Ashton Nutrient Solution Research Articles

MITIGAÇÃO DA TOXICIDADE DE ALUMÍNIO EM MUDAS DE GLYCYRRHIZA GLABRA L. USANDO SILÍCIO

Background: Silicon is a beneficial element for the plant, with the primary role in increasing plant resistance to heavy metals' toxicity and considering the importance of phytoremediation to remove heavy metals from contaminated soils. It could be used for the exogenous application for alleviating the harmful effects of heavy metals on the plant. Aim: This study aimed to investigate the role of Silicon in balancing the destructive effects of aluminum on Glycyrrhiza glabra L. Methods: the seedlings were grown under a hydroponic system using Long Ashton nutrient solution; the 15-day-old seedlings were exposed to Silicon (0, 0.5, 1.5 mM) for 110 days and afterward stressed by interactions of aluminum chloride (AlCl3.6H2O; 0, 100, 250, and 400 M). Result and Discussion: the interactive effects of Silicon significantly ameliorated the negative consequences of aluminum toxicity. The combination of Si 1.5 mM and Al 400 ?M produced the highest biomass in shoots (45.67 g). The simple effect of Si 1.5 mM (12.14 g) made the highest shoot dry weight. On the other hand, the highest quantity of root fresh and dry weight (12.52 and 3.22 g, respectively) was observed in Si 1.5 mM. Among the treatments, Si 0.5 mM + Al 100 ?M had the most stem height (38 cm) among interaction treatments. Similarly, photosynthetic pigments affected by Silicon, Al 250 ?M + Si 1.5 mM had the highest content of chlorophyll a (1.91 ?g/g FW), while Al 400 + 1.5 mM indicated the most increase in chlorophyll b (0.78 ?g/g FW) among interaction effects. This treatment by producing 0.663 ?g/g FW yielded the highest carotenoid content. The highest proline content in shoots and roots (69.54 and 81.46 ?g/g FW, respectively) were observed in the interaction of Al 400 ?M and Si 1.5 mM. Additionally, this treatment was observed to have the highest concentration of catalase (1.22 U/mg protein). The lowest malondialdehyde content was marked in Si 1.5 mM + Al 100 ?M (0.702 nM/g FW). Conclusion: overall, Glycyrrhiza Glabra L. seems to have high Al phytoremediation potential that can be enhanced with the exogenous application of a moderate Silicon level.

MITIGATING ALUMINUM TOXICITY IN SEEDLINGS OF GLYCYRRHIZA GLABRA L. USING SILICON

Background: Silicon is a beneficial element for the plant, with the primary role in increasing plant resistance to heavy metals' toxicity and considering the importance of phytoremediation to remove heavy metals from contaminated soils. It could be used for the exogenous application for alleviating the harmful effects of heavy metals on the plant. Aim: This study aimed to investigate the role of Silicon in balancing the destructive effects of aluminum on Glycyrrhiza glabra L. Methods: the seedlings were grown under a hydroponic system using Long Ashton nutrient solution; the 15-day-old seedlings were exposed to Silicon (0, 0.5, 1.5 mM) for 110 days and afterward stressed by interactions of aluminum chloride (AlCl3.6H2O; 0, 100, 250, and 400 M). Result and Discussion: the interactive effects of Silicon significantly ameliorated the negative consequences of aluminum toxicity. The combination of Si 1.5 mM and Al 400 ?M produced the highest biomass in shoots (45.67 g). The simple effect of Si 1.5 mM (12.14 g) made the highest shoot dry weight. On the other hand, the highest quantity of root fresh and dry weight (12.52 and 3.22 g, respectively) was observed in Si 1.5 mM. Among the treatments, Si 0.5 mM + Al 100 ?M had the most stem height (38 cm) among interaction treatments. Similarly, photosynthetic pigments affected by Silicon, Al 250 ?M + Si 1.5 mM had the highest content of chlorophyll a (1.91 ?g/g FW), while Al 400 + 1.5 mM indicated the most increase in chlorophyll b (0.78 ?g/g FW) among interaction effects. This treatment by producing 0.663 ?g/g FW yielded the highest carotenoid content. The highest proline content in shoots and roots (69.54 and 81.46 ?g/g FW, respectively) were observed in the interaction of Al 400 ?M and Si 1.5 mM. Additionally, this treatment was observed to have the highest concentration of catalase (1.22 U/mg protein). The lowest malondialdehyde content was marked in Si 1.5 mM + Al 100 ?M (0.702 nM/g FW). Conclusion: overall, Glycyrrhiza Glabra L. seems to have high Al phytoremediation potential that can be enhanced with the exogenous application of a moderate Silicon level.

Nitrogen and phosphorus influence Acacia saligna invasiveness in the fynbos biome

This study attempts to understand how invasive legumes such as Acacia saligna may compete with indigenous legumes such as Virgilia divaricata. The two species are trees with similar growth forms. We studied the competitive ability of invasive and indigenous seedlings under variations in soil phosphorus availability. South African fynbos vegetation is threatened by invasive Acacia. The indigenous tree legume, Virgilia, grows in similar phosphorus soil conditions as Acacia although there is a gap in the knowledge of their physiology. We investigated the utilization of different inorganic P sources by the invasive A. saligna and the native V. divaricata in the presence and absence of root nodules in each species. Plant performance in terms of photosynthesis and biomass production was also analysed. Plants were cultivated in silica sand supplied with Long Ashton nutrient solution, modified to contain either 50 μM P or 500 μM P applied as NaH2PO4·2H2O. Rate of growth was estimated as the increase in mass in plants harvested after 4 and 8 weeks of growth. After 4 weeks of growth, the seedlings of Virgilia grew quicker and produced more biomass than Acacia, under both phosphorus conditions. However, this was reversed after 8 weeks of growth, with Acacia out-competing Virgilia. Increased growth of the invasive legumes was achieved by relying on soil nitrogen under high phosphorus conditions and shifting to atmospheric sources under lower phosphorus levels. The strategies of altering photosynthetic carbon balance and nitrogen acquisition under varying soil phosphorus conditions potentially underpin the invasive potential of Acacia in fynbos soils.

Differential physiological responses of Tunisian wild grapevines (Vitis vinifera L. subsp. sylvestris) to NaCl salt stress

The effects of salt stress on growth, organic and inorganic solute accumulation and chlorophyll florescence were studied on 3-month-old plants of six Tunisian wild grapevine accessions in order to identify salt tolerance mechanisms and select tolerant genotypes. Potted plants were grown under controlled conditions and irrigated for 14 days with 0, 100 and 150 mM NaCl Long Ashton nutrient solution. Salt begins to adversely affect plant growth and plant nutrition at 100 mM NaCl. Compared to control, shoot growth rates were 21.5% less for Khedhayria, Tebaba and Ouchteta, 33% for Djebba and Zouarâa and 49% for Houamdia. They were assigned to stomatal and non-stomatal factors. Stomatal conductance decreased after 1 day at 150 mM NaCl in all accessions in response to reduced leaf water potential. Leaves in tolerant accessions were well hydrated through efficient osmotic adjustment, sufficient potassium flux and selectivity of K+ versus Na+. In addition, salt tolerance of wild grapes was related to limiting Na+ transport to lamina and to compartmentalization of Cl− on root and leaf vacuoles, improved in Tebaba and Khedhayria by the uptake of K+. At the same time, disturbances of the PSII have been noted as non-stomatal factors, and the most important photoprotective mechanism against photosynthetic damages was non-photochemical energy dissipation. However, chlorophyll fluorescence parameters were more stable in Tebaba compared to Khedhayria, thus showing better salt tolerance. Based on our results, wild grapevine accessions could be classified from most tolerant to most sensitive as follows: Tebaba > Khedhayria > Ouchteta > Zouarâa > Djebba > Houamdia.

The reallocation of carbon in P deficient lupins affects biological nitrogen fixation

It is not known how phosphate (P) deficiency affects the allocation of carbon (C) to biological nitrogen fixation (BNF) in legumes. The alteration of the respiratory and photosynthetic C costs of BNF was investigated under P deficiency. Although BNF can impose considerable sink stimulation on host respiratory and photosynthetic C, it is not known how the change in the C and energy allocation during P deficiency may affect BNF. Nodulated Lupinus luteus plants were grown in sand culture, using a modified Long Ashton nutrient solution containing no nitrogen (N) for ca. four weeks, after which one set was exposed to a P-deficient nutrient medium, while the other set continued growing on a P-sufficient nutrient medium. Phosphorus stress was measured at 20 days after onset of P-starvation. During P stress the decline in nodular P levels was associated with lower BNF and nodule growth. There was also a shift in the balance of photosynthetic and respiratory C toward a loss of C during P stress. Below-ground respiration declined under limiting P conditions. However, during this decline there was also a shift in the proportion of respiratory energy from maintenance toward growth respiration. Under P stress, there was an increased allocation of C toward root growth, thereby decreasing the amount of C available for maintenance respiration. It is therefore possible that the decline in BNF under P deficiency may be due to this change in resource allocation away from respiration associated with direct nutrient uptake, but rather toward a long term nutrient acquisition strategy of increased root growth.

PHENOTYPIC EVALUATION OF 'THOMPSON SEEDLESS' GRAPES TRANSFORMED WITH ATNHX1 GROWING IN HYDROPONICS AND POTTED SOILS

Overexpression of vacuolar Na+/H+ antiport AtNHX1 has been reported to improve plant salt tolerance. We produced transgenic plants of Vitis vinifera ?Thompson Seedless? via Agrobacterium tumefaciens carrying the gene encoding for AtNHX1 under the control of the constitutive promoter CaMV35S. Independent transgenic lines with improved tolerance to salt stress were selected in first round evaluations. The objective of this study was to analyze the response of the selected lines to NaCl stress in hydroponics and potted soils. Untransformed and transgenic plants were acclimated to greenhouse conditions and grown hydroponically using Long Ashton nutrient solution. In the salinity treatments, NaCl concentrations were increased stepwise by 25 mM every 10 days up to 150 mM. In addition, untransformed and transgenic plants were grown in a mix of 7-3 grape pomace-sand soil and watered with Long Ashton nutrient solution with and without increasing concentrations of NaCl. Analysis of plant growth variables confirmed the improved tolerance of the transgenic lines, which showed higher shoot length, leaf number, leaf area, and fresh and dry weight of shoots and roots. However, their improved performance was not correlated with higher Na accumulation in root and/or shoot tissue compared to the untransformed controls. Na and Cl tissue contents were higher in plants grown in hydroponics; and roots accumulated 1.5-2.5 times more NaCl than aerial parts

Low-phosphorus conditions affect the nitrogen nutrition and associated carbon costs of two legume tree species from a Mediterranean-type ecosystem

The role of phosphorus nutrition in two-legume tree species from the Mediterranean-type ecosystem of the Cape Floristic Region (CFR) in South Africa was investigated. There is very little information about the functional adaptations of nitrogen (N) and phosphorus (P) nutrition in these legume trees growing in nutrient-poor soils. Nodulated Virgilia divaricata and V. oroboides tree saplings were grown in sterilised sand and supplied with Long Ashton nutrient solution, which was modified to contain either sufficient-phosphate (500 µM) or low-phosphate (5 µM) nutrient solution for 90 days. During low-P conditions, the growth of V. divaricata was not affected, whereas V. oroboides showed a decrease in growth. The decrease in V. oroboides under low-P conditions was related to the lower P uptake, which resulted in an alteration in belowground biomass allocation, which consequently affected on the N nutrition and carbon (C) cost of growth. In this regard, V. oroboides plants allocated less biomass to roots and nodules, as a proportion of whole plant growth. The impact of this was a decline in N nutrition, growth respiration and photosynthetic costs in V. oroboides. In contrast, V. divaricata maintained its P concentrations, photosynthetic costs and increased its nodule allocation under low-P conditions, to the benefit of N nutrition. The two CFR tree legumes appear to have different adaptations to low-P conditions, which may influence their N and P acquisition in their naturally low-P environment.

Phosphorus-deficiency reduces aluminium toxicity by altering uptake and metabolism of root zone carbon dioxide

The role of phosphorus (P) status in root-zone CO 2 utilisation for organic acid synthesis during Al 3+ toxicity was assessed. Root-zone CO 2 can be incorporated into organic acids via Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31). P-deficiency and Al 3+ toxicity can induce organic acid synthesis, but it is unknown how P status affects the utilisation of PEPC-derived organic acids during Al 3+ toxicity. Two-week-old Solanum lycopersicum seedlings were transferred to hydroponic culture for 3 weeks. The hydroponic culture consisted of a standard Long Ashton nutrient solution containing either 0.1 μM or 1 mM P. Short-term Al 3+ toxicity was induced by a 60-min exposure to a pH-buffered solution (pH 4.5) containing 2 mM CaSO 4 and 50 μM AlCl 3. Al 3+ toxicity induced a decline in root respiration, adenylate concentrations and an increase in root-zone CO 2 utilisation for both P sufficient and P-deficient plants. However during Al 3+ toxicity, P deficiency enhanced the incorporation and metabolism of root-zone CO 2 via PEPC. Moreover, P deficiency led to a greater proportion of the PEPC-derived organic acids to be exuded during Al 3+ toxicity. These results indicate that P-status can influence the response to Al 3+ by inducing a greater utilisation of PEPC-derived organic acids for Al 3+ detoxification.

Arbuscular Mycorrhiza and Petroleum-Degrading Microorganisms Enhance Phytoremediation of Petroleum-Contaminated Soil

While plants can phytoremediate soils that are contaminated with petroleum hydrocarbons, adding microbes to remediate contaminated sites with petroleum-degrading microorganisms and arbuscular mycorrhizal fungi (AMF) is not well understood. The phytoremediation of Arabian medium crude oil (ACO) was done with a Lolium multiflorum system inoculated with an AMF (Glomus intraradices) and a mixture of petroleum-degrading microorganisms—the bacterium, Sphingomonas paucimobilis (Sp) and the filamentous fungus, Cunninghamella echinulata (Ce, SpCe)—or with a combination of microorganisms (AMF + SpCe). Based on an earlier study on screening plants for phytoremediation of ACO, L. multiflorum (Italian ryegrass) was selected for its tolerance and rapid growth response (Alarcón, 2006). The plants were exposed to ACO-contaminated soil (6000 mg kg−1) for 80 d under greenhouse conditions. A modified Long Ashton Nutrient Solution (LANS) was supplied to all treatments at 30 μg P mL−1, except for a second, higher P, control treatment at 44 μg P mL−1. Inoculation with AMF, SpCe, or AMF + SpCe resulted in significantly increased leaf area as well as leaf and pseudostem dry mass as compared to controls at 30 μg P mL−1. Populations of bacteria grown on a nitrogen-free medium and filamentous fungi increased with AMF + SpCe and SpCe treatments. The average total colonization and arbuscule formation of AMF-inoculated plants in ACO-contaminated soil were 25% and 8%, respectively. No adverse effects were caused by SpCe on AMFcolonization. Most importantly, ACOdegradation was significantly enhanced by the addition of petroleum-degrading microorganisms and higher fertility controls, as compared to plants at 30 μg P mL−1. The highest ACOdegradation (59%) was observed with AMF + SpCe. The phytoremediation of ACO was also enhanced by single inoculation of AMF or SpCe. The effect of AMF and petroleum-degrading microorganisms on plant growth and ACOdegradation was not attributable to differences in proline, total phenolics, nitrate reductase levels, or variation in plant–gas exchange.

The role of arbuscular mycorrhizal colonization in the carbon and nutrient economy of the tripartite symbiosis with nodulated Phaseolus vulgaris

In the tripartite symbiosis between nodulated legume roots and arbuscular mycorrhizal (AM) fungi, symbiont sink strength may depend upon developmental stage and the nutrient benefits to the host plant. The cost-benefits of the tripartite symbiosis were investigated in terms of C-economy and nutrition. Nodulated Phaseolus vulgaris seedlings, with and without AM, were hydroponically grown under high (2 mM) and low (1 μM) P conditions in an N-free Long Ashton nutrient solution. Plants were sequentially harvested at 17, 24 and 31 days after emergence. At each harvest, measurements for biomass, N 2-fixation, photosynthesis, root respiration, calculated C and nutritional economy were taken. Nodular growth was suppressed by the early development of AM colonization. This coincided with higher photosynthetic and respiratory rates in AM plants. These effects were most pronounced under low P when AM colonization peaked. Once AM levels reached the plateau phase, the efficiency of P nutrition increased. This was followed by improved nodular and host growth and enhanced N 2-fixation. This indicates that the AM was the dominant symbiont for host C in the tripartite symbiosis, due to its rapid development and subsequent role in supplying P more effectively to both host and nodules.

(149) Phytoremediation of Petroleum Hydrocarbons with a Lolium multiflorum–Glomus intraradices–Inorganic Fertilization System: Influence on Plant Growth, Antioxidant Activity, Microbial Respiration, and Hydrocarbon Degradation

A phytoremediation study in a 3 × 3 × 2 factorial experimental design was conducted to determine the effect of Glomus intraradices (AMF) inoculation and inorganic fertilization on the growth and development of Lolium multiflorum cv. Passarel Plus, and on the degradation of total petroleum hydrocarbons (TPH). The 80-day study was done with pots containing sandy soil. Seedlings of L. multiflorum were transplanted to uncontaminated or soil contaminated with Arabian crude oil (ACO) at concentrations of 3000 and 15,000 mg·kg-1. Half of the seedlings were inoculated with 500 spores of AMF. Plants were fertilized with Long Ashton Nutrient Solution (LANS) at 0.5×, 1.0×, or 2.0× strength, modified to supply 30 μg·mL-1 P to maximize the AMF establishment. Total plant dry weight and leaf antioxidant activity were reduced by ACO when compared to control plants. The LANS fertilization enhanced plant growth under ACO-contamination, and allowed similar antioxidant activity in plants exposed to 15,000 mg·kg-1. Soil rhizosphere respiration was increased by LANS, particularly with 15,000 mg·kg-1 ACO. AMF inoculation did not enhance plant growth, antioxidant activity, or microbial respiration. The average root colonization was around 30% in contaminated and uncontaminated rhizospheres, indicating that the tolerance of AMF symbiosis to ACO. Greater TPH degradation was achieved in non-AMF plants at 3000 mg·kg-1 ACO in combination with 0.5× LANS. LANS-fertilization with 1.0× or 2.0× did not enhance TPH-degradation when compared to 0.5× LANS.

Influence of Arbuscular Mycorrhizae Indigenous to Peru and a Flavonoid on Growth, Yield, and Leaf Elemental Concentration of `Yungay' Potatoes

The influence of arbuscular mycorrhizal fungi (AMF) [two Peruvian mixed isolates, a pure isolate of Glomus intraradices] and the flavonoid, formononetin, were tested on growth, yield, and leaf elemental concentration of the Peruvian potato (Solanum tuberosum L.) `Yungay'. Plants started from tissue culture-produced prenuclear minitubers of `Yungay' were subjected to seven treatments, which included noncolonized (non-AMF) plants fertilized with Long Ashton nutrient solution modified to supply P at 11 and 44 μg·mL-1. All AMF plants received low P (11 μg·mL-1) and were inoculated with either a sierra-maize mixed isolate, sierra-papa mixed isolate, pure isolate of G. intraradices, sierra-maize mixed isolate + formononetin, or a sierra-papa mixed isolate + formononetin. Plants were grown in 3-L containers under shade house conditions in Lima, Peru. Non-AMF plants at low P had the poorest growth, while high P plants had the greatest overall growth. All AMF plants had greater growth, including a higher root to shoot ratio, higher phosphorus use efficiency [(g tuber)/(g P/kg tissue)], and a lower leaf to tuber ratio (indicating greater leaf efficiency in producing tuber dry matter), compared to non-AMF plants at low P. The mycorrhizal inoculation effect (MIE) ranged from +44% to +57%, indicating that `Yungay' was moderately to highly mycorrhizal dependent. Plants colonized with the sierra-papa isolate + formononetin had the same tuber development and leaf to tuber ratio, compared to high P, non-AMF plants. Formononetin increased extraradical hyphae formation. Mycorrhizal enhancement was in part due to greater P, Fe, and Mg uptake, a higher phosphorus-use efficiency and greater extraradical hyphae formation.

A feasibility study of a Salix viminalis gravel hydroponic system to renovate primary settled wastewater

A Salix viminalis/gravel system based on hydroponics was developed for wastewater renovation in order to avoid the problems of soil damage and pollution associated with long-term application of wastewater to soil. For such a system to work the mineral elements applied must match closely the requirements of the tree species. To examine this the growth and nutrient uptake of S. viminalis in wastewater was compared with that in Long Ashton nutrient solution (1/4 strength). S. viminalis grew more slowly in wastewater than in Long Ashton solution, but exhibited no obvious deficiency or toxicity symptoms. Since industrial wastewaters often contain metals, the extent to which copper might inhibit wastewater treatment in this system was also examined. S. viminalis was grown in wastewater amended with 10 and 100 ppm copper. Trees were unaffected by wastewater with 10 ppm copper when compared to trees grown in wastewater alone. Wastewater containing with 100 ppm copper was too toxic for the trees to thrive and wastewater treatment was reduced. Treatment efficiencies for unamended wastewater were 57.7% for nitrogen, 90.6% for phosphorus and 24.9% for potassium. These efficiencies are much greater than those quoted for a Salix/soil system, and thus Salix/gravel systems may have potential for wastewater treatment in environmentally sensitive areas or situations.

Mycorrhizal fungi enhancement of growth and gas exchange of micropropagated guava plantlets ( Psidium guajava L . ) during ex vitro acclimatization and plant establishment

L.) plantlets was determined during acclimatization and plant establishment. Guava plantlets were asexually propagated through tissue culture and grown in a glasshouse for 18 weeks. Half of the plantlets were inoculated with a mixed endomycorrhiza isolate from Mexico, ZAC-19, containing Glomus diaphanum, G. albidum and G. claroides. Plantlets were fertilized with modified Long Ashton nutrient solution that supplied 11 μg P ml−1. Gas exchange measurements were taken at 2, 4, 8, and 18 weeks after inoculation using a portable photosynthesis system. All micropropagated guava plantlets survived transplant shock. After 6 weeks, mycorrhizal plantlets had greater shoot growth rates and leaf production than non-mycorrhizal plantlets. This also corresponded with increased photosynthetic rates and stomatal conductance of mycorrhizal plants. By 18 weeks, mycorrhizal plantlets had greater shoot length, leaf area, leaf, stem, and root dry mass. However, gas exchange was comparable among treatments, in part because the container size was restricting growth of the larger mycorrhizal plantlets. Non-mycorrhizal plantlets had greater leaf area ratios and specific leaf areas than mycorrhizal plantlets. Increased leaf tissue mineral levels of P, Mg, Cu, and Mo also occurred with mycorrhizal plantlets. Roots of inoculated guava plantlets were heavily colonized with arbuscules, vesicles and endospores. Guava plantlets were highly mycotrophic with a mycorrhizal dependency index of 103%.

Influence of Phosphorus and Endomycorrhiza (Glomus Intraradices) on gas exchange and plant growth of Chile Ancho Pepper (Capsicum Annuum L. cv. San Luis)

Seedlings of chile ancho pepper were grown in pots containing a pasteurized mixture of sand and a low phosphorus (P) sandy loam soil, and either inoculated (VAM) or not inoculated (NVAM) with the endomycorrhizal fungus Glomus intraradices. Long Ashton nutrient solution (LANS) was modified to supply P to the seedlings at 0, 11, and 44 g(P) m-3 (P0, P11, P44, respectively). Low P depressed net photosynthetic rate (PN), stomatal conductance (gs), phosphorus use efficiency (PN/P), and internal CO2 concentration (Ci). The mycorrhiza alleviated low P effects by increasing PN, gs, PN/P, and decreasing Ci. At P0, Ci of NVAM plants was equal to or higher than that of VAM plants, suggesting nonstomatal inhibition of photosynthesis. Gas exchange of VAM plants at P0 was similar to that of NVAM plants at P11. Endomycorrhiza increased leaf number, leaf area, shoot, root and fruit mass at P0 and P11 compared to NVAM plants. Reproductive growth was enhanced by 450 % in mycorrhizal plants at P44. Root colonization (arbuscules, vesicles, internal and extraradical hyphae development) was higher at lower P concentrations, while sporulation was unaffected. The enhanced growth and gas exchange of mycorrhizal plants was in part due to greater uptake of P and greater extraradical hyphae development.

322 Influence of Mycorrhiza and an Isoflavonoid on Plant Growth and Gas Exchange of Potatoes Started from Minitubers

The influence of the mycorrhizal fungus Glomus intraradices and reduced levels of G. intraradices treated with the isoflavonoid formononetin was tested on growth and gas exchange of container-grown potato plants. Tissue culture-produced minitubers of Solanum tuberosum cv. Russet Norkotah and Russet Norkotah selection TX112 were subjected to four treatments: 1) G. intraradices at 750 propagules per container, 2) G. intraradices at 376 propagules per container, 3) G. intraradices at 376 propagules per container treated with the isoflavonoid formononetin, and 4) noncolonized plants. Plants were grown under glasshouse conditions in 1500-mL containers containing a sterilized sand: sandy loam soil, and fertilized with Long Ashton nutrient solution modified to supply phosphorus at 11 ug P/mL. The experiment was initiated on 4 May 1998 and terminated on 27 Aug. 1998, during which the plants were exposed to adverse high temperatures (mean high: 30.7 °C). Both cultivars responded similarly to mycorrhizal treatments. Formononetin enhanced growth of myocorrhizal plants and increased total colonization, arbuscule, and hyphae development. Only formononetin-treated mycorrhizal plants had increased shoot growth. Net photosynthesis and stomatal conductance were generally greatest with reduced levels of mycorrhiza and formononetin treated mycorrhizal plants.

Effect of Mycorrhizal Fungi on Gas Exchange of Micropropagated Guava Plantlets (Psidium guajava L.) during Acclimatization and Plant Establishment

The effect of mycorrhizal fungi on gas exchange of micropropagated guava plantlets (Psidium guajava L.) during acclimatization and plant establishment was determined. Guava plantlets (Psidium guajava L. cv. `Media China') were asexually propagated through tissue culture and acclimatized in a glasshouse for eighteen weeks. Half of the plantlets were inoculated with ZAC-19, which is a mixed isolate containing Glomus etunicatum and an unknown Glomus spp. Plantlets were fertilized with modified Long Ashton nutrient solution containing 11 (g P/ml. Gas exchange measurements included photosynthetic rate (A), stomatal conductance (gs), internal CO2 concentration (Ci), transpiration rate (E), water use efficiency (WUE), and vapor pressure deficit (VPD). Measurements were taken at 2, 4, 8 and 18 weeks after inoculation using a LI-6200 portable photosynthesis system (LI-COR Inc. Lincoln, Neb., USA). Two weeks after inoculation, noninoculated plantlets had greater A compared to mycorrhizal plantlets. However, 4 and 8 weeks after inoculation, mycorrhizal plantlets had greater A, gs, Ci and WUE. At the end of the experiment gas exchange was comparable between noninoculated and mycorrhizal plantlets.

Influence of Mycorrhizal Fungi on Growth and Nutrient Uptake of Micropropagated Guava Plantlets (Psidium guajava L.) during Acclimatization and Plant Establishment

The effect of mycorrhizal fungi on growth and nutrient uptake during acclimatization and plant establishment of micropropagated guava plantlets (Psidium guajava L. cv. Media China) was determined. Half of the plantlets were inoculated with the endomycorrhizae isolate ZAC-19 and grown in a glasshouse for 18 weeks. The isolate ZAC-19 was collected from the Chihuahuan Desert in Zacatecas State, Mexico, and is a mixed isolate containing Glomus etunicatum and unknown Glomus spp. Plantlets were fertilized with modified Long Ashton nutrient solution containing 11 μg P/ml. Shoot length, leaf area, leaf number, and dry mass partitioning were positively affected by mycorrhizae compared to noninoculated plantlets; however, noninoculated plantlets had greater leaf area ratios and specific leaf area. Mycorrhizal plantlets generally had increased leaf tissue mineral levels, particularly P, Mg, Cu, and Mo. However, noncolonized plantlets had higher N, K, and Mn. At the end of the experiment, roots of inoculated guava plantlets had colonization levels of 94.3%.

San Luis (Chile Ancho pepper) with a Mixed Glomus spp. from Mexico and Glomus intraradices

The effect of a mixed isolate of arbuscular mycorrhizal (VAM) fungi [Glomus spp. from Veracruz, Mexico] and a pure isolate of Glomus intraradices was assessed on the growth and gas exchange of `Chile Ancho' (Capsicum annuum L. cv. San Luis) under phosphorus (P) stress. The experiment was carried out under glasshouse conditions in 1-L plastic pots containing a pasteurized mixture of 1 sand: 1 sandy loam (v/v). Plants were inoculated or noninoculated with VAM. Plants were fertilized with a modified Long Ashton nutrient solution (LANS) containing 0 or 11 (g phosphorus/ml). Gas exchange measurements were taken 21 and 70 days after the experiment was initiated. Mycorrhizal plants at both 0 and 11 (g P/ml) had greater leaf area, fruit, root, stem and leaf dry mass, and a lower specific leaf area and root/shoot ratio than nonmycorrhizal plants. Nonmycorrhizal plants not supplied with P had a higher leaf area ratio than plants colonized with G. intraradices. Net photosynthesis and stomatal conductance were not consistent with growth responses. There were no significant differences in growth and gas exchange between the two mycorrhizal isolates.

Hydroponic culture of the mycorrhizal fungus Glomus mosseae with Linum usitatissimum L., Sorghum bicolor L. and Triticum aestivum L.

Linum usitatissimum, Sorghum bicolor and Triticum aestivum plants were further colonised by the arbuscular mycorrhizal fungus, Glomus mosseae, during a four week period of hydroponic culture after a pre-culture period of three weeks with the fungus in perlite substrate. The viability of mycorrhizal colonisation of T. aestivum was indicated by an initial experiment where G. mosseae from mycorrhizal plants colonised non-mycorrhizal plants when the plants were grown together in the same hydroponic container using modified Long Ashton nutrient solution. Intermittant aeration of the plant roots (2 h periods, four times per day) provided a compromise between adequate aeration and minimal disturbance of the fungus. In a second experiment, two nutrient media, modified Long Ashton and modified Knop plus Hoagland medium were compared for culturing G. mosseae on T. aestivum. A significantly higher root dry weight was found for the mycorrhizal versus the non-mycorrhizal wheat plants in modified Long Ashton nutrient medium, which contained 10 µM P and an organic buffer. Modified Knop plus Hoagland nutrient medium contained a high P concentration (0.9 mM) and did not produce viable cultures of mycorrhizal colonisation. In a third experiment, modified Long Ashton medium was used for hydroponic culture of mycorrhizal L. usitatissimum, S. bicolor and T. aestivum. The root colonisation percentages for T. aestivum (73%), S. bicolor (36%) and L. usitatissimum (65%) were within the range of colonisation rates obtained with solid substrate culture in perlite. Viability of the mycorrhizal structures in hydroponic culture was assessed by monitoring activity of fungal succinate dehydrogenase and found to be similar to cultures in perlite. No difference in the P concentration of mycorrhizal and non-mycorrhizal plants was observed, possibly owing to the lack of diffusion limits for P in hydroponic solution. This report describes a system for the viable culture of G. mosseae with different plant species where a high mycorrhizal colonisation rate was produced under conditions of a short culture period using intermittent aeration, a low concentration of P supply and an organic buffer.