Changes in the root system of the herbaceous peony and soil properties under different years of continuous planting and replanting

The herbaceous peony (Paeonia lactiflora Pall.) has high ornamental value. Replanting problems occur when seedlings are replanted into previous holes. We studied the root system and soil environment of the 'Dongjingnvlang' variety under a continuous planting regime of 1, 4, and 7 years, and a replanting regime of 1 and 4 years. Under the condition of continuous planting, with the increase of number of years, pH, ammonium nitrogen, and nitrate nitrogen decreased in the rhizosphere and non-rhizosphere soils, whereas organic matter, available phosphorus and potassium, enzyme activities, and the number of bacteria, fungi, and actinomycetes increased. Under the condition of replanting, with the increase of number of years, fungi and actinomycetes in both soils increased, while pH, organic matter, nutrients, enzyme activities, and bacterial number decreased. pH, organic matter, nutrient content, enzyme activity and the number of bacterial were lower in soil replanted for 4 years, whereas the abundance of fungi and actinomycetes was higher, altering the soil from "bacterial high-fertility" to "fungal low-fertility" with increasing years of replanting. The activity of antioxidant enzymes and MDA content in roots of peony in replanting were higher than those in continuous planting, while the content of osmotic regulatory substances in replanting was lower than that in continuous planting. The results showed that there were no obvious adverse factors in soil during 7 years of continuous planting, and herbaceous peony could maintain normal growth and development. However, soils after 4 years of replanting were not suitable for herbaceous peony growth. Benzoic acid increased with years of replanting, which potentially caused replanting problems. This study provides a theoretical basis for understanding the mechanism of replanting problems in the herbaceous peony.