Soil Microbial Polymorphism In Oasis Of Northern Xinjiang As Influenced By Different Cropping Patterns

[Objective] The microbial functions and construction diversity are seriously affected by different cropping patterns or the duration of continuous cropping. This study compared the difference of soil characters under a couple of classic cropping patterns in XinJiang to understand the effect of cropping pattern and the duration of continuous cropping on the dynamic change of soil nutrients and the microbial functions and structural diversity, and to link cotton wilting with microbial structure. Finally, this study is aimed to make an evaluation of microbial diversity, prevent and cure soil-borne diseases and create an environmentally-friendly oasis farmland in North Xinjiang. All this will provide supports for sustainable cotton production in Xinjiang.[Method] This study aimed on the soil characters of a couple of classic cropping pattern. Different layers (0-20cm,20-40cm) of soils subjected to different cropping patterns or different durations of continuous cropping were selected to assay the physiochemical properties, in order to understand the influence of cropping pattern on soil nutrients. The top soil layer (0-15cm) was used to assay enzyme activities associated closely with the nutrient cycling of C, N, P and S. Soil enzyme activities represented the change of microbial functional diversity; meanwhile, microbial structural diversity was characterized by using molecular biology approach (PCR-DGGE).[Result] 1) For the soils subjected to different cropping patterns and durations of continuous cropping, the pH values were significantly lower in surface soil (0-20 cm) than in the subsurface soil (20-40 cm), but no differences were found between the treatments and soil layers.2) The soil fertility was significantly higher in surface soil (0-20 cm) than in the subsurface soil (20-40 cm).3) Among different cropping patterns, the soil enzyme activities related closely to C, N, P and S cyclings were significantly higher in the treatment with wheat/sunflower rotation for 10 years (WSR), suggesting that rotation can improve enzyme activity.4) Soil enzyme activities associated with C cycling decreased as the duration of continuing cotton cropping lasted. Due to cotton wilting, replanting alfalfa in these cotton farmlands significantly improved soil conditions (WCtR-AR), with a consequence if enzyme activity increment. Soil enzymes activities related to C cycling were higher in wilting-affected cotton fields than in wilting-unaffected cotton fields, depending somewhat on soil enzymes.5) The soil enzymes activities related to N, P and S cyclings all trended to decrease and then increase with the duration of cotton moncropping. For the same duration of cotton monocropping, no difference was observed between wilting-affected and wilting-unaffected fields.6) Significant differences (p<0.05) in microbial biomass C and N were found among different cropping patterns. Microbial biomass C decreased with duration of continuous cotton monocropping (5-10-15 years), but no consistent trend of change was found for microbial biomass N.7) For soils subjected to different cropping patterns and durations of continuous moncropping, soil respiration gradually decreased with incubation time (at 120 h), and then stayed steady. Significant difference (p<0.05) was found in soil respiration quotation (q(CO2)) among different cropping patterns. And among different durations of continuous cotton monocropping, soils collected from a field plot with cotton monocropping for 15 years (CtN15) had the highest respiration quotation, and soils collected from Rotation with alfalfa following cotton monocropping for 5 years (CtR-AR) had the lowest. There were significant differences among different cropping patterens.8) Community structures for total bacterial, total fungi, bacillus, ammonia-oxidizing bacteria and archaea amoA were significantly different in soils subjected to different cropping patterns, showing that cropping pattern deeply affected the microbial structural diversity.9) For the different durations of continuous monocropping, the structure of total bacterial, total fungi, bacillus and Fusarium clearly changed, with some communities disappeared and some others appeared. These results suggest that long-term continuous mono cropping has notable effects on microbial structure.[Conclusion] The soil physiochemical properties were significantly affected by cropping patterns and duration of continuous cropping with a result of soil fertility degradation. In the meantine soil microbial structural and functional diversity was changed. Rotation with green manure following long-term continuous monocropping is a better cropping pattern which can improve soil microbial activity and soil fertility.