Abstract: It is a challenge for ecologists to afforest successfully and to accelerate plant growth in sand dune. Mycorrhizal inoculants play a role in improving habitat and regulating plant growth. However, it’s still unknown whether the effects of mycorrhizal inoculants depend on plant species identity and how to apply mycorrhizal inoculants to plants based on different habitat conditions and goals. We examined the effects of mycorrhizal inoculants on seedling growth of three woody species commonly used for afforestation in Horqin Sand Land. The arbuscular mycorrhizal inoculants (Rhizophagus intraradices) were applied to Amorpha fruticosa and Ligustrum obtusifolium, while the ectomycorrhizal inoculants (Pisolithus tinctorius) were applied to Pinus sylvestris var. mongolica at doses of 0, 100, 200, and 300 g·m^-2 through adding into holes around the plant. The mycorrhizal colonization rate and seedling growth indices were measured after one year treatment. The colonization rate of P. sylvestris var. mongolica increased significantly with increasing doses of ectomycorrhizal inoculants, and was the highest at the dose of 300 g·m^-2 (17.8%). The colonization rate of A. fruticosa did not change with the mycorrhizal amounts. The mycorrhizal colonization rate of L. obtusifolium decreased significantly with the mycorrhizal amounts, and was the highest at 100 g·m^-2 (19.3%). L. obtusifolium had the highest mycorrhizal dependency and A. fruticosa had the lowest mycorrhizal dependency. Except for plant height (200 g·m^-2: 26%) and absorptive root mass (100 g·m^-2: 79.2%), all the other indices of P. sylvestris var. mongolica decreased after the application of ectomycorrhizal inoculants. Plant height, aboveground biomass, and total biomass of A. fruticosa increased significantly by 21.7% on average at the treatment of 300 g·m^-2. The basal diameter, transport root mass, aboveground biomass, root biomass and total biomass of L. obtusifolium increased significantly compared with the control, with the maximum increase rates as 47%, 156.3%, 207.6%, 154.7% and 186.6% at 100 g·m^-2, respectively. At the treatments of 100 and 200 g·m^-2, all growth indices of L. obtusifolium were significantly increased compared to the other two species. At 300 g·m^-2, main root length (38.5%), transporter root mass (45.5%), and root biomass (45.3%) of A. fruticosa were significantly increased compared to the other two species. Our results indicated that mycorrhizal inoculants have a significant effect on plant height, absorptive root mass, aboveground biomass, total biomass, and root-shoot ratio. Mycorrhizal inoculants can promote the aboveground growth of L. obtusifolium but restrict underground growth of P. sylvestris var. mongolica. Only high amount of mycorrhizal inoculants can promote the belowground growth of A. fruticosa. This study provides evidence for the rational application of mycorrhizal inoculants for afforestation in sand land to accelerate vegetation restoration.

Key words: mycorrhizal inoculant, mycorrhizal colonization rate, plant growth, mycorrhizal application.