Abstract:

Soil microorganisms are an important component of a soil ecosystem. Long term continuous mono-cropping of potato was found to have altered the soil eco-system, thus affecting yield and quality of the crop. To confirm the finding, rhizospheric soil samples were collected from potato field sunder continuous mono-cropping different in cultivation history and fields under crop rotation (potato and sesame) for analysis of allelo chemicals and community structure and functions of soil microbes using gas chromatography-mass spectrometry(GC-MS), and the phospholipid fatty acids (PLFAs) biomarker method, separately. Results show that from the soil samples collected from fields under mono-cropping, the educts extracted with ethyl acetate, despite in what phase, acid, neutral and basic, all contained over 50% of iso-butyl phthalate ester and some cis-14-twenty nonaene, indicating apparent accumulation of esters, olefins and benzene substances in the soil, as compared with the soil under crop rotation. With mono-cropping going on, the soil microbial community displayed a trend, rising in the first 2-4 years, peaking after the 4th year , declining after 7-10 years and lingering in general at a low level after 10 years, in carbon utilization capacity. The groups of microbes living on carbohydrates as carbon source decreased significantly in metabolism and the groups living on carbohydrates, carboxylic acids and amino acid as metabolic substances were apparently inhibited. Among the main phospholipids fatty acids (PLFAs), those characterized by C16:1, C16:0, C18:2ω6t, C18:1ω9 caccounted for a high proportion. Contents of various fractions of PLFA varied with mono-cropping going on, all displaying a single peak curve. In the field under 4 years of mono-cropping, the soil biomass was the highest, and the biomass ratio of bacteria/microbial community increased, while the ratio of fungi/soil microbial community declined with mono-cropping going on. In the fields under crop rotation, community structure and biomass of the soil microbes were obviously improved. Iso-butyl phthalate ester and cis-14-twenty nonaene accumulated in the fields under long-term mono-cropping of potato may be the major allelo chemicals that hinder continuous mono-cropping of potato. These chemicals significantly alter community structure and functions of the soil microbes. The 5th year may be the critical point for continuous mono-cropping of potato.

Key words: Potato, Obstacle for continuous cropping, Gas chromatography-mass spectrometry (GC-MS), Community level physiological profiles (CLPPs), Phospholipid fatty acids (PLFAs)