近年来大气氮(N)沉降的增加, 导致森林土壤中有效N含量增加、N:P发生改变, 研究N沉降对低磷(P)胁迫下林木根系分泌和P效率的影响具有重要意义。该文以马尾松(Pinus massoniana)家系作为试验材料, 设置模拟N沉降与同质低P (介质表层与深层均缺P)、异质低P (介质表层P丰富、深层缺P)耦合的二年生盆栽实验, 系统研究了模拟N沉降对低P胁迫下马尾松根系分泌性酸性磷酸酶(APase)活性、有机酸分泌以及P效率的影响。结果表明: (1)同质低P和异质低P下, 模拟N沉降均显著提高了植株N:P化学计量比、增加了P素的相对匮乏程度, 从而诱导根系增加了APase和有机酸的分泌, 而同质低P比异质低P下增加幅度更大, 其中有机酸分泌均与马尾松生长呈正相关关系, 而APase活性与P效率相关性较小; (2)同质低P下, N沉降虽然增加了根系分泌, 但未提高马尾松P素吸收和生长量, 其原因在于, 同质低P下植株N:P过高, 因而植株对N沉降敏感性低; 在异质低P下, 植株表现为N、P共同限制, 因而对N敏感性较高, N沉降增加了根系分泌, 同时提高了N和P吸收效率、增加了生物量; (3)马尾松根系分泌对模拟N沉降的响应存在较大的家系差异。同质低P下, 家系71×20的有机酸分泌和生物量对N沉降的响应幅度较大; 异质低P下, 家系36×29、71×20和73×23对N沉降的响应幅度较大。

Aims Atmospheric nitrogen (N) deposition largely increased in recent years, resulting in an increased N availability and N:P ratio in forest soils. The objective of this study was to determine the effects of simulated N deposition on P efficiency and root secreted acid phosphatase and organic acids in Pinus massoniana under low P stress.
Methods Treatments included two P conditions, i.e. homogeneous low P availability vs. heterogeneous low P availability among soil layers, in combination with two N deposition levels in a two-year pot experiment. Four full-sib progenies collected from the second-generation breeding population of P. massoniana were used.
Important findings Under both the homogeneous and heterogeneous low P conditions, N:P stoichiometric ratio in P. massonianaseedlings was significantly increased by simulated nitrogen deposition, which stimulated the amount of root acid phosphatase and organic acid secretion. The amount of root exudates was higher under the homogeneous low P condition than under the heterogeneous low P condition. The level of root secreted organic acids was significantly correlated with the growth in P. massonianaseedlings. Under the homogeneous low P condition, P acquisition efficiency and biomass in P. massonianaseedlings were not affected by simulated N deposition, mainly due to the high N:P ratios and low sensitivity to N addition; whereas under the heterogeneous low P condition, greater growth response to N addition was observed due to the higher N:P ratio. An increased root secretion of organic acids contributed to enhancement of P acquisition efficiency and growth under the high N deposition level. Significant variations among families in growth response to the simulated N deposition were observed. Under the homogeneous low P condition, seedlings in the family 71 × 20 were found to respond to the simulated N deposition with increased root organic acids and biomass. Under the heterogeneous low P condition, seedlings in the families of 36 × 29, 71 × 20, and 73 × 23 responded to the simulated N addition with increased biomass and root secretion.