Effects of fertilization regime on the functional diversity of microbial carbon and nitrogen metabolism in reclaimed soil

Soil reclamation has become a fundamental requirement for ecological environment restoration, total dynamic balance of cultivated land resources, and soil quality improvement in mining areas. This study was carried out at the long-term reclaimed base of a coal mining subsidence area in Xiangyuan county, Shanxi province, China. Surface soil samples of 0-20 cm were collected under various fertilization regimes in the 4- and 8-year experiment. Biolog-ECO and qPCR technologies were used to investigate the effect of various fertilization regimes on the soil microbial functional diversity of carbon metabolism, and functional gene abundance of nitrogen metabolism. Four fertilization treatments were applied within each reclamation stage, including no fertilizer (CK), chemical fertilizer only (CF), manure only (M), and 50% chemical fertilizers co-applied with 50% manure (MCF). The results showed that the M treatment can significantly improve the ability of soil microorganisms to utilize total carbon sources, compared with other treatments with the increase of reclamation years. The relative utilization rate of microorganism to carbon sources in reclaimed soil under various treatments were successively amino acids, carbohydrate, polymers, carboxylic acids, amine and miscellaneous from high to low. The M treatment improved the utilization rate of carboxylic acids, amino acids, and amines to a greater extent than those of other carbon sources. The differences of microbial carbon metabolism between various fertilizer treatments were mainly concentrated in five kinds of sugars, (including I-Erythritol, D-Mannitol, N-Acetyl-D-glucosamine, D-Cellobiose and α-D-Lactose), and four amino acids (including L-Arginine, L-Asparagine, L-Serine and L-Threonine). No significant change was observed in the Simpson index (D) under various reclamation years and fertilization regimes, indicating that the fertilization measures and reclamation years did not contribute to the dominant distribution of soil microbial physiological groups. The MCF treatment significantly improved the Shannon-wiener index (H') and Pielou evenness index (J), compared with other treatments. The functional gene abundance of nitrogen conversion was ranked in a descend order: amoA (AOA) > amoA (AOB) >nisS, nirK> nifH, in the reclaimed soil under various treatments. It infers that the nitrification was stronger than the denitrification and nitrogen fixation in the nitrogen cycle process of reclaimed soil. The abundance of five functional genes in the MCF treatment was the highest than that in other treatments, where increasing with the increase of reclamation time. The increase amplitude of amoA gene of AOA and AOB was the highest, indicating that the amoA gene was more sensitive than other functional genes to environmental factors, such as fertilization. The content of organic matter was significantly correlated with the abundance of nirS, nirK, nifH genes, and AWCD values in reclaimed soil, where the correlation coefficient was 0.707-0.807. Meanwhile, the abundance of five nitrogen conversion function genes was significantly or extremely significantly correlated with maize yield, where the correlation coefficient was between 0.824-0.949. Single application of manure can significantly increase the content of soil organic matter, and then enhance the intensity of microbial carbon metabolism, while, the combination of manure and chemical fertilizer was more conducive to improve the function diversity of carbon and nitrogen metabolism in reclaimed soil, and thereby to promote the crop yield. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.