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A pot experiment was carried out to investigate the tolerance of cucumber plants (Cucumis sativus L.) to root-knot nematode after inoculation with Glomus intraradices. Plants were inoculated with G. intraradices for four weeks and then transplanted in soil treated with Meloidogyne incognita for a further five weeks. The low phosphorus (P) loamy soil was amended with 50 and 100 mg P kg-1 soil. Mycorrhizal colonization increased shoot dry weight, shoot length, leaf numbers, root fresh weight and shoot P concentration, whereas nematode penetration and reproduction were significantly decreased. Similarly, P fertilization usually increased shoot growth and significantly decreased the number of galls and the number of egg masses and eggs per g root. Our results indicate that inoculation with G. intraradices and P fertilizer confer tolerance of cucumber plants to M. incognita by enhancing plant growth and by suppressing reproduction and/or galling of nematodes during the early stages of plant growth. [ABSTRACT FROM AUTHOR]

A pot experiment investigated the response of two maize inbred lines with contrasting root morphology and phosphorus (P) efficiency to inoculation with Glomus mosseae or Glomus etunicatum compared with non-mycorrhizal controls. Soil phosphorus was supplied at rates of 10, 50, and 100 mg P kg -1 soil. Root length, specific root length, and specific phosphorus uptake of maize line 178 (P-efficient) were significantly higher than of line Hc (P-inefficient). Percentage of root length colonized showed the opposite trend regardless of soil P supply level. The two maize lines did not differ significantly in growth response to mycorrhizal colonization. Root colonization rate decreased with increasing soil phosphorus supply. The beneficial effect of the two AM fungi on plant growth and P uptake was greatest at low soil P level and the responses were negative at high P supply. Mycorrhizal responsiveness also decreased with increasing P supply and differed between the two mycorrhizal fungal isolates. [ABSTRACT FROM AUTHOR]

The influence of sulfur (S) supply and mycorrhizal colonization on the growth and pungency of spring onion (Allium fistulosum L.) seedlings grown for four months in Perlite and nutrient solution containing three levels of sulfate [0.1, 1.75, and 4 mM sulfate (SO42-)] were investigated. Plants were inoculated with Glomus etunicatum, Glomus intraradices, or Glomus mosseae, and uninoculated controls were included. Shoot and root dry weights of mycorrhizal and control plants supplied with 4 mM SO42+ were higher than with 0.1 or 1.75 mM SO42-. Enzyme produced pyruvic acid (EPY) and plant sulfur concentrations increased with increasing SO42- supply. The EPY and plant S concentrations were usually higher in mycorrhizal plants than controls irrespective of S supply, and shoot total S concentrations and EPY were strongly correlated. Arbuscular mycorrhizal colonization appeared to make a substantial contribution to the sulfur status of spring onion, and may thus have had a strong influence on its flavor characteristics. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted out to investigate the yield and pungency of spring onion ( Allium fistulosum L.) as affected by inoculation with arbuscular mycorrhizal (AM) fungi and addition of nitrogen (N) and sulfur (S) fertilizers. Plants were inoculated with either Glomus mosseae or Glomus intraradices or grown as uninoculated controls. Two levels of N and S were applied to the soil in factorial combinations of 50 and 250 mg N kg -1 soil and 0 and 60 mg S kg -1 soil. Plants were grown in a greenhouse for 25 weeks and then harvested. Mycorrhizal colonization resulted in increased shoot dry weight, shoot-to-root ratio, shoot length, sheath diameter, and phosphorus (P) concentrations. Shoot dry-matter yield was significantly affected by added N, but not by S. Shoot dry weight increased with increasing N supply (except for non-mycorrhizal controls without additional S fertilizer). Shoot total S concentration (TSC), enzyme-produced pyruvate (EPY), and organic sulfur concentration (OSC) in plants inoculated with Glomus mosseae were significantly lower than those of non-mycorrhizal controls, while these parameters in plants inoculated with Glomus intraradices were comparable to or higher than in the controls. Neither N nor S supply affected shoot EPY or OSC, whereas shoot TSC (except in plants inoculated with Glomus mosseae ) and SO 4 2- concentrations were usually significantly increased by S supply. In soil of high S and low P availability, mycorrhizal colonization had a profound influence on both the yield and the pungency of spring onion. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to study the growth and pungency of Allium cepa L. grown in Perlite as affected by colonization by the arbuscular mycorrhizal (AM) fungi Glomus versiforme and Glomus intraradices BEG141 and by ammonium:nitrate (NH 4 + :NO 3 - ) ratios of 3:1, 1:1, and 1:3 in 4 m M solutions. Plants were harvested when bulb formation commenced. In general, mycorrhizal colonization resulted in increased shoot dry weight, shoot length, sheath diameter, root nitrogen (N) and phosphorus (P) content (except with G. intraradices and a NH 4 + :NO 3 - ratio of 1:3), shoot N and P concentrations (except with G. versiforme and a NH 4 + :NO 3 = ratio of 3:1) and content. Plants inoculated with G. versiforme had higher growth parameters and N and P content than those with G. intraradices , whereas N and P concentrations showed the opposite trends. Growth parameters and N and P content of non-mycorrhizal plants were highest at a NH 4 + :NO 3 = ratio of 1:3, while those of plants inoculated with G. versiforme or G. intraradices were highest at a ratio of NH 4 + :NO 3 - 3:1 or 1:1. Neither mycorrhizal colonization nor proportion of inorganic N species significantly affected bulb enzyme-produced pyruvate or total or organic sulfur (S) concentrations in plant shoots. Colonization by AM fungi made a substantial contribution to onion growth and may not have been directly related to bulb pungency at early stages of plant growth. However, the influence of AM fungi on plant N and P metabolism may have implications for onion flavor at later stages of plant growth. [ABSTRACT FROM AUTHOR]

A glasshouse pot experiment was conducted to investigate the impact of inoculation of cucumber at the germination stage with Glomus etunicatum BEG168 on plant yield and incidence of Fusarium oxysporum f.sp. cucumerinum inoculated 28 days after the start of the experiment. Inoculation with the AM fungus decreased both disease incidence and disease index. Mycorrhizal inoculation also increased P concentrations in the cucumber seedlings. The mycorrhizal seedlings had higher concentrations of proline and polyphenol oxidase activity but lower malondialdehyde than non-mycorrhizal seedlings, indicating that AM inoculation may have protected membrane permeability and reduced the extent of the damage caused by F. oxysporum . The results indicate that the mycorrhizal fungus may influence plant secondary metabolites and increase resistance to wilt disease in cucumber seedlings and may therefore have some potential as a biological control agent. [ABSTRACT FROM AUTHOR]

A series of field experiments were conducted over a three-year period to test a modified N-Expert system (the decision support system for nitrogen recommendations) with different irrigation regimes for a rotation of amaranth (Amaranthus tricolor L.), spinach (Spinacia oleracea L.), and cauliflower (Brassica oleracea L.). Local commercial fertilizer practice based on farmer surveys was selected as the control, and irrigation treatments followed conventional practice with a balanced irrigation schedule. Some parameters, notably target yields and net mineralization rates, were modi- fied according to local conditions, and most were referenced from the database of the N-Expert system in the first cultivation year of the rotation. Parameters were tested in earlier field experiments and were fine-tuned in later experiments. No significant yield reduction occurred below conventional nitrogen (N) practice using the recommended N treatment (N2) with different water treatments, except for irrigation treatments between 60% and 90% of PESW (plant extractable soil water: the difference between field capacity and wilting point) in 2000 and conventional irrigation practice in 2001 for cauliflower. There was a significant decrease in residual Nmin at harvest in treatments using the modified N-Expert recommendation system compared with conventional N practice. This indicates that there is considerable potential for use of the N recommendation system for sustainable vegetable production in the North China Plain. [ABSTRACT FROM AUTHOR]

Twenty commonly used winter wheat genotypes collected throughout China were used in field screening for phosphorus (P)-efficient germplasm in a calcareous soil with and without fertilizer P application; the same genotypes were also evaluated for high and low P inputs in a greenhouse experiment. The overall criterion for P efficiency was the capacity to produce a relatively high yield with low P availability. Significant differences in grain yield production occurred between efficient and inefficient genotypes. Four parameters were calculated to determine which was the most useful for describing P efficiency: (1) percentage of relative yield with no applied P; (2) total P uptake; (3) P-harvest index (PHI: grain P/total P uptake); and (4) P-utilization efficiency (PUE: grain yield produced per unit of P taken up). A simple but satisfactory criterion in screening P-efficient wheat genotypes, 85% of relative grain yield at low P/high P, was recommended and proved to be more effective than the other three parameters.With this criterion, 12 out of 20 genotypes were classified as P-efficient (⩽15% yield reduction with no P applied) from both field and pot experiments. Phosphorus efficiency may have resulted from either P uptake or P-utilization efficiency. Three parameters, namely relative yield without applied P, PHI and PUE, were found to be useful, together with P uptake, in determining overall P efficiency. Successful selection for P efficiency was found to be possible at the shooting stage (but not at tillering) by comparing P uptake and P-utilization efficiency of plants at this growth stage with those of plants at maturity. [ABSTRACT FROM AUTHOR]

Three ectomycorrhizal fungal isolates, Cenococcum geophilum SIV, a putative isolate of Pisolithus microcarpus and a Pisolithus sp., were cultured in vitro without potassium (K) and with three levels of K supply (as K2SO4). Some growth stimulation by K was observed among the fungi. Potassium in the liquid medium led to increased concentrations of nitrogen (N) and K in the fungi compared to K-free controls, and to higher phosphorus (P) concentrations in Pisolithus sp., but lower P in C. geophilum SIV. In a second experiment, the K influx rates of the fungi from external solutions followed Michaelis-Menten kinetics, indicating that K influx was an active process. Mycorrhizal fungi showed quite small Cmin values for K influx, ranging from 2.12 to 5.39 µmol L-1, in relation to K concentrations in the external solution. Such low Cmin values might allow the external hyphae to extract K efficiently from K-deficient soils. Furthermore, the fungi had low Km values for K uptake (<14.85 µmol L-1), indicating high affinities and efficiencies of K carriers. Both Pisolithus sp. and P. microcarpus exhibited similar Cmin and Km values but were different from C. geophilum SIV. Furthermore, Imax values varied significantly among the fungi, ranging from 9.60 to 21.63 µmol g-1 DM h-1, perhaps due to variation in the intracellular K concentrations in the ectomycorrhizal fungi. [ABSTRACT FROM AUTHOR]

Field observations have indicated that Fe deficiency chlorosis symptoms in peanut are more severe and widespread in monoculture than intercropped with maize in calcareous soils of northern China. Here we report a pot experiment that investigated the mechanisms underlying the marked improvement in Fe nutrition of peanut grown in mixture with maize. Iron deficiency chlorosis occurred in the young leaves of peanut in monoculture and was particularly obvious at the flowering stage, while the young leaves of peanut grown in mixture with maize remained green throughout the experiment. The chlorophyll and HCl-extractable Fe concentrations in young leaves of peanut grown in mixture were much higher than those in monoculture, indicating that maize may have markedly improved the peanut Fe nutrition. Growth in mixture was associated with greatly altered root morphology and microbial populations in the rhizosphere of peanut. Visual observation of peanut roots in monoculture showed that they were larger in diameter and shorter than those in mixture. Moreover, peanut roots in mixture with maize produced more lateral roots and had increased root length compared with plants in monoculture. Peanut grown together with maize showed obvious rhizodermal transfer cells in the subapical root zone, but cells with cell wall ingrowths were poorly developed in peanut in monoculture. Mixed culture resulted in a significantly decreased abundance of bacteria in the rhizosphere of peanut compared with monoculture, and electron microscope observations indicated that this was associated with a thicker mucigel layer on the root surface of peanut in mixture with maize. Several root morphological and rhizosphere microbial factors may thus have contributed to the improvement in Fe nutrition of peanut in mixed culture. [ABSTRACT FROM AUTHOR]

One-third of all the cultivated land area is used for multiple cropping and half of the total grain yield is produced with multiple cropping in China. There have been numerous studies on nutrient acquisition by crops in legume/non-legume intercropping systems, but few on nutrient uptake in cereal/cereal intercropping. This paper describes a field experiment in which integrated wheat/maize and maize/faba bean systems were compared with sole wheat and sole faba bean cropping to assess the effects of intercropping on nutrient uptake by wheat, maize, and faba bean under various application rates of nitrogen (N) and phosphorous (P) fertilizers. Results show that both N and P fertilizers and intercropping enhanced N uptake by wheat, while only P fertilizer and intercropping increased P acquisition by wheat. The advantage of N uptake by border rows of wheat intercropped with maize declined with increasing N fertilizer application rate, but that of P acquisition was not affected by P fertilizer. The amounts of both N and P taken up by maize intercropped with faba bean were much higher than those by maize intercropped with wheat throughout the period of intercropping. Both fertilization and intercropping did not influence the N and P uptake by faba bean. [ABSTRACT FROM AUTHOR]

Three wheat (Triticum aestivum L.) genotypes with high, intermediate and low phosphorus (P) efficiency were grown in a pot experiment with low P supply and adequate P supply either inoculated with the arbuscular mycorrhizal fungus Glomus versiforme or uninoculated. The mycorrhizal dependency of the genotype with relatively high P efficiency was lower than that of the genotypes with lower P efficiencies. Linear correlation analysis revealed that mycorrhizal dependency was primarily controlled by P uptake efficiency. More carbohydrate was translocated to the roots of genotypes with low P efficiency than of those with high P efficiency. In a second pot experiment the same three genotypes were grown in low P soils. Higher hyphal length density arising from carbohydrate translocation led to more P uptake, and this may account for higher mycorrhizal dependency. [ABSTRACT FROM AUTHOR]