Abstract :
[en] Long-term intensive fertilizations are often accompanied by inefficiences that result in pollution and soil degradation of Mollisols in northeast China, especially the overuse of inorganic nitrogen (N) input. Organic manure can improve soil quality and may be potential as substitution of N fertilizer. However, we know less about the impacts of inorganic fertilizer and organic manure applications on microbial community composition, which functions as sensitive indicators for soil biological fertility. To broaden our knowledge, high throughput pyrosequencing and quantitative PCR were used to explore the responses of soil property and microbial community composition to long-term fertilization strategies. Soils were collected from a 35-year experimental field of Chinese Mollisols with six treatments: 1) no fertilizer (CK), 2) inorganic phosphorus and potassium fertilizer (PK), 3) inorganic N, P and K fertilizer (NPK), 4) manure (M), 5) inorganic P, K fertilizer plus manure (MPK), and 6) inorganic N, P, K fertilizer plus manure (MNPK). Treatments 1), 2) 3) and 5) were analyzed for bacterial and fungal community, and treatments 1), 3), 4) and 6) were used for arbuscular mycorrhizal fungi (AMF). All fertilization strategies significantly changed soil properties and increased the crop yields, with the highest increase observed in chemical fertilizers plus manure treatments. The application of manure also had beneficial effects on soil acidification alleviation and soil organic matter (OM) accumulation, while long-term chemical fertilizer application (NPK and PK) significantly decreased soil pH. With regards to microbial abundance, 16S rRNA gene copies were significantly increased in MPK regime. Compared with CK, long-term MPK application indicated a good effect on the soil shift from “fungal-based” to healthier one, namely “bacterial-based” soil, by decreasing ITS gene copy numbers and increasing the Bacteria-to-Fungi ratio, while chemical fertilization application exhibited the opposite pattern. Furthermore, the community richness indices (CHAO1 and ACE) in MPK regime were also higher than those in other regimes, probably indicating resilience of microbial diversity and stable agroecosystem. The diversity and richness of AMF were negatively affected by chemical fertilizer applications, likely resulting in a reduction of mutualism in plant–AMF symbiosis; however, a reverse trend was observed for the application of manure. Regarding bacterial community composition, Proteobacteria, Acidobacteria, Actinobacteria and Verrucomicrobia were dominated phyla, and phylun Ascomycota was absolutely dominated in fungi in all samples, followed by Zygomycota, Basidiomycota, Chytridiomycota and Glomeromycota. The community composition considerably varied by different fertilization strategies at each taxonomic level. NPK application might induce the incidence rate of disease, because more harmful fungal taxa were overrepresented in this regime, such as order Chaetothyriales, family Chaetothyriaceae, Genuses Corynespora, Bipolaris, Pleosporaceae, Cyphellophora, Sphingomonas and Xanthomonas. Although such of them were not crop pathogens, their present in soil would no doubt increase the environmental risk. Additionlly, NPK application might cause a loss of plant-fungal symbioses, N loss in soil and greenhouse gas emission, probably due to the shift of classes Leotiomycetes and Eurotiomycetes. In contrast, more taxa with positive impact on soil quality were overrepresented in MPK regime, including phyla Proteobacteria, Bacteroidetes, class Alphaproteobacteria, family Claroideoglomeraceae, and genera Variovorax, Chthoniobacter, Massilia, Lysobacter, Claroideoglomus, Catelliglobosispora and Steroidobacter. These beneficial bacteria were in association with plant growth promotion, OM accumulation, P acquisition, pathogen suppression, and soil enzyme activity arising. In summary, different fertilization strategies led to distinct variances in microbial community composition. Such shifts primarily derived from the changes of soil pH and OM. Our findings determined the responses of microbial community composition to long-term application of inorganic fertilizer and organic amendment, and highlighted the benefits of substitution of inorganic N fertilizer by manure for sustainable development of agriculture in Chinese Mollisols.
