The widespread use of polyethylene (PE) mulch films has led to a significant accumulation of plastic waste in agricultural soils. The biodegradation of plastic waste by microorganisms promises to provide a cost-effective and environmentally-friendly alternative for mitigating soil plastic pollution. A large number of microorganisms capable of degrading PE have been reported, but degradation may be further enhanced by the cooperative activity of multiple microbial species. Here, two novel strains of Arthrobacter sp. and Streptomyces sp. were isolated from agricultural soils and shown to grow with PE film as a sole carbon source. Arthrobacter sp. mainly grew in the suspension phase of the culture, and Streptomyces sp. formed substantial biofilms on the surface of the PE film, indicating that these strains were of different metabolic types and occupied different microenvironments with contrasting nutritional access. Individual strains were able to degrade the PE film to some extent in a 90-day inoculation experiment, as indicated by decreased hydrophobicity, increased carbonyl index and CO₂ evolution, and the formation of biofilms on the film surface. However, a consortium of both strains had a much greater effect on these degradation properties. Together, these results provide new insights into the mechanisms of PE biodegradation by a microbial consortium composed of different types of microbes with possible metabolic complementarities.

Bacillus amyloliquefaciens FZB42 is a plant growth-promoting rhizobacteria that stimulates plant growth, and enhances resistance to pathogens and tolerance of salt stress. Instead, the mechanistic basis of drought tolerance in Arabidopsis thaliana induced by FZB42 remains unexplored. Here, we constructed an exopolysaccharide-deficient mutant epsC and determined the role of epsC in FZB42-induced drought tolerance in A. thaliana. Results showed that FZB42 significantly enhanced growth and drought tolerance of Arabidopsis by increasing the survival rate, fresh and dry shoot weights, primary root length, root dry weight, lateral root number, and total lateral root length. Coordinated changes were also observed in cellular defense responses, including elevated concentrations of proline and activities of superoxide dismutase and peroxidase, decreased concentrations of malondialdehyde, and accumulation of hydrogen peroxide in plants treated with FZB42. The relative expression levels of drought defense-related marker genes, such as RD29A, RD17, ERD1, and LEA14, were also increased in the leaves of FZB42-treated plants. In addition, FZB42 induced the drought tolerance in Arabidopsis by the action of both ethylene and jasmonate, but not abscisic acid. However, plants inoculated with mutant strain epsC were less able to resist drought stress with respect to each of these parameters, indicating that epsC are required for the full benefit of FZB42 inoculation to be gained. Moreover, the mutant strain was less capable of supporting the formation of a biofilm and of colonizing the A. thaliana root. Therefore, epsC is an important factor that allows FZB42 to colonize the roots and induce systemic drought tolerance in Arabidopsis.

The photosynthetic characterization of the oriental lily (Lilium) cv. Sorbonne and its response to increasing water stress were analyzed based on the net photosynthetic rate (P _n), stomatal conductance (g _s), intercellular CO₂ concentration (C_i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (Ls) in the Horqin Sandy Land of western China. A photosynthesis-PAR response curve was constructed to obtain light-compensation and light-saturation points (LCP and LSP), the maximum photosynthetic rates (P _max) and dark respiration rates (R _D). The growth of lilies in the pots was analyzed after anthesis. Various intensities of water stress (5, 10, and 20 days without water, and an unstressed control) were applied. The results indicated that drought stress not only significantly decreased P _n, E, g _s, photosynthetic pigment content (Chl a, Chl b, and Chl (a + b)) and increased intrinsic water use efficiency (WUE), but also altered the diurnal pattern of gas exchange. Drought stress also affected the photosynthesis (P _n)-PAR response curve. Drought stress increased LCP and R _D and decreased LSP and P _max. There were both stomatal and nonstomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, whereas nonstomatal limitation dominated in the afternoon. Thus, drought stress decreased potential photosynthetic capacity and affected the diurnal pattern of gas exchange and P _n-PAR response curves, thereby reducing plant quality (lower plant height, flower length, flower diameter, and leaf area). Water stress is likely the main limitation to primary photosynthetic process in the lily. Appropriate watering is recommended to improve photosynthetic efficiency and alleviate photodamage, which will increase the commercial value of the lily in the Horqin Sandy Land.