Root exudation of sugars,amino acids,and organic acids by maize as affected by nitrogen,phosphorus, potassium,and iron deficiency

Root exudates play a major role in the mobilization of sparingly soluble nutrients in the rhizosphere. Since the amount and composition of major metabolites in root exudates from one plant species have not yet been systematically compared under different nutrient deficiencies, relations between exudation patterns and the type of nutrient being deficient remain poorly understood. Comparing root exudates from axenically grown maize plants exposed to N, K, P, or Fe deficiency showed a higher release of glutamate, glucose, ribitol, and citrate from Fe‐deficient plants, while P deficiency stimulated the release of γ‐aminobutyric acid and carbohydrates. Potassium‐starved plants released less sugars, in particular glycerol, ribitol, fructose, and maltose, while under N deficiency lower amounts of amino acids were found in root exudates. Principal‐component analysis revealed a clear separation in the variation of the root‐exudate composition between Fe or P deficiency versus N or K deficiency in the first principal component, which explained 46% of the variation in the data. In addition, a negative correlation was found between the amounts of sugars, organic and amino acids released under deficiency of a certain nutrient and the diffusion coefficient of the respective nutrient in soils. We thus hypothesize that the release of dominant root exudates such as sugars, amino acids, and organic acids by roots may reflect an ancient strategy to cope with limiting nutrient supply.     

Soluble root exudates of maize: Influence of potassium supply and rhizosphere microorganisms

Maize was grown for 36 days in solution culture with roots either under axenic conditions or in the presence of rhizosphere organisms. In other experiments with sterile roots the plants were grown with different concentrations of potassium. At the end of the experiments sugars, organic acids and amino acids in the nutrient solutions were determined. Under axenic conditions the exudates consisted of up to 65% sugars, up to 33% organic acids and only up to 2% amino acids. The same substances were detected in non-sterile nutrient solutions. In the presence of microorganisms fructose, arabinose and the predominating glucose decreased to almost one half, while sucrose was not affected. The amounts of organic acids were not changed by microbial growth. The main amino acid, glutamic acid, was nearly doubled by the presence of microorganisms, whereas other amino acids remained unchanged. The lower O₂ content of the nutrient solutions of non-sterile roots suggested microbial decomposition of monosaccharides. In another experiment with roots grown under axenic conditions and with different K treatments low K supply significantly increased the total amounts of sugars, organic acids and amino acids exuded g^?1 root dry matter. As in the previous experiment glucose, fumaric and oxalacetic acid as well as glutamic and aspartic acid dominated in the respective fractions. Again sugars and organic acids represented the major quantity of exudates, while amino acids amounted to less than 2%. In an additional experiment with another cultivar, with nitrate as N source and a 5-day longer growth period, somewhat different results were obtained. In the exudates sugars were found in lower amounts, probably due to a higher growth rate. Under these conditions organic acids were the prevailing root exudates. Unlike sugars and amino acids, their total quantity was not affected by K nutrition, but the proportion of malic acid increased with increasing K supply, while oxalacetic acid dominated at low K nutrition. Similarly the total amount of organic acids within the root was independent of K nutrition. However malic acid content increased with increasing K application, while the likewise dominating citric and oxalacetic acid decreased.     

Gas chromatography–mass spectrometry associated global analysis of rice root exudates under aseptical conditions

Components of rice root exudates were surveyed by gas chromatography–mass spectrometry (GC-MS) and the effect of phosphate (P) starvation was investigated. Rice seedlings were aseptically grown in controlled environments under P-supplied (+P) or P-deficient (–P) conditions. Root exudates were collected from the culture solution 4 and 8 days after treatment (D4 and D8, respectively), which contain the first and second 4-day intervals. The collected solution was lyophilized and then eluted with methanol. In the present study, primary metabolites, such as sugars, amino acids, organic acids and fatty acids, were mainly targeted. After derivatization with methoxyamine hydrochloride and N-methyl-N-trifluoroacetamide, the samples were analyzed by GC-MS. Sugars and various amino acids (such as aspartic acid and l -isoleucine) were mainly detected and the components changed with the growth stage rather than the P content in the culture solution. The relative amount of sugars (such as glucose and fructose) and amino acids (such as aspartic acid and l -isoleucine) decreased in the D8 samples. Of the 78 detected compounds, orthogonal partial least-squares discrimination analysis (O-PLS-DA) showed that four compounds were related to the P content of the nutrient solution and 58 were related to the sampling date (days after treatment). The results suggest that the physiological change during seedling development was unexpectedly large and that the response to the environment was rather small.     

Qualitative and quantitative analysis of water‐soluble root exudates in relation to plant species and development

The composition of root‐derived substances is of great importance for the understanding of processes in the rhizosphere. Therefore, methods allowing a comprehensive collection and chemical analysis of the organic root exudates are necessary. In this study, we compare different methods with regard to their suitability to collect and characterize root exudates. Because the percolation or water logging method failed to quantitatively extract root exudates, a dipping method was developed which allowed an almost complete sampling of coldwater‐soluble root exudates. By ¹⁴CO₂ labeling of the shoots the composition of root exudates was found to be influenced by plant species and growth stage. In comparison to pea plants maize plants had a higher share of carboxylic acids and a lower share of sugars. Younger maize plants exuded considerably higher amounts of ¹⁴C labeled organic substances per g root dry matter than older ones. During plant development the relative amount of sugars decreased at the expense of carboxylic acids. The described methods are well suited for the elucidation of the influence of growth factors on root exudation.     

不同抗性蚕豆品种根系分泌物对枯萎病菌的化感作用及根系分泌物组分分析

蚕豆枯萎病是土传病害,其发生与蚕豆根系分泌物有密切关系。本文以3个枯萎病不同抗性蚕豆品种——‘89-147’(高抗)、‘8363’(中抗)和‘云豆324’(感病)为材料,通过水培试验收集根系分泌物,测定根系分泌物对镰刀菌孢子萌发和菌丝生长的影响,分析对枯萎病表现出不同抗性的蚕豆品种根系分泌物中糖、氨基酸和有机酸的含量,分离鉴定了根系分泌物中氨基酸和有机酸的组分。结果表明,抗病品种的根系分泌物抑制了尖孢镰刀菌的孢子萌发和菌丝生长,在加入5 mL中抗品种根系分泌物时,显著促进尖孢镰刀菌孢子萌发,但对菌丝生长无显著影响;而在加入1 mL感病品种根系分泌物时,就能显著促进尖孢镰刀菌孢子萌发和菌丝生长。不同抗性蚕豆品种根系分泌物中氨基酸总量和总糖含量随抗性的降低而升高,有机酸分泌总量则随蚕豆品种对枯萎病的抗性增加而升高。感病品种和中抗品种中检出15种氨基酸,而高抗品种中检出14种,组氨酸只存在于中抗品种中,脯氨酸仅在感病品种中检出,3个蚕豆品种根系分泌物中均未检出精氨酸。蚕豆根系分泌物中天门冬氨酸、谷氨酸、苯丙氨酸、酪氨酸和亮氨酸含量高,可能会促进枯萎病的发生,而蛋氨酸、赖氨酸和丝氨酸含量高可能抑制枯萎病发生。酒石酸仅在抗病品种中存在,根系分泌物中有机酸种类丰富,有助于提高蚕豆对枯萎病的抗性。蚕豆对枯萎病的抗性不同,根分泌物对镰刀菌孢子萌发和菌丝生长的影响也不同,而这种抗病性差异与蚕豆根系分泌物中糖、氨基酸、有机酸的含量和组分密切相关。     

Variation of wheat root exudates under aluminum stress

The wheat (Triticum aestivum L.) cultivar Yangzhou 158 was used as a reference. The wheat root exudates were collected using a hydroponic mode. The changes of the electrolytes, H+, sugar, organic acids, amino acids, and secondary metabolites in wheat root exudates induced by aluminum (Al) were studied. The research results show that Al stress affects wheat root exudation. The secreted electrolytes and sugar increase with the increasing of the external Al3+ concentration. The total amount of secreted amino acids has a specific correlation with the external Al3+ concentration. At first, the amino acids secrete normally, but when Al3+ concentration is over 10 mg.L-1, the amino acid constitution varies obviously. Under Al stress, some original secondary metabolites disappear gradually, and other new secondary metabolites release simultaneously. Increasing the external Al3+ concentration gradually stimulates the exudation of organic acids. The organic acid levels in the wheat root zone increase in response to Al treatments. Active Al ions are accumulated in wheat roots. This Al-dependent variation in wheat root exudates suggests a specific Al-induced response of the wheat.     

Release of zinc mobilizing root exudates in different plant species as affected by zinc nutritional status

The effect of zinc nutritional status of the plant on the release of zinc mobilizing root exudates was studied in various dicotyledonous (apple, bean, cotton, sunflower, tomato) and graminaceous (barley, wheat) plant species grown in nutrient solutions. In all species, zinc deficiency increased root exudation of amino acids, sugars and phenolics. However, the root exudates of zinc deficient dicotyledonous species did not enhance zinc mobilization from a synthetic resin (Zn chelite), or a calcareous soil, although mobilization of iron from Fe^III hydroxide was increased. By contrast in the graminaceous species, root exudates from zinc deficient plants greatly increased mobilization of both zinc and iron from the various sources. These differences in capability of mobilization of zinc and iron between the plant species are the result of an enhanced release of phytosiderophores with zinc deficiency in the graminaceous species.     

Ability of various water‐insoluble fertilizers to supply available phosphorus in hydroponics to plant species with diverse phosphorus‐acquisition efficiency: Involvement of organic acid accumulation in plant tissues and root exudates

Previous studies describe the suitability of a new type of phosphorus (P) fertilizer, called “rhizosphere‐controlled fertilizer” (RCF), to supply available P to plants while reducing soil phosphorus fixation. In order to explore the involvement of organic acid root exudation in P uptake from RCF, we investigated the relationship between shoot and root P concentrations, and the concentration of the main polycarboxylic organic acids in roots, shoots, and plant exudates. Plant species with different P‐acquisition efficiency (low: maize; medium: chickpea; high: lupin) were grown in hydroponics with three different P fertilizers: The water‐insoluble P fraction of RCF (RCF); Phospal, a slow‐release source of phosphate composed of calcium and aluminum phosphates (PH); monopotassiumphosphate (KP), and a control treatment without P (P–). RCF was as efficient as KP in supplying P to plants in the case of chickpea and lupin, and slightly less efficient than KP in maize. However, P from PH was not available for maize and less available compared to KP and RCF in chickpea and lupin. This variation reflects the different efficiencies in P acquisition for the three plant species. Except in the case of maize, plants receiving KP presented the lowest concentration of organic acids in roots and exudates, while those plants suffering severe P deficiency (P– and PH) showed the highest organic acid concentration. However, RCF had a high concentration of organic acids in roots and exudates, as well as a high P concentration in the shoot indicating that P uptake from RCF is enhanced due to root release and action of specific organic acids.     

Metabolite profiling of wheat grains (Triticum aestivum L.) from organic and conventional agriculture

In some European community countries up to 8% of the agricultural area is managed organically. The aim was to obtain a metabolite profile for wheat (Triticum aestivum L.) grains grown under comparable organic and conventional conditions. These conditions cannot be found in plant material originating from different farms or from products purchased in supermarkets. Wheat grains from a long-term biodynamic, bioorganic, and conventional farming system from the harvest 2003 from Switzerland were analyzed. The presented data show that using a high throughput GC-MS technique, it was possible to determine relative levels of a set of 52 different metabolites including amino acids, organic acids, sugars, sugar alcohols, sugar phosphates, and nucleotides from wheat grains. Within the metabolites from all field trials, there was at the most a 50% reduction comparing highest and lowest mean values. The statistical analysis of the data shows that the metabolite status of the wheat grain from organic and mineralic farming did not differ in concentrations of 44 metabolites. This result indicates no impact or a small impact of the different farming systems. In consequence, we did not detect extreme differences in metabolite composition and quality of wheat grains.     

间作对玉米根系分泌物及团聚体稳定性的影响

通过田间小区试验种植玉米(玉米单作、玉米∥大豆、玉米∥马铃薯),测定3个生育期(拔节期、大喇叭口期、抽雄期)玉米根系分泌总糖含量、总有机酸含量和土壤团聚体状况,分析间作对玉米根系分泌物及团聚体稳定性的影响。结果表明:玉米根系分泌总糖含量和总有机酸含量随生育期的推移而增加,间作显著提高玉米根系分泌总糖含量和总有机酸含量,玉米∥马铃薯玉米∥大豆。在抽雄期,玉米∥大豆、玉米∥马铃薯相比玉米单作0.25mm水稳性团聚体含量(R_(0.25))分别显著提高6.19%,8.17%;平均质量直径(MWD)分别提高5.04%,10.08%;几何平均直径(GMD)分别提高6.12%,12.24%;分形维数(D)分别显著降低0.72%,1.09%;团聚体破坏率(PAD)分别显著降低16.77%,26.08%。在根系分泌物最大的抽雄期,玉米根系分泌总糖含量、总有机酸含量与R_(0.25),GMD,D,PAD呈极显著相关关系(P0.01)。因此,间作可通过增加玉米根系分泌总糖含量和总有机酸含量,进而提高土壤团聚体的稳定性。     

Adsorption efficiency of a continuous trapping system and its use for the collection of root exudates from cucumber

Root exudates comprising soluble low‐molecular‐weight organic compounds (LMWOCs) play a crucial role in the rhizosphere processes. Therefore, accurate determination of the composition and quantity of these compounds is of importance. A continuous trapping system (CTS) with XAD‐4 macroporous resin is widely used for collecting root exudates in hydroponics, and ion exchange resins are used in the separation of root exudates into neutral, acid and basic fractions. Here, we studied the adsorption equilibrium isotherms and dynamic adsorption properties of 27 standard LMWOCs on XAD‐4 resin. The adsorption isotherms of most LMWOCs matched the Langmuir isotherm equations. Furthermore, we investigated the adsorption efficiency of the CTS for LMWOCs and the recovery ratios during fractionation by ion exchange resins. The adsorption capacities of the CTS for LMWOCs which are non‐polar or having large non‐polar moieties were higher. The recovery ratios of most LMWOCs were larger than 80% during fractionation. The overall recovery ratios of LMWOCs were ca. 10, 20, and 30% for sugars, organic acids, and amino acids, respectively. Using this collection method, we present the composition and quantity of root exudates of cucumber (Cumumis sativus L.) at four different growth stages. The major components of root exudates were similar to previous works, whereas the quantities were different. The various collection methods may be the main reason for these differences. Therefore, it is necessary to study the overall recovery ratios when the compositions of root exudates via different collection methods are compared.     

Low molecular weight organic acids released from roots of durum wheat and flax into sterile nutrient solutions

Knowledge of the composition and quantity of organic substances released from roots of different plant species is necessary for understanding the chemical and biological processes in the rhizosphere. The present study was undertaken to quantify low molecular weight organic acids (LMWOAs) released from roots of five cultivars/lines of durum wheat (Triticum turgidum var. durum L.): Kyle, Sceptre, DT618, DT627, and DT637 and four cultivars/ lines of flax (Linum usitatissiumum L.): Somme, Flanders, AC Emerson, and YSED 2. Plants were grown in sterile nutrient solution cultures and amounts of organic acids exuded by roots were analyzed by gas chromatography. The LMWOAs varied significantly among both durum wheat and flax cultivars and oxalic, malonic, fumaric, succinic, acetic, malic, citric and tartaric acids were detected in root exudates of both species. Generally, oxalic and acetic acids were predominant in durum wheat exudates and oxalic, acetic and malic acids were predominant in flax root exudates. High oxalic acid concentrations occurred in root exudates of durum wheat cultivars DT627 and DT637, and flax cultivar YSED 2. Compared with the other durum wheat cultivars, Kyle released the lowest total amount of LMWOAs, whereas among the flax cultivars, YSED 2 had the highest total amount of acids secreted from roots. The data showed that the release of LMWOAs from roots was cultivar dependent. The results provide valuable background information for studying the role of root exudates in soil‐plant relationships.     

Transformation of organic rhizodepositions by rhizosphere bacteria and its influence on the availability of tertiary calcium phosphate

This study assesses the influence of saccharides in the rhizodeposition on the phosphate solubilizing ability of rhizosphere bacteria. Water‐soluble rhizodeposits were analyzed of ¹⁴C‐labeled pea plants (Pisum sativum, cv. ‘Grapis’) which were grown at two different levels of P‐nutrition. The sugars produced were fed in vitro either as single compounds or as synthetic mixtures to three bacterial strains and the ability of the bacteria to mobilize Ca₃(PO₄)₂ was measured. The relative glucose proportion of pea exudates decreased under P deficiency while the content of galactose, ribose, xylose and fucose increased. In vitro feeding of single sugars and sugar mixtures showed that the ability of Pseudomonas fluorescens (PsIA12) to dissolve tertiary calcium phosphate was lower with pentoses and the mixed sugars of the P‐deficient plants than with glucose. On the other hand, the shifted sugar pattern observed under P deficiency increased the phosphate mobilization ability of Pantoea agglomerans (D5/23) and Azospirillum sp. (CC 322) considerably. This observation can only partly be explained by the acidification of the nutrient medium. Bacteria also produced different carboxylic anions depending on sugar supply. In addition to low‐molecular mono‐, di‐, and tricarboxylic acids which are known as P‐solubilizing substances, sugar acids also played an important role in cultures D 5/23 and CC 322.     

籽粒苋不同富钾基因型根系分泌物中有机酸和氨基酸的变化特点

采用溶液培养试验研究了籽粒苋(Amaranthus.spp.)不同富钾基因型在不同供钾水平条件下3个不同生长时期内根系分泌物中氨基酸和有机酸的种类及含量变化情况。结果表明,1)籽粒苋根系分泌物中氨基酸和有机酸含量随着供钾水平的升高而降低,且富钾基因型始终大于一般基因型。在低钾胁迫时,根系分泌物中有10种氨基酸和5种有机酸出现,而在供钾正常时则缺少谷氨酸、甘氨酸、苯丙氨酸、草酸和柠檬酸等;酪氨酸、-氨基丁酸和丝氨酸的含量约占氨基酸分泌总量的一半以上;苹果酸含量约占有机酸分泌总量的60%以上。2)籽粒苋生长50d时,一般基因型氨基酸和有机酸的分泌总量较生长40d时迅速降低,而富钾基因型降低速度则相对较为平稳。在3个生长期内,酪氨酸、-氨基丁酸和丝氨酸均为两类基因型根系分泌物中的主要氨基酸种类,苹果酸则是主要的有机酸类型,其在氨基酸和有机酸分泌总量中所占相对比例均随生长期的延长而升高。3)籽粒苋根系分泌物处理后的土壤速效钾含量均高于清水对照处理,富钾基因型在低钾胁迫时的根系分泌物对土壤钾的活化作用明显大于一般基因型。     

连作马铃薯不同生育期根系分泌物的成分检测及其自毒效应

为探讨马铃薯连作障碍的可能机理,在大田条件下,以轮作为对照(CK),收集连作5年(CP5)马铃薯植株在不同生育期的根系分泌物,采用GC-MS对根系分泌物的主要成分进行了鉴定,并通过生物检测验证了根系分泌物的自毒效应。结果表明:CK和CP5处理的马铃薯在不同生育期的根系分泌物均鉴定出糖类、酸类、胺类、脂类、醇类和嘧啶类等成分,以糖类和酸类物质居多;CP5处理根系分泌物的成分较CK复杂,酸类物质含量有升高的趋势。连作改变了马铃薯根系分泌物的化学组成和含量:CP5处理在苗期、现蕾期和开花期的根系分泌物中均鉴定出邻苯二甲酸二丁酯,相对含量分别为0.16%、0.21%和0.24%,CK处理未检测到;CP5处理在苗期、现蕾期和开花期的根系分泌物中均鉴定出棕榈酸,相对含量分别为0.34%、1.12%和0.47%,CK处理仅在现蕾期和开花期鉴定出棕榈酸的存在,但相对含量仅为0.56%和0.24%。生物检测试验结果表明,棕榈酸和邻苯二甲酸二丁酯显著抑制了马铃薯生长,1 mmol·L-1棕榈酸和邻苯二甲酸二丁酯对马铃薯生长的抑制作用远远大于0.5 mmol·L-1的抑制作用。棕榈酸和邻苯二甲酸二丁酯是马铃薯根系分泌的自毒物质,但二者未表现出物质的叠加效应。现蕾期马铃薯根系分泌物所含的物质最多,是马铃薯根系分泌物收集的适宜时期。     

氯化钾对玉米根系糖和酚酸分泌的影响及其与茎腐病菌生长的关系

通过溶液培养试验,研究了氯化钾（KCl）对不同抗性品种玉米根系糖和酚酸分泌量的影响,以及在不同浓度糖和酚酸的培养基上禾谷镰刀菌（Fusarium graminearum Schwabe）的生长状况,探讨KCl抑制玉米茎腐病发生过程中,根系分泌物中糖和酚酸所发挥的作用。结果表明,感病品种吉单327的总糖、还原糖和其蔗糖分泌量均高于抗病品种吉单180;正常供钾条件下,总糖、还原糖和蔗糖的分泌量均表现出不同程度的下降,且还原糖下降幅度最大。阿魏酸和绿原酸是玉米根系分泌物中主要的两种酚酸组分。抗病品种吉单180分泌的阿魏酸量明显高于感病品种吉单327,而绿原酸分泌量低于吉单327。正常供钾时,阿魏酸分泌量明显增加,但绿原酸分泌量则有所减少。一定浓度的蔗糖和葡萄糖均能显著促进F. graminearum的生长,且还原糖（葡萄糖）的促进效果较蔗糖更明显;阿魏酸和绿原酸均能抑制F. graminearum的生长,但阿魏酸的抑制效果远远高于绿原酸。KCl 可明显减少不同抗性品种玉米根系的还原糖分泌量,增加阿魏酸的分泌,从而一定程度上抑制了病原菌F. graminearum在根际的快速生长。     

不同品种小麦与蚕豆间作对蚕豆枯萎病发生、根系分泌物和根际微生物群落功能多样性的影响

通过田间小区试验和盆栽试验,研究了3个不同品种小麦［云麦42（YM42）,云麦47（YM47）和绵阳29（MY29）］与蚕豆间作对蚕豆枯萎病发生、 根系分泌物和根际微生物群落功能多样性的影响。结果表明,云麦42与蚕豆间作处理（YM42//B）和云麦47与蚕豆间作处理（YM47//B）使蚕豆枯萎病病情指数分别降低47.6%和33.3%,而绵阳29与蚕豆间作处理（MY29//B）对蚕豆枯萎病病情指数无显著影响。与蚕豆单作相比,YM42//B和YM47//B处理显著增加了根系分泌物中有机酸的含量,显著降低了根系分泌物中可溶性总糖和游离氨基酸含量; 显著提高了蚕豆根际微生物对碳源的利用强度,明显改变了蚕豆根际微生物群落结构,并且YM42//B处理的影响大于YM47//B; 而MY29//B处理对碳源利用强度、 根际微生物群落结构和根系分泌物中有机酸、 可溶性总糖和游离氨基酸含量均无显著影响。 YM42//B处理根际微生物利用碳源的种类比YM47//B处理多,同时YM42//B和YM47//B处理利用的糖类、 氨基酸类和羧酸类碳源种类完全不同。表明云麦42和云麦47与蚕豆间作通过增加有机酸含量,从而提高根际微生物活性和多样性,促进了根际微生物利用更多的碳源,同时云麦42和云麦47与蚕豆间作抑制了氨基酸和总糖的分泌,而最终控制了蚕豆枯萎病的发生。表明不同品种小麦与蚕豆间作系统根系分泌物-根际微生物的互作是影响蚕豆枯萎病抗性的重要原因。小麦与蚕豆间作控病效果受小麦品种的影响,以云麦42与蚕豆间作效果最好,其次为云麦47与蚕豆间作,而绵阳29与蚕豆间作无显著控病效果。     

Positive correlation between the number of root nodule primordia and seed sugar secretion in soybean (Glycine max L.) seedlings inoculated with a low density of Bradyrhizobium japonicum

Sufficient rhizobium population in the rhizosphere of legume seedlings is required for early and enough setting of root nodules. Potential of seed and seedling root exudates for proliferation of Bradyrhizobium japonicum PNT119 was evaluated in the soybean cvs. Enrei and Tachinagaha. In both cultivars, seed exudates showed a higher potential than root exudates. In the seed exudates, a low-molecular high-polarity fraction including sugars and amino acids showed a higher potential than both high-molecular fraction and low-molecular low-polarity fraction. The correlations between the sugar or amino acid contents of seed exudates and the number of root nodule primordia at 7 d after sowing were investigated among 12 soybean cultivars. When seeds were inoculated with a low rhizobium density, a high correlation coefficient was detected between them. However, there was no positive correlation in the plants inoculated with a high rhizobium density. These results suggest that the amount of low molecular substances in the seed exudates determines the number of root nodule primordia through rhizobium proliferation around seed and young roots when the rhizobium density is the limiting factor. The genetic trait relating to seed coat secretion should be considered as a possible key factor contributing to adequate root nodulation in soybean seedlings cultivated in fields with a low rhizobium density.     

油菜根系分泌物的GC-MS检测方法研究

为筛选建立BP-5MS毛细管柱检测油菜根系分泌物的方法,本文采用水培试验,利用CH2Cl2提取油菜幼苗的根系分泌物,通过GC-MS检测分离鉴定。结果表明,根据待测物质组分性质,采用合适的溶剂延迟,分阶段细化升温程序,检测出来的特征峰较多且分布密集,特征峰分离相对比较好。从检测结果看,油菜苗期根系分泌物主要包括烃类、醇类、酯类和酸类化合物,且烃类和醇类化合物的相对含量较高,这些物质大多数具有化感作用,对植物在逆境环境中的生长和发育有一定的影响。     

糖醇和氨基酸对小白菜钙营养及生长、 品质的影响

【目的】小分子有机物在农业上的应用研究大多针对其促进作物生长、 改善品质等的营养效果,较少研究其对养分有效性及吸收利用的影响,对中微量元素吸收利用影响的研究更少。本研究选用糖醇和氨基酸为研究对象,研究了小分子有机物质对小白菜生长、 品质和养分吸收以及对钙有效性的影响。【方法】以小白菜为供试作物进行盆栽试验。试验以喷清水为对照,设置氨基酸(甘氨酸、 谷氨酸), 糖醇(甘露醇和木糖醇)和硝酸钙单独喷施,氨基酸(甘氨酸、 谷氨酸)和糖醇(甘露醇和木糖醇)分别与硝酸钙配合喷施,共计10个处理,每个处理6次重复,随机区组排列。试验中氨基酸喷施浓度为250 mg/L,糖醇喷施浓度为150 mg/L,硝酸钙喷施浓度为Ca2+ 130 mg/L。收获后测定植株生物量和维生素C、 可溶性糖、 硝酸盐和可溶性蛋白的含量,分析植株矿质元素氮、 磷、 钾和钙的吸收量。【结果】 1)叶面喷施糖醇和氨基酸明显促进了小白菜生长和养分吸收,并改善了其品质。与喷施清水(CK)相比,喷施糖醇和氨基酸可使小白菜生物量平均增加9.17%,维生素C、 可溶性糖和可溶性蛋白含量分别平均增加20.96%、 50.78%和30.66%,硝酸盐含量平均降低31.07%,氮、 磷、 钾吸收量分别平均增加12.43%、 15.24%和42.16%,钙吸收量增加显著,平均增加25.65%; 2)糖醇和氨基酸分别与硝酸钙混合施用可有效促进钙的吸收,提高硝酸钙在小白菜上的应用效果。与单独喷施硝酸钙相比,糖醇和氨基酸与硝酸钙混合喷施可使小白菜生物量平均增加17.44%,小白菜维生素C、 可溶性糖和可溶性蛋白含量分别平均增加14.23%、 45.27%、 33.43%,对氮、 磷、 钾养分吸收量分别平均提高38.25%、 16.13%、 25.11%,对钙养分的吸收量平均增加27.75%;与单独喷施小分子有机物(氨基酸和糖醇)相比,糖醇和氨基酸与硝酸钙混合喷施使小白菜生物量平均增加12.04%,对钙养分的吸收量平均增加17.60%。【结论】叶面喷施糖醇和氨基酸能有效增加小白菜生物量、 改善其品质并促进其对养分的吸收,糖醇和氨基酸分别与硝酸钙混合施用可有效促进钙的吸收,提高硝酸钙在小白菜上的应用效果。因此,小分子有机物糖醇和氨基酸可用作钙肥的有效助剂,用以促进作物对钙的吸收利用,提高钙养分的有效性和钙肥的应用效果。