Abstract: The enhanced atmospheric N deposition in recent years has brought the increases in N availability and N/P ratio in forest soils, which would impact the growth and productivity of plants. Pinus massoniana, Cunninghamia lanceolata and Schima superba are the main afforestation tree species with different growth and biological characteristics in southern China. Taking seedlings of the three tree species as test materials, a pot experiment was conducted to simulate low P soil conditions in combination with two N deposition levels, to study interspecific differences in growth and adaptation mechanism to low P stress under N addition. The results showed that: 1) The aboveground part growth of P. massoniana and S. superba was promoted by simulated N deposition, but their root growth and root biomass accumulation were inhibited. The whole plant biomass of P. massoniana and S. superba were not significantly changed under simulated N deposition. The aboveground part and root growth of C. lanceolata were severely inhibited by simulated N deposition, so its whole plant biomass was significantly decreased; 2) The degree of low P stress of the three tree species seedlings was increased by simulated N deposition, which led to the increase of root secreted APase activity and organic acids. The increased degrees of total amount of root secretion of P. massoniana and S. superba were greater than that of C. lanceolata; 3) Simulated N deposition increased leaf N contents of the three tree species, but decreased their leaf P contents, thus increased their leaf N/P ratios. The increased degree of leaf N/P of C. lanceolata was the maximum, and that of P. massoniana was the minimum. The rapid increase of leaf N/P ratio of C. lanceolata resulted in the relative scarcity of its leaf P content and imbalance of leaf N and P nutrients, finally influenced C. lanceolata leaf photosynthesis. The increased degree of leaf N/P ratios of P. massoniana and S. superba were relatively small. The increase of leaf N contents of P. massoniana and S. superba promoted their leaf net photosynthetic rates; 4) Under simulated N deposition, the acidification of surface soil of P. massoniana and S. superba was greater than that of C. lanceolata, while soil hydrolytic N contents of P. massoniana and C. lanceolata were increased as compared to S. superba due to greater N absorption and N leaching of surface soil of S. superba, and stronger surface soil N leaching of P. massoniana compared to C. lanceolata. In addition, soil available P contents of the three species were all decreased, and they were higher in the topsoil than in the subsoil under simulated N deposition.

Key words: flowering stage, drought stress, carbon metabolism., α-naphthaleneacetic acid (NAA), soybean