有机酸对土壤无机态磷转化和速效磷的影响

土壤有效磷含量低是影响作物生产的重要限制因素之一.作物根分泌活化难溶性磷的有机酸对改善其磷素营养具有重要意义.采用张守敬和Jackson无机磷分级方法,以湖北省3种pH值土壤为材料,加入不同磷源和有机酸,经过室温培养后,测定速效磷含量和无机磷组分的变化.结果表明:施磷显著提高了土壤中速效磷含量,中性土、酸性土Fe-P和Al-P含量大幅上升, Fe-P占增加量的50%以上,而碱性土Ca-P含量显著增加.加施有机酸使中性土速效磷含量增多,除苹果酸处理的变幅较小外,草酸和柠檬酸的加入速效磷显著增加.由于有机酸的作用,中性土Al-P含量下降,Ca-P含量上升,变幅大小依次为草酸＞柠檬酸＞苹果酸;酸性土中Al-P含量呈下降趋势,碱性土中Ca-P含量有不同程度的减少,3种土壤中O-P含量均有所增加.说明有机酸活化的磷主要来源于中性土和酸性土Al-P、Fe-P及碱性土Ca-P中的磷,同时有机酸能够促进土壤中闭蓄态磷(O-P)的形成与积累.     

低分子量有机酸对大豆磷积累和土壤无机磷形态转化的影响

采用土培试验方法研究了低分子量有机酸（柠檬酸、草酸、苹果酸及其混合酸）对大豆磷积累和土壤无机磷形态转化的影响。结果表明：低分子量有机酸促进了大豆植株磷的吸收积累,大豆不同生育时期,不同有机酸对大豆磷的吸收积累均有促进作用,但作用效果有差异;外加低分子量有机酸使无机磷总量、难溶态磷（Ca₁₀-P、Al-P和O-P）含量均显著降低,而可溶态磷的Ca₈-P含量显著增加,柠檬酸和草酸使Ca₂-P含量显著增加,表明低分子量有机酸促进了土壤难溶态磷向可溶态磷转化,作用大小顺序为柠檬酸＞草酸＞混合酸＞苹果酸;同时,大豆根系分泌物也促进部分难溶态磷向可溶态磷转化,使无机磷总量、除Ca₂-P外的其他无机磷组分均有所降低,按磷释放比例的大小来看,对大豆吸磷的贡献大小顺序为O-P＞Fe-P＞Ca₁₀-P＞Al-P＞Ca₈-P＞Ca₂-P.     

外源有机酸对玉米磷吸收及其生长发育的影响

以玉米品种郑单958为材料,通过施加外源有机酸的盆栽试验方法,设置了土壤中不施磷肥和有机酸(CKo)、仅施磷肥(CKP)、施柠檬酸(Tca)、施苹果酸(Tma)和施草酸(Toa)处理,研究外源有机酸对玉米生长过程中的磷素吸收及其生长发育的影响.结果显示:(1)3种外源有机酸均可显著提高土壤中速效磷含量和磷素利用效率,Tca、Tma和Toa处理玉米根际土壤的速效磷含量分别为CKo的2.25、1.96和2.04倍,且各处理间的磷素利用效率依次为:CKp>Tca>Tma>Toa>CKo.(2)在拔节期、抽雄期和成熟期,Tca处理玉米的磷素利用效率依次为CKo的1.16、1.05和1.04倍.(3)3种外源有机酸均可显著提高玉米根系体积和根系活力、单株玉米的氮磷钾的累积量、玉米的生物量及相对籽粒产量.研究表明,外源柠檬酸、苹果酸和草酸均可显著提高玉米根际土壤中固态磷的溶解,促进植株体内营养元素的累积,保证植物生长发育的需要,从而提高玉米的生物量和产量;并以外源柠檬酸处理对玉米磷吸收及其生长发育效果最好.     

自生固氮菌活化土壤无机磷研究

以土壤为磷源,通过液体培养试验研究了5株自生固氮菌(Azotobacter sp.)对土壤无机磷的活化利用.结果表明,自生固氮菌能释放大量的氢离子,使液体培养基的pH大幅度降低,氢离子的浓度至少提高58倍以上.自生固氮菌分泌有机酸的种类与数量因菌株不同而异,这些有机酸包括甲酸、乙酸、草酸、丁二酸、柠檬酸、苹果酸和乳酸等,其中均能分泌草酸和苹果酸.在接种自生固氮菌的液体培养基中,全磷含量显著高于不接种的液体培养基,土壤无机磷总量则显著降低.由于土壤是培养基磷的唯一来源,故自生固氮菌促进了土壤无机磷的溶解释放.相关分析表明,培养基的pH值与土壤无机磷总量呈极显著正相关(r=0.959**,n=6),与液体培养基中的无机磷和全磷呈显著或极显著负相关(r =-0.850*;r=-0.918**,n=6),说明自生固氮菌分泌的氢离子可能是溶解土壤无机磷的原因之一.接种自生固氮菌显著降低土壤钙磷,土壤中的铁磷、铝磷和闭蓄态磷的降幅因菌株不同而异,其原因可能与有机酸分泌的数量和种类有关.     

低磷胁迫下AM真菌对枳实生苗吸磷效应及根系分泌有机酸的影响

在温室沙培灭菌条件下,以Al-P为磷源、枳为试材、Glomus mosseae (G.m)和G.versiforme (G.v)为菌剂,研究低磷胁迫下AM真菌对枳实生苗干物重、吸磷效应及根系分泌有机酸的影响。结果表明,接种AM真菌显著增加枳地上部、地下部干物重,增幅16.79%~135.25%;同时显著增加其吸磷量,菌丝对植株的吸磷贡献率为17.04%~71.95%(G.m>G.v),施Al-P显著提高菌丝吸磷贡献率。接种AM真菌的根系分泌的有机酸种类与对照有所不同,未接种处理枳分泌的有机酸有草酸、苹果酸、乳酸、乙酸、顺丁烯二酸和柠檬酸等6种,而接种G.m的则检测到草酸、酒石酸、苹果酸、乳酸、乙酸、柠檬酸、丁二酸等7种,G.v处理的检测到酒石酸,接种处理均未检测到顺丁烯二酸;接种丛枝菌根真菌增加了枳根系分泌有机酸的量(比未接种处理增加19.80~56.87 mg/kg,且施用AlPO₄后有机酸含量显著增加(增加20.06~21.84 mg/kg);未接种植株根系仅分泌少量有机酸;接种植株根系分泌的有机酸以苹果酸(42.87%)、柠檬酸(39.22%)和草酸(12.06%)为主。     

磷与信号抑制剂对外生菌根真菌分泌草酸的调控作用

摘要:【目的】磷是树木生长的必需营养元素之一,磷素营养丰缺条件下,研究外生菌根真菌的草酸分泌及调控有益于揭示它们活化利用土壤无机磷的机理。【方法】试验设置低、正常、高3种不同磷浓度,液体培养外生菌根真菌,研究了磷和Ca2+信号/阴离子通道抑制剂对草酸分泌的调控作用。【结果】外生菌根真菌能分泌大量的氢离子和草酸、乙酸、苹果酸、柠檬酸和丁二酸等多种有机酸,对溶解难溶性无机磷有重要作用。在外生菌根真菌分泌的有机酸中,草酸占15.14%－36.01%;低磷促进草酸分泌,正常和高磷则产生抑制作用;培养液磷浓度和菌丝含磷量分别与供试菌种的草酸分泌速率呈显著或极显著负相关,相关系数依次为r=－0.264*和r=－0.349＊＊,n=60,*表示显著(P0.05),＊＊表示极显著(P 0.01),说明磷能调控外生菌根真菌分泌草酸。在低磷胁迫下,钙调蛋白抑制剂、Ca2+通道抑制剂、Ca2+内膜通道抑制剂和阴离子通道抑制剂显著抑制外生菌根真菌分泌草酸。但是,在正常和高磷条件下,草酸分泌速率低,未响应Ca2+信号/阴离子通道抑制剂。【结论】供试外生菌根真菌能分泌大量的氢离子和有机酸(尤其是草酸),有益于溶解土壤无机磷,改善寄主植物的磷营养;供磷水平调控草酸分泌速率;在低磷胁迫下,Ca2+信号是介导外生菌根真菌分泌草酸的信号因子。     

喀斯特不同植被恢复阶段土壤有机酸季节变化与有效氮磷的关系

植物分泌有机酸在提高土壤养分有效性方面起到重要作用。为了解喀斯特地区不同植被恢复阶段土壤有机酸含量季节性变化与氮磷有效性的关系,在灌木林和原生林各选择3种优势植物,测定雨季和旱季两个季节根际土和非根际土的有机酸含量、碳氮磷含量和比值、有效性氮磷含量及微生物生物量碳。结果表明:原生林植物根际土的草酸含量高于灌木林,而苹果酸和乙酸含量则低于灌木林;根际土草酸含量均高于非根际土;2个植被根际土和非根际土的草酸含量在雨季高于旱季,而苹果酸和乙酸含量则低于旱季;土壤草酸含量与有机碳、全氮、全磷和N∶P值呈显著正相关,与C∶N呈显著负相关;土壤有效氮和有效磷与草酸和微生物生物量碳呈显著正相关。上述结果表明,植物分泌有机酸的季节性变化与土壤养分状态和自身养分需求相关,而有机酸耦合微生物对养分有效性的提高具有积极的作用。因此,根际土的有机酸季节变化可能是喀斯特生态系统中植物适应土壤养分限制的一种重要机制。     

喀斯特不同植被恢复阶段土壤有机酸季节变化与有效氮磷的关系

植物分泌有机酸在提高土壤养分有效性方面起到重要作用。为了解喀斯特地区不同植被恢复阶段土壤有机酸含量季节性变化与氮磷有效性的关系,在灌木林和原生林各选择3种优势植物,测定雨季和旱季两个季节根际土和非根际土的有机酸含量、碳氮磷含量和比值、有效性氮磷含量及微生物生物量碳。结果表明:原生林植物根际土的草酸含量高于灌木林,而苹果酸和乙酸含量则低于灌木林;根际土草酸含量均高于非根际土; 2个植被根际土和非根际土的草酸含量在雨季高于旱季,而苹果酸和乙酸含量则低于旱季;土壤草酸含量与有机碳、全氮、全磷和N∶P值呈显著正相关,与C∶N呈显著负相关;土壤有效氮和有效磷与草酸和微生物生物量碳呈显著正相关。上述结果表明,植物分泌有机酸的季节性变化与土壤养分状态和自身养分需求相关,而有机酸耦合微生物对养分有效性的提高具有积极的作用。因此,根际土的有机酸季节变化可能是喀斯特生态系统中植物适应土壤养分限制的一种重要机制。     

黑麦对难溶性磷酸盐的吸收及活化机制研究

以2个黑麦品种冬牧70和King为材料,研究了植物对难溶性磷酸盐的吸收及活化,以揭示植物抵御酸性土壤逆境的机制.结果显示,(1)在活性铝含量高的赤红壤中施用磷酸铝、磷酸铁、磷酸钙等难溶性磷酸盐后,植株的生物产量和磷的积累量分别增加了0.84~6.38倍和0.60~20.5倍,且施用难溶性磷酸盐后冬牧70的生物产量和磷的积累量的增加量明显高于King.(2)铝胁迫下2种黑麦根系分泌物中的阴离子组分均能溶解难溶性磷酸盐,而在中性或阳离子组分中的难溶性磷酸盐溶解不显著;HPLC图谱显示,阴离子组分中含有柠檬酸和苹果酸.(3)铝胁迫下根系有机酸分泌量随铝处理浓度(10、30、50μmol/L AlCl3)的增加而增加,而且在柠檬酸或苹果酸溶液中难溶性磷酸盐的溶解度显著增加,其溶解的磷随有机酸浓度的增加而增加.(4)黑麦冬牧70品种对难溶性磷酸盐的吸收、阴离子组分对难溶性磷酸盐的溶解及有机酸分泌作用均较King强.结果表明,在铝胁迫下根系分泌的有机酸是黑麦活化、吸收土壤中难溶性磷的有效机制.     

有机酸对Pb、Cd的土壤化学行为和植株效应的影响

有机酸对Pb、Cd的络合作用将其对土壤吸附Pb、Cd的影响和植株效应差异的研究表明,柠檬酸、草酸与Pb、Cd络合能力的大小与重金属本身的性质有关,络合作用影响土壤对Pb、Cd的吸附量,柠檬酸降低土壤对Pb、Cd的吸附,草酸则增加土壤对Pb、Cd的吸附.水培试验表明,柠檬酸可减轻Pb对小麦、水稻幼苗的毒害.柠檬酸对Cd的植株外观毒性效应影响不显著,但能促使植株茎叶、根中Cd含量下降.Pb和Cd复合处理条件下,Cd存在促使水稻植株对Pb吸收量增加,Pb存在抑制水稻植株对Cd的吸收.     

Low-molecular-weight aliphatic carboxylic acids in soil solutions under different vegetations determined by capillary zone electrophoresis

Concentrations of low-molecular-weight aliphatic carboxylic acids in soil solution were determined by a newly developed capillary zone electrophoresis method. Soil solution samples were collected by centrifugation of soil from the A horizon of a Danish, homogeneous, nutrient-rich Hapludalf in adjacent forested and arable plots. The forested plots of 0.5 ha were 33-year old stands of beech (Fagus sylvatica L.), oak (Quercus robur L.), grand fir (Abies grandis Lindl.), and Norway spruce (Picea abies (L.) Karst.), while sugar beet (Beta vulgaris L.) and winter wheat (Triticum aestivum L.) were the agricultural crops this year. High variability in soil solution concentrations of metal cations (Al, Ca, K, Mg, Na), monocarboxylic acids (formic, acetic, lactic, and valeric acids), and di- and tricarboxylic acids (oxalic, malic, succinic, and citric acids) were found within each plot. Despite this short-range within-plot variability, higher concentrations of di- and tricarboxylic acids were found in the forested soils than in the arable soils. The vegetation seemed to favour some monocarboxylic acids, but the total monocarboxylic acid concentrations showed little relation to the vegetation. Probably due to much less soil water in the Norway spruce plot, the low-molecular-weight aliphatic carboxylic acid concentrations in the samples from that plot were much higher than those found in samples from the other plots. Carbon in low-molecular-weight aliphatic carboxylic acids only accounts for a few percent of dissolved organic carbon, and no general relation was found between carbon in low-molecular-weight aliphatic carboxylic acids and dissolved organic carbon, although the correlation between carbon in di- and tricarboxylic acids and dissolved organic carbon was significant. This revised version was published online in June 2006 with corrections to the Cover Date.     

红壤中镉在有机酸作用下的解吸行为

采用平衡批处理法,研究了3种有机酸及其两两混合液在序列pH值梯度下（pH 3.0～7.0）对华南山地红壤Cd解吸行为的影响.结果表明,草酸与苹果酸不利于Cd的解吸,反而促进了吸附,其中草酸只是在较高浓度(20 mmol·L^-1)且土壤溶液pH＞5.0时促进解吸.随着pH值升高,草s酸、苹果酸以及不含有机酸的对照溶液对红壤中Cd的解吸率都快速下降.柠檬酸在pH＜5.0时不利于Cd解吸;在pH＞5.0时显著促进Cd解吸,但两种浓度柠檬酸解吸特征有所不同,在低浓度(2 mmol·L^-1)下对镉的解吸率呈降低-升高-降低变化,在高浓度(20 mmol·L^-1)下呈降低-升高变化.在低pH条件下（pH 3.0、4.0）,苹果酸最有利于Cd的解吸,但3种酸对Cd解吸率差别不大,在较高pH条件下(pH 5.0～7.0),柠檬酸最有利于解吸,且解吸率大大高于草酸与苹果酸.有机酸混合没有明显的交互作用,对Cd的解吸率介于相应单独有机酸之间.     

Influence of Short-Chain Aliphatic Acids on the Phenanthrene Desorption and Mobilization from Contaminated Soil

This study was performed to investigate the influence of short-chain aliphatic acids (SCAAs) on the desorption of phenanthrene from artificially contaminated soils with this polycyclic aromatic hydrocarbon. Five SCAAs examined, including acetic acid, oxalic acid, malic acid, tartaric acid and citric acid, were related to the increase of phenanthrene desorption from two kinds of soil. Citric acid and oxalic acid enhanced phenanthrene desorption to a more significant extent than other organic acids. The effects of pH, SCAA concentration, and ionic strength were further evaluated. The phenanthrene desorption was enhanced as the pH increased. An increase in desorbed phenanthrene from pH 3 to pH 8 was observed, but that was followed by a slight decrease above pH 8 for most SCAAs. The phenanthrene desorption performance showed increments with increasing organic acid concentrations. However, the increase of phenanthrene desorption became less remarkable when SCAA concentrations were above 100 mmol/L. Moreover the results suggested that high ionic strength hindered the desorption of phenanthrene in the presence of SCAAs.     

Comparing phosphorus mobilization strategies using Aspergillus niger for the mineral dissolution of three phosphate rocks

Phosphorus deficiencies are limiting crop production in agricultural soils worldwide. Locally available sources of raw phosphate rock (PR) are being recognized for their potential role in soil fertility improvement. Phosphorus bioavailability is essential for the efficiency of PRs and can be increased by acid treatments. The utilization of organic acid producing micro-organisms, notably Aspergillus niger , presents a sustainable alternative to the use of strong inorganic acids, but acid production of A. niger strongly depends on the mineral content of the growth media. This study compared the phosphorus mobilization efficiency of two biological treatments, namely addition of acidic cell-free supernatants from A. niger cultivations to PRs and the direct cultivation of A. niger with PRs. The results show that addition of PR to cultivations leads to significant differences in the profile of organic acids produced by A. niger . Additions of PR, especially igneous rocks containing high amounts of iron and manganese, lead to reduced citric acid concentrations. In spite of these differences, phosphorus mobilization was similar between treatments, suggesting that the simpler direct cultivation method was not inferior. In addition to citric acid, it is suggested that oxalic acid contributes to PR solubilization in direct cultivations with A. niger , which would benefit farmers in developing countries where conventional fertilizers are not adequately accessible.     

低分子量有机酸对红壤无机态磷转化及酸度的影响

以鄂南、赣北两红壤样品为材料,加入不同有机酸并经室温培养后,测定不同P组分、pH及活性Al含量的变化。结果表明,供试有机酸均使土壤Ca2－P含量增高,增幅大小依次为柠檬酸＞苹果酸＞琥珀酸＞乙酸;2种土壤的Ca8－P和Ca10－P含量无明显变化规律,Fe-P、Al-P和O－P含量有所下降,除乙酸处理的土壤pH值无显著变化外,其它有机酸的加入使pH下降0．65－1．96;有机酸引起活性Al量增多,除乙酸处理的变化较小外,其它有机酸或混合物的加入使土壤中0．02mol.L^-1CaCl2提取Al增加4．7－50．3倍,1mol.L^-1提取Al增加4．0－67．3倍。可见,有机酸具有双重作用,既增加P的有效性,又增加土壤酸度和Al毒。     

Firing range soils yield a diverse array of fungal isolates capable of organic Acid production and pb mineral solubilization

Anthropogenic sources of lead contamination in soils include mining and smelting activities, effluents and wastes, agricultural pesticides, domestic garbage dumps, and shooting ranges. While Pb is typically considered relatively insoluble in the soil environment, some fungi may potentially contribute to mobilization of heavy metal cations by means of secretion of low-molecular-weight organic acids (LMWOAs). We sought to better understand the potential for metal mobilization within an indigenous fungal community at an abandoned shooting range in Oak Ridge, TN, where soil Pb contamination levels ranged from 24 to >2,700 mg Pb kg dry soil(-1). We utilized culture-based assays to determine organic acid secretion and Pb-carbonate dissolution of a diverse collection of soil fungal isolates derived from the site and verified isolate distribution patterns within the community by 28S rRNA gene analysis of whole soils. The fungal isolates examined included both ascomycetes and basidiomycetes that excreted high levels (up to 27 mM) of a mixture of LMWOAs, including oxalic and citric acids, and several isolates demonstrated a marked ability to dissolve Pb-carbonate at high concentrations up to 10.5 g liter(-1) (18.5 mM) in laboratory assays. Fungi within the indigenous community of these highly Pb-contaminated soils are capable of LMWOA secretion at levels greater than those of well-studied model organisms, such as Aspergillus niger. Additionally, these organisms were found in high relative abundance (>1%) in some of the most heavily contaminated soils. Our data highlight the need to understand more about autochthonous fungal communities at Pb-contaminated sites and how they may impact Pb biogeochemistry, solubility, and bioavailability, thus consequently potentially impacting human and ecosystem health.     

Environmental Control of Root Exudation of Low-Molecular Weight Organic Acids in Tropical Rainforests

The availability of phosphorus (P) can limit net primary production (NPP) in tropical rainforests growing on highly weathered soils. Although it is well known that plant roots release organic acids to acquire P from P-deficient soils, the importance of organic acid exudation in P-limited tropical rainforests has rarely been verified. Study sites were located in two tropical montane rainforests (a P-deficient older soil and a P-rich younger soil) and a tropical lowland rainforest on Mt. Kinabalu, Borneo to analyze environmental control of organic acid exudation with respect to soil P availability, tree genus, and NPP. We quantified root exudation of oxalic, citric, and malic acids using in situ methods in which live fine roots were placed in syringes containing nutrient solution. Exudation rates of organic acids were greatest in the P-deficient soil in the tropical montane rainforest. The carbon (C) fluxes of organic acid exudation in the P-deficient soil (0.7?mol?C?m^?2?month^?1) represented 16.6% of the aboveground NPP, which was greater than those in the P-rich soil (3.1%) and in the lowland rainforest (4.7%), which exhibited higher NPP. The exudation rates of organic acids increased with increasing root surface area and tip number. A shift in vegetation composition toward dominance by tree species exhibiting a larger root surface area might contribute to the higher organic acid exudation observed in P-deficient soil. Our results quantitatively showed that tree roots can release greater quantities of organic acids in response to P deficiency in tropical rainforests.