Effects of planting years on functional diversity of carbon-metabolic microbial community in rhizosphere soils of alfalfa

The present paper studied the effects of planting years (2 and 10 years) of three alfalfa varieties (Medicago sativa cv. Zhaodong, M.sativa Zhongmu No.1, and M.sativa Argangjin) on the functional diversity of carbon source metabolism of microbial community in rhizosphere soils using BiologMT technology. The average well color development (AWCD) which symbolized the metabolic activity of soil microbes in the alfalfa soil of 10-year-age planting was obviously higher than that in the same alfalfa soil of 2-year-age planting. For all of three varieties, 10-year-age M.sativa Argangjin had the highest AWCD, while 2-year-age M.sativa cv. Zhaodong had the lowest AWCD. Between the two different planting years of the same alfalfa varieties, the McIntosh index was higher in the alfalfa soil for 10-year-age planting than that for 2-year-age planting, however, the Shannon index and Simpson index had no difference between the two different planting years. These results showed that the alfalfa of 10-year-age changed the composition and enhanced the diversity of the microbial community in the rhizosphere of soil. Principal component analysis (PCA) showed that there was no significant difference between the the carbon source utilization mode of the soil microbial community of the same variety for two planting ages. However, microbial carbon source modes of the 10-year-age alfalfa plantings soil were varied. The main carbon sources were carbohydrate, carboxylic acid, and amino acid.