大气氮沉降量及其组分变化对红壤旱地土壤酸化过程的影响

Atmospheric nitrogen deposition (AND) is one of the important factors influencing soil acidification. Globally, human activities have driven a rapid increase in AND and associated variations in its composition in recent years, resulting in an alteration in the mechanism of soil acidification, and further affecting the structure and function of the soil ecosystem. So far few quantitative studies and no long-term experiments have been reported on the impacts of AND on soil acidification, especially in farmlands. The mechanism of variations inAND component is poorly understood. Based on the AND data from long-term experiments in a red soil farmland area, this research is proposed to be conducted by 15N isotopic tracer technique in a typical red soil upland (Red Soil Ecological Experiment Station, Chinese Academy of Sciences). During the period 2013-2015, the contributions of AND on soil acidification in relation to applied nitrogen fertilizer will be quantified and associated acidification rates will be estimated in an in situ field experiment. In addition, the mechanisms through which increasing fluxes and changing NH4+-N/NO3- - N rates affect soil acidification will be studied by establishing inner relations between the nitrogen in atmospheric deposition and H+,Al forms, base cations (BCs) and nitrogen forms in different depths of undisturbed loessal soil cores under laboratory conditions. Then the effects of variations in AND fluxes and its components on soil acidification in the upland will be discovered by the two experiments. Results above could provide scientific basis for taking measure against red soil acidification and assessing the health of red soil agro-ecosystem, as well as sustainable agricultural development.

大气氮沉降是影响土壤酸化的重要因素之一。然而目前尚缺少大气氮沉降快速增加及其组分变化过程中对农田土壤酸化程度的定量化和长期定位研究，大气氮沉降及其组分变化对农田土壤酸化过程的影响机理亦不明晰。本项目依托中国科学院红壤生态实验站红壤旱地长期试验基地，以农田长期定位观测的大气氮沉降数据为依据，以氮同位素示踪为关键技术，田间原位试验研究大气氮沉降在红壤旱地土壤酸化过程中的关键作用，定量大气氮沉降对土壤酸化的相对贡献和速率；同时，通过原状土柱室内淋洗试验，建立大气沉降氮与土柱不同深度土壤及土壤溶液中H+、Al形态、BCs和氮形态的联系，明确大气氮沉降量增加及NH4+-N/NO3- - N比变化对红壤旱地土壤酸化过程的影响机制。最后，田间原位试验和室内培育试验相互验证，解析大气氮沉降量及其组分变化对红壤旱地土壤酸化过程的影响。研究结果，有望为治理红壤旱地土壤酸化及评价红壤旱地生态环境效益提供科学依据。

大气氮沉降是影响土壤酸化的重要因素之一。近年来，人类活动引起大气氮沉降的快速增加及组分变化，必然导致土壤酸化过程及机理的改变，进而影响土壤生态系统结构和功能的变化。然而，迄今为止，尚缺少大气氮沉降对土壤特别是农田土壤酸化程度的定量化研究和长期定位研究，大气氮沉降组分变化对农田土壤酸化过程的影响机理仍不明晰。本项目依托中国科学院红壤生态实验站，在农田长期定位观测大气氮沉降的数据基础上，选择第四纪红黏土发育的典型红壤旱地，借助氮同位素示踪技术，建立了氮沉降模拟长期定位田间定位试验，发现了单位尿素氮和沉降氮的土壤年酸化速率为0.010和0.008-0.046 H+ kmol/(ha•kgN)，沉降氮相对尿素氮对土壤年酸化速率的贡献为0.78%-520.01%；当沉降组分中氨硝比由1增至4时，沉降氮相对肥料氮对土壤酸化速率的贡献为由37.05%增加到671.85%。通过室内重建土柱培养试验，发现Al3+和Ca2+含量是沉降氮作用下控制土壤加速酸化的关键因子。结合作物和土壤信息，发现影响区域土壤酸化的氮沉降阈值为60kgN/ha和氨硝比2:1。以上结果，可为治理红壤旱地土壤酸化措施的制定及红壤旱地生态环境效益的评价提供科学依据和参考。