Effects of Forest Soil and Soil-borne Fungi on Seed Germination and Seedling Survival of Toona ciliata var. pubescens

Objective The barrier factors influencing the natural regeneration of Toona ciliata var. pubescens were explored through investigating the effects of forest soil and fungi in different natural communities on seed germination and seedling survival.

Method Soil samples were collected from the root zone at three distances (2.5, 5.0, and 7.5 m) from the mother trees as well as the natural forest stands 25 m away from the mother trees in Jiulianshan National Nature Reserve. The seed germination trial on soils was carried out in the laboratory with non-forest soil as the control. In addition, the seedling infection trial in soil was also performed in the laboratory with root irrigation by fungi isolated from root zone soil and suspended with water or root exudates. The seed germination, seedling survival and seedling susceptibility were observed.

Result The germination of seed in all kinds of soil revealed the tendency of increasing at initial and then decreasing, and reached the peak during the eighth to tenth day after sowing. There were no significant differences between forest soil and non-forest soil in germination rate, while the seedling survival rate of forest soil was significantly lower than that of non-forest soil. There were significant differences between root zone soil and non-root zone soil in seedling survival rate, and the seedling mortality of root zone soil was higher. It was also found that there were no significant differences in seedlings survival rate of root zone soil among different distances from the mother trees. It addition, there were extremely significant differences in seedling infection treatments, and the seedling disease incidence rates of RS₂, RS₅ soil-borne fungi were significantly higher than those of the two blank controls, water (W) and root exudates (R). Moreover, the disease infection rate of RS₂ root exudates suspension was significantly higher than that of RS₂ water suspension.

Conclusion Forest soil of different natural communities has no effect on seed germination of T. ciliata var. pubescens, However, the seedling establishment is disturbed by root zone soil of the same species; the interaction between root exudates and pathogens can significantly reduce the seedling survival rate. It could be inferred that there are potential pathogens in root zone soil of T. ciliata var. pubescens and root exudates can enhance their pathogenicity.