RESULTS
The results of Cox PH models for the three-year seedling survival indicate that the HR of O. semicastrata seedling mortality, i.e., the risk of mortality under warming, was significantly less than 1 (p = 0.04, Figure 2a), while warming had no significant effect on the HR of C. patelliormis seedling mortality (p = 0.56, Figure 2b). Additionally, the HR of O. semicastrata seedling mortality significantly decreased with increasing distance from their parent trees (p = 2e-6, Figure 2a) and with pesticide treatment (p < 2e-16). In contrast, seedlings of the congeneric tree species, O. pinnata , and the other focal species, C. patelliformis , which were planted together under O. semicastrataparent trees (Figure 1b), did not respond to pesticide treatment (Figure S1). Conversely, the mortality HR of C. patelliormis seedlings significantly increased with distance from their parent trees (p= 0.01, Figure 2b), while pesticide and warming treatments had no effect on C. patelliormis seedling mortality (p = 0.45 andp = 0.56, respectively, Figure 2b). Similar results were observed for its congeneric species (C . hui ) and the other focal species (O. semicastrata ) (Figure S1), whose seedlings were planted under the same C. patelliormis parent trees (Figure 1b).
Among the fungal OTUs, 41.76% (4093 out of 9802) were identified to the genus level, and 96.56% of these (3952 out of 4093) were further successfully grouped into functional guilds, including plant-pathogenic fungi (10.65%) and EcM fungi (9.92%). OTU9 (Laccaria sp., an EcM fungus) was the most abundant fungus, contributing 3.94% of the sequence numbers to the total fungal OTUs. In total, 421 fungal OTUs were identified as plant-pathogenic fungi.
Warming significantly decreased the relative abundance of plant-pathogenic fungi (p < 2e-16, Table 1), but increased that of EcM fungi (p < 2e-16, Table 2). With the increasing distance from parent trees, the relative abundances of plant-pathogenic fungi and ECM fungi decreased (p < 2e-16, Tables 1 and 2). Pesticide treatment decreased the relative abundance of plant-pathogenic fungi (p < 2e-16, Table 1), but increased the relative abundance of EcM fungi (p = 8e-16, Table 2), which may be responsible for the decreased seedling mortality of O. semicastrata at pesticide treatment (p < 2e-16, Figure 2a). However, changes in the relative abundance of plant-pathogenic fungi and the relative abundance of EcM fungi under warming and pesticide treatments seemed to have no effect on C. patelliormis seedling mortality (p = 0.45 and p = 0.56, respectively; Figure 2b), which might suggest that load levels of plant-pathogenic and EcM fungi are not critical for seedling survival of EcM fungi-associated tree species (possibly due to the protection of Hartig nets against pathogens’ attack on roots).