低分子量有机酸对土壤有效磷及重金属释放影响的研究进展

农药化肥的过量施用、重金属矿产开发冶炼、污水灌溉等导致土壤磷素养分降低和重金属污染,对生态环境、粮食安全和人类健康带来一定的风险隐患。土壤低分子量有机酸是一类重要的土壤有机活性物质,在土壤质地、养分循环和重金属毒害等方面起重要作用,但低分子量有机酸对土壤磷素和重金属释放影响的研究尚没有系统归纳。本文结合国内外研究进展,综述了土壤低分子量有机酸的来源、浓度、功能及其影响因素,举例说明了低分子量有机酸种类、浓度等对土壤磷及重金属释放的影响。系统总结了低分子量有机酸对土壤磷活化及重金属释放的机制。低分子量有机酸与其他物质协同提升土壤磷素有效性和降低重金属污染,这些结果为土壤磷素有效性的提升和重金属污染土壤修复提供科学依据和技术支撑。     

低分子量有机酸对土壤磷组分影响的Meta分析

【目的】过量施用磷肥导致土壤磷素累积，全磷含量升高，但是有效磷含量往往较低。低分子量有机酸能活化土壤难溶性磷、提高土壤磷素有效性，已成为研究热点之一。为探索提高土壤磷素有效性的途径，本文综合分析了低分子量有机酸对不同类型土壤磷组分的影响，为低分子量有机酸的合理施用和土壤有效磷的提升提供理论依据。【方法】通过收集近30年 (1990—2018年) 来国内外发表的低分子量有机酸活化土壤磷的文章，建立了831组包含“有效磷 (available-P)”相关内容的数据库。基于Meta分析 (Meta-analysis)，定量研究了不同土壤pH、全磷、有效磷含量、不同培养方式和培养时间及不同酸种类 (苹果酸、柠檬酸及草酸等) 和浓度等条件下，低分子量有机酸对土壤有效磷含量的影响。【结果】检索论文中的低分子量有机酸添加浓度在0～1 mol/L范围内。与不施低分子量有机酸的对照相比，低分子量有机酸可使土壤中钙磷、铝磷、铁磷、闭蓄态磷和有机磷含量分别降低27.1%、21.3%、15.5%、8.22%、5.42%，有效磷含量增加213%。石灰性土壤中，低分子量有机酸可将难溶性八钙磷 (Ca₈-P)、十钙磷 (Ca₁₀-P) 转化为可吸收态的二钙磷 (Ca₂-P)，Ca₈-P、Ca₁₀-P含量分别降低8.36%、11.8%，而Ca₂-P含量增加7.90%。在全磷含量 < 1 g/kg和有效磷含量 < 20 mg/kg的低磷土壤中，低分子量有机酸分别能使有效磷含量增加331%和343%，增磷效果分别比对应的全磷含量 ≥ 1 g/kg、有效磷 ≥ 20 mg/kg的高磷土壤高107%和189%。在酸性 (pH < 6) 和中性 (pH 6～8) 土壤中，低分子量有机酸分别能提高土壤有效磷含量329%和320%，在碱性 (pH > 8) 土壤中其增磷效果仅为56.9%。低分子量有机酸活化难溶性磷具有速效性和时效性，培养第1天土壤有效磷含量可增加257%，之后持续增加，在第10～20天达到最高值372%，20天后增磷效果持续减弱。振荡培养试验条件下，低分子量有机酸能使土壤有效磷含量增加334%，高于常规培养试验294%。当低分子量有机酸的添加浓度低于90 mmol/L时，酸浓度越高，其提升土壤磷有效性的效果越好。在所用的低分子有机酸中，草酸和柠檬酸提升磷有效性的效果较好，分别能增加有效磷含量288%和185%。【结论】低分子量有机酸活化土壤难溶性磷的效果受到土壤pH、全磷和有效磷含量的影响，也与添加的有机酸类型和浓度及添加的时间有关。低分子量有机酸提升土壤磷有效性的效果，在酸性和中性且全磷含量较低的土壤中较好。在低分子量有机酸添加量 < 90 mmol/L范围内，提升效果随添加量的增加而增加。作用的最佳效果出现在添加后的10～20天。添加草酸和柠檬酸对土壤有效磷的提升效果较好。     

低分子量有机酸对土壤磷活化影响的研究

研究两种低分子量有机酸（柠檬酸和苹果酸）对土壤磷活化影响，并用修正的Hedley法测定土壤磷活化前后磷组分的变化。结果表明，低分子量有机酸能持续活化土壤磷，活化强度随低分子量有机酸浓度的增大而增强，并且柠檬酸活化土壤磷的能力强于苹果酸。低分子量有机酸能促进作物有效态无机磷组分（H2O-P和NaHCO3-Pi）的释放；同时还促进有机磷组分（NaHCO3-Po和NaOH-Po）的矿化。在低分子量有机酸浓度达到0.5 mmol/L以上时，其对土壤磷组分的活化量的顺序为:NaOH-Pi HCl-P NaHCO3-Pi H2O-P，即铁铝结合态磷 钙结合态磷 作物有效态磷。低分子量有机酸活化土壤磷的过程中伴有大量铁、铝释放，且铁或铝的释放量与磷活化量之间显著正相关（P0.05）。说明铁、铝结合态磷是低分子量有机酸活化土壤磷的主要磷源，并且其活化机制可能与铁、铝结合态磷的螯合溶解有关。     

淋溶条件下低分子量有机酸对淋出液及三峡库区典型土壤性质的影响

[目的]研究低分子量有机酸(草酸、柠檬酸、酒石酸)作用下淋出液及土壤(紫色潮土和灰棕紫泥)性质的变化,以期为三峡库区的环境管理提供参考和科学依据。[方法]采用间歇式土柱模拟试验进行研究。[结果]高浓度低分子量有机酸(≥50mmol/L)能够破坏灰棕紫泥的酸碱缓冲体系,当草酸、柠檬酸和酒石酸浓度≥50mmol/L时,灰棕紫泥土壤pH值均从8左右降到了4.11以下;而紫色潮土的缓冲性能较强,经淋溶后土壤pH值变化不大,仍然维持在6.84~8.71左右,与空白处理差异性不显著。另外,灰棕紫泥淋出液电导率变化较紫色潮土明显,高浓度低分子量有机酸处理下,灰棕紫泥淋出液电导率最高值达到了34.400mS;灰棕紫泥在3种低分子量有机酸淋洗下淋溶出离子量的大小顺序为:柠檬酸酒石酸草酸。[结论]低分子量有机酸的酸解作用和络合作用是影响淋出液pH值、淋出液电导率和土壤pH值变化的主要原因,并能够参与紫色潮土和灰棕紫泥的化学和生物化学过程。低分子量有机酸的存在对三峡库区水环境恶化存在一定的风险。     

低分子量有机酸对可变电荷土壤和矿物表面化学性质的影响

低分子量有机酸是土壤中广泛存在的,它们参与土壤中许多化学过程,在营养元素活化、解铝毒和矿物风化等方面发挥重要作用。本文综述了可变电荷土壤和矿物对低分子量有机酸的吸附及这类有机酸对土壤的表面电荷、动电性质和土壤吸附无机阴、阳离子的影响,为从事相关研究工作的同志提供参考。     

集约经营下雷竹林土壤低分子量有机酸的初步研究

低分子量有机酸对养分循环与植物生长起着重要作用,雷竹具有发达的鞭根系统,因此了解其土壤中的有机酸状况显得尤为重要。本研究采集了雷竹主产区浙江省临安市太湖源镇不同种植年限的雷竹土样,通过高效液相色谱法对其中的低分子量有机酸进行初步的定性和定量分析。结果表明:雷竹林土壤中主要含有马来酸和丁二酸,并含有少量富马酸;随着雷竹种植年限的增加,土壤中有机酸总量有增加的趋势。     

土壤有机酸与磷素相互作用的研究

土壤有机酸包括低分子量有机酸和腐殖酸,它们构成土壤有机组分中性质较活跃的部分。特别是低分子量有机酸,在土壤形成、养分和污染物的转化过程中起着十分重要的作用,受到土壤、植物营养和环境科学工作者的高度重视。本文着重从它们与磷素相互作用的角度,阐述有关研究进展。主要内容包括:(1)磷营养与植物根系分泌有机酸的特征;(2)有机酸对土壤吸附磷的影响;(3)有机酸与磷的解吸、释放与转化。旨在促进研究工作的深入,并为合理利用磷素,保护生态环境提供科学依据。     

低分子量有机酸对砖红壤表面电荷的影响

本文研究了4种低分子量有机酸对砖红壤表面电荷性质的影响,结果表明存在于体系中的有机酸增加了表面负电荷量,同时减少表面正电荷的量。在低有机酸加入量下,有机酸对正电荷的影响程度比其对负电荷的影响程度大得多。4种酸对土壤表面电荷影响的大小顺序为:柠檬酸>苹果酸>草酸>醋酸。有机酸对表面电荷的影响随体系pH而变化,它们对正电荷的影响程序随pH的增加而减小,而对负电荷的的影响呈相反的变化趋势。有机酸主要通过其阴离子在土壤表面的吸附来影响土壤的表面电荷性质。     

低分子量有机酸对可变电荷土壤中铝吸附的影响

铝毒是酸性土壤上植物生长不良的主要限制因素,铝的生物毒性与铝离子的化学形态有密切的关系[1, 2],而铝的化学形态又受包括低分子量有机酸在内的多种因素的影响[3, 4].低分子量有机酸是土壤中广泛存在的一类非常活泼的物质,植物在生长过程中其根系会不断分泌出各种有机酸,植物残体分解过程中和土壤微生物代谢过程中均会产生有机酸[5, 6].一些有机酸阴离子可以被可变电荷土壤吸附,并影响土壤的某些表面化学性质;另一方面某些有机酸阴离子能够与铝形成稳定的络合物从而改变铝离子在溶液中的存在形态,这两方面的原因都有可能对可变电荷土壤中铝的吸附产生影响.     

外源低分子量有机酸对土壤中钙素迁移特征的影响

论文采用室内土柱模拟的方法,研究了草酸和柠檬酸2种外源低分子量有机酸对土壤中钙素迁移特征的影响。研究结果表明:添加草酸在淋溶前期抑制了土壤钙素的淋失,在后期则促进了土壤钙素的淋失;添加柠檬酸则极大地促进了土壤钙素的淋失。增加2种低分子量有机酸的浓度均可促进土壤中钙素的淋失。对土壤钙素淋失的作用为柠檬酸草酸。其中添加草酸和柠檬酸解离产生的H+对钙素的淋失影响相对较大。施入2种有机酸后促进了钙素的淋失,减少了土柱剖面土壤全钙的含量,但淋洗后仍增加了土壤剖面有效钙的含量。     

植物多酚与低分子量有机酸联合作用对紫色土铁形态分布的影响

植物多酚(PP)和低分子量有机酸(LMWOA)对土壤铁形态转化有重要影响。以酸性、中性和石灰性紫色土为研究对象,采用不完全随机区组试验,用2种PP(即表没食子儿茶素没食子酸酯(EGCG)和芦丁)和2种LMWOA(即柠檬酸和草酸)溶液浸提供试土壤,测定其可溶铁(Fes)、游离铁(Fed)、活性铁(Feo)、络合铁(Fep)含量,探讨了PP与LMWOA对紫色土铁形态分布的影响。结果表明:PP与LMWOA各自单独作用均能使酸性紫色土Fes增加、中性紫色土Fes减少;对于石灰性紫色土,PP会促进其Fes增加,而LMWOA作用相反。EGCG与LMWOA联合作用,在酸性和石灰性紫色土上均表现为LMWOA通过促使本应转化为Fes的转化为Fep而掩蔽EGCG对铁的溶解作用;芦丁与LMWOA联合作用,在酸性紫色土铁的溶解上表现为协同效应,在石灰性紫色土上则表现为LMWOA会抑制芦丁对铁的溶解作用;对于中性紫色土,PP与LMWOA联合作用可促进Fed向Fes转化而削弱PP对铁溶解的抑制作用。     

Low‐molecular‐weight organic acids enhance desorption of polycyclic aromatic hydrocarbons from soil

The impact of low‐molecular‐weight organic acids (LMWOAs) on desorption of phenanthrene and pyrene as representative polycyclic aromatic hydrocarbons (PAHs) from a contaminated soil was investigated by using a laboratory batch experiment. Three LMWOAs were used in this study and were citric, oxalic and malic acids. The LMWOAs in aqueous solution promoted desorption of PAHs from soil significantly and demonstrated an increasing trend as the concentration of LMWOAs increased. When compared with desorption of phenanthrene and pyrene from soil to water, the addition of LMWOAs enhanced desorption of test PAHs by up to 285 and 299%, respectively. Among the three LMWOAs studied, citric acid demonstrated the greatest efficiency in promoting PAH desorption from soil. Solutions of LMWOA continuously promoted PAH removal from soil during the multiple cycles of desorption. Overall, the experimental results suggest that LMWOAs in aqueous solution could disrupt soil organic matter (SOM)–metal cation–mineral linkages in soils, resulting in the release of SOM from soil and simultaneous increase of dissolved organic carbon (DOC) in solution. The loss of SOM from soil and increase of DOC in solution are responsible for the enhanced PAH desorption from soil. The positive correlation between DOC in solution and desorbed PAHs from soil suggests that the loss of SOM from soil plays an important role in LMWOA‐enhanced desorption of PAHs from soil.     

Effects of Low-Molecular-Weight Organic Acids on Soil Micropores and Implication for Organic Contaminant Availability

Experiments were conducted to study the effects of low-molecular-weight organic acids (LMWOAs) on micropore properties of black soil, red soil, lignin, and humin. Black soil and red soil were treated with four LMWOAs including malic, citric, succinic, and tartaric acids, whereas lignin and humin were treated with malic and citric acids. The results indicated that soil micropore distribution was changed by LMWOAs. Citric and malic acids reduced soil micropore surface area and volume significantly, but lignin micropores were not changed significantly by these two acids. Therefore, clogging may not be a main reason for the surface area and micropore volume reduction of soil organic matter. The release of metal ions from humin and soils was enhanced by LMWOAs, indicating the dissolution of soil mineral particles. Therefore, soil micropore reduction may result from the destruction of soil aggregates due to dissolution of mineral particles and extraction of metals from bridging sites.     

不同镉积累类型小麦根际土壤低分子量有机酸与镉的生物积累

采用土壤培养方法研究低镉积累小麦烟 86103和高镉积累小麦莱州 953不同生育期土壤低分子量有机酸含量与组成 ,及其与镉生物积累的关系。结果表明 ,不同镉积累类型小麦在高镉土壤中其根系镉含量差异不显著 ,但地上部镉浓度烟 86103显著低于莱州 953,而在低镉土壤中根系和地上部镉浓度烟 86 10 3均显著低于莱州 95 3。根际土壤有机酸 (柠檬酸、酒石酸、乙酸和丙酸 )含量及有机酸总量均为低镉品种烟 86103显著低于高镉品种莱州953。两个品种不同生育期有机酸含量均表现为柠檬酸 酒石酸 丙酸 乙酸 ,且各有机酸含量占有机酸总量的百分数表现稳定。小麦镉的生物积累与有机酸种类没有特异性关系 ,但与有机酸的总量有关。根际不同有机酸的水平对于土壤镉的复合或螯合溶解 ,在引起两品种地上部镉生物积累的差异方面起重要作用。     

Impact of low-molecular-weight organic acids on the availability of phenanthrene and pyrene in soil

The impact of low-molecular-weight organic acids (LMWOAs) on the availability of phenanthrene and pyrene was investigated using laboratory batch assays. Experiments were conducted with two types of soil with different organic contents. The LMWOAs used were citric and oxalic acid. A mild solvent extraction procedure and a sorption-desorption experiment were used to predict the availability of phenanthrene and pyrene. Results showed that the extractable amounts of phenanthrene and pyrene in both soil types increased with increased citric or oxalic acid concentration. Citric acid addition promoted phenanthrene and pyrene extraction to a greater degree than oxalic acid. Compared with freshly spiked soils, the extractable amounts of phenanthrene and pyrene with the addition of LMWOAs decreased significantly after 60 days of cultivation. Soils with higher values of soil organic carbon content (f_oc) showed decreased phenanthrene and pyrene availability after the addition of LMWOAs. The sorption and desorption results also demonstrated the enhanced availability of PAHs with LMWOA addition. Phenanthrene sorption could be described using a linear model, regardless of the addition of LMWOAs. The simulated distribution constants (K_d) for phenanthrene sorption decreased significantly with the addition of LMWOAs. In contrast, phenanthrene desorption clearly increased with the addition of LMWOAs. These results suggest that the availabilities of phenanthrene and pyrene can be increased with the addition of suitable LMWOAs.     

Effects of Low Molecular Weight Organic Anions on the Release of Arsenite and Arsenate from a Contaminated Soil

Low-molecular-weight-organic-anions (LMWOAs) are important exudates of plants and may influence the mobility and bioavailability of metals or metalloids. In the present study the effects of selected LMWOAs, citrate, malate and oxalate, on the release of arsenite (As(III)) and arsenate (As(V)) in a contaminated soil were investigated. The organic anions have significant influence upon the release of arsenic from the soil, and a linear relationship exits between the released arsenic and the concentration of LMWOAs in the extractants. pH effects on the arsenite and arsenate adsorption were not significant over the range from 3 to 7. The amounts of arsenite and arsenate released were significantly correlated with the release of Fe, Mn and Al, suggesting that arsenic was mainly released from Fe-, Mn- and Al-oxides or hydroxides in soil. The ratio of released arsenite to arsenate was not influenced by LMWOAs.     

低分子量有机酸作用下土壤中菲和芘的残留及形态

采用微宇宙试验方法,以菲和芘为多环芳烃(PAHs)代表物,研究了几种低分子量有机酸作用下黄棕壤中菲和芘的残留和形态。结果表明,老化60 d后土壤中菲和芘的残留含量明显减少;不施加有机酸的对照土壤中,菲和芘的残留含量为10.13和29.18 mg kg-1,去除率为87.33%和63.50%。与对照相比,供试浓度(0～64 mg kg-1)范围内,柠檬酸、草酸、酒石酸等3种低分子量有机酸作用下土壤中PAHs残留含量提高,去除率减小,表明供试条件下有机酸抑制土壤中菲和芘的降解;进一步分析发现,少量(≤4 mg kg-1)的有机酸即可对PAHs降解产生高的抑制效果。微生物降解在PAHs的去除中起重要作用,且芘比菲更抗微生物降解。供试条件下,可脱附态和有机溶剂提取态是土壤中菲和芘存在的主要形态,而结合态残留占总残留的比例很小(<8.5%)。3种有机酸均提高了土壤中可脱附态和有机溶剂提取态菲和芘的残留含量,施加有机酸使土壤中菲和芘的可脱附态含量较对照分别提高了46.67%～749.1%和1.83%～80.20%,有机溶剂提取态则提高了8.73%～375.2%和22.63%～114.3%;低分子量有机酸作用下结合态的菲和芘含量仍很小。     

Water-soluble low-molecular-weight organic acids in automorphic loamy soils of the tundra and taiga zones

The formation features of water-soluble low-molecular-weight organic acids (LMWOAs) in a zonal series of automorphic soils on loose silicate rocks from the middle taiga to the southern tundra (typical podzolic, gley-podzolic, and surface-gley tundra soils) were first revealed by gas chromatography mass spectrometry and gas-liquid chromatography. The content of LMWOAs varies within the range of 1–14 mg/dm³, which corresponds to 1–5% of the total carbon of the water-soluble soil organic matter. It has been shown that a subzonal feature of gley-podzolic soils in the northern taiga is the high content of LMWOAs, including primarily the strongest aliphatic hydroxyl acids. Possible mechanisms of their formation and accumulation in soils have been considered.     

Organic acid concentrations in soil solution: effects of young coniferous trees and ectomycorrhizal fungi

Organic acids may play a key role in rhizosphere and pedogenic processes. The effects of young trees and ectomycorrhizas on the soil solution concentrations of low molecular weight organic acids (LMWOAs) were studied in soil columns (E horizon) in the presence or absence of Pinus sylvestris and Picea abies with or without three ectomycorrhizal fungi. Several LMWOAs were identified at concentrations ranging from <0.1 to 11 μM. Compared to soil columns without tree seedlings, the presence of non-mycorrhizal or mycorrhizal tree seedlings sometimes resulted in small but statistically significant increases in citrate, formate, malonate and oxalate concentration. The general nutrient concentration and low P had little short-term effect on soil solution organic acid concentrations. The results suggest that biodegradation rather than production may be the major factor regulating soil solution organic acid concentrations.     

低分子有机酸对土壤中重金属的解吸及影响因素

研究了柠檬酸、草酸、酒石酸和苹果酸对矿区土壤中重金属Pb、Cd、Cu和Zn的解吸行为,并探讨了介质pH值对其解吸土中重金属的影响。振荡解吸试验结果表明四种低分子有机酸对供试污染土壤中Pb、Cd、Cu和Zn都具有一定的解吸能力。由于土壤中重金属有效态含量较低,各重金属的解吸率都不高。在对Pb和Cd的解吸中,各低分子有机酸能力大小顺序为柠檬酸>酒石酸≈苹果酸>草酸;Cu的解吸顺序为柠檬酸>草酸>酒石酸≈苹果酸;Zn的解吸顺序为酒石酸>柠檬酸≈苹果酸>草酸。低分子有机酸随浓度的增加,其解吸能力提高。低分子有机酸对重金属的解吸量随pH值的降低而增加。