Effects of Nitric Oxide on Iron-Deficiency Stress Alleviation of Peanut

The aim of this research was to study the role of nitric oxide (NO) in alleviating iron deficiency induced chlorosis of peanut (Arachis hypogaea L.). For this study, sodium nitroprusside (SNP) was used to supply NO for hydroponic peanut plants. After 18 days, the peanut seedlings growing without iron exhibited significant leaf interveinal chlorosis, and this iron-deficiency induced symptom was completely prevented by NO. An increased content of chlorophyll and active iron was observed in NO-treated young leaves, suggesting an improvement of iron availability in plants. In addition, the improved rhizosphere acidification and increased secretion of organic acids by root in NO-treated plants suggesting that NO is effective in modulating iron uptake and transport inside the peanut plants. Furthermore, NO treatment alleviated the increased accumulation of superoxide anion (O₂^??) and malondialdehyde (MDA), and modulated the antioxidant enzymes. However, the SNP with a prior sunlight treatment that does not release NO had no significant effect on the chlorophyll levels in iron-deficient plants. Therefore, these results support a physiological action of NO on the availability, uptake and transport of iron in the plant.     

Effect of application of exogenous nitric oxide at different critical growth stages in alleviating Fe deficiency chlorosis of peanut growing in calcareous soil

This study was to investigate peanut response to application of nitric oxide (NO) at different growth stages and the effects of NO application on peanut yield and quality in calcareous soil. Sodium nitroprusside (SNP, a NO donor) solution was poured into calcareous soil at sowing, seedling, flowering, and podding stages, respectively, or at each aforesaid critical stage. Results showed that NO application increased the content of active Fe and leaf chlorophyll, which improved the photosynthesis of peanut; enhanced the ability of resistance to oxidative stress by decreased the accumulation of O₂^??, H₂O₂, and MDA and increased the activity of antioxidant enzymes. Nitric oxide increased the content of soil available Fe and root FCR activity, which can promote peanut absorb more Fe from the calcareous soil. What's more, peanut plants may pump a large amount of H⁺ from root cell membrane to consume in neutralization of HCO₃^?, and decrease the pH in apoplast, cytoplasm, and xylem, finally balance the mineral elements (Fe, Ca, Mg, Zn, and Cu) uptake and distribution. These results indicated that NO could improve peanut growth and development, increase peanut yield and quality. Furthermore, the application of NO at sowing or seedling stage did the most obvious effect on alleviating chlorosis of peanut in calcareous soil.     

波尔多液营养保护剂对石灰性土壤铜、铁有效性及花生产量的影响研究

选用山东省花生主产区的代表性石灰性土壤，通过土培试验的方法，研究了波尔多液营养保护剂BNPP和美国铜基杀菌剂Koeide两种可湿性粉剂对石灰性土壤pH值和铜、铁有效性及其对花生产量的影响。结果表明，与CK（喷清水）相比，喷施BNPP后，土壤pH值有所降低，而土壤有效铁、铜含量都有所提高。同时喷施BNPP后土壤有效铜含量要低于Kocide处理。另外．BNPP处理花生叶绿紊、活性铁、全铁含量以及生物量都有显著提高，产量比CK提高了1．25～1．53倍。波尔多液营养保护剂效果要优于美国Kocide产品。     

Effects of Exogenous Nitric Oxide and 24-Epibrassinolide on the Physiological Characteristics of Peanut Seedlings Under Cadmium Stress

Cadmium(Cd) is highly toxic to plants, animals, and humans. Limited information is available on the role of nitric oxide(NO)and/or 24-epibrassinolide(EBR) in response of plants to Cd stress. In this study, a hydroponic experiment was performed to investigate the effects of NO and/or EBR on peanut plants subjected to Cd stress(200 μmol L~(-1)) with sodium nitroprusside(SNP, an exogenous NO donor)(250 μmol L~(-1)) and/or EBR(0.1 μmol L~(-1)) addition. The results showed that Cd exposure inhibited plant growth, and this stress was alleviated by exogenous NO or EBR, and especially the combination of the two. Treatment with Cd inhibited the growth of peanut seedlings, decreased chlorophyll content, and significantly increased the Cd concentration in plants. Furthermore, the concentration of reactive oxygen species(ROS) markedly increased in peanut seedlings under Cd stress, resulting in the accumulation of malondialdehyde(MDA) and proline in leaves and roots. Under Cd stress, applications of SNP, EBR, and especially the two in combination significantly reduced the translocation of Cd from roots to leaves, increased the chlorophyll content, decreased the concentrations of ROS, MDA, and proline, and significantly enhanced the activities of superoxide dismutase(SOD), peroxidase(POD), and catalase(CAT) in peanut seedlings. Exogenous NO and/or EBR also stimulated the activities of nitrate reductase(NR)and nitric oxide synthase(NOS) and increased the contents of antioxidants, such as ascorbic acid(AsA) and reduced glutathione(GSH). Furthermore, exogenous NO and/or EBR enhanced Cd accumulation in the cell wall and thus decreased Cd distribution in the organelles in the roots. The concentrations of calcium(Ca), iron(Fe), magnesium(Mg), and zinc(Zn) were also regulated by exogenous NO or EBR, and especially by the two in combination. These results indicated that SNP and EBR, alone and particularly in combination, can mitigate the negative effects of Cd stress in peanut plants.     

酸性根际肥对石灰性土壤pH和铁有效性的影响研究

在无植物栽培的条件下通过肥料在土壤中的扩散试验研究酸性根际肥对石灰性土壤 pH值、有效铁含量的影响 ,利用盆栽试验验证对石灰性土壤上花生缺铁失绿黄化症的矫正效果。结果表明 ,酸性根际肥 (pH 1.0～ 2 .0 )中的酸在土壤中扩散的影响半径可达 6cm ,但对土壤pH降低作用最显著的是在距肥料 2cm内 ;在施肥 2 8d内 ,距肥料 2cm处 ,土壤 pH值降低了 0 .9个单位 ,土壤铁有效性 (DTPA浸提量 )增加了 5 .9mg kg ;施用酸性根际肥可使花生叶绿素SPAD值与叶片活性铁含量显著提高 ,克服了花生缺铁黄化症状 ,使施肥区 (肥料周围 2cm内 )土壤pH值显著降低 ,并显著提高了该区土壤铁的有效性和花生对土壤Fe的吸收量。     

Effects of Exogenous Salicylic Acid and Nitric Oxide on Peanut Seedlings Growth under Iron Deficiency

Salicylic acid (SA) and nitric oxide (NO), which are known as important signaling molecules in plants, could be promising compounds for the reduction in stress sensitivity. The aim of the present work was to study the physiological changes in peanut (Arachis hypogaea L.) seedlings grown in growth medium that contained 0.1 mM SA, 0.25 mM sodium nitroprusside (SNP, a NO donor), or in full (SA+SNP) or half [1/2 (SA+SNP)] combined strengths under iron (Fe) deficiency. After 21 days of treatment, Fe deficiency significantly inhibited peanut plant growth, destroyed photosynthetic system, and caused oxidative damages. Addition of SA, SNP, and 1/2 (SA+SNP), especially SA+SNP, alleviated the stress, increased the contents of chlorophylls, and promoted plant growth. They improved Fe uptake, transport, and availability in peanut plants by increasing the activities of H⁺-ATPase and ferric chelate reductase (FCR), and promoting Fe translocation from cell wall to cell organelle and soluble fraction in leaves. Furthermore, they also effectively mitigated oxidative damages by increasing the activities of antioxidant enzymes in peanut leaves and roots. The results from the present study indicate that application of SA, SNP, or 1/2 (SA+SNP) can overcome the adverse effect of Fe deficiency, but the combined application of SA+SNP is more effective in alleviating Fe deficiency stress.     

Genetic Differences in Resistance to Iron Deficiency Chlorosis in Peanut

Iron (Fe) deficiency has been a widespread problem in peanut (Arachis hypogaea L.) grown on calcareous soils of northern China and has resulted in significant yield losses. Field observations showed considerable variability in visual chlorosis symptoms among peanut cultivars in the same soil. The objective of this study was to confirm the genetic differences in resistance to Fe-deficiency chlorosis in peanut and to identify feasible indicators for screening Fe-efficient genotypes. Resistance to Fe chlorosis of sixteen peanut cultivars grown on calcareous soil was evaluated in the field and physiological responses to Fe-deficiency stress were studied in nutrient solution. There were significant differences in resistance to Fe-deficiency chlorosis among the sixteen peanut cultivars tested, which was identified with SPAD readings, active Fe concentrations in young leaves in the early growth stages, and the pod yield. For Fe-resistant peanut cultivars, Fe-reduction capacity and quality of releasing hydrogen ions from roots increased under Fe-deficiency stress. Highly correlated relationships were observed between the summation of root Fe reduction and field chlorosis scores for sixteen cultivars (r² = 0.79). It was concluded that Fe-reduction capacity was a better physiological indicator for screening Fe-efficient peanut genotypes of the mechanisms measured.     

Iron Availability as Affected by Soil Moisture in Intercropped Peanut and Maize

Abstract

Pot and rhizobox experiments were carried out to investigate the iron availability in intercropped peanut and maize as affected by soil moisture. Results from pot experiment showed that the root growth of peanuts were significantly inhibited at 25% soil water content compared to those at 15% soil water content. The chlorophyll content in the new leaves of intercropped peanut decreased and leaves became chlorotic at 25% soil water content. There were no significant differences in the active iron concentration in new leaves of peanut between 15% and 25% soil water content. The soil pH were higher in peanut rhizosphere than in bulk soil at the early, middle, and harvest stages for both 15% and 25% soil water content. The soil bicarbonate content was also higher in peanut rhizosphere than in bulk soil for both 15% and 25% soil water content. There was significant difference in soil bicarbonate of peanut rhizosphere between 15% and 25% soil water content at the harvest stage. The available iron content in both rhizosphere soil and bulk soil were lower than 3.5 mg kg^?1 in all growth stages at both 15% and 25% soil water content. Results from rhizobox experiment showed that citric acid, maleic acid, and fumaric acid in exudates of peanuts significantly increased at 25% soil water content compared to that at 15% soil water content. The apoplastic iron content of peanut roots decreased by 0.216 and 0.409 µmol g^?1 fresh weight^?1 (FW) from the 28th growth day to 42nd growth day at 25% and 15% soil water content, respectively. The mobilizing ability of apoplastic iron in intercropped peanuts at 15% soil water content was 20.1% higher compared to that at 25% soil water content. It is concluded that improvement of iron nutrition of peanuts with intercropping with maize could be affected by soil moisture condition.     

CHLOROSIS IN WILD PLANTS: IS IT A SIGN OF IRON DEFICIENCY?

ABSTRACT

Chlorosis in crops grown on calcareous soil is mainly due to iron (Fe) deficiency and can be alleviated by leaf application of soluble Fe²⁺ or diluted acids. Whether chlorosis in indigenous plants forced to grow on a calcareous soil is also caused by Fe deficiency has, however, not been demonstrated. Veronica officinalis, a widespread calcifuge plant in Central and Northern Europe, was cultivated in two experiments on acid and calcareous soils. As phosphorus (P) deficiency is one of the major causes of the inability of many calcifuges to grow on calcareous soil we added phosphate to half of the soils. Leaves in pots with the unfertilized and the P-fertilized soil, respectively, were either sprayed with FeSO₄ solution or left unsprayed. Total Fe, P, and manganese (Mn) in leaves and roots and N remaining in the soil after the experiment were determined. In a second experiment, no P was added. Leaves were either sprayed with FeSO₄ or with H₂SO₄ of the same pH as the FeSO₄ solution. Degree of chlorosis and Fe content in leaves were determined. Calcareous soil grown plants suffered from chlorosis, which was even more pronounced in the soils supplied with P. Newly produced leaves were green with Fe spray but leaves that were chlorotic before the onset of spraying did not totally recover. H₂SO₄ spray even increased chlorosis. This demonstrated that chlorosis was due to Fe deficiency. As total leaf Fe was similar on acid and calcareous soil, it was a physiological Fe deficiency, caused by leaf tissue immobilization in a form that was not metabolically “active”. Iron in the leaves was also extracted by 1,10-phenanthroline, an Fe chelator. In both experiments, significant differences between leaves from acid and calcareous soil were found in 1,10-phenanthroline extractable Fe but not in total leaf Fe, when calculated on a dry weight basis. Differences in 1,10-phenanthroline extractable Fe were more pronounced when calculated per unit dry weight than calculated per leaf area, whereas the opposite condition was valid for total leaf Fe.     

Iron fertilizers applied to calcareous soil on the growth of peanut in a pot experiment

A greenhouse pot experiment was conducted with peanuts (Arachis hypogaea L., Fabceae) to evaluate iron compound fertilizers for improving within-plant iron content and correcting chlorosis caused by iron deficiency. Peanuts were planted in containers with calcareous soil fertilized with three different granular iron nitrogen, phosphorus and potassium (NPK) fertilizers (ferrous sulphate (FeSO₄)–NPK, Fe–ethylendiamine di (o-hydroxyphenylacetic) (EDDHA)–NPK and Fe–citrate–NPK). Iron nutrition, plant biomass, seed yield and quality of peanuts were significantly affected by the application of Fe–citrate–NPK and Fe–EDDHA–NPK to the soil. Iron concentrations in tissues were significantly greater for plants grown with Fe–citrate–NPK and Fe–EDDHA–NPK. The active iron concentration in the youngest leaves of peanuts was linearly related to the leaf chlorophyll (via soil and plant analyzer development measurements) recorded 50 and 80 days after planting. However, no significant differences between Fe–citrate–NPK and Fe–EDDHA–NPK were observed. Despite the large amount of total iron bound and dry matter, FeSO₄–NPK was less effective than Fe–citrate–NPK and Fe–EDDHA–NPK to improve iron uptake. The results showed that application of Fe–citrate–NPK was as effective as application of Fe–EDDHA–NPK in remediating leaf iron chlorosis in peanut pot-grown in calcareous soil. The study suggested that Fe–citrate–NPK should be considered as a potential tool for correcting peanut iron deficiency in calcareous soil.     

A study on the improvement iron nutrition of peanut intercropping with maize on nitrogen fixation at early stages of growth of peanut on a calcareous soil

Abstract

A glasshouse study employing a split-root technique was conducted to investigate the influence of intercropping with maize (Zea mays L.) in a calcareous soil on N₂ fixation by peanut (Arachis hypogaea L.) at early stages of growth. In this intercropping system, competitive interactions between maize and peanut for N and improvement of Fe uptake were likely to be important factors affecting N₂ fixation of peanut. The experiment was comprised of three treatments which included treatment I: peanut monocropping; treatment II: maize/peanut intercropping (the major and the minor compartments with low N, 50 mg kg^?1); treatment III: maize/peanut intercropping (the major compartment with low N, 50 mg kg^?1 and the minor compartment with high, N 200 mg kg^?1). The minor compartment of treatment III was fertilized with 200 mg kg^?1 N for reducing or eliminating the competition of N coming from intercropping maize. Intercropping with maize corrected Fe chlorosis of peanut by significantly increasing plant Fe concentration and uptake. Compared with the monocropping treatment, iron uptake increased from intercropping treatment II and III by 22 and 24% per plant, 30 and 29% shoots, 38 and 60% nodules. Iron uptake by the root nodules was especially enhanced in the intercropping system. In contrast, intercropping with maize had little effect on NO₃ ^?1-N concentrations in the soil rhizosphere of peanut or on N concentrations and uptake by peanut compared with plants in monoculture. The results indicate that the improvement in Fe nutrition was an important factor promoting N₂ fixation by peanut in the intercropping system at the flowering stage of peanut growth, and that competition for N by intercropped maize had little effect on N₂ fixation by peanut under the experimental conditions.     

Effects of exogenous SA supplied with different approaches on growth,chlorophyll content and antioxidant enzymes of peanut growing on calcareous soil

To assess the role of salicylic acid (SA) supplied with 5 approaches in alleviating chlorosis induced by iron (Fe) deficiency in peanut plants growing on calcareous soil, SA was supplied as soil incorporation, making slow-release particles, seed soaking, irrigation and foliar application. SA application, particularly, SA supplied by slow release particles, dramatically increased growth parameters, yield and quality of peanut, and increased Fe concentration in peanut grain. Meanwhile, SA application increased the H⁺-ATPase activity, reduced pH of soil, increased Fe³⁺-Chelate Reductase (FCR) activity in roots, and increased Fe concentration in roots. Furthermore, SA increased active Fe content and increased chlorophyll content. In addition, SA improved enzymes activities containing superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and protected Fe deficiency induced oxidative stress. Therefore, SA has a good effect on alleviating chlorosis induced by Fe deficiency on calcareous soil. However, in the 5 SA supplied approaches, foliar application and making slow release particles were more effective.     

Influence of Iron Application Methods on Seasonal Variations in Antioxidant Activity of Peanut

The influence of foliar and soil applications of iron (Fe) on variations in antioxidant activity of peanut was investigated in a field experiment. For each method, five levels of Fe–ethylenediamine-N,N'-bis (EDDHA) (in the soil application, 0, 5, 10, 15 and 20 kg ha^?1, and in the foliar application, 0, 1, 2, 3 or 4 gL^?1) were applied. The results revealed that the Fe content of leaves increased significantly by both application methods. In addition, immediately after every spraying of Fe on the leaves, the activities changed significantly: Catalase and peroxidase increased but superoxide dismutase decreased during the growing season. By soil applications, the enzyme activities increased gradually and yet continuously decreased at the last period of the plant growth. For both applications, greater levels of Fe (4 gL^?1 and 20 kg Fe-EDDHA ha^?1 for sprayed and soil applications, respectively) had more positive effects on the activities of peroxidase and catalase than on superoxide dismutase.     

Mechanisms of exogenous nitric oxide and 24-epibrassinolide alleviating chlorosis of peanut plants under iron deficiency

Iron(Fe) is a crucial transition metal for all living organisms including plants; however, Fe deficiency frequently occurs in plant because only a small portion of Fe is bioavailable in soil in recent years. To cope with Fe deficiency, plants have evolved a wide range of adaptive responses from changes in morphology to altered physiology. To understand the role of nitric oxide(NO) and 24-epibrassinolide(EBR) in alleviating chlorosis induced by Fe deficiency in peanut(Arachis hypogaea L.) plants, we determined the concentration of chlorophylls, the activation, uptake, and translocation of Fe, the activities of key enzymes, such as ferric-chelate reductase(FCR),proton-translocating adenosine triphosphatase(H~+-ATPase), and antioxidant enzymes, and the accumulation of reactive oxygen species(ROS) and malondialdehyde(MDA) of peanut plants under Fe sufficiency(100 μmol L~(-1)ethylenediaminetetraacetic acid(EDTA)-Fe) and Fe deficiency(0 μmol L~(-1)EDTA-Fe). We also investigated the production of NO in peanut plants subjected to Fe deficiency with foliar application of sodium nitroprusside(SNP), a donor of NO, and/or EBR. The results showed that Fe deficiency resulted in severe chlorosis and oxidative stress, significantly decreased the concentration of chlorophylls and active Fe, and significantly increased NO production. Foliar application of NO and/or EBR increased the activity of antioxidant enzymes, superoxide dismutase,peroxidase, and catalase, and decreased the ROS and MDA concentrations, thus enhancing the resistance of plants to oxidative stress.Application of NO also significantly increased Fe translocation from the roots to the shoots and enhanced the transfer of Fe from the cell wall fraction to the cell organelle and soluble fractions. Consequently, the concentrations of available Fe and chlorophylls in the leaves were elevated. Furthermore, the activities of H~+-ATPase and FCR were enhanced in the Fe-deficient plants. Simultaneously,there was a significant increase in NO production, especially in the plants that received NO, regardless of Fe supply. These suggest that NO or EBR, and, especially, their combination are effective in alleviating plant chlorosis induced by Fe deficiency.     

土壤水分对花生根际分泌物中低分子量有机酸的释放及根质外体中铁的积累的影响

A three-compartments rhizobox was designed and used to study the low-molecular-weight organic acids in root exudates and the root apoplastic iron of “lime-induced chlorosis“ peanut grown on a clacareous soil in realtion to different soil moistrue conditions.Results showed that chlorosis of peanuts developed under condition of high soil mositure level(250 g kg^-1),while peanuts grew well and chlorosis did not develop when soil moisture was managed to a normal level(150 g kg^-1).The malic acid maleic acid and succinic acid contents of chlorotic peanut increased by 108.723,0.029,and 22.446ug cm^-1 ,respectively,compared with healthy peanuts.The content of citric acid and fumaric acid also increased in root exudates of chlorotic peanuts.On Days 28 and 42 of peanut growth,the accumulation of root apoplastic iron in chlorotic peanuts was higher than that of healthy peanuts.From Day 28 to Day 42,the mobilization percentages of chlorotic peanuts and healthy peanuts to root apoplastic iron were almost the smae,being 52.4% and 52.8%,respectively,indicating that the chlorosis might be caused by the inactivation of iron within peanut plant grown on a calcareous soil under soil moisture conditions.     

Cover Crops and Soil Phosphorus Availability

Plants affect soil phosphorus (P) solubility through root exudates, but studies are lacking on species used as relay or cover crops in tropical environments. We evaluated the effect of cover crops on soil phosphorus (P) availability in an oxisol. Ruzigrass (Brachiaria ruziziensis), pearl millet (Pennisetum glaucum), peanut (Arachis hypogaea), crambe (Crambe abyssinica), and sorghum (Sorghum bicolor) were grown in pots with soil. Phosphorus uptake, soil inorganic and organic P, maximum P adsorption capacity, and plant root systems were assessed. When root length density is high, the efficiency of P uptake is low due to root competition. Crambe results in greater soil P availability, while peanut and sorghum decrease the soil maximum P adsorption capacity, probably by exuding or stimulating microbial production of organic acids and phenolic compounds. Hence, crambe, peanut, and sorghum are species that may be of interest to increase P use efficiency in cropping systems.     

Copper induced iron deficiency in wheat (Triticum aestivum L)

Abstract

A pot experiment was conducted to study the interaction effects of phosphorus and copper on wheat. The soils used were calcareous loamy sand (ls) and non calcareous sandy loam (sl). Four levels of Cu (0, 5, 10 and 20?mg Cu kg^?1 soil) and six levels of P (0, 25, 50, 100, 200 and 400?mg P kg^?1 soil) were applied in all possible combinations with three replications. Soil pH decreased with Cu application while Olsen P increased with P application in both soils. Growth and yield of wheat improved significantly with graded levels of applied P. However, when any level of P was combined with 20?mg Cu kg^?1 soil, severe iron chlorosis of leaves, a drastic reduction in growth and chlorophyll content was observed in calcareous ls only. The results indicated that it was Cu and not P that induced Fe deficiency in wheat grown in alkaline calcareous soil and the Cu requirement of the crop seemed to be much lower in the calcareous ls. Root dry matter, grain and straw yield decreased with increasing levels of applied Cu in ls but in sl maximum increase of 62.5, 74.3 and 63.7 per cent in root, grain and straw yield was observed with a combined application of 400?mg P and 5?mg Cu kg^?1 soil over control. Accumulation of Cu in roots decreased the Fe absorption by roots which indicated that Fe chlorosis of wheat leaves is expected when Cu: Fe concentration ratio in root is > 0.30.     

Effect of Fe-Glycine Aminochelate on Pod Quality and Iron Concentrations of Bean (Phaseolus vulgaris L.) Under Lime Soil Conditions

Iron (Fe) has very low solubility and plant availability in calcareous soils, and this generally results in restricted plant production and low quality. During last decades, various commercial chelated fertilizers have been used in agricultural systems to meet iron requirements of crops. However, despite extensive application of these commercial chelate fertilizers, there is real doubt and high concerns regarding many aspects of their action, dynamics, efficiency, and safety in plant-soil–environment systems. In the present study, growth and quality of green bean plants (Phaseolus vulgaris L.) were evaluated under foliar and soil applications of Fe-glycine chelate (iron glycine aminochelate) and commercial Fe-EDDHA chelate in a lime soil. The results showed that morphophysiological parameters were improved by the application of Fe-glycine and Fe-EDDHA treatments. Foliar application of Fe-glycine has significantly improved leaf area and Soil-Plant Analyses Development (SPAD) values compared to control and Fe-EDDHA treatments. Pod yield, shoot (but not root) dry weight, and iron concentrations in leaves and pods (but not in root) were significantly higher when plants were treated by Fe-glycine rather than Fe-EDDHA in both soil and foliar applications. Vitamin C and protein contents were significantly improved and phenolic compounds were reduced by foliar application of Fe-glycine and soil application of Fe-EDDHA. The results indicate that foliar application of Fe-glycine can significantly increase Fe concentrations and quality of beans under lime soils with restricted iron availability.     

Mineral Content and Root Respiration of In Vitro Grown Kiwifruit Plantlets Treated with Two Humic Fractions

ABSTRACT

In vitro grown kiwifruit (Actinidia deliciosa, Liang and Ferguson) plantlets were treated with two humic fractions distinguished by two different relative molecular mass and characterized through their elemental composition and ¹³Carbon (C) nuclear magnetic resonance. The effects exerted on plant growth, root morphology, and nutrition were evidenced by means of leaves and roots mineral content, root respiration, and nitrate reductase activity. The two humic substances differentially influenced the studied parameters. The lower molecular fraction humic substance, endowed with a higher content of phenolic and carboxylic groups, caused an enhanced content of micro- and macro-elements, together with a higher root respiration at lower concentrations (0.5–1 mg C L^{? 1}). The high molecular fraction humic substance, needed higher concentrations (> 5 mg C L^{? 1}) in order to achieve similar effects. This fraction also caused major changes on root morphology. The ability to improve micronutrient assimilation, in particular iron, confirmed the agronomic importance of humic substances on soil fertility.     

Interaction study of biochar with phosphate-solubilizing bacterium on phosphorus availability in calcareous soil

A large proportion of phosphate fertilizer applied to calcareous soils reacts with calcium. Changes in soil phosphorus (P) availability after single application of biochar and phosphate-solubilizing bacteria have been reported. However, interaction of biochar (increasing soil pH) and phosphate-solubilizing bacteria (decreasing soil pH) on P availability in calcareous soil is not well known. An incubation experiment was conducted to study how the interactive effects of biochars (produced from wheat straw and cow manure at 300°C and 500°C with residence time of 1, 3 and 6 h) at different rates (0, 5 and 10 t ha^?1) and phosphate-solubilizing Pseudomonas sp. IS8b2 affected on content of soil available P after 0, 60, 120 and 180 days of incubation (DOI) in a calcareous soil. After 60 DOI, the maximum value of available P (50.31 mg kg^?1) was observed in the compound treatment of Pseudomonas sp. IS8b2 and wheat straw biochar (10 t ha^?1) produced at 500°C with residence time of 3 h. We conclude that the combination use of wheat straw biochar and phosphate-solubilizing bacterium is promising to potentially improve soil P availability in calcareous soil, but further research at field scale is needed to confirm this.