Abstract: Mixed sowing of white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) is an important pasture species combination. Arbuscular mycorrhizal fungi (AMF) can form common underground mycorrhizal networks capable of both intra- and inter-species metabolite transfer and signal transduction between plants. The signal transduction is mainly mediated by salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). In this study, pure white clover and pure ryegrass swards were grown in separate pots, either linked by a 7 cm soil filled tube to facilitate formation of AMF bridges between white clover and perennial ryegrass plants in their separate pots, or with white clover and ryegrass pots unlinked to prevent AMF bridge formation. Acupuncture was performed on plants as described below to simulate aphid feeding and SA and JA were determined to study if a stress response signal was transferred between plant species through AMF bridges. Acupunture treatments on clover/ryegrass pot pairs included: no acupuncture; acupuncture of ryegrass with sampling of both species after 8 hours, and acupuncture of clover with both species sampled after 8 or 12 hours. These four treatments were implemented either with or without an AMF bridge present between clover and ryegrass (eight treatments, five replicates). The study aimed to provide theoretical information to facilitate the utilization of arbuscular mycorrhizal fungi to improve the plant stress resistance. It was found that AMF bridges with white clover increased the shoot biomass of ryegrass by 9.97% (P<0.05) and the total biomass by 10.68% (P<0.05). However the AMF bridges had no effect on the total biomass of white clover. The peroxidase activity of ryegrass was decreased by 43.01% (P<0.05) at 12 h after acupuncture and white clover was increased by 104.09% (P>0.05). Meanwhile, AMF bridges reduced SA concentration of ryegrass and white clover by 12.99% (P>0.05) and 24.18% (P<0.05), respectively, at 12 h after acupuncture, and JA concentration increased by 44.69% (P<0.05) and 79.32% (P<0.05) respectively. In a summary: 1) In white clover-perennial ryegrass mixtures, arbuscular mycorrhizal fungi can link the white clover and perennial ryegrass through AMF bridges to achieve nutrient redistribution, therefore promoting aboveground growth of perennial ryegrass. 2) In the presence of AMF bridges, white clover and perennial ryegrass have different stress responses. 3) AMF bridges enable participating species to respond more quickly to stress. 4) AMF bridges can transfer stress tolerance signals between white clover and perennial ryegrass, and this process is mainly mediated by JA.

Key words: Trifolium repens, Lolium perenne, common mycorrhizal networks, signal transduction, salicylic acid, jasmonic acid