Quantitative estimation of root exudation of maize plants

Summary The rate of root exudation of maize plants was estimated by measuring the rate of denitrification in a hermetically sealed root system. While CO₂ production measured in the rhizosphere results both from root respiration and microbial respiration N₂O production during nitrate respiration is solely related to the amount of root exudates available for bacterial degradation. With 4 week old plants growing in quartz sand or soil root exudation amounted to 7% of the net photosynthates. Calculations revealed that about 25% of the organic matter flowing into the root system was excreted into the rhizosphere.     

根分泌物对根际矿物营养及根际微生物的效应

综述了根系分泌物对植物生长的生理生态学效应,并就根系分泌物的定义、产生机制、组成成分和影响因素等方面进行了讨论。指出根系分泌物在缓解低矿物营养胁迫对植株造成的伤害及决定根际微生物的种群密度和数量方面起着重要的作用;根系分泌物的产生机制多样,组成成分复杂,影响因素繁多。对根分泌物的深入研究有助于进一步了解植物体与土壤间进行的生理生化过程及其调控机制。     

Effects of foliar sprays of azoxystrobin on take-all in wheat

Average percentages of winter wheat plants with severe take‐all were decreased by up to half by azoxystrobin applied as foliar sprays in four field experiments. Decreased take‐all in three of the experiments was associated with increased grain yield but effects on other diseases may have contributed to these responses. Standard fungicide sprays were ineffective. The effects differed, but not consistently, among different cultivars that were tested in three of the experiments. One, two or three sprays of azoxystrobin or kresoxim‐methyl, in autumn, spring or summer, were tested in the fourth experiment. Unlike azoxystrobin, kresoxim‐methyl had no consistent effects but a smaller amount was applied. Two or three sprays of azoxystrobin were more effective than a single spray but their timing was unimportant. Such control of a root disease by a foliar‐applied fungicide is unusual but may help to explain some of the unexpectedly large yield responses to azoxystrobin that have been reported. This relatively broad‐spectrum fungicide may have the potential to contribute to the practical management of take‐all but further research is needed to determine how best to exploit its effects consistently.     

Response of tomato plants infected with cucumber mosaic virus to foliar sprays of gibberellic acid

The effect of spraying tomato plants infected with cucumbermosaic virus (CMV) with gibberellic acid (GA) 1 and 5 ppm hasbeen studied in a glasshouse. Measurements showed that the differencein size between GA-treated healthy and infected plants eitherdisappeared or became insignificant and this was true at bothhigh and low planes of nutrition. Virus content was not reducedby GA. Virusinduced checks to leaf production and stem elongationtended to disappear in unsprayed plants but leaf area and shootweight did not show natural recovery. The stimulating effectof GA was primarily on leaf expansion and secondarily on shootweight.     

Effects of a vesicular-arbuscular mycorrhizal fungus and other soil microorganisms on growth,mineral nutrient acquisition and root exudation of soil-grown maize plants

Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-m nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shootroot ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.     

Differences between calcifuge and acidifuge plants in root exudation of low-molecular organic acids

The nature and quantity of low-molecular organic acids (LOAs) exuded by the roots of nine species of calcifuge and nine species of acidifuge wild plants from northern Europe were determined by ion chromatography. Particular attention was paid to differences between the calcifuge and the acidifuge species in the proportions of different LOAs in their root exudates. Great differences in mol% root exudation between the calcifuge and the acidifuge species were found in some acids. The calcifuge species exuded more acetic acid, the acidifuge species more oxalic acid and much more citric acid. In three calcifuge species, however, root exudation of oxalic acid was appreciable, whereas acetic acid exudation was low in these species. The phosphate- and Fe-solubilizing ability of eight LOAs in a rhizosphere limestone soil was also tested. Oxalic acid was the most efficient phosphate solubilizer and citric acid, by far, the most efficient Fe-solubilizer at the concentration (10 mM) tested. It might be hypothesized that acidifuge species use oxalate to solubilize phosphate and citrate to solubilize Fe, in limestone soil. The inability of calcifuge species to grow in limestone soil might, therefore, be due to low root exudation of these acids and, as a result, inability to solubilize phosphate and Fe in limestone soil.     

Modeling root loss reveals impacts on nutrient uptake and crop development

Despite the widespread prevalence of root loss in plants, its effects on crop productivity are not fully understood. While root loss reduces the capacity of plants to take up water and nutrients from the soil, it may provide benefits by decreasing the resources required to maintain the root system. Here, we simulated a range of root phenotypes in different soils and root loss scenarios for barley (Hordeum vulgare), common bean (Phaseolus vulgaris), and maize (Zea mays) using and extending the open-source, functional–structural root/soil simulation model OpenSimRoot. The model enabled us to quantify the impact of root loss on shoot dry weight in these scenarios and identify in which scenarios root loss is beneficial, detrimental, or has no effect. The simulations showed that root loss is detrimental for phosphorus uptake in all tested scenarios, whereas nitrogen uptake was relatively insensitive to root loss unless main root axes were lost. Loss of axial roots reduced shoot dry weight for all phenotypes in all species and soils, whereas lateral root loss had a smaller impact. In barley and maize plants with high lateral branching density that were not phosphorus-stressed, loss of lateral roots increased shoot dry weight. The fact that shoot dry weight increased due to root loss in these scenarios indicates that plants overproduce roots for some environments, such as those found in high-input agriculture. We conclude that a better understanding of the effects of root loss on plant development is an essential part of optimizing root system phenotypes for maximizing yield.

Root loss has a major impact on crop development and nutrient uptake; modeling reveals that the magnitude of the effect depends on species, root phenotype, and soil conditions.     

植物根系养分捕获塑性与根竞争

为了更有效地从土壤中获取养分, 植物根系在长期的进化与适应中产生了一系列塑性反应, 以响应自然界中广泛存在的时空异质性。同时, 植物根系的养分吸收也要面对来自种内和种间的竞争。多种因素都会影响植物根竞争的结果, 包括养分条件、养分异质性的程度、根系塑性的表达等。竞争会改变植物根系的塑性反应, 比如影响植物根系的空间分布; 植物根系塑性程度差异也会影响竞争。已有研究发现根系具有高形态塑性和高生理塑性的植物在长期竞争过程中会占据优势。由于不同物种根系塑性的差异, 固定的对待竞争的反应模式在植物根系中可能并不存在, 其响应随竞争物种以及土壤环境因素的变化而变化。此外, 随着时间变化, 根系塑性的反应及其重要性也会随之改变。植物对竞争的反应可能与竞争个体之间的亲缘关系有关, 有研究表明亲缘关系近的植物可能倾向于减小彼此之间的竞争。根竞争对植物的生存非常重要, 但目前还没有研究综合考虑植物的各种塑性在根竞争中的作用。另外根竞争对群落结构的影响尚待深入的研究。     

Root exudation pattern of Typha latifolia L. plants after copper exposure

Aims

Typha latifolia L. is an aquatic plant that has been widely exploited for the aims of phytoremediation. The main reason why we have chosen this plant species for the current study is its capacity to accumulate and detoxify heavy metals. The main topic of the investigation focused on the root uptake of copper (II) nitrate and copper (II) sulfate and the impact of different chemical copper species on the excreted organic acids.

Methods

Oxalic, malic, acetic and lactic acids were determined using capillary electrophoresis; a comparison between the concentration and the time course during 7 days of treatment was performed.

Results

There is a correlation between the total copper (II) sulfate concentration in the roots and the total amount of the excreted organic acids. In addition to that organic acids are involved in the detoxification mechanisms of Typha latifolia for copper (II) nitrate and copper (II) sulfate.

Conclusions

Different from so far investigated plant species the highest amounts of organic acids are excreted from T. latifolia roots not in the first hours after treatment, but up to 7 days later.     

Differing organic Acid exudation pattern explains calcifuge and acidifuge behaviour of plants

Many vascular plant species are unable to colonize calcareous sites. Thus, the floristic composition of adjacent limestone and acid silicate soils differs greatly. The inability of calcifuge plants to establish in limestone sites seems related to a low capacity of such plants to solubilize and absorb Fe or phosphate from these soils. Until now, mechanisms regulating this differing ability of plants to colonize limestone sites have not been elucidated. We propose that contrasting exudation of low-molecular organic acids is a major mechanism involved and show that germinating seeds and young seedlings of limestone plants exude considerably more di- and tricarboxylic acids than calcifuges, which mainly exude monocarboxylic acids. The tricarboxylic citric acid is a powerful extractor of Fe, and the dicarboxylic oxalic acid a very effective extractor of phosphate from limestone soils. Monocarboxylic acids are very weak in these respects. The study is based on ten species from limestone soils and ten species from acid silicate soils.     

Variety specific relationships between effects of rhizobacteria on root exudation,growth and nutrient uptake of soybean

Aims

It has been increasingly recognized that only distal lower order roots turn over actively within the <2 mm fine root system of trees. This study aimed to estimate fine root production and turnover rate based on lower order fine roots and their relations to soil variables in mangroves.

Methods

We conducted sequential coring in five natural mangrove forests at Dongzhai Bay, China. Annual fine root production and turnover rate were calculated based on the seasonal variations of the biomass and necromass of lower order roots or the whole fine root system.

Results

Annual fine root production and turnover rate ranged between 571 and 2838 g m^?2 and 1.46–5.96 yr^?1, respectively, estimated with lower order roots, and they were increased by 0–30 % and reduced by 13–48 %, respectively, estimated with the whole fine root system. Annual fine root production was 1–3.5 times higher than aboveground litter production and was positively related to soil carbon, nitrogen and phosphorus concentrations. Fine root turnover rate was negatively related to soil salinity.

Conclusions

Mangrove fine root turnover plays a more important role than aboveground litter production in soil C accumulation. Sites with higher soil nutrients and lower salinity favor fine root production and turnover, and thus favor soil C accumulation.

     

Impact of phosphorus supply on root exudation, aerenchyma formation and methane emission of rice plants

This study evaluated the impact of P supply on rice plant development and the methane budget of rice fields by 2 different approaches: (1) root growth, exudation and aerenchyma formation were recorded in an experiment with hydroponic solution; (2) dissolved CH₄ concentration and CH₄ emission were investigated in a pot experiment. In both approaches, we used three different cultivars and three levels of P supply. In the experiment with solution culture (0.5 ppm, 5 ppm, and 10 ppm P), root exudation ranged between 0.5 to 36.7 mol C plant^–1 h^–1 and increased steadily with plant growth at given P level. Low P supply resulted in

Effects of foliar sprays of daminozide on the incidence of potato common scab

Single foliar sprays of the growth retardant daminozide (1.5–12 g/l) approximately halved the incidence of common scab, caused by soil-borne Streptomyces scabies, on potted potato plants in the glasshouse. Two analogues of daminozide (N-dimethylaminomaleamic and N-(dimethylamino)-methylsuccinamic acids) also decreased scab, but others were inactive. Of 22 other unrelated growth regulators and translocated chemicals tested as foliar sprays, only gibberellic acid (0.1 g/l) decreased scab incidence, but many of the tubers were distorted. Chlormequat chloride and chlorphonium chloride, as root treatments, were inactive. In other experiments with daminozide, scab incidence was decreased after application to soil. In tests with two plants per pot, spraying one of each pair decreased its rate of stem extension, but did not affect the other, indicating that little or no daminozide passed into the soil from the roots of the sprayed plant. The decrease in scab brought about by foliar sprays was not altered by varying their timing during the period before symptom development (1 to 5 wk after potting). In agar plate tests, daminozide was only weakly toxic to S. scabies. It is concluded that daminozide probably decreased scab by altering the physiology of the plants, so that scab symptoms did not develop.     

Effects of raw and diluted municipal sewage effluent with micronutrient foliar sprays on the growth and nutrient concentration of foxtail millet in southeast Iran

In this study, the effect of irrigation with raw or diluted municipal sewage effluent accompanied by foliar micronutrient fertilizer sprays was examined on the growth, dry matter accumulation, grain yield, and mineral nutrients in foxtail millet plants. The experimental design was a split plot with three irrigation sources: raw sewage, 50% diluted sewage, and well water comprising the main treatments, and four combinations of Mn and Zn foliar sprays as sub-treatments that were applied with four replications. The experiment was conducted in 2009 at the Zabol University research farm in Zabol, south Iran. The applied municipal sewage effluent contained higher levels of micronutrients and macronutrients and exhibited greater degrees of electrical conductivity compared to well water. Because of the small scale of industrial activities in Zabol, the amount of heavy metals in the sewage was negligible (below the limits set for irrigation water in agricultural lands); these contaminants would not be severely detrimental to crop growth. The experimental results indicated that irrigation of plants with raw or diluted sewage stimulates the measured growth and productivity parameters of foxtail millet plants. The concentrations of micronutrients and macronutrients were also positively affected. These stimulations were attributed to the presence of high levels of such essential nutrients as N, P, and organic matter in wastewater. Supplied in sewage water alone, Mn and Zn were not able to raise the productivity of millet to the level obtained using fertilizers at the recommended values; this by itself indicated that additional nutrients from fertilizers are required to obtain higher levels of millet productivity with sewage farming. Despite the differences in nutrient concentrations among the different irrigation water sources, the micronutrient foliar sprays did not affect the concentrations of micronutrients and macronutrients in foxtail millet plants. These results suggested that municipal sewage effluent could be utilized efficiently as an important source of water, and that the nutrients used in growing foxtail millet with sewage water irrigation did not have any significant harmful effect on crop productivity. In contrast, the nutrients proved beneficial to soil fertility and millet productivity and quality.     

紫胶蚧寄生对寄主植物营养成分的影响

报道了1个世代中紫胶蚧Kerria laccaKerr寄生对寄主植物营养成分产生的影响。结果表明:紫胶蚧寄生对寄主植物营养成分有影响,被寄生枝条的氨基酸、无机盐和营养成分总量都出现变化。以久树Schleichera oleosa(Lour)为例,紫胶蚧寄生使久树枝条中氨基酸总量减少了35%。其中,天门冬氨酸、苏氨酸、丝氨酸、甘氨酸、丙氨酸、缬氨酸、异亮氨酸、亮氨酸、酪氨酸、苯丙氨酸的含量也都存在不同程度减少。但是,蛋氨酸、组氨酸、赖氨酸、精氨酸、色氨酸含量比对照枝条中高。被寄生枝条中氮、磷(P2O5)、铁等呈现下降趋势,钠元素含量几乎没有发生变化,而钾、钙、镁、铜、锌、锰等却有不同程度的增加,特别是钙元素含量,被寄生枝条中钙元素的含量是对照枝条的5.3倍左右。紫胶蚧寄生对枝条中总糖、蛋白质、脂肪、粗纤维、水溶性物质以及灰分含量都产生不同程度影响,被寄生枝条中蛋白质、粗纤维含量比对照枝条中含量低;而被寄生枝条中总糖、脂肪、水溶性物质、灰分含量比对照枝条中高。     

Application of Bacillus species in the control of root rot diseases of crop plants

Bio control potential of three Bacillus spp viz., Bacillus subtilis, B. thuringiensis and B. cereus, against soil borne root-infecting fungi on cowpea and mash bean plants were tested both in vitro and in vivo. All three species showed efficiency and produced nodules on mash bean and cow pea plants. In vitro dual culture plate method showed significant inhibition of Fusarium spp. by all these three species of Bacillus with the appearance of a prominent zone of inhibition while a maximum zone of inhibition of Fusarium spp. was observed by B. thuringiensis, whereas in case of Macrophomina phaseolina and Rhizoctonia solani, the highest zone of inhibition was observed by B. subtilis. Bacillus spp. used as seed dressing and soil drenching showed a significant increase in shoot length, shoot weight, root length and root weight in cow pea and mash bean plants. Maximum shoot length was observed in cow pea plants where Bacillus spp. were drenched in soil, whereas maximum root length and root weight in cow pea was observed when B. thuringiensis used as seed dressing. Seed dressing and soil drenching with species of Bacillus viz., B. subtilis, B. thuringiensis and B. cereus, were found to be an effective method for the control of soil borne root-infecting fungi like M. phaseolina, R. solani and Fusarium spp., on cow pea and mash bean plants.     

Variations in the foliar nutrient content of mire plants: effects of growth-form based grouping and habitat

We determined concentrations of major nutrients in the vegetation of six habitat types (hummock, scrub, lawn, fen meadow, hollow and marginal stream), spanning a broad range of environmental conditions as regards water-table depth and water chemistry, in five mires on the southern Alps of Italy. Our study was based on chemical analyses of living tissues of plant species, grouped into growth-form based plant functional types (PFTs). We aimed at assessing to what extent the observed differences in tissue nutrient content were accounted for by community composition (both in terms of species and PFTs) and by habitat. Nutrient concentrations were overall lowest in Sphagnum mosses and highest in forbs, although the latter showed large variations presumably due to heterogeneity in mechanisms and adaptations for acquiring nutrients among species within this PFT. Nutrient content patterns in the other three PFTs varied greatly in relation to individual nutrients, with evergreen shrubs showing low nitrogen (N) concentrations, graminoids showing high N concentrations but low potassium (K) and magnesium (Mg) concentrations and deciduous shrubs showing rather high phosphorus (P) concentrations. Habitat accounted for a modest fraction of variation in tissue concentration of all nutrients except P. We concluded that the nutrient status of mire vegetation is primarily controlled by community composition and structure although habitat does exert a direct control on P concentration in the vegetation, presumably through P availability for plant uptake.