Effect Of Long-term Fertilization On Diversity Of Soil Microbial Community Structure Under Different Cropping Systems

Microorganism, mainly bacteria and fungi, play crucial roles in making nutrients available to plants, thus changes in a microbial community can thus be used to indicate alteration in soil quality. Since some biological parameters such as microbial biomass and hydrolase enzyme activities are robust bulk parameters, biochemical properties like phospholipids fatty acids(PLFAs) reflecting potential functional diversity and molecular techniques including polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE) indicating changes in microbial populations have been paid increasing attention. In this research, soil microbial biomass, hydrolase enzyme activities, and community diversity were detected based on three long term fertilizer experiments, including a calcareous fluvo-aquic soil with winter wheat and summer maize rotation system in Xinji of Hebei province performed in 1979, a paddy soil derived from yellow brown earth with winter wheat and rice rotation system in Wuhan of Hubei province in 1981, and a paddy soil derived from red earth with double cropping rice in Jinxian of Jiangxi province in 1981. Basic treatments in three long-term experiments included (1) CK(no fertilizer added), (2) nitrogen(N), (3)nitrogen and phosphorus(NP), (4) nitrogen, phosphorus and potassium (NPK); (5) organic manure (M), and (6) NPK plus organic manure (NPKM). Microbial community diversity was investigated using PLFA profile method as well as PCR-DGGE fingerprinting techniques. The main findings obtained are as follows:1. Crop yield. For three major cropping systems, the grain yield was the lowest in CK, and the highest in NPK or NPKM. Compared to CK, NPK and NPKM significantly increased grain yield of wheat by 577.1% and 560.9%, and maize by 173.2% and 170.4%, respectively in the calcareous Fluvo-aquic soil, wheat by 75.8% and 167.6%, rice by 11.1% and 11.0% respectively in the paddy soil derived from yellow brown earth, and early rice by 64.5% and 112.5%, and late rice by 18.6% and 35.5% respectively in the paddy soil derived from red earth. A relatively high yield was achieved in M treatment in both calcareous fluvo-aquic soil and paddy soil derived from yellow brown earth.2. Soil fertility. Compared with CK and chemical fertilizer alone, M and NPKM significantly increased the contents of soil OM, total N, total P, dissolved organic C (DOC), NO3--N, available P and available K in three major cropping systems. Soil C/N was found to be reduced in the treatments of M and NPKM in comparison with CK and chemical fertilizer alone. Organic manure addition significantly alleviated soil alkalization in both calcareous fluvo-aquic soil and paddy soil derived from yellow brown earth, but there's no significant difference between six treatments in the paddy soil derived from red earth.3.Microbial biomass C, N and P. Biomass C, N and P in two paddy soils derived from yellow brown earth and red earth were generally found to be higher than those in calcareous fluvo-aquic soil. The trends of soil microbial biomass C, N and P was similar, with an order of NPKM, M>NPK, NP>N, CK under three major cropping systems, indicating that the combined application of organic and chemical fertilizers could increase the amount of biomass C, N and P. There is a significant positive correlation between amount of microbial biomass and soil OM content.4.Hydrolase enzymes activity. Acid phosphatase and sulfatase activity was generally found to be in an order of paddy soil derived from red earth > paddy soil derived from yellow brown earth > calcareous fluvo-aquic soil, and NPKM, M>NPK, NP, N and CK for each soil; Protase and urease activities in paddy soil derived from yellow brown earth and calcareous fluvo-aquic soil were generally found to be higher than those in paddy soil derived from red earth, the tendency of those was in an order of NPKM>M>NPK, NP, N and CK for each soil; In general, the sucrase andβ,D-glucosidase activities were significantly different (P<0.05) among six treatments with the following order as NPKM>M>NPK>NP, N and CK for all three soils. It was found that acid phosphatase activity correlated significantly with OM and available P content, and both protase and urease correlated significantly with OM and NO3--N content.5. PLFA profiling of microbial community structure. PLFAs were generally found to follow the order of paddy soil derived from red earth>paddy soil derived from yellow brown earth > calcareous fluvo-aquic soil, and NPKM, M>NPK, NP, N and CK for each soil. Fungi PLFA content and fungi to bacteria ratio in paddy soil derived from yellow brown earth and calcareous fluvo-aquic soil were generally found to be higher than those in a paddy soil derived from red earth. Compared with CK and chemical fertilizer alone, M and NPKM significantly increased proportion of the bacteria PLFAs (i16:0 and i19:0), fungal PLFAs (18:1ω9), and abuscular my-corrhizae (AM) PLFA (16:1ω11) in paddy soil derived from yellow brown earth and calcareous fluvo-aquic soil, and the proportion of the bacteria PLFA (16:0) and abuscular my-corrhizae (AM) PLFA (16:1ω11) in paddy soil derived from red earth. NP and NPK increased the proportion of Gram-negative bacteria (G-) PLFA (18:1ω5) and Actinomyces PLFA (17:0(10Me)) in each soil. Principal component analysis(PCA)of PLFA also showed that microbial community structure was affected by manure and chemical fertilizers application in different ways. Significant positive correlations existed between PLFAs and selected fertility parameters including OM, total P and available P content in each soil, and between fungi to bacteria ratio and available K content in paddy soil.6. Soil bacteria and ammonium oxidizers diversity. Bacteria production obtained by PCR amplified and Shannon diversity index (H) were generally found to be in the order of paddy soil derived from yellow brown earth > calcareous fluvo-aquic soil > paddy soil derived from red earth. Diversity of ammonia oxidizers (AOB) and bacteria were higher in NPKM and M than in the CK and chemical fertilizer alone for each soil. Sequencing of PCR products separated in DGGE showed that Proteobacterium or Agrobacterium were dominant bacteria, and Nitrosomonas and Nitrosospira which belongs toβ-Proteobacterium were dominant AOB in calcareous fluvo-aquic soil and paddy soil derived from yellow brown earth. Acidobacterium were dominant bacteria in paddy soil derived from red earth. NPKM and M increased the amount of Proteobacterium and Nitrosomonas in calcareous fluvo-aquic soil, as well as Nitrosospira in paddy soil derived from yellow brown earth.