Effects Of Long-term Fertilization And Plastic Film Mulching On Soil Microbial Communities In A Brown Earth Of Northeast China

Long-term fertilization and plastic film mulching have great influence on soil microbial community diversity regarded as indicators of soil health and productivity. Several long-term fertilization and plastic film mulching studies have been conducted to primarily focus on soil fertility at Shenyang Agricultural University brown soil experimental station (established in 1987). Results indicated that long-term fertilization and film mulching had tremendous influence on soil physicochemical properties, including abiotic and biotic factors. However, these studies lacked the taxonomic resolution to classify microorganisms into specific taxa and results could not reflect precise responses of microbial community structure and diversity to different applications of fertilizer regimes and film mulching, simply because robust technologies were not used to investigate soil microbes. In this study, quantitative real-time polymerase chain reaction (qPCR), denaturing gradient gel electrophoresis (DGGE), and high through-put sequencing methodologies were used to unravel the long-term effect of fertilization and plastic film mulching on soil microbial communities. The main findings were as follows:(1) Long-term application of combined nitrogen and manure fertilization greatly reduced diversity. Differences in community composition among the treatments regardless of mulching were observed. Plastic mulch either directly or indirectly was a key driver in structuring microbial communities. Soil organic carbon (SOC), total nitrogen (N), available phosphorus (P), soil pH, and moisture were the key soil properties structuring phylum level diversity of the soil microbial communities. Long-term application of manure fertilization resuscitated the bacterial community diversity and richness. The non-fertilization control treatments significantly increased bacterial diversity and richness compared to fertilized treatments regardless of film mulching. The dominant bacterial phyla were:Proteobacteria, Acidobacteria. Actinobacteria, Bacteroidetes, and Firmicutes.(2) The abundances of AOA (ammonia-oxidizing archaea) amoA genes exceeded AOB (ammonia-oxidizing bacteria) for June, July, and October samples. The abundances of AOB and AOA in June were far greater than those in July and October respectively. Long-term fertilization of manure application and non-fertilized control plots significantly increased the abundances of AOB and AOA communities. Generally, the abundances of AOB and AOA were reduced under plastic film mulching. The fertilization treatments significantly decreased AOB diversity and richness compared to non-fertilization control treatment. Long-term application of nitrogen fertilization significantly reduced AOB diversity and richness in July, while the opposite effect was seen in October. Long-term application of manure fertilization and film mulching played a significant role in AOB community diversity and richness. The community structure of AOB was mainly driven by fertilization. Long-term application of nitrogen fertilization significantly increased the ribotypes of AOB communities regardless of mulching status for July and October. The following species were common among all treatments for both July and October:uncultured ammonia-oxdizing bacterium, uncultured Nitrosospira sp, Uncultured Nitrosomonas sp, Nitrosospira sp, and uncultured beta Proteobacterium, Uncultured Methylobacillus sp, and uncultured bacterium.(3) The dominant phyla in all samples were:Proteobacteria, Actinobacteria, and Acidobacteria. Long-term application of combined manure and nitrogen fertilization significantly increased the relative abundances of bacterial phyla for samples collected in summer and autumn, which is contrary to our previous study. Seasonal changes greatly affected the abundances of bacterial phyla. Long-term application of nitrogen fertilization significantly reduced soil bacterial diversity and richness compared with non-fertilization control for July and October, though nitrogen fertilization increased bacterial richness for October. Under long-term fertilization, soil bacterial diversity and richness were consistent with increase in maize grain yield productivity, except for the non-fertilization control which had high bacterial diversity and richness, but yet very low maize grain yield production. Soil bacterial community was mainly driven by fertilization. The following soil properties:soil pH, moisture, SOC, NH4+-N (ammonia-nitrate), NO3--N (nitrate-nitrogen), total N, K (potassium), and P (phosphorus) played vital role in shaping the bacterial community structure for July and October. Our results have provided strong evidence that long-term application of chemical fertilization reduced microbial activity of field plots, and this may have direct or indirect effect on maize grain yield production in the future.