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1.
ABSTRACT

Root exudate is derived from plant metabolites and its composition is affected by plant nutrient status. A deficiency of mineral nutrients, such as nitrogen (N) and phosphorus (P), strongly affects the type and amount of plant metabolites. We applied a metabolite profiling technique to investigate root exudates of rice plants under N and P deficiency. Oryza sativa was grown in culture solution containing two N levels (0 and 60 mg N L?1) or two P levels (0 and 8 mg P L?1). Shoot extracts, root extracts, and root exudates were obtained from the rice plants 5 and 15 days after transplanting and their metabolites were determined by capillary electrophoresis/time-of-flight mass spectrometry. Shoot N concentration and dry weight of rice plants grown at ?N level were lower than those of plants grown at +N level. Shoot P concentration and dry weight of rice plants grown at ?P level were lower than those of plants grown at +P level. One hundred and thirty-two, 127, and 98 metabolites were identified in shoot extracts, root extracts, and root exudates, respectively, at the two N levels. One hundred and thirty-two, 128, and 99 metabolites were identified in shoot extracts, root extracts, and root exudates, respectively, at the two P levels. Seventy-seven percent of the metabolites were exuded to the rhizosphere. The concentrations of betaine, gamma-aminobutyric acid, and glutarate in root exudates were higher at both ?N and ?P levels than at their respective high levels. The concentration of spermidine in root exudates was lower at both ?N and ?P levels than at their respective high levels. The concentrations of the other metabolites in root exudates were affected differently by plant N or P status. These results suggest that rice roots actively release many metabolites in response to N and P deficiency.  相似文献   

2.
Two barley cultivars (‘Sahara’ = Zn-efficient and ‘Clipper’ = Zn-inefficient) were grown at different soil Zn fertilization (0, 0.2, 0.8, 1.6 and 3.2 mg Zn kg?1 soil). Root exudates were collected 16 and 28 days after sowing. At Zn = 0, shoot dry matter was decreased in both genotypes, but more distinctly in ‘Clipper’. At 0.2 mg Zn kg?1, the ‘Sahara’ shoot concentrations of Zn was 130% higher and shoot Zn content 44% greater compared with ‘Clipper’. Low-molecular-weight organic acid anions (=carboxylates) (malate, maleate, fumarate and cis-aconitate) and amino acids (alanine, valine, proline, aspartic acid and glutamic acid) were detected in root exudates, with the highest concentration at Zn = 0.2 mg kg?1 soil. Higher concentrations of organic acid anions as well as amino acids were noted in the rhizosphere of ‘Sahara’ than ‘Clipper’. The genotypic differences in Zn acquisition from soil may be linked to differential carboxylate and amino acid composition of root exudates.  相似文献   

3.
Abstract

The large variation in phosphorus acquisition efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus (P) soil. To explain the differences in P efficiency of winter maize (Zea mays L.), wheat (Triticum aestivum L.), and chickpea (Cicer arietinum L.), a green house pot experiment was conducted by using P‐deficient Typic ustochrept loamy sand soil (0.5 M NaHCO3‐extractable P 4.9 mg kg?1, pH 7.5, and organic carbon 2.7 g kg?1) treated with 0, 30, and 60 mg P kg?1 soil. Under P deficiency conditions, winter maize produced 76% of its maximum shoot dry weight (SDW) with 0.2% P in shoot, whereas chickpea and wheat produced about 30% of their maximum SDW with more than 0.25% P in shoot. Root length (RL) of winter maize, wheat, and chickpea were 83, 48, and 19% of their maximum RL, respectively. Considering relative shoot yield as a measure of efficiency, winter maize was more P efficient than wheat and chickpea. Winter maize had lower RL/SDW ratio than that of wheat, but it was more P efficient because it could maintain 2.2 times higher P influx even under P deficiency conditions. In addition, winter maize had low internal P requirement and 3.3 times higher shoot demand (i.e., higher amount of shoot produced per cm of root per second). Even though chickpea had 1.2 times higher P influx than winter maize, it was less P efficient because of few roots (i.e., less RL per unit SDW). Nutrient uptake model (NST 3.0) calculations satisfactorily predicted P influxes by all the three crops under sufficient P supply conditions (CLi 48 µM), and the calculated values of P influx were 81–99% of the measured values. However, in no‐P treatment (CLi 3.9 µM), under prediction of measured P influx indicated the importance of root exudates and/or mycorrhizae that increase P solubility in the rhizosphere. Sensitivity analysis showed that in low P soils, the initial soil solution P concentration (CLi) was the most sensitive factor controlling P influx in all the three crops.  相似文献   

4.
Intercropping has been shown to increase total yield and nutrient uptake compared to monocropping. However, depending on crop combinations, one crop may dominate and decrease the growth of the other. Interactions in the soil, especially in the rhizosphere, may be important in the interactions between intercropped plant genotypes. To assess the role of the rhizosphere interactions, we intercropped a P-inefficient wheat genotype (Janz) with either the P-efficient wheat genotype (Goldmark) or chickpea in a soil with low P availability amended with 100 mg P kg−1 as FePO4 (FeP) or phytate. The plants were grown for 10 weeks in pots where the roots of the genotypes could intermingle (no barrier, NB), were separated by a 30 μm mesh (mesh barrier, MB), preventing direct root contact but allowing exchange of diffusible compounds and microorganisms, or were completely separated by a solid barrier (SB). When supplied with FeP, Janz intercropped with chickpea had higher shoot and grain dry weight (dw) and greater plant P uptake in NB and MB than in SB. Contact with roots of Janz increased shoot, grain and root dw, root length, shoot P concentration and shoot P uptake of chickpea compared to SB. Root contact between the two wheat genotypes, Janz and Goldmark, had no effect on growth and P uptake of Janz. Shoot and total P uptake by Goldmark were significantly increased in NB compared to MB or SB. In both crop combinations, root contact significantly increased total plant dw and P uptake per pot. Plant growth and P uptake were lower with phytate and not significantly affected by barrier treatment. Differences in microbial P, available P and phosphatase activity in the rhizosphere among genotypes and barrier treatments were generally small. Root contact changed microbial community structure (assessed by fatty acid methyl ester (FAME) analysis) and all crops had similar rhizosphere microbial community structure when their roots intermingled.  相似文献   

5.
Abstract

The distribution of secretory acid phosphatase and organic acids enhanced by phosphorus deficiency in lupin rhizosphere was investigated using a rhizobox system which separated the rhizosphere soil into 0.5 mm fractions. In the soil fraction closest to the root surface, the lupin exudates displayed an acid phosphatase activity of 0.73 u g?1 dry soil and citrate concentration of 85.2 μmol g?1 dry soil, respectively. The increase of the acid phosphatase activity-induced an appreciable depletion of organic P in the rhizosphere, indicating that lupin efficiently utilized the organic P from soil through the enzyme activitye The sterile treatments demonstrated that the acid phosphatase in the rhizosphere was mainly derived from lupin root secretions. The secretory organic acids enhanced considerably the solubility of the inorganic P in three types of soil and a sludge. However, the secretory acid phosphatase and organic acids from lupin roots were only detected in a considerable amount in 0-2.5 mm soil fractions from root surface.  相似文献   

6.
Compared to other crops, Brassicas are generally considered to grow well in soils with low P availability, however, little is known about genotypic differences within Brassicas in this respect. To assess the role of rhizosphere properties in growth and P uptake by Brassicas, three Brassica genotypes (mustard, Brassica juncea cv Chinese greens and canola, Brassica napus cvs Drum and Outback) were grown in an acidic soil with low P availability at two treatments of added P: 25 and 100 mg P kg−1 as FePO4 (P25 and P100). The plants were harvested at the 6-leaf stage, at flowering and at maturity. Shoot and root dry weight (dry weight) and root length increased with time and were lower in P25 than in P100. In P25, shoot dry weight was lowest in Outback and highest in Chinese greens. In the P100 treatment, Chinese greens had a higher shoot dry weight than the two canola cultivars. Chinese greens had a lower root dry weight and root length at flowering and maturity than the canola genotypes in both P treatments. Irrespective of P treatment, shoot P concentration was lower in Chinese greens than in the two canola genotypes. Specific P uptake (μg P m−1 root length) decreased with time. In P25, Chinese greens had the lowest specific P uptake at the 6-leaf stage but it was higher than in the two canola genotypes at flowering and maturity. In P100, Outback had the lowest specific P uptake. Available P in the rhizosphere (resin P) decreased over time with the greatest decrease from the 6-leaf stage to flowering. In P25, resin P in the rhizosphere was greatest in Chinese greens at the 6-leaf stage and flowering and smallest in Outback at flowering. Microbial P and acid phosphatase activity changed little over time, were not affected by P treatment and there were only small differences between the genotypes. The rhizosphere microbial community composition [assessed by fatty acid methyl ester (FAME) analysis] of Outback and Chinese greens differed from that of the other two genotypes at the 6-leaf stage and flowering, respectively. At maturity, all three genotypes had distinct microbial communities. Plant traits such as production of high biomass at low shoot P concentrations as well as the capacity to maintain high P availability in the rhizosphere by P mobilisation can explain the observed differences in plant growth and P uptake among the Brassica genotypes.  相似文献   

7.
Root exudates help drive the formation of the rhizosphere by binding soil particles, but the underlying physical mechanisms have not been quantified. This was addressed by measuring the impact of a major component of root exudates, polygalacturonic acid (PGA), on the interparticle bond energy and fracture toughness of clay. Pure kaolinite was mixed with 0, 1.2, 2.4, 4.9 or 12.2 g PGA kg?1 to form test specimens. Half of the specimens were washed repeatedly to remove unbound PGA and evaluate the persistence of the effects, similar to weathering in natural soils. Fracture toughness, KIC, increased exponentially with added PGA, with washing increasing this trend. In unwashed specimens KIC ranged from 54.3 ± 2.5 kPa m?1/2 for 0 g PGA kg?1 to 86.9 ± 4.7 kPa m?1/2 for 12.2 g PGA kg?1. Washing increased KIC to 61.3 ± 1.2 kPa m?1/2 for 0 g PGA kg?1 and 132.1 ± 4.9 kPa m?1/2 for 12.2 g PGA kg?1. The apparent bond energy, γ, of the fracture surface increased from 5.9 ± 0.6 J m?2 for 0 g kg?1 to 12.0 ± 1.1 J m?2 for 12.2 g kg?1 PGA in the unwashed specimens. The washed specimens had γ of 13.0 ± 1.9 J m?2 for 0 g kg?1 and 21.3 ± 2.6 J m?2 for 12.2 g PGA kg?1. Thus PGA, a major component of root exudates, has a large impact on the fracture toughness and bond energy of clay, and is likely to be a major determinant in the formation of the rhizosphere. This quantification of the thermodynamics of fracture will be useful for modelling rhizosphere formation and stability.  相似文献   

8.
Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na+) and calcium (Ca2+) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (ECe), 2.2, 6.7, 9.2 and 11.8?dS?m?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO3)2?·?4H2O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg?1?soil in the form of KH2PO4. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na+ and chlorine ion (Cl?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg?1 soil reduced Cl? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.  相似文献   

9.
ABSTRACT

A simple screening method is needed to identify rice genotypes tolerant to low phosphorus (P) in soil. Nagina 22 (N22) mutants were classified as gain of function (gof) and loss of function (lof) for tolerance to very low P (soil Olsen P 2.01 mg kg?1). Two gof and two lof mutants were grown in hydroponics and in pot experiment at three P levels (-P, +P and +2P). Comparing response at +P and +2P in hydroponics we found that shoot and root dry weight were significantly less in gof and significantly more in lof in +2P. In pots with soil, tiller number and yield/plant was 3 fold less in gof but 2.5 to 3 fold more in lof and N22 in +2P compared to +P. That 2P can be used to identify low-P tolerant genotypes was validated using 3 low-P tolerant and 3 sensitive varieties whose response to low P soil is well documented. Both shoot and root dry weight was significantly less in +2P than in +P in tolerant and significantly more in sensitive genotypes. Thus screening in hydroponics in +2P can help identify low-P- tolerant genotypes easily and rapidly avoiding field screening.  相似文献   

10.
Development of phosphate (P)-deficiency tolerant rice cultivars is constrained by lack of suitable, reproducible, and consistent seedling stage screening methods in breeding programs. This study reports the screening and characterization of M5 mutants derived from an ethyl methane sulfonate treated population of rice cv. Nagina 22 (N22) in low-P field (soil Olsen P 1.94–2.01 mg kg?1; alkaline Vertisol; pH 7.94) for high yield. The present study showed that seedling growth responses such as increase in root weight, root length, root/shoot weight, and dry weight in P-deficient medium can be taken as indices of low-P tolerance in mature plants in field. Total phosphorus content in seedlings showed an inverse relationship with total phosphorus content and low-P tolerance in mature plants in the field. But, phosphorus content in seeds and acid phosphatase activity in the seedling stage were positively correlated with survival and seed set in low-P field. In low-P field, plant height correlated most with yield per plant, and the number of productive tillers in mature plants was highly correlated with tiller number at vegetative stage. These mutants (NH776, NH710, and NH719) have agronomic importance because of their ability to grow and give higher yield than N22 in P-deficient field.  相似文献   

11.
We applied a metabolite profiling technique to investigate root exudates under phosphorus (P) deficiency. Oryza sativa was grown in culture solution containing three P levels (0, 1, and 8 mg P L?1). Shoot extracts, root extracts, and root exudates were obtained from 18 and 23-day-old plants and their metabolites were determined by capillary electrophoresis/time-of-flight mass spectrometry. Eighty, 90, and 65 metabolites were identified in shoot extracts, root extracts, and root exudates, respectively. Sixty-three to eighty-four percent of the metabolites were exuded to the rhizosphere. More than 33% of the metabolites in the root exudates showed higher concentration at low P than at high P. On the other hand, only 14% of the metabolites in the root extracts showed lower concentration at low P than at high P. These results suggest that rice roots actively release many metabolites in response to P deficiency.  相似文献   

12.
A pot experiment was conducted to evaluate the foliar applied phosphorous with and without pre-plant dose (50 kg hac.?1) of phosphorous on growth, chlorophyll contents, gas exchange parameters and phosphorous use efficiency (PUE) of wheat. The experiment was conducted in net house at Department of Crop Physiology, University of Agriculture Faisalabad, Pakistan. Two promising wheat cultivar AARI 2011 and FSD 2008 were used as a test crop with 5 foliar phosphorus (P) rates (0, 2, 4, 6, 8 kg ha?1). The foliar applied P with pre-plant performed better than without pre-plant and control treatments. Foliar treatment of phosphorus at 6 kg ha?1 P proved to be the best among other foliar treatments followed by 8 kg ha?1 P. The foliar application of phosphorous at 6 kg hac.?1 with pre-plant soil applied P increased the shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight. The chlorophyll contents (Chl. a and b) were increased with the foliar application of phosphorous. The gas exchange parameters (net carbon dioxide (CO2) assimilation rate, transpiration rate, stomatal conductance and sub-stomatal CO2 rate) were significantly improved by foliar applied P. The maximum values of net CO2 assimilation rate (5.27 μ mol m?2 sec.?1), transpiration rate (3.44 μ mol m?2 sec.?1), stomatal conductance (0.81 μ mol m?2 sec.?1) and sub-stomatal CO2 (271.67 μ mol m?2 sec.?1), were recorded in the treatment where P was foliar applied at 6 kg hac.?1 with pre-plant soil applied Phosphorous. The foliar application of phosphorous with pre-plant soil applied P enhanced Phosphorous use efficiency (PUE) in both varieties. The maximum value of PUE (15.42%) was recorded in the treatment where foliar feeding of P was done at 6 kg hac.?1 with pre-plant soil applied P in both genotypes.  相似文献   

13.
A genotype effect on associative (rhizosphere) N2-fixation was observed with two cultivars of Sorghum bicolor (nutans) with a maximum rate of 8 μmol C2H4 · h?1 · plant?1 in one genotype compared to 0.9 μmol in the other. Characteristics of the high fixing genotype were a reduced transpiration rate, a lower number of stomata and increased root exudate production per gram root dry weight with higher concentration of dicarboxylic acids. The bacterial rhizosphere composition revealed a three times higher number of N2-fixing bacteria, a tenfold reduction of actinomycetes and a threefold reduction of Arthrobacter associated with the high fixing cultivar compared to the low fixing genotype. From these and other plant rhizospheres two new nitrogen fixing bacteria, Pseudomonas stutzeri and Erwinia herbicola, were characterized. With the N2-fixing bacteria Azospirillum brasilense and Klebsiella pneumoniae an enhancement of specific nitrogenase activity by aromatic compounds, for example phenolics, the herbicide alachlor and the insecticide carbofuran was demonstrated. An oscillating nitrogenase activity in Azospirillum brasilense under microaerobic conditions was found, resulting from an encystation and deencystation under those conditions. Experiments with wheat roots demonstrated that reduced oxygen tensions, essential for a maximum rhizosphere N2-fixation, reduced root growth significantly and altered the N-metabolism of the roots.  相似文献   

14.
Influence of Soil Structure on Root Growth and P Uptake of Spring Wheat The effect of soil structure (fine aggregat, coarse aggregate and compacted structure) on root growth, root morphology, and P availability of spring wheat (Triticum aestivum L.) was studied in pot and split root experiments using three soils (2 × Alfisol-Udalf, Alluvium). CAL-soluble P was 63–90 mg P · kg?1 soil, indicating a sufficient P supply. Root length, root surface, root fresh weight, shoot weight, and seed yield were decreased due to coarse aggregate and compacted structure. Roots were significantly thickened and roots hairs were longer in the fine aggregate structure than in the compacted and coarse aggregate structures. P concentration in the shoot and P uptake of spring wheat growing in the coarse aggregate and compacted structure were lower because root growth was decreased. In the split root experiment, in contrast to pot experiment, P uptake was lower in the compacted than in the fine aggregate treatment. The results demonstrate that P availability was influenced by soil structure via the influence on root growth and thus access of roots to P.  相似文献   

15.
Upland rice is an important crop in South America, including Brazil. Nutrient interactions are important in determining crop yields. A greenhouse experiment was conducted to evaluate interaction among nitrogen (N), phosphorus (P), and potassium (K) in upland rice production. The treatments applied to upland rice grown on an Oxisol were three levels of N (N0, N150 and N300 mg kg?1), three levels of P (P0, P100 and P200 mg kg?1) and three levels of K (K0, K100 and K200 mg kg?1). These treatments were tested in a 3 × 3 × 3 factorial arrangement. Grain yield, shoot dry weight, plant height, root dry weight, maximum root length, panicle number, 1000-grain weight, and grain harvest index were significantly influenced by N, P, and K treatments. The treatment that did not receive P fertilization did not produce panicle or grain. Hence, P was most yield-limiting nutrient compared to two other nutrients. At the N0P0K0 treatment, rice did not produce grains, indicating severe deficiency of these nutrients in Brazilian Oxisols. Maximum grain yield was obtained with the N300P200K200 treatment. Grain yield had significant positive association with plant height, shoot dry weight, root dry weight, maximum root length, 1000-grain weight, panicle number, and grain harvest index. Among these growth and yield components, shoot dry weight had the highest positive association with grain yield and root length minimum positive association with grain yield. Hence, adopting adequate soil and crop management practices can improve growth and yield components and increase grain yield of upland rice.  相似文献   

16.
Tropical legume cover crops are important components in cropping systems because of their role in improving soil quality. Information is limited on the influence of nitrogen (N) fertilization on growth of tropical legume cover crops grown on Oxisols. A greenhouse experiment was conducted to evaluate the influence of N fertilization with or without rhizobial inoculation on growth and shoot efficiency index of 10 important tropical cover crops. Nitrogen treatment were (i) 0 mg N kg?1 (control or N0), (ii) 0 mg N kg?1 + inoculation with Bradyrhizobial strains (N1), (iii) 100 mg N kg?1 + inoculation with Bradyrhizobial strains (N2), and (iv) 200 mg N kg?1 of soil (N3). The N?×?cover crops interactions were significant for shoot dry weight, root dry weight, maximal root length, and specific root length, indicating that cover crop performance varied with varying N rates and inoculation treatments. Shoot dry weight is considered an important growth trait in cover crops and, overall, maximal shoot dry weight was produced at 100 mg N kg?1 + inoculation treatment. Based on shoot dry-weight efficiency index, cover crops were classified as efficient, moderately efficient, and inefficient in N-use efficiency. Overall, the efficient cover crops were lablab, gray velvet bean, jack bean, and black velvet bean and inefficient cover crops were pueraria, calopo, crotalaria, smooth crotalaria, and showy crotalaria. Pigeonpea was classified as moderately efficient in producing shoot dry weight.  相似文献   

17.
Abstract

Zinc (Zn) nutrition and plant genotype are two factors that may affect the tolerance of wheat to root-rot diseases. The aim of the present study was to determine the effect of Zn on shoot yield, root permeability and infection by Fusarium solani in six wheat genotypes with different Zn efficiency. A greenhouse (solution culture) experiment was carried out in which five bread wheat genotypes (Triticum aestivum L. cvs Rushan, Kavir, Cross, Pishtaz and Falat) and one durum wheat genotype (Triticum durum L. cv. Yav79), which are common in Zn-deficient soils of Iran and were exposed to two levels of Zn (0 and 1?μmol?L–1?Zn?kg?1, as ZnSO4.7H2O) and two F. solani infection levels (0 and 106?spore?mL?1). Zinc deficiency significantly decreased shoot dry matter in five of the genotypes (Yav79, Kavir, Rushan, Cross and Falat), but had no effect on shoot growth in Pishtaz. Infection with F. solani significantly decreased the shoot dry matter in Yav79, but did not affect the shoot dry weight of the other wheat genotypes. Root membrane permeability was lower in the Zn treatments than in the Zn-free treatments. Zinc deficiency caused a decrease in root reactive sulfhydryl (SH) groups, particularly in the Cross genotype. Root sulfhydryl groups decreased with Fusarium infection. Zinc application sharply increased the Zn content and decreased the Mn content of the shoots. Application of Zn had a positive effect on the tolerance of wheat to F. solani root rot. The relationship between Zn nutrition and disease tolerance suggests that Zn deficiency should be treated before evaluating the cost-effectiveness of fungicides. No correlation was found between the Zn efficiency of the wheat genotypes and Fusarium root-rot disease severity in this solution culture experiment.  相似文献   

18.
Cultivars of Triticum aestivum, T. durum, and Secale cereale were grown at low (2 μM) and sufficient (500 μM) phosphorus (P) under ambient carbon dioxide (380 μmol mol?1; aCO2) and elevated CO2 (700 μmol mol?1, eCO2) to study responses of cereal species in terms of growth and P utilization efficiency (PUE) under P x CO2 interaction. Dry matter accumulation increased under eCO2 with sufficient P. Nevertheless, dry matter accumulated at eCO2 with low-P was similar to that obtained at aCO2 with sufficient P. Leaf area was 43% higher under eCO2 with sufficient P. Significant increase in lateral root density, length and surface area were noted at low-P under eCO2. Phosphorus use efficience (PUE) increased by 59% in response to eCO2­ in low-P plants. Thus, eCO2 can partly compensate effect of low-P supply because of improved utilization efficiency. Among cereals, durum wheat was more suitable in terms of PUE under high CO2 and limiting P supply.  相似文献   

19.
Laboratory culture experiments were conducted with common reed (Phragmites australis) to elucidate the role of root exudates on CH4 production in wetland soils as well as the importance of different plant organs as routes of CH4 to the atmosphere. In the 50 d experiment period, root exudates ranged from 0.03 to 1.53 µmolg?1d?1, which increased with reed growth. CH4 production rate of soil was stimulated as root exudates collected was added. CH4 transport capacity rate also increased with plant growth and influenced by light intensity. Root tips were the most important part of controlling diffusion of CH4 into reed shoots, and leave transport accounted for 45.34% of total emissions into the atmosphere.  相似文献   

20.
Seedlings of Norway spruce (Picea abies [L.] Karst.), which had been grown under sterile conditions for three months, were treated for one week in a hydroculture system with either 500 μM AlCl3 or 750 μM CaCl2 solutions at pH 4. Organic acids were determined in hot‐water extracts of ground root tissue. Oxalate (3.3—6.6 μmol (g root dry weight)—1) was most abundant. Malate, citrate, formate, acetate, and lactate concentrations ranged between 1—2 μmol (g root dry weight)—1. Organic substances and phosphate found in the treatment solutions at the end of the experimental period were considered to be root exudates. Total root exudation within a 2‐day period ranged from 20—40 μmol C (g root weight)—1. In root exudates, organic acids, and total carbohydrates, total amino acids, and total phenolic substances were quantified. Citrate and malate, although present in hot‐water extracts of root tissue, were not detected in root exudates. Phosphate was released from Ca‐treated plants. In Al treatments, there was indication of Al phosphate precipitation at the root surface. Oxalate and phenolics present in the exudates of Norway spruce seedlings are ligands that can form stable complexes with Al. However, concentrations of these substances in the treatment solutions were at micromolar levels. Their importance for the protection of the sensitive root apex under natural conditions is discussed.  相似文献   

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