磷酸盐氧同位素技术在土壤磷循环中的应用

磷是土壤生态系统中的重要组成元素,开展土壤磷循环研究对提高磷肥利用效率和降低磷的生态环境风险具有重要意义。磷酸盐氧同位素技术已经被证明是一种示踪环境中磷生物地球化学行为的有效方法。本文系统综述了磷酸盐氧同位素技术的研究进展和未来发展方向。详细介绍了磷酸盐氧同位素的技术原理、样品处理和测定方法;阐述了无机磷和有机磷的氧同位素特征及时空分布特征;从评估土壤磷微生物利用状况和示踪土壤磷循环两个方面探讨了磷酸盐氧同位素技术在土壤磷循环研究中的应用前景,分析了磷来源、环境条件、生物活动和样品前处理过程对土壤磷酸盐氧同位素特征的影响,最后展望了该技术未来的研究方向。以期为磷酸盐氧同位素技术在土壤学和环境科学领域的发展和应用提供新的视角和科学指导。     

盐酸提取的土壤无机磷酸盐中氧同位素分析

【目的】 磷酸盐中的P—O键在自然条件下稳定。磷酸盐中最重和最轻氧同位素 (18O和16O) 的比值,即δ18O-P,可以表征生态系统中磷的转化。由盐酸提取的土壤无机磷 (HCl-Pi) 难以被作物直接吸收利用,但在根系分泌物和土壤微生物的作用下,可转化为有效形态。建立δ18O-P测定方法可以为示踪土壤中HCl-Pi的循环、转化过程提供基础。 【方法】 本文选择潮土和黑土长期定位试验中NK (不施磷肥)、NPK (施用无机磷肥)、NPKM (施用无机磷肥 + 粪肥)、NPKS (NPK + 秸秆还田) 4个施肥处理土样,按照土壤磷化学分级方法逐级浸提,收集1 mol/L HCl浸提液,通过磷钼酸铵沉淀、磷酸铵镁沉淀等过程分离纯化其中磷酸盐,获得磷酸银沉淀,利用元素分析仪稳定性同位素比例质谱仪测定氧同位素组成δ18O-P值。 【结果】 磷酸盐经过分离纯化沉淀3个关键过程,回收率均达到92%以上,损失较少,未出现氧同位素分馏。X射线衍射仪和氧含量测定表明,实验获取磷酸银样品纯度较高。潮土与黑土各处理中HCl-Pi的δ18O-P值分别为17.21‰ 和17.90‰ (NK)、17.25‰ 和17.61‰ (NPK)、17.62‰和17.87‰ (NPKM)、17.95‰ 和17.70‰ (NPKS),4个施肥处理之间土壤δ18O-P值无显著差异。 【结论】 本研究建立盐酸提取土壤磷酸盐中氧同位素分析测定方法,可为农田土壤中磷的循环转化及其溯源研究提供技术支撑。      

磷同位素示踪技术在生态与资源环境科学研究中的新进展

同位素示踪技术广泛应用于土壤-植物-动物生产-环境系统中磷的活化、形态转化、吸收利用、迁移规律等方面的研究,极大地推动了生态、资源环境科学的发展。本文介绍了几种利用同位素示踪技术研究磷在土壤-植物-动物生产-环境系统中动态行为方法的进展,其中放射性同位素磷稀释技术已应用于盆栽和大田试验的研究,主要包括直接标记水溶性磷肥磷或土壤易交换性磷、间接标记难溶性磷和难溶性磷酸盐通过中子堆照活化3种方法。磷酸盐中氧稳定性同位素示踪技术是新近发展起来、并不断完善的方法,为磷从农田到水体环境迁移过程的定量研究提供了可能,但该技术在土壤-植物系统中的应用还存在一定的局限性,有待技术与理论上的进一步完善。核磁共振技术为生态系统中磷形态变化,尤其是有机磷形态的定性与定量研究提供新的研究手段。     

草酸青霉菌HB1溶磷能力及作用机制

一些功能微生物具有溶磷能力且同一菌株对不同难溶性磷酸盐的溶解能力存在差异。该研究以草酸青霉菌HB1为研究对象,通过固体平板培养试验、摇瓶培养试验和土壤培养试验系统研究了不同磷源(磷酸钙、磷矿粉、磷酸铁、磷酸铝)与氮源(铵态氮、硝态氮)供应下HB1溶磷能力及其作用机制,并验证了其在高、低不同磷水平土壤中的溶磷能力。结果表明,接种HB1的不同磷源培养基上均有溶磷圈出现,根据溶磷圈直径/菌落直径初步确定HB1溶解磷酸钙的能力较强;摇瓶培养试验表明供试磷源为磷酸钙、磷酸铁时HB1发酵液中有效磷含量为884、265 mg/L(铵态氮),或945、206 mg/L(硝态氮),其溶磷能力不受氮源形态影响;磷矿粉为磷源时,HB1发酵液中有效磷含量可达199 mg/L(供应铵态氮),为硝态氮供应的7.14倍;而磷酸铝为磷源时,HB1发酵液中有效磷含量为120 mg/L(供应硝态氮),为铵态氮供应的3.29倍;此外,供应铵态氮条件下,HB1对难溶性磷酸盐的溶解能力与介质中pH值呈显著的负相关关系。HB1接种于不同磷水平的土壤中培养21 d,在低磷和高磷土壤中HB1均能有效定殖且增加了土壤有效磷含量,比不接菌对照分别增加45.00%和14.17%。综上,草酸青霉菌HB1对磷酸钙和磷矿粉的溶磷效果较好,并通过分泌氢质子酸解含磷矿物实现溶磷作用,且HB1在低磷土壤中溶磷能力较强。     

石灰性土壤与磷酸盐的反应及吸持态磷的同位素交换性

本文研究了种石灰性土壤（Ｌｏｕ土）与磷酸盐的反应动态过程，短期反应的等温吸附研究表明，在低磷浓度下，以吸附反应机制为主，吸持态磷的同位素交换性随着吸持量的增加而增加；在高磷浓度下，以形成磷酸盐的沉淀反应机制为主，吸持态磷的同位素交换性随着反应时间的延长和吸持量磷数量的增加而了降低。认为在低施磷水平下，土壤中铁，铝氧化物对磷的吸持起重要作用。本文还探讨了在长期（２６０天）恒温恒湿培养过程中，土壤可溶     

土壤磷组分的通径分析及其相对有效性

本文在土壤有机磷和有机磷分组的基础上，通过土壤磷组分与植株磷量的相关分析及土壤有效磷含量的通径分析，研究比较了土壤各组磷的相对有效性。结果表明，除了土壤无机磷组分中的铝磷和铁磷的相对有效性较高外，某些活性较高的土壤有机磷组分与植株吸磷量也呈显著相关，对土壤有效磷含量的变化有着不可忽视的影响。在一定条件下，可能成为植物有效磷源之一，从而为正确评价土壤有机磷在整个磷营养循环中的地位和作用提供新的方法和途径。     

氢氧稳定同位素技术在土壤水研究上的应用进展

土壤水是水资源的重要组成部分,是连接自然界水循环的重要环节;一个地区的土壤水资源状况与当地作物生产、生态环境质量以及社会经济发展息息相关。应用稳定氢、氧同位素技术可从宏观和微观的结合上把握土壤水循环过程,阐明其相关机理;近年来这一技术有了长足进步,正在逐渐发展成为研究土壤水循环特别是探究土壤水分运移和转化规律的有效手段。在简述土壤水氢、氧同位素基本知识的基础上,从水的地球化学循环原理出发,讨论影响土壤水氢、氧同位素富集的因素,着重介绍了土壤水循环研究中的同位素技术的要点和特点,并对这一研究领域未来的发展进行了展望。     

施磷对吉林省西部盐碱土水田土壤无机磷组分的影响

为探明磷肥施用对盐碱土水田土壤无机磷组分的影响,以吉林省西部地区盐碱土水田土壤为研究对象,通过田间试验结合室内分析的方法,研究了不同磷肥施用量的情况下,土壤不同形态无机磷在水稻生育期内含量的动态变化。结果表明:施用磷肥可以在整个水稻生育期间提高盐碱土水田土壤中的有效磷源及潜在磷源的含量,包括Ca_2-P、Ca_8-P、Al-P和Fe-P等不同形态的无机磷含量;O-P是土壤无机磷组分中含量较高且极稳定的磷,在一个水稻生育期内,施肥不会引起O-P含量的明显变化;虽然以往认为Ca_(10)-P是土壤中不可利用的磷,但本研究中发现,Ca_(10)-P在水稻生育期间仍可发生一定的转化,较高磷肥施用量有利于土壤中Ca_(10)-P的积累。研究表明,盐碱土水田磷肥的施用,在水稻生育前期可以形成可被水稻吸收的有效态磷源和潜在磷源,水稻生育后期则开始向无效态磷转化并在土壤中积累。     

酸性土壤磷分级新方法建立与生物学评价

土壤磷分级方法可用于估算土壤有效磷数量、不同土壤磷组分库数量及其对土壤有效磷的补充能力。以云南赤红壤、黄红壤及湖北棕红壤为供试材料,运用张守敬方法、蒋柏藩方法及本文提出的新方法,对三种酸性土壤和其石灰改良后的土壤磷进行分级研究,探讨石灰改良对酸性土壤磷组分数量及其生物有效性的影响。结果表明:Ca2-P、Al-P和Fe-P是酸性土壤主要的有效磷源,O-P(闭蓄态磷)也是潜在有效磷源,土壤中活性有机磷库相对比较稳定,可转化为高活性有效磷源供植物吸收利用。与两种经典磷分级方法相比,新方法将O-P划分为O-Al-P和O-Fe-P,O-Fe-P较好地反映了石灰处理与对照之间的土壤磷植物有效性差异。     

有机酸对不同磷源施入石灰性潮土后无机磷形态转化的影响

采用室内培养和化学分析的方法研究了几种有机酸对石灰性潮土无机磷形态转化的影响。结果表明,1)石灰性潮土中磷素主要以有效性很低的磷酸盐(Ca10-P等)形式存在,而有效性较高的磷酸盐(Ca8-P等)含量较少,Ca2-P就更少。2)不同磷源施入土壤后,无机磷总量相应增加。磷酸二氢钾与磷酸二钙主要向Ca8-P、Al-P等有效性相对较差的磷素形态转化,磷酸八钙、氟磷灰石、磷酸铁、磷酸铝等有效性较差的磷源,在较短的时期内主要以自身的形态存在。3)施加各种有机酸可以不同程度地降低土壤中Fe-P、Al-P和Ca10-P含量,增加Ca2-P、Ca8-P和O-P含量,总的趋势是促进土壤中植物难以利用的无机磷形态向植物可以利用的形态转化。这种促进能力因有机酸种类和性质的不同而不同,其作用大小顺序为草酸柠檬酸酒石酸。     

A method for the analysis of the δ18O of inorganic phosphate extracted from soils with HCl

The oxygen isotope composition of phosphate (δ¹⁸O‐PO₄) has successfully been used to study the biological cycling of phosphorus (P) in seawater and marine sediments. However, only a few studies have used this approach in soils. In order to analyse δ¹⁸O‐PO₄, phosphate must be extracted from the soil, purified and converted to silver phosphate (Ag₃PO₄). The published extraction methods, successfully applied to marine waters and sediments, lead to the precipitation of impure Ag₃PO₄when used with soils or organic‐rich samples. Here we present an improved purification protocol, designed for soils and other organic‐rich samples. After extraction with HCl, phosphate is purified with multiple mineral precipitations that do not require extreme pH adjustments of the solutions. We show that contaminant‐free Ag₃PO₄ can be produced from fertilizers and various soils with different chemical and physical characteristics. Our first isotopic results confirm that differences in P status and availability in soils are expressed in the δ¹⁸O‐PO₄ signal, indicating the potential of this isotopic tracer to understand P dynamics in soil systems.     

镉同位素分馏在土壤-植物体系中的研究进展

镉污染土壤因其导致粮食作物超标以及通过食物链对居民健康构成威胁,引起了人们的高度关注。土壤镉的迁移转化、植物根部对镉的吸收、植物体内对镉的装载转运和贮存是土壤-植物体系镉生物地球化学循环的重要过程。近年来,稳定同位素分馏技术被广泛应用于土壤-植物系统中镉的迁移和储存,为研究镉在不同土壤库和植物部位中的迁移和转化提供了新的思路和视角。本文首先介绍了镉同位素组成分析的基本原理和方法;其次对土壤矿物溶解、共沉淀、吸附和有机质螯合配位等四个关键过程引起的镉同位素分馏方向和程度进行综述,并重点针对植物根部对镉的吸收、根部-地上部转运和籽粒储存等三个关键过程阐述植物体内镉同位素分馏机制;最后基于目前研究现状,展望了土壤-植物体系镉同位素分馏尚需解决的科学问题和未来的研究方向。有助于深入理解镉在土壤-植物体系中的生物地球化学过程与机制,以期为镉污染土壤的安全利用与治理修复、农产品减毒脱毒等应用技术的研发提供科学依据。     

Perspectives from the Fritz‐Scheffer Awardee 2019. Oxygen isotopes in phosphate—The key to phosphorus tracing?

Phosphorus (P) tracing in natural environments is challenging, lacking stable P isotopes Oxygen isotope ratios in phosphate (δ¹⁸O_P) represent a novel tool for tracing the biological cycling of P from the global scale down to hotspots at the micro‐scale and within particular soil compartments such as aggregates or pores. Despite the small number of studies available so far, existing data indicate that δ¹⁸O_P values point to where, at what extent and how efficiently P is recycled in soils.     

稳定同位素示踪土壤中重金属环境行为的研究进展

随随着以多接收器电感耦合等离子体质谱仪（MC-ICP-MS）为代表的高精度质谱分析技术的革命性突破,稳定同位素的研究取得了跨越式发展。重金属稳定同位素成为了示踪土壤环境介质中重金属地球化学循环的有效工具,在识别污染来源、解析关键过程、跟踪环境行为等方面展现出极大的应用潜力。从同位素基本概念出发,系统介绍了利用重金属稳定同位素示踪土壤环境重金属污染的来源与归趋、土壤-植物体系重金属元素的迁移转化以及金属纳米颗粒的环境过程等方面的研究进展,并进一步总结了氧化还原、沉淀溶解、吸附解吸、络合反应、生物作用等影响重金属稳定同位素分馏的相关机制,最后针对当前应用和研究现状,提出了拓展稳定同位素示踪重金属环境行为的潜在研究方向和研究内容,对土壤重金属污染防治及修复具有重要的指导意义。     

Acceleration of N mineralization by release of enzymes and substrates from soil mineral particles with phosphates

A study was conducted to develop an improved method for measuring organic N (net) mineralization in which chemical extraction takes place in combination with suspension incubation in ammonia-absorbing membrane bottles. To obtain direct evidence of the extent to which extracted organic N is mineralizable, the extraction suspension was further incubated immediately after the extraction procedure with mild and selective extractants. In this ‘extraction incubation’ method, extraction continues during the incubation but only relatively easily mineralizable organic matter is released. Standard incubation is usually carried out in sealed N₂-flushed bottles. However, when phosphate or pyrophosphate soil suspensions are incubated, mineralization is much higher than in soil water suspensions. Further, accumulation of ammonia+(ammonium) and other gases, i.e. CO_2, can affect the reaction rate and final reaction equilibrium in the sealed incubation flask. It was to avoid these effects that the membrane method was developed. With this procedure, the flask is closed with an ammonia-absorbing membrane permeable to other gases. Water, phosphate and pyrophosphate suspensions were incubated at 37 °C in sealed bottles (SB), in sealed N₂ gas-flushed bottles (SBN₂), and in bottles with ammonia-trapping filters (MB). The maximum amount of released during 10 days' incubation was 133.0 mg kg⁻¹ in the water, 208.0 mg kg⁻¹ in the phosphate and 454.1 mg kg⁻¹ in the pyrophosphate suspension (soil total C content 6.2% and N 0.25%). During incubation in phosphate and pyrophosphate suspensions, the mobilization was nearly linear in membrane bottles. The variation between replicates was also smallest in these bottles. It was concluded that membrane bottles were best suited to incubation when mobilization reactions were accelerated with phosphate or pyrophosphate extractants. The method was easy to perform and gave results with good replicability.     

Differentiating sources of CO2 from organic soil under bioenergy crop cultivation: A field-based approach using C

We tested here a plant-soil system to separate recent, plant-derived and native, soil-derived carbon in soil respiration. The approach uses a perennial crop cultivated on an organic soil where upper soil layers have been removed as a result of peat extraction. There, the ¹⁴C signal from native organic matter is highly depleted compared to that in vegetation established at the site after peat extraction ceased. Radiocarbon was analyzed in carbon dioxide respired from soil over one growing season, and a two-pool isotope mixing model was applied to calculate the relative contribution of old vs. new carbon sources. The analysis showed that the approach is reliable for source partitioning with isotopes. After six years of cultivation, old peat decomposition contributed less to total soil respiration than respiration of recent plant material (30% vs. 70% on average, respectively), but the relative proportions were highly variable over the growing season. The approach offers a new possibility to follow the fate of old, native soil organic matter in highly organic soils.     

Differentiating sources of CO2 from organic soil under bioenergy crop cultivation: A field-based approach using 14C

We tested here a plant-soil system to separate recent, plant-derived and native, soil-derived carbon in soil respiration. The approach uses a perennial crop cultivated on an organic soil where upper soil layers have been removed as a result of peat extraction. There, the ¹⁴C signal from native organic matter is highly depleted compared to that in vegetation established at the site after peat extraction ceased. Radiocarbon was analyzed in carbon dioxide respired from soil over one growing season, and a two-pool isotope mixing model was applied to calculate the relative contribution of old vs. new carbon sources. The analysis showed that the approach is reliable for source partitioning with isotopes. After six years of cultivation, old peat decomposition contributed less to total soil respiration than respiration of recent plant material (30% vs. 70% on average, respectively), but the relative proportions were highly variable over the growing season. The approach offers a new possibility to follow the fate of old, native soil organic matter in highly organic soils.     

Characterization of Soil Phosphorus in Differently Managed Clay Soil by Chemical Extraction Methods and 31P NMR Spectroscopy

Changes in land use alter the natural cycling of phosphorus (P) in soil. Understanding the chemical nature of these changes is important when developing sustainable management practices for cultivated soils. In this study, we evaluated the ability of commonly used laboratory methods to characterize land use–induced changes in various P pools. Also, the characteristics of soil P revealed by different methods are discussed. Soil samples were taken from three differently managed field plots of the same clay soil: uncultivated grassland and organic and conventional crop rotations. Soil P reserves were characterized using Chang and Jackson and Hedley sequential fractionation procedures and by sodium hydroxide (NaOH)–ethylenediaminetetraacetic acid (EDTA) extraction followed by ³¹P NMR spectroscopy. Both of the tested fractionation methods identified differences in the P pools and provided evidence regarding land use–induced changes. However, the ³¹P NMR analysis suggests that the quality of organic P in this soil was not affected by the change in land use.