生物炭输入土壤后表层特性变化及其对磷吸附-解吸的影响机制

Phosphorus (P) is a major element causing the eutrophication in many freshwater and estuary coast ecosystems, while the environmental effects of biochar amendment become the hotspot in environmental science research. The mechanism of the effect of biochar amendment on the envrionmental behavors of P in soils is still unclear. Morphology analysis, chemical structure characteristics, element composition, functional group analysis of the biochar surface layer will be investigated during biochar incubation in soils. The contents and distribution of elements (P, Fe, Al, Mg and Ca) in surface layer of biochar will be studied during biochar incubation by element analyzer, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy - energy dispersive spectrometer (SEM-EDS), respectively. Cation exchange capacity (CEC), anion exchange capacity (AEC) and the zeta potential of biochar will be also analyzed. The effect of incubated biochar on the adsorption and desorption of P will be conducted employing with the batch experiment and the distribution of elements (P, Fe, Al, Mg and Ca) in surface layer of biochar will be also conducted after the adsorption and desorption of P. Based on elucidation of property and structure of the biochar surface layer and the distribution of P on biochar surface after P adsorption and desorption, the mechanism of the effect of biochar amendment on soil P availablity will be elucidated. The studied results will be helpful for assessing increasing soil nutrient retention and environmental effects dues to application of biochar.

磷是重要的生命元素和导致水体富营养化的关键元素，而生物炭环境效应是环境科学的研究热点。吸附-解吸是磷在土壤环境中重要的化学行为，而当前生物炭输入土壤后对磷的吸附-解吸机制尚不明确。本研究拟从生物炭输入土壤后形成新表层的视角，应用SEM-EDS和XPS方法分析生物炭表层形貌、化学结构、官能团和元素组成变化，并观测磷、铁、铝、镁和钙元素在生物炭表层微域分布特征差异，同时分析生物炭CEC、AEC和表面电荷量变化；观测生物炭对磷吸附-解吸后磷、铁、铝、镁和钙元素在生物炭表层微域分布特征；结合分析输入土壤后生物炭对磷吸附-解吸动力学特征的影响，探讨生物炭表层结构、官能团、元素组成和电荷量等特性与生物炭对磷吸附-解吸动力学特征间的联系，阐述输入土壤后生物炭固磷和释磷的机制。研究结果可为评估生物炭保肥效应和环境效应提供科学依据。

本项目研究了不同温度制备和洗涤处理的生物炭在不同水分条件下经6个周期共720天培养后表层性质和对磷的吸附-解吸特征；并研究了相同培养条件和培养周期添加生物炭的土壤对磷吸附-解吸特征和磷素组分特征。结果表明洗涤处理均显著降低培养前2种制备温度生物炭的对外源磷的吸附，增加了350℃生物炭对磷解吸率和降低了600℃生物炭对磷解吸率；生物炭制备温度和洗涤处理对添加生物炭土壤对外源磷吸附-解吸影响具有相似现象，但差异显著降低；培养240天内，添加生物炭降低土壤对外源磷吸附和增加对磷解吸，75%田间持水量培养下该现象相对于淹水条件和干湿交替表现更为强烈；样品采集时间和培养水分条件对添加生物炭土壤磷素组分影响大于生物炭添加与否、生物炭制备温度和洗涤处理的影响；样品采集时间和培养水分条件也是培养后生物炭对外源磷吸附-解吸特征变化的主要因素，而制备温度和洗涤处理的影响未表现出明显规律性；培养120天后，SEM分析表明600℃生物炭铁、铝和镁含量高于350℃生物炭，与不同温度制备生物炭对外源磷吸附-解吸特征相吻合。综上所述，培养时间和水分条件是影响培养后生物炭和添加生物炭土壤对外源磷吸附-解吸特征的主要因素。