酸雨胁迫下南方红壤丘陵果园面源磷流失特征及响应机制

Due to the dual effects of soil erosion and acid rain stress, the loss of non-point source phosphorus in the south hilly red soil orchard of China leads to a greater risk of eutrophication of the receiving water. At present, the research on the effect of acid rain deposition on the phosphorus characteristics of red soil is mostly from the perspective of plant nutrition, but the understanding of the characteristics and transformation mechanism of phosphorus in agricultural non-point source runoff in red soil hilly region under acid rain stress is insufficient. In this study, the typical representative of the orchard in the red soil hilly region, the Gannan Navel Orange Orchard, was selected as the research object. The field long-term positioning observation experiment, field in-situ simulation experiment, indoor leaching experiment and adsorption\desorption experiment were used to collect data, and the structural equation model was used for data analysis. The microscopic characterization methods such as SEM, FT-IR and XRD were used to analyze the spatiotemporal variation characteristics of the loss of phosphorus under different acid rain erosion and the threshold effect of acidity change response, and the rhizosphere of navel orange under the change of rainfall acidity was studied to reveal the microscopic mechanism of rainfall acidity change affecting phosphorus form transformation in runoff. This study might provide theoretical and practical basises for the prevention of non-point source pollution in the southern China hilly red soil orchard under the acid rain erosion.

由于受土壤侵蚀和酸雨胁迫的双重影响，我国南方红壤丘陵区果园面源磷流失导致受纳水体富营养化的风险较大。目前，关于酸雨沉降影响红壤磷特征的研究多从植物营养学的角度出发，而对酸雨胁迫下红壤丘陵区农业面源径流中磷赋存形态特征及转化机制认识不足。本研究选取红壤丘陵区果园典型代表——赣南脐橙园为研究对象，综合应用野外长期定位观测试验、野外原位模拟试验、室内淋溶试验和吸附解吸实验等观测方法采集数据，利用结构方程模型等数学分析方法进行数据分析，并结合SEM、FT-IR、XRD等微观表征手段，分析探究降雨酸度变化对土壤、径流磷赋存形态特征影响的阈值效应，发掘降雨酸度变化下脐橙根际效应特征及对面源磷流失的影响规律，揭示降雨酸度变化影响径流中磷形态转化的微观机理。该研究可为防治南方红壤丘陵区果园酸雨侵蚀下面源污染问题奠定理论基础。

酸雨是全球性的环境问题之一，其长期沉降会影响土壤中磷素转化过程并导致次生面源污染问题。以脐橙种植为主要经济支柱产业的赣南地区是我国酸雨与酸性土壤重叠分布的生态敏感区，长期过量施肥导致土壤中累积了大量的磷素。因此，研究酸雨胁迫下南方丘陵区脐橙园土壤中磷流失特征及对降雨酸度变化的响应，对于脐橙产业绿色发展和生态环境保护有重要意义。本项目采用野外调查采样和室内模拟酸雨淋溶实验等手段，通过采集脐橙根区和非根区土壤，设置不同pH梯度的酸雨淋溶实验，结合土壤理化性状分析和数理解析模型等手段，主要研究了不同酸雨处理下脐橙根区和非根区分层土壤磷素流失量、磷素有效性、磷素潜在流失风险及背后的影响机制。主要研究结论如下：（1）在不同强度酸雨作用下，从红壤中溶出到滤液中的总磷、溶解态总磷和溶解态活性磷均表现出根区内大于根区外的相同规律，即靠近根区的土壤在酸雨作用下磷流失量更大，且在酸雨pH为4.5时，靠近根区的土壤中流失的总磷和溶解态总磷均为最大，这可能是受到脐橙园日常管理的影响。（2）不同pH酸雨淋溶之后，靠近根区的表层土和深层土的有效磷含量与淋溶前相比发生了相反的变化，变化情况在各pH处理下几乎一致，即表层土中有效磷含量有较大幅度增加，深层土中有效磷含量略有下降。对于非根区土壤，表层和深层土中有效磷含量与淋溶前相比没有太大差别。这表明酸雨沉降对磷素有效性的影响是多种因素协同作用的结果。（3）当经过pH为2.5的强酸雨淋溶之后，脐橙根区表层土壤中CaCl2-P含量最高，深层土壤中CaCl2-P含量在各pH下无显著性差别。无论是根区还是非根区土壤，经过酸雨淋溶后的磷吸持指数（PSI）和磷吸附饱和度（DPS）值均超出环境阈值，且非根区土壤DPS值更高，表明其流失风险更高。本研究揭示了酸雨胁迫下脐橙园土壤中磷素流失特征及其有效性的变化规律，评价了酸雨沉降后土壤潜在磷素流失风险，可为指导脐橙园日常管理和降低酸雨危害奠定一定的理论基础。