The Enhancement Effect of Calcium Ions on Ectomycorrhizal Fungi-Mediated Drought Resistance in Pinus sylvestris var. mongolica

This study evaluated the overall influence of ectomycorrhizal fungi (ECMF) and exogenous Ca2+ supplementation on the growth, physiological, and metabolic traits of Pinus sylvestris var. mongolica seedlings under water stress and well-watered conditions. Several analytical methodologies pertinent to mycology, biochemistry, and ecology were applied. Exogenous Ca2+ was applied to 1-year-old mycorrhizal P. sylvestris var. mongolica, and the growth and physiological traits of various parts of P. sylvestris var. mongolica were assessed under water stress and well-watered conditions. The results showed that Ca2+ has an additional effect on the growth of P. sylvestris var. mongolica ECMF-inoculated under water stress. Ca2+ and ECMF together can enhance the activity of antioxidant enzymes, such as CAT, POD, SOD, and APX in the seedlings, and resist the accumulation of reactive oxygen species (ROS) caused by water stress. An appropriate combination of Ca2+ and ECMF can reduce the MDA content more efficiently in P. sylvestris var. mongolica and alleviate the extent of cellular stress. However, whether the free proline content is related to ECMF/Ca2+ inoculation remains to be further studied. The current findings indicate that, in the early stage of seedling development, it is feasible to apply exogenous Ca2+ and ECMF to improve growth and drought resistance.