Butachlor (BUT) is a chloroacetanilide herbicide widely applied to rice paddies to control annual grass and broad-leaf weeds. A BUT-degrading bacterial strain (PK) was isolated from paddy soils. Biochemical and 16S rRNA sequencing characteristics confirmed the strain as Pseudomonas aeruginosa (99% resemblance). The isolate dissipated BUT (100 μg/mL) in an M9 liquid medium with a rate of 0.5 ± 0.03 day-1 and DT50 and DT90 of 1.38 ± 0.10 days and 4.58 ± 0.32 days, respectively. Soil dissipation of BUT was investigated under flooded conditions. In sterile soils, the isolate increased the dissipation of BUT (200 μg/g) (DT50 = 12.38 ± 1.83 days, DT90 = 41.12 ± 6.09 days, k = 0.06 ± 0.01 day-1) compared to sterile non-inoculated samples (DT50 = 26.87 ± 2.82 days, DT90 = 89.25 ± 9.36 days, k = 0.03 ± 0.00 day-1). In non-inoculated non-sterile soil experiments, the dissipation of BUT was faster (DT50 = 15.17 ± 2.11 days, DT90 = 50.38 ± 7.02 days, k = 0.05 ± 0.00 day-1) compared to non-inoculated sterile ones, and inoculating the isolate accelerated the removal of BUT in non-sterile soils significantly (DT50 = 8.03 ± 1.20 days, DT90 = 26.68 ± 3.97 days, k = 0.09 ± 0.01 day-1). BUT inhibited soil respiration (SR) initially for 5 days, followed by an increase until day 20. The increase in SR was more pronounced in the co-presence of BUT and the isolate. The results of this research suggest P. aeruginosa PK as a suitable candidate for BUT bioremediation.

The need of more food production, an increase in acidic deposition and the large capacity of paddy to emit greenhouse gases all coincide in several areas of China. Studying the effects of acid rain on the emission of greenhouse gases and the productivity of rice paddies are thus important, because these effects are currently unknown. We conducted a field experiment for two rice croppings (early and late paddies independent experiment) to determine the effects of simulated acid rain (control, normal rain, and treatments with rain at pH of 4.5, 3.5 and 2.5) on the fluxes of CO₂, CH₄ and N₂O and on rice productivity in subtropical China. Total CO₂ fluxes at pHs of 4.5, 3.5 and 2.5 were 10.3, 9.7 and 3.2% lower in the early paddy and 28.3, 14.8 and 6.8% lower in the late paddy, respectively, than the control. These differences from the control were significant for pH 3.5 and 4.5. Total CH₄ fluxes at pHs of 4.5, 3.5 and 2.5 were 50.4, 32.9 and 25.2% lower in the early paddy, respectively, than the control. pH had no significant effect on CH₄ flux in the late paddy or for total (early + late) emissions. N₂O flux was significantly higher at pH 2.5 than 3.5 and 4.5 but did not differ significantly from the flux in the control. Global-warming potentials (GWPs) were lower than the control at pH 3.5 and 4.5 but not 2.5, whereas rice yield was not appreciably affected by pH. Acid rain (between 3.5 and 4.5) may thus significantly affect greenhouse gases emissions by altering soil properties such as pH and nutrient pools, whereas highly acidic rain (pH 2.5) could increase GWPs (but not significantly), probably partially due to an increase in the production of plant litter.