Responses of root morphology and nutrient content of Pinus sylvestris var. mongolica seedlings to nitrogen addition and inoculation treatments

  Objective  The aim of this study was to investigate the responses of root architecture and nutrient absorption capacity of one-year-old Pinus sylvestris var. mongolica to nitrogen addition and inoculation of ectomycorrhizal fungi.

  Method  The one-year-old mycorrhizal (mixed inoculated with 8 ectomycorrhizal fungi, HJ) and non-mycorrhizal (no inoculation, WJ) seedlings of P. sylvestris var. mongolica were selected. Four nitrogen addition treatments were set, including no nitrogen (CK, 0 kg/(ha·year)), low nitrogen (LN, 15 kg/(ha·year)), middle nitrogen (MN, 30 kg/(ha·year)) and high nitrogen (HN, 60 kg/(ha·year)) treatments. The root morphology (including the total root length, surface area, volume, bifurcations, tips, average diameter) and nutrient content of the seedlings were measured.

  Result  (1) There were significant differences between the seedling biomass of two inoculation treatments under CK, MN and HN treatments. Under CK treatment, the biomass of mycorrhizal seedlings increased by 54.3% than that of the non-mycorrhizal seedlings. Under MN and HN treatments, the biomass of mycorrhizal seedlings decreased by 17.8% and 23.7% than that of non-mycorrhizal seedlings, respectively. (2) The total root length, surface area, number of tips of one-year-old P. sylvestris var. mongolica seedlings with diameter of 0 − 0.5 mm were affected significantly by the nitrogen addition and inoculation treatments. Increasing of nitrogen addition, the root morphological indexes of non-mycorrhizal seedlings showed a tendency of first increased and then decreased, but that of mycorrhizal seedlings showed a decreasing tendency. (3) Compared with CK, the nitrogen and phosphorus contents of the non-mycorrhizal seedlings were significantly increased by nitrogen addition treatments, but that of mycorrhizal seedlings was promoted by LN treatment and inhibited by HN treatment.

  Conclusion  There is a synergistic effect of low nitrogen addition and inoculation treatments on the root morphology and nutrient content of seedlings. The effect of inoculation on root morphology and nutrient content of seedlings is weakened by high nitrogen addition.