ObjectivesThis paper focused on how nitrogen (N) deposition impacts growth of different clones of Pinus massoniana under phosphorus (P) deficient soils. The results could formulate the breeding strategy of P. massoniana under N deposition.

MethodsTaking five representative clones of P. massoniana which were cultivated for one year from full-sib progenies as test materials, a pot experiment was conducted to investigate variations of growth, root morphology and N/P efficiency in response to simulated N deposition under both homogeneous low P stress (low P level in all soil layers) and heterogeneous low P stress (high P level in the topsoil and low P level in the bottom soil), respectively.

Results1) Large variations were detected in seedling height and dry matter accumulation among the P. massoniana clones under both the homogeneous and heterogeneous low P stress, moreover, significant clone and N interaction effect was detected in the homogeneous P deficiency. 2) The adaptive mechanism to the N deposition was different under different types of low soil phosphorus. Under the homogeneous low-P condition, the adaptive responses of root length (RL), root surface area (RSA) and APase activity were present in clones with strong growth vigor by simulated N deposition such as "33-4" and "19-5", while it was not observed in clones with weak growth vigor. Meanwhile, the correlation between dry matter accumulation and APase activity was enhanced by the simulated N deposition. Under the heterogeneous low-P condition, RL and RSA were significantly improved by the simulated N deposition, while the special root length (SRL) was decreased, thus having the greater ability for nutrition absorption and having lower consumption. 3) The P absorption efficiency (PAE) of P. massoniana clones was significantly affected by the nitrogen deposition and showed a significant positive correlation with nitrogen absorption efficiency (NAE) under different N and P conditions (P < 0.01). It indicated that the nitrogen deposition could increase the P mobilization and uptake of P. massoniana clones under the P deficiency. In contrast, there was no significant effect on P use efficiency (PUE). 4) The amplitudes of variations of dry matter accumulation, RL, RSA and APase were wider and the repeatability (R) of these traits exceeded 0.75 (P < 0.05), respectively.

ConclusionsOur results revealed the possibility of selecting clones with optimal root morphology and active APase was increased for wood production of P. massoniana under the low-P and high-N conditions.