杨树响应土壤酚酸胁迫的氮同化机理研究

The accumulation of phenolic acids in the soil is one of the main causes of the obstacle of continuous cropping of poplar. Phenolic acids could reduce the absorption of mineral elements by Poplar, especially nitrogen, which seriously restrict the productivity of Poplar plantation. Nitrate nitrogen and ammonium nitrogen in the soil needs to be assimilated by the plant in order to be used. However, it is not clear about the metabolism mechanism of the effect of soil phenolic acid stress on the assimilation process. Therefore, the existing research on revealing the effects of soil phenolic acid on poplar plantation nitrogen nutrition is limited. In this project, the I-107 poplar (Populus×euramericana ‘Neva’) is used as the experimental material, and the content of phenolic acids in the rhizosphere soil of the second generation poplar plantation is reference. In order to reveal the effect of phenolic acids on the absorption and assimilation of nitrate nitrogen and ammonium nitrogen, 7 kinds of soil phenolic acid gradients are setup to study the mechanism of the effect of soil phenolic acid stress on poplar nitrogen assimilation and to clarify the relationship between the assimilation process and photosynthetic productivity of poplar under phenolic acid stress. The results will provide theoretical basis for solving the continuous cropping obstacle of poplar and improving the productivity of poplar.

土壤中累积的酚酸类物质是引起杨树人工林连作障碍的主要原因之一。酚酸类物质能降低杨树对氮元素的吸收，严重制约了杨树的生产力。土壤中的硝态氮和铵态氮需要经过植物的同化过程才能被利用。而有关土壤酚酸胁迫对杨树氮同化过程的影响机制尚不清楚，致使现有研究不能全面揭示土壤酚酸导致杨树氮素匮乏的氮代谢机制。因此，本项目以I-107杨树（Populus×euramericana‘Neva’）作为试验材料，以二代杨树人工林根际土壤中的酚酸含量为参考，设置7种土壤酚酸浓度，研究不同土壤酚酸胁迫对杨树氮同化过程的影响机制，揭示土壤酚酸类物质对杨树硝态氮和铵态氮的吸收、同化途径的影响；明确土壤酚酸胁迫下，杨树氮同化过程和光合生产力的关系；为杨树人工林克服连作障碍，提高生产力提供理论基础。

杨树人工林连作障碍与土壤中累积的酚酸类物质有密切的关系，酚酸类物质能降低杨树氮同化作用，限制杨树光合生产力。本研究探讨了土壤酚酸胁迫对杨树氮素吸收和同化的影响机制，明确了土壤酚酸胁迫下杨树光合生产力和氮同化的关系。研究发现，①杨树为喜硝植物，酚酸可抑制杨树根系硝态氮转运蛋白的表达，导致杨树吸收硝态氮的过程受阻；同时酚酸还降低了硝态氮和铵态氮同化蛋白组含量，引起某些氮代谢产物积累。②酚酸降低了杨树根、茎、叶硝酸还原酶(NR)和谷氨酰合成酶(GS)的活性，导致杨树硝态氮的无机同化过程受阻；酚酸影响了杨树根、茎、叶GS、谷氨酸合酶（GOGAT）、天冬氨酸转氨酶(AST)、丙氨酸转氨酶(ALT)的活性，导致杨树铵态氮的有机同化过程受阻。③酚酸对杨树光合作用具有显著抑制作用，表现为叶片净光合速率(Pn)、最大光合速率(Pnmax)、光合量子效率(Φ)、PSII最大和实际光化学效率(Fv/Fm和ФPSII)等都明显下降；酚酸导致PSⅡ反应中心电子传递受阻，氧化状态的QA含量减少，稳定的还原型QA积累，光化学效率降低，过多光能以热耗散(NPQ)的形式散失；随着酚酸浓度的升高，限制杨树光合作用因素转变，在低酚酸胁迫下，PSⅡ反应中心暂时失活，以气孔限制因素为主；在高酚酸胁迫下，PSⅡ反应中心受破坏，发生光抑制，以非气孔限制因素为主。总体来看，土壤酚酸胁迫限制杨树根系硝态氮转运蛋白的表达，致使根系吸收硝态氮能力下降，影响杨树根、茎、叶氮同化酶活性及硝态氮含量，限制杨树叶片中各种蛋白质、核酸、叶绿素等含氮产物的生成，导致杨树光合效率下降，生产力低下。研究结果可为连作杨树人工林生产力衰退的氮同化机理构建提供理论基础。