周悦(1997—),女,河南济源人,硕士研究生,主要研究方向为农林废弃物安全利用及其环境效应。E-mail:
土壤可溶性有机质(DOM)是土壤有机物中的高活性组分,在土壤养分的生物地球化学循环、重金属和有机污染物的迁移转化、土壤矿物质的活化及土壤肥力的保持等过程中发挥着重要作用。农艺措施可通过内外源同步作用显著影响土壤DOM的含量、组分及性质,本文综述了近年来相关研究中不同农艺措施下土壤DOM的变化,总结了不同耕作管理、种植制度、施肥措施以及新型土壤改良剂等对土壤DOM的影响。分析表明,免耕加秸秆覆盖方式可显著提高土壤DOM含量,与单一耕作相比轮作可提升土壤DOM含量,绿肥配施有机肥较单一化肥施用可显著改善土壤DOM的组成和结构,合理调控热解炭和水热炭等土壤调理剂的施用时间、施用量、C/N等性质可优化土壤DOM结构和性能。本综述分析了农艺措施对土壤DOM的影响效果及作用途径,指出了当前的研究热点和难点,并对未来研究方向进行了展望,可为今后合理的农艺措施管理和土壤健康调控提供科学指导。
Soil soluble organic matter (DOM) is a highly active component of soil organic matter, which plays an important role in regulating the biogeochemical cycle of soil nutrient elements, the migration and conversion of heavy metals and organic pollutants, the activation of soil minerals and the maintenance of soil fertility. Agronomic measures can significantly affect the content and composition of soil DOM through the simultaneous effect of internal and external sources. Through analyzing the changes of soil DOM in recent years under different agronomic measures in the related studies, the effects of different tillage methods, planting systems, fertilization and new soil ameliorants on the physicochemical properties and biological components of soil DOM were summarized in this review. The results showed that no-tillage combined with straw mulching could significantly increase soil DOM content. Compared with single tillage, the rotation could significantly increase soil DOM content, besides, green manure combined with organic fertilizer could significantly improve soil DOM composition and structure compared with single chemical fertilizer application. Applying soil conditioners such as pyrolysis biochar and hydrochar at appropriate time, amount and C/N ratio could optimize structure and performance of soil DOM. Meanwhile, the effect and mechanism of agronomic measures on soil DOM and the hot spots and difficulties of current research were discussed, and the future research directions were proposed. This review can provide scientific guidance for the rational management of agronomic measures and soil health regulation in the future.
可溶性有机质(dissolved organic matter,DOM)广泛存在于水体和土壤等自然环境中,其中土壤DOM通常是指土壤中活体微生物和植物根系释放的及植物残渣和可溶性颗粒部分分解后产生的可溶性有机物质[
从来源看,土壤DOM分为两种:一种是土壤内源性的,通过土壤微生物降解土壤有机质产生,例如土壤腐殖质、植物凋落物、根系分泌物等[
土壤DOM仅占土壤有机质的一小部分,但其对土壤质量具有很强的指示性。DOM在土壤聚集(形成有机金属络合物)、微生物的物质能量来源(碳源、氮源等)以及碳的储存、循环和有效养分供给等方面发挥着关键作用[
研究土壤DOM的组成、含量及形态变化有助于更好地了解土壤碳氮循环及与之相关的地球生物化学过程。土壤DOM具有很强的溶解性,易通过土壤溶液转移[
DOM可通过静电吸附、配体交换、络合、分配、氢键和阳离子桥联机制与土壤结合[
土壤DOM可增强土壤供肥能力,一是提高土壤养分的有效性,DOM中的有机酸等组分可活化土壤矿物质,增强土壤微生物活性;二是DOM可促进植物对营养元素的吸收,例如促进作物根系对Fe、Zn等元素的吸收,从而提高作物产量,已有研究证实外源DOM施用可提高水稻植株的株高、根长、茎重等生长指标[
土壤DOM易受到气候条件、耕作管理条件、土壤类型和土壤性质等多种因素影响[
耕作管理可通过改变土壤有机质的输入和底物质量以及微生物降解的速率、程度和途径,进而影响土壤DOM的含量和性质[
申军强等[
地膜覆盖技术能够改变土壤温度和水分等条件,在我国北方寒旱区广泛应用。土壤DOM本身易受到温度、水分等条件变化影响,因此地膜覆盖对土壤DOM也会产生较大影响。在武佳颖等[
总的来说,相比传统翻耕模式,免耕加秸秆覆盖等保护性措施可显著提高土壤DOM含量进而改善土壤肥力。地膜覆盖可通过调节土壤温度和水分状况来影响土壤DOM的含量与性质。但由于各试验的背景条件不同,受自然环境等不同因素驱动影响,具体的研究结果间仍存在较大差异,不同耕作管理措施间的交互作用影响及对土壤DOM作用程度的量化研究仍有待进一步加强。
Li等[
土壤DOM的含量与性质对不同作物种植类型的响应也有所不同。李瑞鑫[
施肥作为重要的农艺措施,是影响土壤DOM的关键因素(
不同施肥措施对土壤DOM的影响
Effects of different fertilization on soil DOM
施肥分类 | 文献来源 | 主要化学组分 | 荧光组分 | 特性 | 主要物质 | |||||||
DOC | DON | 类富里酸 | 类络氨酸 | 类腐殖酸 | 类蛋白质 | 腐殖度 | 芳香度 | 疏水性 | 糖、醇及羧酸类物质 | 酰胺类物质 | ||
注:a表示不施肥情况下的标准值,b表示单施化肥情况下的标准值;↑表示施肥处理后的该组分较不施肥处理显著增加, |
||||||||||||
化肥 | [ |
↑[ |
a+182.0% | ↑ | ↑ | ↑ | ||||||
绿肥 | [ |
a+29.0% | a+257.0% | ↑ | ↑ | |||||||
化肥+绿肥 | [ |
↑ | ↑ | |||||||||
商业有机肥 | [ |
a+37.0% | a+334.0% | ↑ | ↑ | |||||||
粪肥 | [ |
↓ | 先↑后↓ | ↑ | 先↑后↓ | ↑ | ||||||
化肥+粪肥 | [ |
a+29.7%[ |
a+41.3%[ |
↑ | ↑ | ↑ | ↑ | |||||
秸秆有机肥 | [ |
先↓后↑ | ↑ | ↑ | ↑ | ↑ | ↓ | |||||
化肥+秸秆有机肥 | [ |
b+72.5% | ↑ | ↑ | ↑ | |||||||
沼液有机肥 | [ |
↑ |
化肥处理主要通过影响土壤微生物活性及作物生长而影响土壤DOM的含量及结构。王萍[
与化肥相比,施用绿肥和有机肥后,土壤DOM含量的增加更为明显。常单娜[
长期施用有机肥会显著增加土壤中DOM的含量[
秸秆还田也在一定程度上促进了土壤DOM含量的增加。张常仁等[
沼液作为有机肥应用是一种具有潜力的畜禽粪便污水资源化方法。研究表明,猪沼液中含有大量营养物质,可作为肥料施入农田以改善养分吸收和土壤结构,降低施肥成本[
综合来看,绿肥和有机肥具有成本低廉、可循环利用、种类丰富等优点,对提高土壤DOM含量和改善土壤肥力具有重要作用,然而目前研究主要聚焦于DOM含量与性质的变化效果,对于微生物-植物-有机肥的耦合作用机制研究较少。此外,分析技术上,基于新兴的质谱技术进行分子水平的机制研究较少。
近年来,生物质炭由于其在土壤改良方面的优异效果引起了广泛关注,根据制备过程可将其分为热解炭和水热炭[
Zhang等[
水热炭在温室气体减排、水体净化和土壤修复等方面具有很大的应用前景[
土壤DOM正凭借着极高的活跃性和生物有效性为土壤健康和地球生物化学循环等研究提供更好的指示效果。如何更好地运用农艺措施强化对土壤DOM的调控作用,改善土壤健康质量,提升农田养分管理效率,值得研究者进一步深入探讨。
1) 免耕和秸秆覆盖等保护性措施有助于提高土壤DOM含量,进而起到提升土壤肥力、增加作物产量的功效。但需要注意的是,在耕作方式和种植制度对土壤DOM的影响研究中,由于气候和环境条件的差异,有些相同措施在不同的试验中得到的效果可能不同甚至相反,因此,在后续利用农艺措施调控土壤DOM过程中,有必要强化DOM与不同环境条件的交互作用研究并尽量考虑气候、海拔、土壤类型、土壤特性等性质变化进行综合调控。
2) 在施肥措施对土壤DOM影响调控研究中,相比单一化肥,绿肥和有机肥有着低成本和环境友好的显著优势,然而当前研究仍主要聚焦于施肥方式对DOM中养分元素含量的变化,对于不同施肥方式对DOM调控的主要作用机制及微生物-植物-有机肥对DOM的耦合作用机制研究较少。
3) 新兴的土壤改良/修复剂,如热解炭、水热炭等,其对土壤DOM及肥力的影响仍存在两面性,不合理的施用会出现抑制土壤活性,对微生物和植物生长产生毒害作用等情况。如何合理控制新型土壤改良剂的施用比例,最大化发挥其正面作用并消除其不利影响,这些问题仍有待探索。
4) 在分析不同农艺措施对土壤DOM的影响时,也注意到DOM反作用于植物、重金属迁移转运等方面的影响及作用机制方面的研究较为空缺。此外,目前农艺措施对土壤DOM的影响研究仍主要侧重于对其含量和基本性质的影响,其变化机制等深层机理仍有待进一步研究,如何利用傅里叶变换离子回旋共振质谱等新兴技术发展进一步从分子角度探明DOM的变化机制,也逐渐成为下一步的研究焦点。
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