Abstract:

Ectomycorrhiza plays an effective role in the water absorption and drought resistance of host plants and contributes to the stability maintenance of the forest ecosystem. Pinus sylvestris var. mongolica is one of the typical tree species for windbreak shelterbelts in northern China, which depends on ectomycorrhiza during its life process. In this study, seedlings infected by three important ectomycorrhizal fungi, namely, Suillus granulatus (Sg), Tricholoma sp. (Ts), and Suillus luteus (Sl), were tested to compare the drought resistance of mycorrhizal seedlings. A controlled experiment was conducted under the following drought stress gradients: 80% (sufficient water supply), 40% (moist water supply), 20% (suitable water supply), 10% (mild drought), and 5% (severe drought) of saturated soil moisture content. The physiological parameters of P. sylvestris var. mongolica seedlings were measured accordingly. Results indicated that (1) the Sl treatment efficiently alleviated the damage of reactive oxygen by increasing antioxidant enzyme activities to resist drought stress. Under mild drought, superoxide dismutase (SOD) and peroxidase activities reached the maximum values of 425.16 U·g^-1 and 202.73 U·g^-1, respectively. (2) Sg treatment not only increased the antioxidant enzyme activities to resist drought stress but also relieved this impact by accumulating proline to regulate penetration. Under mild drought, the maximum SOD and soluble sugar levels were 397.01 U·g^-1 and 199.50 μg·mL^-1, respectively. (3) The Ts treatment largely increased the maximum photosynthetic efficiency. Under normal moisture content and mild drought stress, the maximum photosynthetic efficiency was significantly higher than that of the referenced group (P<0.05). To resist drought stress, ectomycorrhiza maintained the regular physiological activities of P. sylvestris var. mongolica seedlings by improving antioxidant enzyme activities, regulating osmotic substance contents, and increasing the photochemical efficiency. However, the approaches of ectomycorrhiza were different in the drought resistance improvement of P. sylvestris var. mongolica seedlings. This study provided the physiological evidence of ecological functions of ectotrophic mycorrhiza and contributed to investigations on afforestation technology by using mycorrhizal seedlings.

Key words: Pinus sylvestris var. mongolica, ectomycorrhizal fungus, drought stress, antioxidant enzyme activities, osmotic regulation substance, photochemical efficiency