酸化背景下海南富硒水耕人为土硒形态分布和转化特征

The content of selenium (Se) in rice is one of the determinant factors of Se intake of physical body. The areas in shortage of Se share the proportion of 72% of the total national area, which explains the reason why the content of Se in human body is below the critical point standard in some areas. The coverage of Se-rich area reaches appropriately 9500 km2, or 27.5% of total area in Hainan Island and Hainan has its weather conditions favorable for growth of Se-rich rice crops. For recent years, the soil pH values have been reducing. Obviously, the reduction of soil Se availability as a result of acidification has become the bottle neck of Se-intakes of rice crops in Se-rich area in Hainan Island. Taking the acid igneous derived Se-rich stagnic anthrosols as the case, this program, on the basis of systematic observation of soils property, chemical composition and soil Se fractionation distribution, in conjuncture of undisturbed soil column leaching experiments, has analyzed the effects of continuous reduction of soil pH on the distribution of Se fractionation and has explored the inner mechanism. The application of stagnic anthrosols with different pH values to represent the degrees of acidification, and study of long-span acidification process on distribution and transformation of soil Se fractionation using quantitatitively specified diagnostic horizon (anthrostagnic epipedon) as sampling units, can provide basis for finding the channels for increase in soil Se availability under context of soil acidification.

大米硒含量的高低是影响人体硒摄入量的关键因素之一。我国缺硒土壤面积约占国土面积的72%，导致部分地区居民的硒摄入量偏低。海南岛集中分布的富硒土壤约为9500km2，且具有得天独厚发展富硒水稻的气候条件。近年来，海南土壤pH持续降低，由土壤酸化导致的水耕人为土的土壤硒有效性降低已成为富硒区水稻硒吸收的限制性因素。本申请项目针对海南富硒区水耕人为土持续而缓慢酸化这一现象，以分布最广泛的酸性火成岩母质发育的水耕人为土为研究对象，在系统观测其水耕表层的土壤基本性质、化学组成、土壤硒形态基础上，结合原状土柱的淋溶实验，分析土壤pH持续降低对其土壤硒形态分布及转化的影响并探讨其内在机制。以不同pH的水耕人为土来代表其持续酸化过程的不同酸化程度，并采用定量规定的诊断层(水耕表层)为取样单元来进行较长时间尺度的酸化过程对土壤硒形态及转化特征研究，可为酸化背景下提高土壤硒有效性的途径探索提供基础。

海南土壤pH持续降低，由土壤酸化导致的水耕人为土的土壤硒有效性降低已成为富硒区水稻硒吸收的限制性因素。针对海南富硒区水耕人为土持续而缓慢酸化这一现象，以分布最广泛的酸性火成岩母质发育的水耕人为土为研究对象，在系统观测其水耕表层的土壤基本性质、化学组成、土壤硒形态基础上，结合原状土柱的淋溶实验，分析土壤pH持续降低对其土壤硒形态分布及转化的影响。结果表明，（1）海南富硒区土壤pH总体为酸性，其土壤pH均值为5.0，水耕人为土的土壤硒含量为0.373 mg/kg，区内水耕人为土的土壤硒含量空间分布范围较宽，并且不同层次的硒含量显著相关；（2）土壤硒形态主要以残渣态和有机结合态为主，此2种形态所占比例之和为89.84%，碳酸盐结合态和可交换态的硒含量比例最低，其含量比例分别为1.64%和2.17%；（3）土壤pH主要影响土壤最易迁移的可溶态（可交换态）硒形态比例，土壤酸化会显著降低该部分硒的比例，导致土壤硒的生物有效性降低，并且在土壤pH高于5.5时，水耕人为土的水耕表层土壤交换态硒含量随着土壤pH的降低显著下降，当土壤pH低于5.5时，其含量比例随土壤pH降低的下降趋势有所减缓；（4）低pH淋溶液淋溶后，其土壤可交换态硒在土柱中表现出向下迁移，其含量比例在土柱下部的比例有所提高。