A high-efficiency N application to minimize N pollution and improve production is urgently needed. Here, we conducted field experiments to identify the effects of a single application of controlled-release urea (CRU), conventional urea (CU), and chicken manure (CM) on N losses and yields improvement in a greenhouse tomato system in Beijing, China. Five treatments were carried out: no N control (CK), lower rate of CRU with CU and CM (CRN1), medium rate of CRU with CU and CM (CRN2), higher rate of CRU with CU and CM (CRN3), and conventional fertilization (CN). The results showed that the single application of CRU, CU, and CM reduced the nitrate N concentration and N 2 O emissions by 22 to 79% and 39 to 51%, respectively, compared with the conventional fertilization. Based on the N application rate, the average nitrate N concentration showed an exponential increase, and the cumulative N 2 O emissions showed a linear increase. Compared to the CN treatment, the CRN1, CRN2, and CRN3 treatments decreased fertilization cost by 44%, 22%, and 3.4%, while raising yields by 9.6%, 17%, and 2.0%, respectively. The apparent N surplus of the CRN1 and CRN2 treatments was reduced by 39% and 13% relative to the CN treatment, whereas the CRN3 treatment was as high as that of the CN treatment. It can be concluded that applying CRU, CU, and CM at the higher rate hardly improved the yield but increased the risk of N losses, whereas the lower and medium rates of CRU could reduce N pollution and improve production. The CRN2 treatment, reducing the CRU rate by 25%, with the highest economic efficiency, was the best choice to achieve greater yields with less environmental impacts in greenhouse tomato systems.

As and Cd in soil can be assimilated and accumulated by vegetables and can be subsequently ingested by humans. Contradictory effects of organic fertilizer application on As and Cd accumulation in soil have been reported in previous studies. An eight-year greenhouse study was conducted on a sandy loam soil in Beijing, China to investigate the effects of organic fertilizer application rate on soil properties, and As and Cd accumulation in soil. The contamination risk of pak choi grown after eight years’ application of organic fertilizer was also evaluated. Soil organic carbon increased 3.0–3.8 times with low, medium and high rates of fertilizer application in 2018 compared to the initial soil. Organic fertilizer application significantly increased soil nutrients and microbial biomass while it mildly affected soil pH. The bioavailability of As/Cd has decreased after eight years’ application of organic fertilizer. Pak choi crop harvested from all three treatments in 2018 did not pose a threat to human health, even for life-time consumption. Soil total As content significantly decreased with organic fertilizer application, mainly due to the lower As content in the applied fertilizer than that in soil. Continuous application of clean organic fertilizer can be adopted to reduce the contamination risk of highly contaminated soil in the soil–plant system.