典型区域大气氮沉降对土壤镉活化及作物镉累积的影响研究

Soil cadmium (Cd) activation is an important limiting factor in the production safety in a high-risk Cd agricultural field. Atmospheric nitrogen deposition and its composition is one of the important elements in the acceleration of the progress of soil acidification, soil Cd activation and crop Cd accumulation. Based on atmospheric nitrogen deposition data obtained from the remediation technology demonstration base of heavy metal contaminated field around a well-known copper flash smelter in Guixi, Jiangxi province in the applicant’s program funded by the National Natural Science Found of China (41201206), this research is proposed to be conducted by 15N isotopic tracer technique in a typical Cd high-risk field. During 2016-2019, the mechanisms through which increasing fluxes and changing compositions of atmospheric nitrogen deposition affect soil Cd activation will be studied by establishing correlations between the nitrogen in atmospheric deposition and solution Cd and soil Cd forms in different depths of undisturbed loessal soil cores under control laboratory conditions. The input and its pathways contributions of atmospheric nitrogen deposition into soil to soil Cd activation and crop Cd accumulation are identified by pot-experiment and field experiment. And it is also ascertained how atmospheric nitrogen deposition affect crop Cd absorption. Furthermore, the atmospheric nitrogen deposition and its composition, namely, the threshold of atmospheric nitrogen deposition affects soil Cd activation and crop Cd accumulation will be determined by a multiple index synthetical evaluation including deposition nitrogen marked 15N, soil Cd content, soil organisms and Cd content in edible parts. These results will provide an important technology back-up for preventing and controlling atmospheric nitrogen deposition and crop production safety, promote awareness on atmospheric nitrogen deposition and its ecologic effect in fields, and strengthen the inter-disciplinary research between atmospheric and soil sciences.

土壤镉活化是镉高风险区农田安全生产的重要限制因子，大气氮沉降增加及组分变化是导致农田土壤酸化进而加速土壤镉活化及促进作物镉吸收累积的重要因素。本项目依托贵溪镉铜污染土壤修复示范基地，以申请者10多年区域氮沉降观测数据及国家自然科学基金青年项目结果（影响土壤酸化的大气氮沉降阈值）为依据，以氮同位素示踪为关键技术，通过原状土柱培育实验，建立氮沉降量增加及组分变化与不同深度土壤溶液镉浓度及土壤镉形态间的联系，明确氮沉降增加及组分变化对区域农田土壤镉活化动态过程和机制；通过盆栽实验和田间原位试验，解析氮沉降及其进入农田土壤的不同途径对土壤镉活化及水稻/油菜镉累积的贡献及机制，进行沉降氮、土壤镉活化、土壤生物、作物镉累积等多指标评价，确定影响区域农田土壤镉活化及作物安全生产的氮沉降量及组分（阈值）。研究结果为镉高风险农田区氮沉降有效控制及农田粮食安全生产提供科学依据，深化大气学科与土壤学科间交叉研究

土壤镉活化是镉高风险区农田安全生产的重要限制因子，大气氮沉降增加及组分变化是导致农田土壤酸化进而加速土壤镉活化及促进作物镉吸收的重要因素。本项目依托贵溪镉铜污染土壤修复示范基地，以申请者10多年区域氮沉降观测数据及国家自然科学基金青年项目结果（影响土壤酸化的大气氮沉降阈值）为依据，以氮同位素示踪为关键技术，通过室内原状土柱培育、水稻盆栽和田间试验，探讨经过冠层（叶面）和不经过冠层（土壤）模拟沉降氮量及组分变化对土壤镉活化及米镉累积的贡献、影响机制及阈值。结果发现，相对无氮肥处理，肥料氮降低了土壤全镉含量，提升了土壤镉在糙米中的累积，增幅为26.0%-134.3%；而相对肥料氮，沉降氮增加了水稻产量，降低了土壤镉在糙米中的累积，但是随着沉降氮增加或组分铵的增加，米镉累积增加。与土壤模拟相比，叶面模拟特别是组分沉降组，降低了米镉的累积，平均降幅为10.7%-15.1%。可能的原因在于：1）叶面模拟增加的氮显著影响了土壤微生物量氮，增加了土壤镉由根-茎叶-籽粒的转运，而土壤模拟的则显著增加了镉由茎叶-谷壳的转运；叶面模拟铵组分的增加，显著增加了茎叶-谷壳间镉的转运，而土壤模拟的则降低了土壤微生物量和茎叶-谷壳间镉的转运。2）无作物时，沉降氮量和组分进入土壤后，铵氮转化为硝氮，影响土壤Al、Cu、BC等溶出过程中，活化土壤镉；作物生长期间，叶面模拟氮被冠层截流，未截流部分通过茎叶导流主要作用于根际土壤。此外，综合分析发现，影响农田土壤镉活化及作物安全生产的氮沉降量及组分的阈值分别为60kgN/ha/yr和铵硝比1：1。研究结果为区域氮沉降控制及镉高风险区农田粮食安全生产提供科学依据，深化大气与土壤学科间交叉研究。