Abstract:

A four compartment-culture system was designed to study P nutrition and the effects of hyphal links on 32P transfer among Larix kaempferi seedlings after inoculation with Paxillus involutus and Pisolithus tinctorius. Results showed that both the donor and the receiver can be inoculated with Paxillus involutus and Pisolithus tinctorius, which indicates that the extraradical mycelia of donor larch seedlings could penetrate air gaps and clay soil and form hyphal links between the donor and the receiver. The biomass of donor seedlings inoculated with Paxillus involutus and Pisolithus tinctorius was greater than that of non-mycorrhizal seedlings, but the growth of receiver seedlings was not significantly affected. The amount of P in the shoots and roots of Larix kaempferi inoculated with Paxillus involutus and Pisolithus tinctorius was significantly higher than in controls, and the amount of P in donor seedlings was much greater than in receiver seedlings. The P nutrition of both the donor and receiver plants was improved after they were inoculated with Paxillus involutus and Pisolithus tinctorius. The P content in the donor seedlings was 39% higher than that of the controls accounting for the greater biomass of donor seedlings. The inoculation rate, biomass and P content of receiver seedlings were all lower than that of donor seedlings, most likely because the receiver was inoculated after the donor's inoculation so that the time of inoculation on the receiver was shorter than that of the donor.32P in receiver seedlings was checked using radioautography and the concentration of 32P radioactivity. The 32P radioactivity of receiver seedlings inoculated with Paxillus involutus and Pisolithus tinctorius was 10 and 6 times higher, respectively, than in controls without hyphal links, and the amount of 32P in the receiver plants was 1.10% and 0.22% of donor seedlings, respectively. 32P radioactivity also was found in control plants, indicating that 32P could diffuse to receiver compartments through the soil and be absorbed by the receiver. The 32P transfer rate from the donor to the receiver after inoculation with Paxillus involutus and Pisolithus tinctorius was 18 and 4 times higher, respectively, than that of the control indicating that the 32P in donor seedlings could be transferred to the receiver seedlings via hyphal links. The 32P transfer rate through hyphal links formed with Paxillus involutus was 4.5 times higher than those formed with Pisolithus tinctorius, which could be attributed to the higher inoculation rate, biomass of extramycelium and hyphal density of Paxillus involutus. 32P was transferred from the donor to the receiver seedlings via hyphal links, but the amount was very limited. P nutrition of receiver seedlings was not significantly improved, but P absorbed by receiver seedlings increased after inoculation with both Paxillus involutus and Pisolithus tinctorius. This effect was attributed to P acquisition of acceptors aided by fungi after hyphal links formed.