Effects of continuous potato cropping on the diversity of soil microorganisms

Alternative cropping (0 year of potato cultivation), and 2, 4, 6, 10 years of continuous monoculture of potato were studied to explain the mechanism of continuous cropping obstacles by using combined BIOLOG and morphological identification techniques of arbuscular mycorrhizal fungi (AMF). The results showed that soil nutrients contents decreased with increasing number of continuous potato cropping years after 4 years continuous cropping. Compared with 4 years continuous potato cropping, 10 years continuous potato cropping decreased soil total phosphorus, available phosphorus, available potassium and available nitrogen respectively by 61.32%, 26.86%, 26.87% and 17.24%. However, no obvious nutrient deficiency or imbalance was noted in the experiment. Soil microbial community structure also changed significantly. The amounts of actinomyces and fungi increased in the first few years and later dropped significantly. The amount of bacteria gradually decreased with increasing number of years of continuous potato cropping, but no significantly changed. Microbial functional diversity of soil microbial community was still strong under 4 6 years of continuous potato cropping. Compared with alternative cropping (0 years), average well color development (AWCD) increased by 3.89% under 6 years of continuous potato cropping. The metabolism ability of soil microbial community using carbohydrate and amino acids as sources of carbon obviously decreased, but metabolism ability diversity tended to unanimous with the extension of continuous potato cropping years. The dominant AMF species changed from Glomus deserticola under alternative cropping (0 years) to G. delhiense and G. formosanum under 2 years of continuous potato cropping, and to G. globiferum under 10 years of continuous potato cropping. Multivariate analysis showed that the diversity of soil microbial structure and function, and AMF diversity were affected by soil pH, total phosphorus, amounts of actynomycetes and bacteria, and soil microbial groups using carbohydrate and amino acids as sources of carbon substrate. It was therefore concluded that continuous potato cropping decreased not only fungi and actinomycetes population but also AMF diversity. The dominant AMF species also changed and soil microbial structure diversity performance was inconsistent with function diversity. There was functional and structural disorder of soil microbial communities under continuous potato cropping.