Influences of fertilization and seasonal variation on microbial community in a Chinese mollisol

Fertilization and seasonal variation play very important roles in affecting microbial structure and activity, as a result, leading to the significant evolution of soil fertility. The effect of manure (MCK) and combined application of chemical fertilizers (NPK) on soil microbial biomass and structure were studied by measuring soil microbial biomass carbon (nitrogen) and phospholipid fatty acid (PLFA) in different microbial communities, with the nil-fertilization (CK) and fallow as controls. Results show the manure application significantly improves the soil nutrient contents and the amounts of Cmic and PLFA of different microbial communities. The amounts of fungal PLFA (8.40 nmol · g-1) and Cmic (322.5 mg · kg-1) and Nmic(57.9 mg · kg-1) are significantly higher than those of CK (5.4 nmol · g-1, 152.6 mg · kg-1, 32.1 mg · kg-1, respectively) or NPK (3.5 nmol · g-1, 144.3 mg · kg-1, 30.7 mg · kg-1, respectively). And the contents of Cmic, Nmic and PLFA of different microbial groups in NPK are lower than those in CK. Correlation analyses show the soil nutrient contents are significantly positively correlated with Cmic, different microbial PLFA contents and G-/total bacteria ratios, while negatively correlated with G+ /G~ bacteria ratio (p less than or equal 0.05). The principle component analysis of PLFA shows the microbial structures in different treatments and sampling dates are significantly different. Seasonal changes are also found to cause great fluctuations in soil basic properties, and microbial community structure in arable soils and fallow respectively cluster strictly together by sampling dates. The amount of Cmic is highest on April 11 (295.6 mg · kg-1), while Nmic (49.3 mg · kg-1) and PLFA contents are highest in summer (July-August); the lowest amounts of Cmic( 184.2 mg · kg-1), Nmic(30.63 mg · kg-1) and PLFA exist on May 31. Fertilization and seasonal variations significantly affect soil fertility, microbial structure and activity.