Interactive effects of organic acids in the rhizosphere

Organic acids released into the rhizosphere may perform many beneficial functions to the plant including metal detoxification and enhancement of nutrient acquisition. Typically, these organic acids are studied in isolation; however, roots simultaneously exude a cocktail of organic acids and other substances, and their combined impact on rhizosphere processes may be quite different. It has been hypothesized that some exudates may play secondary roles (e.g. inhibitors of microbial activity, blockage of sorption sites), which might enhance the longevity and nutrient-mobilization capacity of others. Here we investigated how the decomposition, sorption and P-solubilizing effects of citrate, malate and oxalate are affected by the presence of malonate and shikimate. We found that in a range of agricultural soils the decomposition of citrate, malate and oxalate was rapid, but not influenced by the presence of large quantities of shikimate or malonate. This suggests that the individual organic acids are taken up by different transport mechanisms or components of the microbial community. At large concentrations, malonate decreased sorption of citrate, malate and oxalate on the soil, whilst shikimate had little effect. The capacity of citrate, malate and oxalate to desorb P was significantly greater in cocktails containing malonate compared with the single organic acid; no effect was seen with shikimate. We conclude that neither malonate nor shikimate at realistic concentrations will significantly affect the biodegradation of citrate, malate or oxalate in the rhizosphere, and while malonate did enhance P desorption, this effect is additive rather than synergistic. Overall, we found little evidence that malonate and shikimate act as secondary regulators of citrate, malate and oxalate behavior in soil.     

低分子有机酸/盐对森林暗棕壤铁的释放效应

模拟森林凋落物淋洗液中草酸/草酸盐和柠檬酸/柠檬酸盐的浓度范围,设计了不同浓度草酸/草酸盐和柠檬酸/柠檬酸盐溶液一次性浸提和多次连续浸提等系列实验,结果表明,草酸/草酸盐和柠檬酸/柠檬酸盐对暗棕壤铁具有活化作用,活化作用大小因有机酸/盐种类、浓度和土壤性质而异。随着低分子有机酸/盐浓度的增加,A1层和B层暗棕壤活化释放的铁也逐渐增多。pH 5.16的低分子有机盐溶液对A1层和B层暗棕壤铁的活化作用强于同浓度的相应低分子有机酸,即柠檬酸盐>柠檬酸,草酸盐>草酸,因此推断草酸盐和柠檬酸盐溶液促进暗棕壤铁活化释放的机理主要在于低分子有机酸阴离子的配位反应。柠檬酸/柠檬酸盐对A1层和B层暗棕壤铁的活化作用强于同浓度的草酸/草酸盐,即柠檬酸>草酸,柠檬酸盐>草酸盐,这主要与柠檬酸对铁较强的络合能力及较大的离解常数有关。A1层与B层相比,草酸/草酸盐和柠檬酸/柠檬酸盐均对B层暗棕壤释放的铁量较高。另外,低分子有机酸对暗棕壤铁的释放并不是一次就能完成的,第一次以后的连续4次浸提仍源源不断释放出数量可观的铁。     

Iron Mobilization and Mineralogical Alterations Induced by Iron-Deficient Cucumber Plants (Cucumis sativus L.) in a Calcareous Soil

Dicotyledons cope with ion (Fe) shortage by releasing low-molecular-weight organic compounds into the rhizosphere to mobilize Fe through reduction and complexation mechanisms. The effects induced by these root exudates on soil mineralogy and the connections between Fe mobilization and mineral weathering processes have not been completely clarified. In a batch experiment, we tested two different kinds of organic compounds commonly exuded by Fe-deficient plants, i.e., three organic acids (citrate, malate, and oxalate) and three flavonoids (rutin, quercetin, and genistein), alone or in combination, for their ability to mobilize Fe from a calcareous soil and modify its mineralogy. The effect of root exudates on soil mineralogy was assessed in vivo by cultivating Fe-deficient and Fe-sufficient cucumber plants (Cucumis sativus L.) in a RHIZOtest device. Mineralogical analyses were performed by X-ray powder diffraction. The batch experiment showed that citrate and, particularly, rutin (alone or combined with organic acids or genistein) promoted Fe mobilization from the soil. The combinations of rutin and organic acids modified the soil mineralogy by dissolving the amorphous fractions and promoting the formation of illite. These mineralogical alterations were significantly correlated with the amount of Fe mobilized from the soil. The RHIZOtest experiment revealed a drastic dissolution of amorphous components in the rhizosphere soil of Fe-deficient plants, possibly caused by the intense release of phenolics, amino acids, and organic acids, but without any formation of illite. Both batch and RHIZOtest experiments proved that exudates released by cucumber under Fe deficiency concurred to the rapid modification (on a day-scale) of the mineralogy of a calcareous soil.     

外源低分子量有机酸对碳酸钙预处理的酸性土壤中活性铝钙镁影响的研究

通过在所研究的第四纪红黏土发育的红壤中混入CaCO3,研究在pH缓冲体系中外加低分子量有机酸对土壤中Al、Ca和Mg的影响。结果表明:无论加CaCO3与否,在pH 4.5的条件下外源草酸、柠檬酸、苹果酸的加入均使土壤可溶性Al显著提高,交换性Al显著下降和交换性Ca显著升高;加入CaCO3的情况下,3种有机酸处理的交换性Mg均显著提高。3种有机酸促进Al溶解能力的大小顺序为:柠檬酸>草酸>苹果酸,这一结果与有机酸和Al形成络合物的稳定常数大小一致。另一方面,3种有机酸处理下,CaCO3预处理均引起可溶性Al的显著升高和交换性Al的下降。双因素方差分析表明,有机酸通过络合作用或沉淀作用对可溶性和交换性Al、Ca和Mg均具有绝对的影响优势,CaCO3仅对可溶性和交换性Al、交换性Ca有显著影响,由于实验中pH缓冲体系的控制,这种影响主要通过Al与Ca、Mg的竞争交换作用实现。总体来说,外源低分子量有机酸的加入使土壤活性Al显著升高,活性Ca、Mg略有升高,有机酸在酸性土壤中的作用需从有机酸溶解阳离子的角度进一步评价。     

Organic Acids for the In Situ Remediation of Soils Polluted by Heavy Metals: Soil Flushing in Columns

To compare the soil remediation effectiveness of saltsof weak organic acids with strongchelating agents, three soils of different textures,all polluted by heavy metals, were washed in a column,at optimum pH, with salts of weak organic acids,namely, citrate, tartarate or oxalate + citrate orchelating agents (EDTA or DTPA). For the clay loam,Cr, Mn, Hg and Pb were removed by citrate andtartarate at levels of 43 to 45, 37 to 41, 91 to 92and 75%, respectively. EDTA and DTPA effectivelyleached only Pb after 20 pore volumes. For the loam,citrate leached 98 and 89% of Cd and Pb after 20 porevolumes, respectively, while tartarate leached out 91and 87% of Cd and Pb. EDTA and DTPA removed 93 to97% of these metals after 20 pore volumes. For thesandy clay loam, 84 to 91, 73 to 84, 56 to 70 and 72to 81% of Cd, Cu, Pb and Zn were removedrespectively, by citrate and tartarate. EDTA and DTPAremoved 93 to 97% of these metals after 20 porevolumes. An in situ soil remediation simulation wasalso tested using the sandy clay loam in a tub. After12 hr of retention, the citrate solution washed 81, 82,73 and 90%, of Cd, Cu, Pb and Zn, respectively, aftersix pore volumes. EDTA and DTPA effectively removedall heavy metals, except for Hg, but also extractedlarge quantities of soil nutrients and pollute thesoil by being adsorbed on the soil particles. Thesalts of citrate and tartarate effectively removed theheavy metals from the three polluted soils whileleaching little macro-nutrients and improving soilstructure. Each soil reached C and B levels ofsoil-clean-up criteria after 10 to 20 pore volumes andwithin 10 to 15 hr of flushing.     

Detection of Soil Organic Nitrogen in Xylem Sap Collected from Nonmycorrhizal Plants using an Immunological Technique

Phosphate buffer–extractable organic nitrogen (PEON) is considered to be a ubiquitous high-molecular-weightnitrogen (N) compound in soil and may be an important N source for some plant species. We examined whether nonmycorrhizal plants qing-geng-cai (Brassica rapa var. chinensis) and spinach (Spinacia oleracea L. cv. Atras) could uptake PEON from the soilusing animmunoassay that was previously developed from a PEON determination method using anti-PEON IgG. Xylem sap analysis of spinach using an enzyme-linked immune sorbent assay (ELISA) showed that this plant hadhigh capabilities to take up PEON from the soil. Spinach and qing-geng-cai exuded substantial amounts of oxalate or citrate under inorganic N-deficient conditions, indicating exudation of organic acids is probably involved in PEON mobilization. Further results of immunohistochemical localization of PEON in the root section of qing-geng-cai revealed that intact or at least a fraction of PEON absorbed by the epidermis passes through the cortex cell and intercellular space. Our findings indicated that some specific plants have the ability to mobilize PEON by root exudation and take up mineralizable organic N by endocytic invagination.     

The excretion of citric and malic acid by proteoid roots of Lupinus albus L.; effects on soil solution concentrations of phosphate,iron, and aluminum in the proteoid rhizosphere in samples of an oxisol and a luvisol

Organic acid concentration in the proteoid rhizosphere of White Lupin in different soil samples (Oxisol-A_p = Ox, Luvisol-A_p and Luvisol-C = L_A and L_C) was determined in order to study the influence of root-released carboxylates on the mobilization of phosphate, aluminum, and iron in the rhizosphere. In the L_C, organic acids were accumulated as Casalts extractable with water. In the proteoid rhizosphere of this soil sample 55 μmol citrate and 8 μmol malate per g soil were found. In the Ox, no water extractable organic acids were present. However, determination of citrate in the solid phase of this soil by Diffuse Reflectance Infrared Fourier Transform Spectroscopy gave concentrations of 88 and 68 μmol citrate per g soil without and with P application, respectively. Displaced soil solution from the proteoid root rhizosphere of the Ox and the L_A increased in Fe and Al concentrations from <50 μmol/L (soil from reference pots without plants) to more than 600 μmol Fe+Al/L. The concentration of P was increased by a factor of 2 despite of P uptake by the proteoid roots. The mobilization of Al, Fe, and P is attributed to ligand exchange of phosphate against citrate and to the solubilization of Al and Fe as carboxylate complexes.     

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.     

间作对土壤团聚体有机碳储量的影响及其氮调控效应

基于5年的田间小区定位试验,采用干筛法对不同施氮水平下的玉米单作、马铃薯单作和玉米马铃薯间作土壤进行团聚体分级并测定各粒级团聚体有机碳含量,研究间作对土壤团聚体有机碳储量的影响及其氮调控效应。结果表明:92%以上的土壤有机碳储藏在土壤大颗粒团聚体(2 mm)和小颗粒团聚体(2～0.25 mm)中。间作提高了土壤大颗粒团聚体(2 mm)和小颗粒团聚体(2～0.25 mm)的比例,但对不同粒级团聚体有机碳含量的影响与施氮量相关。对比2种单作,间作在低氮(N1)和常规施氮(N2)下增加了土壤总有机碳储量,在不施氮(N0)和高氮(N3)下无显著影响或降低有机碳储量。其中,间作通过增加土壤大颗粒团聚体(2 mm)的比例及其有机碳含量,在低氮(N1)时产生最强的间作固碳优势,土壤总有机碳储量分别较玉米单作和马铃薯单作提高24.8%和5.7%。因此,适量施用氮肥可以充分发挥间作效应,有效提高土壤有机碳储量。     

Biodegradation of low molecular weight organic acids in rhizosphere soils from a tropical montane rain forest

Root exudation of organic acids could be an important strategy for plant acquisition of phosphorus (P) from P-deficient soils in tropical rain forests. However, the efficacy of organic acids on P mobilization in the rhizosphere could be reduced due to their rapid biodegradation by rhizosphere microorganisms. To assess the dynamics and function of organic acids in the rhizosphere soils in tropical rain forests, we examined the concentrations of oxalate, citrate, and malate in soil solution and the mineralization kinetics of ¹⁴C-radiolabelled oxalate and citrate in the rhizosphere and bulk soil fractions. We compared two tropical montane rain forests from Mt. Kinabalu, Borneo that share similar parent material (i.e., sedimentary rocks) and climate but differ in terms of soil age. The older soil (Tertiary age materials) was affected by podzolization and had less inorganic labile P compared to the younger soil (Quaternary colluvial deposits). In the P-deficient older soil, the rhizosphere soil solution contained markedly higher concentrations of oxalate, citrate, and malate than did the bulk soil, whereas in the P-rich younger soil, the levels of organic acids in the rhizosphere were lower. The higher levels of organic acids in the rhizosphere of P-deficient soils are caused by greater root exudation and the lower sorption capacity for organic acids. The results of mineralization kinetics showed that oxalate and citrate in soil solution were rapidly mineralized in both rhizosphere and bulk fractions of both P-rich and P-deficient soils, having short mean residence times (2.3–13.1 h for oxalate and 0.8–1.6 h for citrate). The mineralization rates of oxalate and citrate were highest in the rhizosphere fraction of the P-deficient soil, where the pool of organic acids was largest and rapidly replenished by root exudation. Our data indicate that consumption as well as production of organic acids in the rhizosphere could be enhanced in P-deficient soil. The efficacy of organic acids on P mobilization in the rhizosphere in tropical montane rain forests appears to vary depending on the level of soil P availability and the anion sorption capacity, attributable to soil aging with podzolization.     

Differential Aluminum Resistance and Organic Acid Anions Secretion in Triticale

Abstract

Triticale (X Triticosecale Wittmack), a hybrid of wheat and rye, shows a high degree of aluminum (Al) tolerance, but variation in Al resistance between cultivars does exist. The mechanisms responsible for differential Al resistance in 10 triticale cultivars were investigated in this study. Triticale roots secreted both malate and citrate in response to Al stress. The amount of organic acid anions secreted was correlated positively to the relative root elongation (an index for Al resistance) and negatively to the Al content in root apices under Al stress, suggesting that the secretion of malate and citrate seems to be involved in the exclusion of Al from root tip. The Al‐induced secretion of malate and citrate was characterized using an Al‐resistant cultivar (ZC 237) and an Al‐sensitive cultivar (OH 1621). Root elongation was significantly inhibited in both ZC 237 and OH 1621 after 24 h of exposure to 30, 50, or 100 µM Al but was more strongly in OH 1621 than in ZC 237 at all Al concentrations tested. A marked lag phase (3 h) between the addition of Al and the secretion of organic acid anions was observed in both triticale cultivars, and the secretion increased with increasing external Al concentration. The two anion‐channel inhibitors, phenylglyoxal and niflumic acid, significantly inhibited the secretion of malate and citrate in ZC 237, with the degree of the inhibition of niflumic acid greater than that of phenylglyoxal. The Al‐induced secretion of malate and citrate decreased to a very low level at low temperature (4°C) in both cultivars. These results indicate that Al‐induced malate and citrate secretion from roots play important roles in excluding Al and thereby detoxifying Al in triticale. The Al‐induced organic acid anions were inhibited by anion‐channel inhibitors and were dependent on temperature.     

Effect of Low Molecular Weight Organic Anions on Adsorption of Aluminum by Variable Charge Soils

To examine the effect of organic anions on adsorption of Al by variable charge soils at different pH values, the adsorption by three soils in the presence of three low-molecular-weight aliphatic carboxylic acids was investigated. The results showed that the effect depended on pH, the type of organic anions and their concentration. The presence of citrate and oxalate led to an increase in the adsorption of Al at low pH and low concentration of organic anions, with citrate showing a stronger effect than oxalate. For example, the maximum increments of Al adsorption in the presence of citrate were 131.9, 104.8 and 32.9% in the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol and the Ferric Acrisol, respectively, whereas in the presence of oxalate it was 36.1% in the Rhodic Ferralsol. At high pH or high concentration of organic anions, they showed an inhibiting effect on the adsorption of Al. For example, citrate caused the increase in Al adsorption by 164.0, 131.0 and 61.0% at pH3.85 and the decrease in Al adsorption by 15.2, 19.5 and 45.6% at pH 4.8 for the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol and the Ferric Acrisol, respectively. In the citrate and oxalate systems, the adsorption of Al increased with the increase in the concentration of organic anions, reaching a maximum values at about 0.4 mmol L^?1, and then decreased. When the concentration of organic anions was higher than about 1.0 mmol L^?1, both citrate and oxalate inhibited the adsorption of Al. The ability of organic anions in increasing the adsorption at low pH and decreasing the adsorption at high pH followed the same order: citrate > oxalate > acetate. The increase of Al adsorption at low pH is caused by the increase in soil negative surface charge as a result of the adsorption of organic anions by variable charge soils, while the decrease of Al adsorption at high pH and high concentration of organic anions is related to the competition of organic ligands for aluminum ions with soil surface. After the removal of free iron oxides from the soil, Al adsorption decreased in the presence of citrate, the anion species most strongly adsorbed by variable charge soils and complexed with aluminum ions. For example, for the Rhodic Ferralsol and the Ferric Acrisol, the removal of free iron oxides caused a decrease in the adsorption of Al in the presence of citrate at pH4.4 by 26.2 and 21.9%, respectively.     

Organic acid behaviour in a calcareous soil implications for rhizosphere nutrient cycling

Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate>citrate>malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000 mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon.     

不同有机肥对采煤塌陷区土壤氮素矿化动态特征研究

为揭示不同有机肥对煤矿复垦土壤氮素矿化特性的影响,以山西省孝义市水峪煤矿采煤塌陷复垦土壤为研究对象,采用室内好气培养法,研究在40%含水量和30℃培养条件下,施用3种有机肥(鸡粪、猪粪、牛粪)后在0~161天的氮素矿化动态特征,以明确不同有机肥对该矿区复垦土壤氮素矿化特征,从而预估不同有机肥的供氮特性,为合理施用有机肥进行低产农田的培肥改造提供科学依据。结果表明:(1)各处理0~14天铵态氮含量均随培养时间的延长迅速下降,与培养时间呈极显著负相关关系(P<0.01),14~161天土壤铵态氮含量维持在较低水平,培养结束时,各处理铵态氮含量均低于1.31mg/kg。(2)各处理土壤硝态氮含量、累积量及矿质氮累积量变化均呈近似的“S”形曲线递增,表现为0~56天缓慢增加,56~84天迅速增加,84天至培养结束(161天)其含量基本不变。培养结束时不同处理间硝态氮含量、累积量及矿质氮累积量整体上均表现为鸡粪>猪粪>牛粪>空白,且鸡粪较猪粪和牛粪处理间存在显著差异,猪粪和牛粪较空白处理间存在显著差异(P<0.05)。(3)不同施肥处理出现氮素净矿化的时间点不同,其中鸡粪处理在第14天时最早出现净矿化现象,而猪粪和牛粪在培养28天后才出现明显的氮素净矿化。(4)不同施肥处理在培养的不同阶段硝态氮和矿质氮累积速率不同,但整体趋势一致,表现为培养0~84天各处理土壤累积矿化波动较大,56~84天达到峰值,培养84~161天各处理矿化速率平稳下降。总体来看,有机肥的施入能有效促进煤矿复垦土壤氮素矿化,从而提高土壤氮素有效性。其中,施鸡粪较猪粪和牛粪对提高矿区复垦土壤有效氮效果更好。4种处理的氮素矿化效果总体表现为鸡粪>猪粪>牛粪>空白。     

半定量RT-PCR研究氮素形态对樱桃番茄果实中有机酸代谢相关酶基因表达的影响

研究了全硝（100%NO-3）、铵硝配施（75%NO-3: 25%NH+4）及全铵（100%NH+4）营养对樱桃番茄果实有机酸含量的影响,测定了与有机酸合成相关的磷酸烯醇式丙酮酸羧化酶（PEPC）、柠檬酸合成酶（CS）、苹果酸脱氢酶（MDH）活性变化,并利用RT-PCR检测了相应的基因在转录水平上的表达差异。结果表明, 1）全硝和铵硝配施处理下果实柠檬酸含量在整个生育期均显著高于全铵处理,而铵硝配施处理下果实中柠檬酸和苹果酸含量在成熟期均显著低于全硝处理。2）不同形态氮素及配施处理下,果实中柠檬酸含量与CS活性的变化趋势均呈单峰型,但到达峰值的时间不同。全铵处理下果实苹果酸含量与PEPC活性呈显著正相关,全硝、铵硝配施处理下果实苹果酸和柠檬酸含量都与MDH活性呈显著正相关。3）在膨大期和成熟期,全硝处理和铵硝配施处理下PEPC基因（PPC1、PPC2）表达显著高于全铵处理; 线粒体苹果酸脱氢酶（mMDH）的表达对果实苹果酸脱氢酶活性和苹果酸积累起主要作用,表明适当比例的铵硝配施可能通过影响果实中PEPC和MDH的活性和基因表达从而显著降低成熟果实有机酸的含量。     

不同有机替代对黄土旱塬土壤碳、氮组分及冬小麦产量的影响

探讨黄土旱塬冬小麦区不同有机肥替代化肥氮对小麦产量及土壤碳氮组分的影响,为该区减施化学氮肥、促进小麦提质增效和农业绿色可持续发展提供理论依据。于2019年在山西黄土旱塬冬小麦种植区设置100%化肥N处理(HF)、10%腐殖酸N+90%化肥N (F1)、30%腐殖酸N+70%化肥N (F3)、50%腐殖酸N+50%化肥N (F5)、10%有机肥N+90%化肥N (Y1)、30%有机肥N+70%化肥N (Y3)、50%有机肥N+50%化肥N (Y5)7个试验处理,系统研究了不同比例腐殖酸、有机肥替代化肥对小麦产量及产量构成和土壤碳、氮组分含量的影响。结果表明:F3、F5、Y3和Y5处理,分别较HF显著提高9.7%,8.0%,9.2%和18.2%。同时,Y5对土壤中各种活性有机碳、氮组分含量的提高均有显著促进作用,提高幅度在36.8%~114.4%和27.8%~105.4%;Y3处理下可溶性、水溶性、微生物有机碳、氮和轻组有机碳、氮组分的含量较HF显著提高21.1%~156.8%;F3和F5处理下土壤中可溶性、微生物和轻组有机碳、氮组分含量较HF显著提高25.4%~119.3%。可溶性有机碳、微生物有机氮、轻组有机氮与籽粒产量呈极显著正相关;可溶性有机氮通过促进公顷穗数增加而提高冬小麦产量;总有机碳、水溶性有机碳和微生物有机氮则通过提高穗粒数达到增产效果。综上,在黄土旱塬冬小麦种植区进行30%~50%的有机肥和腐殖酸替代化肥后,可达到显著增产效果,同时提高土壤中活性碳、氮组分的作用。其中,50%有机肥替代处理的增产与培肥地力效果更为显著,适宜在当地推广应用。     

Nitrogen Mineralization in Soils Related to Initial Extractable Organic Nitrogen: Effect of Temperature and Time

An important source of nitrogen (N) for crops is mineralization of soil organic matter during the growing season. Awareness is growing that dissolved organic nitrogen (DON) plays an important role in mineralization and plant uptake. We studied the influence of temperature and time on extractable organic nitrogen (EON) levels, which is a measure of DON, and their relationship with N mineralization. Aerobic incubation experiments were conducted in the laboratory for five soils at different temperatures (4 20, and 30 °C) and different time intervals with optimal water content (60% of its water-holding capacity). Net N mineralization ranged between 14 and 155 mg kg^–1 within 84 days and was correlated with the initial amount of EON. Net N mineralization among the soils, time, and incubation temperatures was linearly related to the square root of time multiplied by temperature, with mineralization rate k being independent of time and temperature. Because initial EON values were also related to these kvalues, we were able to describe the net N mineralization at different temperatures based on an analysis of initial EON. Preliminary validation with results from pot experiments in the literature suggests that the approach is promising, although the proposed model needs to be calibrated with more soils.     

我国南方不同地带性水稻土有机氮组分变化

采集我国南方不同地带性水稻土,运用封管水解Brerrmer法测定了土壤中氨基酸氮、氨基糖氮、铵态氮、未知氮等酸解性有机氮组分,以探究区域条件对土壤有机氮结构组成的影响。结果表明,从区域地带性来看,水稻土中全氮及有机氮各组分含量无明显规律,这可能与区域性的施肥等管理措施和气候因素综合作用相关。然而,土壤有机氮各组分占全氮比例除氨基酸氮外均与区域纬度呈线性相关,其中酸解总氮、未酸解氮、氨基糖氮、酸解未知氮以及铵态氮线性相关的决定系数R~2分别为0.556 6、0.729 3、0.803 6、0.897 5和0.411 3。可见,人为耕作管理对土壤全氮含量影响很大,而自然环境则对土壤有机氮结构组成起决定作用。     

培肥措施对复垦土壤轻重组有机碳氮的影响

为揭示复垦土壤轻重组分有机碳氮随复垦年限和培肥措施变化的特征,采用密度分组方法研究了不施肥(CK)、单施化肥(CF)、单施有机肥(M)、有机无机配施(MCF)和生物有机肥与化肥配施(MCFB)5种培肥措施下复垦4,8年土壤轻重组分碳氮含量及碳氮比变化规律。结果表明:复垦土壤总有机碳氮与轻重组有机碳氮含量变化趋势总体均表现为随复垦年限的增加而显著提高。经过8年复垦,不同处理间,单施有机肥对总有机碳(TOC)、总有机氮(TON)、轻组有机碳(LFOC)、重组有机碳(HFOC)与轻组有机氮(LFON)、重组有机氮(HFON)的提高效果总体优于其他处理,与生土相比,增加幅度分别为148.10%,68.09%,163.68%,129.51%,35.00%,92.59%。土壤轻组组分C/N重组组分C/N,土壤轻组组分C/N总体表现为随复垦年限增加而提高,以单施化肥最高,达25.48;重组C/N表现为随复垦年限增加而降低,以单施化肥最低,为6.44。施肥对土壤碳氮库管理指数影响显著,各施肥处理均以生物有机肥与化肥配施处理效果最好。综合来看,在等量养分投入的情况下,单施有机肥更有利于采煤塌陷区复垦土壤总有机碳氮库及轻重组有机碳的积累,单施化肥更大程度促进了轻组组分有机碳和重组组分有机氮的提升幅度。     

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.