Effects of atmospheric N sedimentation on growth and P efficiency of Pinus Massoniana mycorrhizal seedlings under low P stress

【Objectives】 The increased atmospheric N sedimentation in recent years has brought the increased N availability and N/P ratio in forest soils, which would impact growth and P efficiency of mycorrhizal symbiosis plant.【Methods】 Taking breeding population of Pinus massoniana as test materials, a pot experiment was conducted to simulate two P conditions, i. e. homogeneous low P availability vs. heterogeneous low P among soil layers, in combination with two N sedimentation levels on growth and P efficiency of Pinus massoniana mycorrhizal seedlings.【Results】 1) The effects of the simulated N sedimentation on growth of mycorrhizal seedlings are relevant to the soil P environment. Under the homogeneous low P condition, N sedimentation reduces the degree of mycorrhizal colonization and infection rates, and significantly increases growth and biomass of Pinus massoniana. Under the heterogeneous low P condition, the N deposition improves root infection by mycorrhizal fungi, and reduces the inhibitory effect of mycorrhizal symbiosis on growth of Pinus massoniana; 2) Under the homogeneous low P condition, the simulated N deposition significantly reduces the root growth of mycorrhizal seedlings, and increases the root APase activity and the secretion of organic acids, especially organic acids secretion (increased nearly three-fold). Correlation analysis shows that organic acid secretion contribution to the growth of mycorrhizal seedlings is significantly higher than APase activity. Under the heterogeneous low P condition, the development degree of the underlying roots of mycorrhizal is greater than that of the surface roots. The increased secretion of organic acids promotes growth of mycorrhizal seedlings; 3) Under different low P environments, the increased N sedimentation decreases the effectiveness of soil P. Mycorrhizal increase the P absorption and utilization and further promote growth of Pinus massoniana; 4) Significant variations among families in growth response of Pinus massoniana mycorrhizal seedlings to the simulated N deposition are observed.【Conclusion】 Atmospheric N sedimentation is able to improve the nutrition of N for mycorrhizal seedlings, and stimulate the degree of mycorrhizal colonization and infection rates, resulting in more absorption of P from soils and the increase of biomass. There are differences to the response of N sedimentation among the different mycorrhizal cultivars, screening of high mycorrhizal symbiosis ability of Pinus massoniana genotypes will be an efficient way to improve soil P biological utilization efficiency.