氮添加下草地植物根际磷酸酶-有机酸对土壤磷活化及植物磷利用能力的影响

Rhizosphere soil phosphorus (P) composition is the primary source of P for plants. Nitrogen (N) addition can promote plants to secrete more phosphatases and organic acids, which may alter rhizosphere soil organic P and inorganic P composition and concentrations and thus affect their availability for plant uptake. However, the systematic study about this remains poorly concerned. This project plans to select five dominant species in meadow steppe of Inner Mongolia as the study object. The program intents to investigate the variation of rhizosphere soil organic P composition and concentrations determined by solution 31P nuclear magnetic resonance techniques with increasing N addition as well as their relationship with phosphatases activities, and analyze the variation of rhizosphere low molecular weight organic acids types and quantities with increasing N addition as well as their mobilization effect on soil inorganic P composition, so as to ascertain which P composition has greater contribution to plants, clarify the effect of grassland plant rhizosphere phosphatases-organic acids on soil P mobilization under N addition; and on this basis to illustrate the utilization difference of different plants to different P composition, explore the variation mechanism of different plants relative biomass with increasing N addition amount and their relation to the variation of P composition in bulk soil. The study can provide us a scientific basis for predicting the effect of N deposition on meadow steppe soil P composition, and establishing grassland operation and management under the background of global change.

根际土壤磷组分是植物所需磷素的主要来源。氮添加会促进植物磷酸酶和有机酸分泌的增加，使植物根际土壤有机磷和无机磷组分及含量发生改变，进而影响植物的磷素养分供应特性，但目前尚缺乏此方面的系统研究。本项目拟以内蒙古草甸草原五种优势植物为研究对象，采用液体31P核磁共振等技术，研究各植物根际土壤有机磷组分在氮素添加梯度下的变化特征及其与磷酸酶活性的关系，分析根际低分子量有机酸随施氮量增加的动态变化及其分泌后对土壤无机磷组分的活化特征，以探明不同施氮水平下对各植物有较大贡献的磷源，解析氮添加下草地植物根际磷酸酶-有机酸对土壤磷活化的影响机理；并在此基础上阐明氮添加下草地不同植物对土壤中不同形态磷素利用的差异，探讨具有不同磷素利用能力的植物相对生物量随施氮量增加的变化及其与土壤磷组分变化的关系，从而为预测未来氮沉降增加对我国草甸草原土壤磷组分的影响，以及全球变化背景下制定草地经营和管理提供科学依据。

本项目以内蒙古草甸草原氮素添加试验平台优势植物为供试对象，研究了植物根际土壤有机磷、无机磷组分在氮素添加梯度下（0、2.5、5.0和10.0 g N m-2 a-1）的变化特征及其与磷酸酶活性的关系，探明了不同施氮水平下对各植物有较大贡献的磷源，并阐明了氮添加下草地不同植物对土壤中不同形态磷素利用的差异。结果发现在N5处理下羊草主要是通过增加根际土壤磷酸酶活性促进中等活性有机磷组分的矿化以及促进中等活性无机磷组分的活化来满足对磷的需要，而在N10处理下，羊草主要是通过对中等活性和高稳定态无机磷组分的活化来满足对磷的需要。与羊草不同，氮添加下针茅主要是利用活性有机磷组分来满足对磷的需要，并且其对活性有机磷组分的利用不受氮添加量增加的影响。此外，氮添加虽然也导致了针茅根际土壤的酸化，但是这种酸化却没有导致针茅根际土壤难溶性无机磷组分的活化，这可能与针茅和羊草根系分泌的低分子量有机酸种类不同有关。总的来说，本研究结果增加了我们对未来氮沉降增加背景下草地优势植物对磷利用机制的理解，同时有助于为在全球变化背景下制定草地经营和管理措施提供科学依据。