Selenium fertigation with nanobubbles influences soil selenium residual and plant performance by modulation of bacterial community.

Although selenium (Se) is an essential microelement for humans and animals, it is a potentially toxic element due to its bioaccumulation potential. In this study, Se fertilizer was supplied in a greenhouse vegetable (cucumber) plantation using an innovative system consisting of nanobubbles (NB_Se) and compared to that under conventional conditions of fertigation (C_Se) with six doses. The results revealed that NB_Se significantly reduced soil Se accumulation (38%-144%) and increased cucumber Se content compared with the C_Se treatments at the same Se dose. NB_Se significantly lowered the soil bacterial diversity, with an initial increase and then decrease with the Se doses. Bacterial associations and potential keystone taxa also differed between the NB_Se and C_Se. The greater abundance of oxidizing bacteria (indicated by the function composition of bacterial community) and the improved soil redox environment created by NBs sustained more available Se for plants, leading to a reduction in soil Se residual and an increase in the plant Se content. Our results highlight the feasibility and efficiency of NB_Se and demonstrate the important implications of Se for the maintenance of soil health and sustainability.

Land use shapes the resistance of the soil microbial community and the C cycling response to drought in a semi-arid area.

The aim of this study was to understand the responses of the microbial community of soil under different land uses to drought in a semi-arid Mediterranean area. In a laboratory incubation, soil samples from different land uses (natural forest, drip-irrigated orchard, rain-fed almond tree cultivation and abandoned area) were maintained at 20% and 60% of the WHC. The microbial biomass and potential enzyme activities were determined after four and fifty days of soil incubation. The diversity and composition of the microbial community were studied after 50 days of incubation. The total mineralisation of soil organic C (SOC), as well as, the mineralisation of fresh organic matter (FOM) and the "priming effect" were analysed after addition of 13C-enriched plant tissue. Both land use and drought had significant effects in the soil microbial community, but the effect of land use was stronger than that of drought. The PLFA content (microbial biomass) of the forests soil was greater under drought. After 50 days of soil incubation, the microbial biomass and most of potential enzyme activities of the almond tree and abandoned soil samples were not significantly affected by drought contrary to those in orchard soil. The total and FOM mineralisation were on average lower in soil under drought than under optimal moisture for all land uses. However, the responses of the priming effect to drought were dependent on the land use. Overall, we conclude that the resistance to drought of the soil microbial community from an agroecosystem having a semi-arid climate is strongly influenced by the previous land use.

Field trial on removal of petroleum-hydrocarbon pollutants using a microbial consortium for bioremediation and rhizoremediation.

Petroleum waste sludges are toxic and dangerous that is why environmental protection agencies have declared their treatment top priority. Physicochemical treatments are expensive and environmentally unfriendly, while alternative biological treatments are less costly but, in general, work at a slower pace. An in situ bioremediation and rhizoremediation field scale trial was performed in an area contaminated with oil refinery sludge under semiarid climate. The bioremediation and rhizoremediation treatments included the use of an artificial consortium made up of plant growth-promoting rhizobacteria and polycyclic aromatic hydrocarbon-degrading bacteria,and the combined use of the mentioned consortium along with pasture plants respectively. Rhizoremediation revealed that the development of vegetation favoured the evolution of indigenous microbiota with potential to remove petroleum wastes. This was inferred as the decline of total petroleum hydrocarbons 7 months after the biological treatment.