Arbuscular mycorrhizal inoculation has similar benefits to fertilization for Thuja occidentalis L. seedling nutrition and growth on peat soil over a range of pH: implications for restoration

Arbuscular mycorrhizal (AM) fungi are hypothesized to assist growth of northern white-cedar in acid peatlands, yet there is little direct evidence that they can provide sufficient resources, especially nitrogen (N), from unfertilized peat soils. Our objective was to determine mycorrhizal efficacy to support cedar growth and nutrient supply as part of a low-impact approach for ecological restoration of cedar in peatlands. We tested the effectiveness of AM inoculation in a greenhouse experiment in factorial combination with fertilization and liming. We also determined AM colonization rate in the different treatment combinations. We found that AM inoculation in the absence of fertilization significantly increased all growth parameters, phosphorus (P) concentrations, and N, P, and copper (Cu) content of the seedlings, and decreased N:P ratios. Fertilizer alone had a similar impact on plant growth and nutrient acquisition when compared to un-fertilized AM inoculation treatments. Liming alone was ineffective at increasing cedar growth and nutrient uptake. There were many interactions of AM inoculation with liming and fertilization. Specifically, the positive effect of AM inoculation on many growth and nutrition metrics was strongly reduced in the presence of fertilization, whereas the P benefit of mycorrhizas appeared to increase under liming. We conclude that addition of AM inoculation alone improved cedar growth and P acquisition, reducing the need for fertilizer and lime in peatlands. However, seedling N limitation might be a problem in strongly N-deficient peat soils