Soil phosphorus mobilization and utilization by Suillus isolates and Suillus-mycorrhized pine plants

Ectomycorrhizal (ECM) fungi form associations with trees, which may be beneficial to improve host growth and phosphorus (P) uptake in P-deficient soils. Therefore, P mobilization and utilization were investigated by growing 13 Suillus spp. in a culture solution using soil as sole P source and Suillus-mycorrhized Pinus massoniana in nursery and field. Suillus isolates significantly varied in the ability to mobilize P in the soil via proton and oxalate efflux. There was a significant positive correlation between soil Olsen P in the culture solution and the nurseries (r = 0.945, n = 13, P ≤ 0.01). Similar mechanisms may thus be involved in soil P mobilization by the Suillus isolates and the Suillus-mycorrhized plants. Fungal P uptake in vitro showed no significant correlation with P uptake by Suillus-mycorrhized plants in nurseries. This significant finding provided additional evidence that ECM fungi should not be screened in vitro to indicate the growth and P uptake of ECM fungus-root symbionts. All Suillus promoted plant growth and P uptake and four of them were more effective than the other nine. After transplanting to the field for five years, Suillus-inoculated plants performed similarly as in the nurseries, whereas only a few non-mycorrhizal plants survived and grew abnormally. The mycorrhizal plant performances in nurseries may be an indicator for selecting Suillus species effective to promote P. massoniana growth and P uptake at least in the early stages of afforestation in fields.