Effects of different N fertilizers on the activity of <Emphasis Type="Italic">Glomus mosseae</Emphasis> and on grapevine nutrition and berry composition

Grapevine N fertilization may affect and be affected by arbuscular mycorrhizal (AM) fungal colonization and change berry composition. We studied the effects of different N fertilizers on AM fungal grapevine root colonization and sporulation, and on grapevine growth, nutrition, and berry composition, by conducting a 3.5-year pot study supplying grapevine plants with either urea, calcium nitrate, ammonium sulfate, or ammonium nitrate. We measured the percentage of AM fungal root colonization, AM fungal sporulation, grapevine shoot dry weight and number of leaves, nutrient composition (macro- and micronutrients), and grapevine berry soluble solids (total sugars or °Brix) and total acidity. Urea suppressed AM fungal root colonization and sporulation. Mycorrhizal grapevine plants had higher shoot dry weight and number of leaves than non-mycorrhizal and with a higher growth response with calcium nitrate as the N source. For the macronutrients P and K, and for the micronutrient B, leaf concentration was higher in mycorrhizal plants. Non-mycorrhizal plants had higher concentration of microelements Zn, Mn, Fe, and Cu than mycorrhizal. There were no differences in soluble solids (°Brix) in grapevine berries among mycorrhizal and non-mycorrhizal plants. However, non-mycorrhizal grapevine berries had higher acid content with ammonium nitrate, although they did not have better N nutrition and vegetative growth.     

Effects of elevated nickel and cadmium concentrations on growth and nutrient uptake of mycorrhizal and non-mycorrhizal Pinus sylvestris seedlings

The effects of Ni and Cd on growth and nutrient uptake of mycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings were investigated in a pot experiment. Seedlings were either inoculated with Laccaria bicolor (Maire) Orton or left uninoculated before being planted in pots containing a mixture of sandy soil from the B-horizon of a coniferous forest, small stones and pure quartz sand. The pots were supplied with small amounts of a balanced nutrient solution every 24 h using peristaltic pumps. Nickel or Cd were added as chlorides to the nutrient solution at levels of 85 M Ni (Ni 1), 170 M Ni (Ni 2), or 8.9 M Cd. Mycorrhizal colonisation of the roots was nearly 100% in the mycorrhizal treatments. The mycorrhizal seedlings grew significantly better than the non-mycorrhizal ones. The weight of mycorrhizal seedlings in the Ni 2 treatment was 29% lower than that of the mycorrhizal controls, but still 34% greater than that of the non-mycorrhizal seedlings not exposed to metals. There was an overall, statistically significant, negative effect of metals on plant yield. Mycorrhizal plants had lower root:shoot (R:S) ratios than non-mycorrhizal plants and the R:S ratio was increased by metal exposure, particularly in the non-mycorrhizal seedlings. Plant concentrations of Cd or Ni were not affected by mycorrhizal colonisation, but total uptake of Cd and Ni was higher in bigger mycorrhizal seedlings. Nickel decreased P concentration in all seedlings and Cd decreased P concentration in the non-mycorrhizal seedlings. Generally, the mycorrhizal seedlings grew better than non-mycorrhizal ones and had better P, K, Mg and S status. Root growth was not significantly affected by the metal treatments. The reduction in mean shoot growth of non-mycorrhizal plants, relative to the metal-free control, appeared higher than in mycorrhizal plants but was not statistically significant due to high variation in the non-mycorrhizal plants not exposed to metals. The main mycorrhizal effect was thus increased nutrient uptake and growth of the seedlings.     

Arbuscular mycorrhizal fungi from three genera induce two-phase plant growth responses on a high P-fixing soil

Plant growth enhancing effects of arbuscular mycorrhizal (AM) fungi are suitably quantified by comparisons of mycorrhizal and non-mycorrhizal plant growth responses to added phosphorus (P). The ratio between the amounts of added P required for the same yield of mycorrhizal and non-mycorrhizal plants is termed the relative effectiveness of the mycorrhiza. Variation in this relative effectiveness was examined for subterranean clover grown on a high P-fixing soil. Plants were either left non-mycorrhizal or inoculated with one of three AM fungal species with well-characterised differences in external hyphal spread. With no P added, plants from all treatments produced <10% of their maximum growth achieved at non-limiting P supply. The growth response of non-mycorrhizal plants was markedly sigmoid. Mycorrhizal growth responses were not sigmoid but their shape was two-phased. The first phase was an asymptotic approach to 25–30% of maximum growth, followed by a second asymptotic rise to maximum growth. Growth effects of Glomus invermaium and Acaulospora laevis were quite similar. Plants in these treatments produced up to four times greater shoot dry biomass than non-mycorrhizal plants. Scutellospora calospora was less effective. The relative effectiveness of AM fungi varied with the level of P application. This is expected to apply to all soils on which a sigmoid response is obtained for growth of non-mycorrhizal plants. In a simple approximation the relative effectiveness was calculated to range from 1.46 to 15.57. Shoot P contents were increased by up to 25 times by A. laevis, significantly more than by the other two fungi. The further mycelial spread of this fungus is thought to have contributed to its relatively greater effect on plant P content.     

Increased drought tolerance of mycorrhizal onion plants caused by improved phosphorus nutrition

Onion plants (Allium cepa L, cv. Downing Yellow Globe) grown in pots and infected by the mycorrhizal fungusGlomus etunicatus Becker and Gerdemann were more drought tolerant than were non-mycorrhizal individials when exposed to several periods of soil water stress separated by periods of high water supply, as shown by greater fresh and dry weights and higher tissue phosphorus levels in the mycorrhizal plants. The tissues of stressed, non-mycorrhizal plants were deficient in P, despite the fact that only non-mycorrhizal plants were fertilized with high levels of P (26 mg P per 440 g soil). Differences in plant water relations (leaf water potentials or transpiration rates) and changes in soil P levels which may have affected plant growth were investigated, and discounted as factors important for the results. The P nutrition of plants has been implicated in the ability of plants to tolerate drought and it was concluded that the ability of the mycorrhizal fungus to maintain adequate P nutrition in the onions during soil water stress was a major factor in the improved drought tolerance. Infection of the root by the fungus was found not to be affected by water stress or P fertilization but fungal reproduction, as determined by spore numbers in the soil, was decreased by water stress and by P fertilization.Michigan Agricultural Experiment Station Article No. 10050     

Response of citronella Java (Cymbopogon winterianus Jowitt) to VA mycorrhizal fungi and soil compaction in relation to P supply

Nutrient acquisition and growth of citronella Java (Cymbopogon winterianus Jowitt) was studied in a P-deficient sandy soil to determine the effects of mycorrhizal symbiosis and soil compaction. A pasteurized sandy loam soil was inoculated either with rhizosphere microorganisms excluding VAM fungi (non-mycorrhizal) or with the VAM fungus, Glomus intraradices Schenck and Smith (mycorrhizal) and supplied with 0, 50 or 100 mg P kg^-1 soil. The soil was compacted to a bulk density of 1.2 and 1.4 Mg m^-3 (dry soil basis). G. intraradices substantially increased root and shoot biomass, root length, nutrient (P, Zn and Cu) uptake per unit root length and nutrient concentrations in the plant, compared to inoculation with rhizosphere microorganisms when the soil was at the low bulk density and not amended with P. Little or no plant response to the VAM fungus was observed when the soil was supplied with 50 or 100 mg P kg^-1 soil and/or compacted to the highest bulk density. At higher soil compaction and P supply the VAM fungus significantly reduced root length. Non-mycorrhizal plants at higher soil compaction produced relatively thinner roots and had higher concentrations and uptake of P, Zn and Cu than at lower soil compaction, particularly under conditions of P deficiency. The quality of citronella Java oil measured in terms citronellal and d-citronellol concentration did not vary appreciably due to various soil treatments.     

Contribution of the VA mycorrhizal hyphae in acquisition of phosphorus and zinc by maize grown in a calcareous soil

An investigation was carried out to test whether the mechanism of increased zinc (Zn) uptake by mycorrhizal plants is similar to that of increased phosphorus (P) acquisition. Maize (Zea mays L.) was grown in pots containing sterilised calcareous soil either inoculated with a mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe or with a mixture of mycorrhizal fungi, or remaining non-inoculated as non-mycorrhizal control. The pots had three compartments, a central one for root growth and two outer ones for hyphal growth. The compartmentalization was done using a 30-m nylon net. The root compartment received low or high levels of P (50 or 100 mg kg^–1 soil) in combination with low or high levels of P and micronutrients (2 or 10 mg kg^–1 Fe, Zn and Cu) in the hyphal compartments.Mycorrhizal fungus inoculation did not influence shoot dry weight, but reduced root dry weight when low P levels were supplied to the root compartment. Irrespective of the P levels in the root compartment, shoots and roots of mycorrhizal plants had on average 95 and 115% higher P concentrations, and 164 and 22% higher Zn concentrations, respectively, compared to non-mycorrhizal plants. These higher concentrations could be attributed to a substantial translocation of P and Zn from hyphal compartments to the plant via the mycorrhizal hyphae. Mycorrhizal inoculation also enhanced copper concentration in roots (135%) but not in shoots. In contrast, manganese (Mn) concentrations in shoots and roots of mycorrhizal plants were distinctly lower, especially in plants inoculated with the mixture of mycorrhizal fungi.The results demonstrate that VA mycorrhizal hyphae uptake and translocation to the host is an important component of increased acquisition of P and Zn by mycorrhizal plants. The minimal hyphae contribution (delivery by the hyphae from the outer compartments) to the total plant acquisition ranged from 13 to 20% for P and from 16 to 25% for Zn.     

Tolerance ofFestuca rubra L. to zinc in relation to mycorrhizal infection

Summary Plant yield of mycorrhizal and non-mycorrhizalFestuca rubra L. was linearly decreased with increasing zinc concentrations in nutrient solution. In all cases, non-mycorrhizal plant growth was significantly greater than that of mycorrhizal plants. Zinc and phosphorus concentrations of root and shoot of mycorrhizal plants were greater in all zinc treatments while mycorrhizal plants showed equal or lower tolerance indices to zinc than non-mycorrhizal plants. Yield depressions of mycorrhizal plants may be the result of enhanced zinc and phosphorus concentrations combined with the cost for growth and maintenance of the mycorrhizal fungi.     

Role of arbuscular mycorrhizal symbiosis in root mineral uptake under CaCO3 stress

This study investigated the effects of increasing CaCO(3) concentrations (0, 5, 10, 20?mM) on arbuscular mycorrhizal (AM) symbiosis establishment as well as on chicory root growth and mineral nutrient uptake in a monoxenic system. Although CaCO(3) treatments significantly decreased root growth and altered the symbiosis-related development steps of the AM fungus Rhizophagus irregularis (germination, germination hypha elongation, root colonization rate, extraradical hyphal development, sporulation), the fungus was able to completely fulfill its life cycle. Even when root growth decreased more drastically in mycorrhizal roots than in non-mycorrhizal ones in the presence of high CaCO(3) levels, the AM symbiosis was found to be beneficial for root mineral uptake. Significant increases in P, N, Fe, Zn and Cu concentrations were recorded in the mycorrhizal roots. Whereas acid and alkaline phosphatase enzymatic activities remained constant in mycorrhizal roots, they were affected in non-mycorrhizal roots grown in the presence of CaCO(3) when compared with the control.     

Mycorrhizal inoculant alleviates salt stress in<Emphasis Type="Italic"> Sesbania aegyptiaca</Emphasis> and<Emphasis Type="Italic"> Sesbania grandiflora</Emphasis> under field conditions: evidence for reduced sodium and improved magnesium uptake

A field experiment was conducted to examine the effect of the arbuscular mycorrhizal fungus Glomus macrocarpum and salinity on growth of Sesbania aegyptiaca and S. grandiflora. In the salt-stressed soil, mycorrhizal root colonisation and sporulation was significantly higher in AM-inoculated than in uninoculated plants. Mycorrhizal seedlings had significantly higher root and shoot dry biomass production than non-mycorrhizal seedlings grown in saline soil. The content of chlorophyll was greater in the leaves of mycorrhiza-inoculated as compared to uninoculated seedlings. The number of nodules was significantly higher in mycorrhizal than non-mycorrhizal plants. Mycorrhizal seedling tissue had significantly increased concentrations of P, N and Mg but lower Na concentration than non-mycorrhizal seedlings. Under salinity stress conditions both Sesbania sp. showed a high degree of dependence on mycorrhizae, increasing with the age of the plants. The reduction in Na uptake together with a concomitant increase in P, N and Mg absorption and high chlorophyll content in mycorrhizal plants may be important salt-alleviating mechanisms for plants growing in saline soil.     

Influence of vesicular-arbuscular mycorrhizal infection and P addition on growth and P nutrition of Anthyllis cytisoides L. and Brachypodium retusum (Pers.) Beauv.

The effect of P applications and mycorrhizal inoculation on the growth and P nutrition of Anthyllis cytisoides L. (Fabaceae) and Brachypodium retusum (Pers.) Beauv. (Poaceae) was studied. Both plants are widely distributed and well adapted to semi-arid habitats in southern Spain. In all treatments, even with high P doses, mycorrhizal plants showed a higher concentration of phosphorus in their tissues than non-mycorrhizal plants. Mycorrhizal inoculation enhanced the growth of the plants when no P was applied. At high P addition, non-mycorrhizal plants showed higher growth than mycorrhizal plants. The response of each plant type to P application was somewhat different.     

Root Distribution and Nutrient Status of Mycorrhizal and Non-mycorrhizal Pinus sylvestris L. Seedlings Growing in a Sandy Substrate with Lignite Fragments

Reclaimed mine soils of the Lusatian mining district are characterised by small-scale heterogeneous distribution of lignite fragments of varying size embedded in a matrix of Tertiary and Quaternary sandy material. Despite amelioration with basic fly ashes, ongoing pyrite oxidation and the subsequent acidification generate a high physical and chemical heterogeneity within the substrate, which could negatively affect root proliferation. We hypothesised that this limitation for the root system may be compensated for by intensive exploration of the porous lignite fragments by roots and/or mycorrhizal hyphae to access water and nutrients stored in these fragments. To test this hypothesis, we compared growth, shoot nutrient content, and root distribution of mycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings in lignite-containing and lignite-free sandy substrate. Rhizotrons used for this experiment were filled with a sandy matrix with 6–9 evenly distributed spots of lignite fragments. Treatments included different levels of water and nutrient availability. After 8 months of growth, root tip vitality as well as growth and shoot nutrient concentration of the plants was higher for treatments with lignite spots in the sandy substrate than for sandy substrate without such amendments. Compared to the non-mycorrhizal plants, the seedlings inoculated with Paxillus involutus (Batsch) Fr. had a higher root dry mass, an increased number of root tips and a higher root length. These results confirm our hypothesis that the lignite fragments are an important nutrient and water reservoir for plants in these mine soils and they indicate that mycorrhizal colonisation may allow an intensive exploration of porous lignite fragments by mycorrhizal hyphae.     

Improved tolerance of maize plants to salt stress by arbuscular mycorrhiza is related to higher accumulation of soluble sugars in roots

The effect of colonization with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe on the growth and physiology of NaCl-stressed maize plants ( Zea mays L. cv. Yedan 13) was examined in the greenhouse. Maize plants were grown in sand with 0 or 100 mM NaCl and at two phosphorus (P) (0.05 and 0.1 mM) levels for 34 days, following 34 days of non-saline pre-treatment. Mycorrhizal plants maintained higher root and shoot dry weights. Concentrations of chlorophyll, P and soluble sugars were higher than in non-mycorrhizal plants under given NaCl and P levels. Sodium concentration in roots or shoots was similar in mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher electrolyte concentrations in roots and lower electrolyte leakage from roots than non-mycorrhizal plants under given NaCl and P levels. Although plants in the low P plus AM fungus treatment and those with high P minus AM fungus had similar P concentrations, the mycorrhizal plants still had higher dry weights, soluble sugars and electrolyte concentrations in roots. Similar relationships were observed regardless of the presence or absence of salt stress. Higher soluble sugars and electrolyte concentrations in mycorrhizal plants suggested a higher osmoregulating capacity of these plants. Alleviation of salt stress of a host plant by AM colonization appears not to be a specific effect. Furthermore, higher requirement for carbohydrates by AM fungi induces higher soluble sugar accumulation in host root tissues, which is independent of improvement in plant P status and enhances resistance to salt-induced osmotic stress in the mycorrhizal plant.     

Variations in water status, gas exchange, and growth in Rosmarinus officinalis plants infected with Glomus deserticola under drought conditions

The influence of the arbuscular mycorrhizal fungus Glomus deserticola on the water relations, gas exchange parameters, and vegetative growth of Rosmarinus officinalis plants under water stress was studied. Plants were grown with and without the mycorrhizal fungus under glasshouse conditions and subjected to water stress by withholding irrigation water for 14 days. Along the experimental period, a significant effect of the fungus on the plant growth was observed, and under water stress, mycorrhizal plants showed an increase in aerial and root biomass compared to non-mycorrhizal plants. The decrease in the soil water potential generated a decrease in leaf water potential (psi(l)) and stem water potential (psi(x)) of mycorrhizal and non-mycorrhizal plants, with this decrease being lower in mycorrhizal water-stressed plants. Mycorrhization also had positive effects on the root hydraulic conductivity (Lp) of water stressed plants. Furthermore, mycorrhizal-stressed plants showed a more important decrease in osmotic potential at full turgor (psi(os)) than did non-mycorrhizal-stressed plants, indicating the capacity of osmotic adjustment. Mycorrhizal infection also improved photosynthetic activity (Pn) and stomatal conductance (g(s)) in plants under water stress compared to the non-mycorrhizal-stressed plants. A similar behaviour was observed in the photochemical efficiency of PSII (Fv/Fm) with this parameter being lower in non-mycorrhizal plants than in mycorrhizal plants under water stress conditions. In the same way, under water restriction, mycorrhizal plants showed higher values of chlorophyll content than did non-mycorrhizal plants. Thus, the results obtained indicated that the mycorrhizal symbiosis had a beneficial effect on the water status and growth of Rosmarinus officinalis plants under water-stress conditions.     

The modelled growth of mycorrhizal and non-mycorrhizal plants under constant versus variable soil nutrient concentration

We studied the response of mycorrhizal and non-mycorrhizal plants to variation in soil nutrient concentration. A model for the relative growth rate (RGR) of plant biomass was constructed with soil nutrients as an explanatory variable. A literature survey was carried out to find the relative magnitudes of parameter values for mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher RGR at low nutrient concentrations and non-mycorrhizal plants at high nutrient concentrations. The RGR of mycorrhizal and non-mycorrhizal plants at constant versus log-normally distributed soil nutrient concentration were compared to see the effect of mycorrhizal status on responses to variation. Variation in nutrient concentration generally reduced RGR, especially in mycorrhizal plants. The RGR of a non-mycorrhizal plant may increase with variation where a growth function threshold exists, i.e. a soil nutrient concentration that must be exceeded to allow growth. Mycorrhizal plants appeared more sensitive to variation in nutrient concentration than non-mycorrhizal plants due to the higher affinity of mycorrhizal roots at low nutrient levels. However, this prediction may be reversed if mycorrhizal symbiosis considerably stabilises flow of nutrients to plant physiological processes, such that mycorrhizal plants experience less variation in soil nutrient concentration than non-mycorrhizal plants. Our results also attain broader significance by suggesting a general trade-off between competitive ability in a constant versus variable resource availability.     

Distribution of lead in mycorrhizal and non-mycorrhizal Norway spruce seedlings

Non-mycorrhizal spruce seedlings (Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus (Scop.) Fr. or two strains of Paxillits involutus (Batsch) Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization, the seedlings were exposed to 1 μM PbCI₂ for 19 weeks. The degree of infection in all of the mycorrhizal treatments approached 100% during the experiment and was not affected by exposure to Pb. However, the number of root tips per root dry weight and the shoot: root ratio, both in the non-mycorrhizal and the mycorrhizal seedlings, had decreased after the 19 week treatment with PbCl₂ Using X-ray microanalysis, the distribution and concentration of Pb in the tissues of mycorrhizal and non-mycorrhizal root tips were compared. In the mycorrhizae of seedlings exposed to Pb no significant accumulation of Pb in the hyphal mantle or in fungal cell walls of the Hartig net were detected. Lead accumulated primarily in the cortex cell walls both of non-mycorrhizal and mycorrhizal root tips. No significant difference of Pb concentrations in root cortex cell walls of non-mycorrhizal and mycorrhizal seedlings was found; except for seedlings colonized with Paxillus involutus strain 537. However, at the endodermis no effect of mycorrhizal fungal colonization on the Pb tissue concentration was detected. The presence of the fungal sheath did not prevent Pb from reaching the root cortex. The endodermis acted as a barrier to Pb radial transport in both mycorrhizal and non-mycorrhizal seedling roots.     

Mycorrhiza formation and nutrient concentration in leeks (Allium porrum) in relation to previous crop and cover crop management on high P soils

An improved integration of mycorrhizas may increase the sustainability in plant production. Two strategies for increasing the soil inoculum potential of mycorrhizal fungi were investigated in field experiments with leeks: Pre-cropping with mycorrhizal main crops and pre-establishment of mycorrhizal cover crops. Experiments on soils with moderate to high P content (26–50 mg kg^–1 bicarbonate-extractable P) showed that the previous crop influenced mycorrhiza formation, uptake of P, Zn, and Cu, and early growth of leek seedlings. A cover crop of black medic, established the previous autumn, increased the colonization of leek roots by mycorrhizal fungi. During early growth stages, this increase was 45–95% relative to no cover crop. However, cover cropping did not significantly increase nutrient concentration or growth. These variables were not influenced by the time of cover crop incorporation or tillage treatments. Differences in colonization, nutrient uptake and plant growth diminished during the growing period and at the final harvest date, the effects on plant production disappeared. High soil P level or high soil inoculum level was most likely responsible for the limited response of increased mycorrhiza formation on plant growth and nutrient concentrations.     

Vesicular arbuscular mycorrhizal mediation of grass response to acidic and heavy metal depositions

Summary The perennial bunchgrassEhrharta calycina was grown with and without V.A.M. fungal infection (Glomus fasciculatum) in a sandy loam exposed to a range of acidic and heavy metal depositions. Heavy metals (Cu, Ni, Pb, Zn, Fe, and Co) were applied in simulated rain (pH 3.0, 4.0, and 5.6) at deposition rates approximating those observed to result from smelter efluents. Metal concentrations in the roots and shoots of mycorrhizal plants were greater than those of non-mycorrhizal plants. Mycorrhizal enhancement of plant metal uptake increased with greater acidity and higher heavy metal content of treatment. The growth of mycorrhizal plants was reduced compared to non-mycorrhizal plants when metal depostion was combined with simulated acid rain. We propose that mycorrhizal enhancement of heavy metal uptake caused reduced growth in plants exposed to acidic and heavy metal depositions.     

Arbuscular Mycorrhizal Fungi Alter Fractal Dimension Characteristics of Robinia pseudoacacia L. Seedlings Through Regulating Plant Growth,Leaf Water Status,Photosynthesis, and Nutrient Concentration Under Drought Stress

The influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Rhizophagus intraradices, on plant growth, leaf water status, chlorophyll concentration, photosynthesis, nutrient concentration, and fractal dimension (FD) characteristics of black locust (Robinia pseudoacacia L.) seedlings was studied in pot culture under well-watered, moderate drought stress, and severe drought stress treatments. Mycorrhizal seedlings had higher dry biomass, leaf relative water content (RWC), and water use efficiency (WUE) compared with non-mycorrhizal seedlings. Under all treatments, AMF colonization notably enhanced net photosynthetic rate, stomatal conductance, and transpiration rate, but decreased intercellular CO₂ concentration. Leaf chlorophyll a and total chlorophyll concentrations were higher in AM seedlings than those in non-AM seedlings although there was no significant difference between AMF species. AMF colonization improved leaf C, N, and P concentrations, but decreased C:N, C:P, and N:P ratios. Mycorrhizal seedlings had a larger FD value than non-mycorrhizal seedlings. The FD value was positively and significantly correlated to the plant growth parameters, photosynthesis, RWC, WUE, and nutrient concentration but negatively correlated to leaf/stem ratio, C:N and C:P ratios, and intercellular CO₂ concentration. We conclude that AMF lead to an improvement of growth performance of black locust seedlings under all growth conditions, including drought stress via improving leaf water status, chlorophyll concentration, photosynthesis, and nutrient uptake. Moreover, FD technology proved to be a powerful non-destructive method to characterize the effect of AMF on the physiology of host plants during drought stress.     

Effect of vesicular arbuscular mycorrhiza and soluble phosphate onAbelmoscus esculentus (L.) Moench

Summary Effect of VA mycorrhiza and soluble phosphorus onAbelmoscus esculentus (L.) Moench was studied in a phosphorus deficient sandy loam soil with pH 5.5. The mycorrhizal infection and spore production were reduced by an increase of added soluble phosphorus. Root, shoot and total plant dry weight were significantly greater in mycorrhizal plants than in non-mycorrhizal controls, at all levels of added soluble P. Mycorrhizal dependency was found to decrease with increase in added soluble P. Depression of growth, as compared with growth at 100% was noticed in mycorrhizal plants when 200% of the recommended P was added.     

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

Psidium guajava 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%. Accepted: 27 December 1999