Changes in the soil nutrient levels, enzyme activities, microbial community function, and structure during apple orchard maturation

• We investigated differences in soil quality during the apple orchard maturation.
• Most soil nutrients and enzyme activities increased initially before decreasing.
• The microbial community function diversity are sensitive indicators.
• The old orchard soil had an inferior micro-ecological environment.

The quality of soil is affected by its microbiological composition, which may change over time. This study investigated differences in the soil quality during the maturation of apple orchards. Soil nutrients, soil enzymes, community-level physiological profiles (CLPP), and terminal restriction fragment length polymorphism (T-RFLP) profiles were determined in soil samples from four apple orchards (aged 3, 7, 15, and 23 years) and a neighboring wasteland. The orchard soil organic matter, total nitrogen, invertase, and urease levels increased initially as the apple orchards matured, before decreasing, while the soil total phosphorus accumulated. The total potassium levels were significantly lower in the orchards than the wasteland (P < 0.05). The 7-year-old orchard soil had the highest carbon source metabolic activity, Shannon diversity index, richness index, and evenness index, whereas the 23-year-old orchard soil had the lowest levels for all four indicators. T-RFLP indicated that the 62-bp and 136-bp T-RFs were enriched, whereas the 129-bp and 285-bp T-RFs declined during apple orchard maturation. This study indicates that the old orchard soil had an inferior micro-ecological environment compared with the younger orchards. Thus, measures such as balanced fertilization, intercropping, and green cover may improve the soil environment in apple orchards.