Phosphorus allocation in P-efficient and inefficient barley cultivars as affected by mycorrhizal infection

A glasshouse experiment was undertaken to investigate the effect of mycorrhizal infection on the allocation of phosphorus (P) in agronomically P-efficient (i.e. high yields at low P supply) and inefficient barley (Hordeum vulgare L.) cultivars. Four barley cultivars differing in agronomic P-efficiency were inoculated or not inoculated with Glomus etunicatum. Cultivars did not differ in percentage of root length infected. The concentration of P in roots of the inefficient cultivars was higher than that of the efficient cultivars. However, because of changes in root to shoot dry weight ratio and below-ground productivity, mycorrhizal infection significantly reduced the percentage of total plant P in roots of the inefficient cultivars. The distribution of P between root and shoot of P-efficient cultivars was not affected by mycorrhizal infection. Root to shoot dry weight ratio of the P-efficient cultivars was lower than that of the inefficient cultivars, and the decrease in the ratio following infection was significant in inefficient but not in P-efficient cultivars. This study indicates that mycorrhizal infection alters the allocation of P in inefficient cultivars and effectively improves the efficiency of P utilization with respect to shoot growth.     

Growth response and phosphorus uptake of rye with long and short root hairs: Interactions with mycorrhizal infection

Plant growth and phosphorus (P) uptake of two selections of rye (Secale cereale L.) differing in length of root hairs, in response to mycorrhizal infection were investigated. Rye plants with short root hairs (SRH) had a greater length of root infected by Glomus intraradices (up to 32 m pot^–1) than those with long root hairs (LRH) (up to 10 m pot^–1). Application of P decreased the percentage of root length infected in both selections. In low-P soil, mycorrhizal infection increased shoot and root P concentration, especially in LRH plants. Generally, LRH had higher shoot dry weight than SRH plants. P uptake was increased both by LRH and by mycorrhizal infection. Differences in specific P uptake and P utilization efficiency between SRH and LRH plants were observed in non-mycorrhizal plants. With low P supply, P utilization efficiency (dry matter yield per unit of P taken up) of LRH plants increased with time. However, mycorrhizal infection reduced P utilization efficiency, particularly of SRH plants. SRH plants, which were agronomically less efficient (i.e. low dry matter yield at low P supply) were more responsive to either mycorrhizal infection or P addition than the LRH plants. No interaction was observed between mycorrhizal infection and root hair length.     

Response of cassava to VA mycorrhizal inoculation and phosphorus application in greenhouse and field experiments

Cassava (Manihot esculenta Crantz) was grown in the greenhouse and in the field at different levels of phosphorus applied, with or without inoculation with VA mycorrhiza in sterilized or unsterilized soil. When grown in a sterilized soil to which eight levels of P had been applied the non-inoculated plants required the application of 3200 kg P ha⁻¹ to reach near-maximum yield of plant dry matter (DM) at 3 months. Inoculated plants, however, showed only a minor response to applied P. Mycorrhizal inoculation in the P check increased top growth over 80 fold and total P uptake over 100 fold. Relating dry matter produced to the available P concentration in the soil (Bray II), a critical level of 15 ppm P was obtained for mycorrhizal and 190 ppm P for non-mycorrhizal plants. This indicates that the determination of critical levels of P in the soil is highly dependent on the degree of mycorrhizal infection of the root system. In a second greenhouse trial with two sterilized and non-sterilized soils it was found that in both sterilized soils, inoculation was most effective at intermediate levels of applied P resulting in a 15–30 fold increase in DM at 100 kg P ha⁻¹. In the unsterilized soil inoculation had no significant effect in the quilichao soil, but increased DM over 3 fold in the Carimagua soil, indicating that the latter had a native mycorrhizal population less effective than the former. When cassava was grown in the field in plots with 11 levels of P applied, uninoculated plants grown in sterilized soil remained extremely P deficient for 4–5 months after which they recuperated through mycorrhizal infection from unsterilized borders or subsoil. Still, after 11 months inoculation had increased root yields by 40%. In the non-sterilized soil inoculation had no significant effect as the introduced strain was equally as effective as the native mycorrhizal population. These trials indicate that cassava is extremely dependent on an effective mycorrhizal association for normal growth in low-P soils, but that in most natural soils this association is rapidly established and inoculation of cassava in the field can only be effective in soils with a low quantity and quality of native mycorrhiza. In that case, plants should be inoculated with highly effective strains.     

Influence of vesicular-arbuscular mycorrhiza and straw mulch on growth of barley

Summary The effects of vesicular-arbuscular mycorrhiza (VAM) and of mulching on growth of barley were investigated in a factorial experiment. Plants were grown in cylinders buried in a field in soil with moderate amounts of available phosphate. VAM infection, dry weight and P uptake were determined at harvest after 10 and 161/2 weeks growth.VAM infection was reduced in the upper soil layer by straw mulch, possibly through a reduction in temperature. By the second harvest VAM increased growth by 56% in the non-mulched plots through increased P uptake but VAM did not increase growth in the mulched plots. Mulch increased growth by 85% in the non-mycorrhizal plots, and 28% in the mycorrhizal plots.     

Nitrogen nutrition,photosynthesis and carbon allocation in ectomycorrhizal pine

Summary Studies examined net photosynthesis (Pn) and dry matter production of mycorrhizal and nonmycorrhizalPinus taeda at 6 intervals over a 10-month period. Pn rates of mycorrhizal plants were consistently greater than nonmycorrhizal plants, and at 10 months were 2.1-fold greater. Partitioning of current photosynthate was examined by pulse-labelling with¹⁴CO₂ at each of the six time intervals. Mycorrhizal plants assimilated more¹⁴CO₂, allocated a greater percentage of assimilated¹⁴C to the root systems, and lost a greater percentage of¹⁴C by root respiration than did nonmycorrhizal plants. At 10 months, the quantity of¹⁴CO₂ respired by roots per unit root weight was 3.6-fold greater by mycorrhizal than nonmycorrhizal plants. Although the stimulation of photosynthesis and translocation of current photosynthate to the root system by mycorrhiza formation was consistent with the source-sink concept of sink demand, foliar N and P concentrations were also greater in mycorrhizal plants.Further studies examined Pn and dry matter production ofPinus contorta in response to various combinations of N fertilization (3, 62, 248 ppm), irradiance and mycorrhizal fungi inoculation. At 16 weeks of age, 6 weeks following inoculation with eitherPisolithus tinctorius orSuillus granulatus, Pn rates and biomass were significantly greater in mycorrhizal than nonmycorrhizal plants. Mycorrhizal plants had significantly greater foliar %P, but not %N, than did nonmycorrhizal plants. Fertilization with 62 ppm N resulted in greater mycorrhiza formation than either 3 or 248 ppm. Increased irradiance resulted in increased mycorrhiza formation.     

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary An experiment was conducted to determine whether wild accessions and cultivars ofLycopersicon esculentum Mill. differed in inherent morphological, physiological or phenological traits and whether such differences would result in variation in response to vesicular-arbuscular mycorrhizal infection. While distinctions between wild accessions and cultivars were apparent (the cultivars generally had higher phosphorus use efficiencies and shorter lifespans than the wild accessions) and the cultivars were, as a group, more responsive to mycorrhizal infection than the wild accessions, there was significant variation among wild accessions and among cultivars in response to infection. Regardless of cultivation status, non-mycorrhizal plant root density was significantly negatively correlated with response to infection. Phosphorus use efficiency was generally not significantly correlated with response to infection. Mycorrhizal infection decreased phosphorus use efficiency in all accessions, but had variable effects on root density, depending upon accession and time. Finally, the vegetative response was not necessarily of the same magnitude as the reproductive response.     

Positive association between mycorrhiza and foliar endophytes in Poa bonariensis, a native grass

The interaction between mycorrhiza and leaf endophytes (Neotyphodium sp.) was studied in three Poa bonariensis populations, a native grass, differing significantly in endophyte infection. The association between endophytes and mycorrhizal fungi colonisation was assessed by analysing plant roots collected from the field. We found that roots from endophyte-infected populations showed a significantly higher frequency of colonisation by mycorrhizal fungi and that soil parameters were not related to endophyte infection or mycorrhiza colonization. In addition, we did not observe significant differences in the number of AM propagules in soils of the three populations sites. We also report the simultaneous development of Paris-type and Arum-type mycorrhiza morphology within the same root systems of P. bonariensis. The co-occurrence of both colonisation types in one and the same root system found in the three populations, which differed in Neotyphodium infection, suggests that foliar endophytes do not determine AM morphology. The percentage of root length colonised by different types of fungal structures (coils, arbuscules, longitudinal hyphae and vesicles) showed significant and positive differences in arbuscular frequency associated with endophyte infection, whereas the much smaller amounts of vesicles and hyphal coils did not differ significantly.     

Vesicular-arbuscular mycorrhizal effectiveness in an acid soil amended with fresh organic matter

A greenhouse investigation was undertaken to determine the influence of fresh organic matter on the formation and functioning of vesicular-arbuscular mycorrhizal symbiosis in Leucaena leucocephala grown in an acid aluminum-rich ultisol. In soil not amended with fresh organic matter or lime, plants failed to grow. Mycorrhizal infection level, mycorrhizal effectiveness measured in terms of pinnule P content of L. leucocephala leaves and dry matter yield of the legume increased with increase in fresh organic matter. Although VAM colonization level and dry matter yield of L. leucocephala were significantly higher if the test soil was limed (7.2 cmole OH^–) than if amended with fresh organic matter, the latter was as effective as lime in off-setting the detrimental effect of aluminum on mycorrhizal effectiveness. The lower mycorrhizal colonization level and the lower dry matter yield noted in the soil treated with fresh organic matter appears to be related to the inadequacy of Ca in the soil amended with fresh organic matter. These observations are supported by the low calcium status of soil and plant tissues in the absence of lime. It is concluded that while fresh organic matter, in appropriate amounts, could protect sensitive plants and VAM symbiosis against Al toxicity in acid soils, maximum mycorrhizal inoculation effects are not likely to be attained unless the soils are also amended with Ca.Contribution from Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No 3740.     

Mycorrhizal dependency of banana (Musa acuminata,AAA group) cultivar

Seven banana cultivars (Musa acuminata, AAA group) were inoculated with two species of vesicular arbuscular mycorrhizal (VAM) fungi (Glomus mosseae and Glomus macrocarpum) in a greenhouse experiment. Inoculated plants had generally greater shoot dry weight and shoot phosphorus concentrations compared to the noninoculated plants. A great variation in dependency on mycorrhizal colonization was observed among the banana cultivars. Cv. Williams showed the highest relative mycorrhizal dependency (RMD) and cv. Poyo the lowest. For all the cultivars studied, inoculation with G. macrocarpum resulted in the highest RMD values. Both root dry weight and root hair length or density of the noninoculated plants were inverserly correlated with the RMD values of cultivars.     

Genetic variation for VA mycorrhiza-dependent phosphate mobilisation in groundnut (Arachis hypogaea L.)

Nine cultivars of groundnut (Arachis hypogaea L.) were grown in a soil poor in available N or P. There was clearly genetic variation of characteristics indicative of VA mycorrhiza-dependent phosphate mobilisation, namely, VA mycorrhiza fungal spore count (SC), percentage of infection (IF) by VA mycorrhizal fungi (VAMF) and acid and alkaline phosphatase activities. Among the cultivars, one was non-nodulating with low values for all characteristics and in another experiment, this non-nodulating cultivar, one of its parents (PI 259747), a national check (Robut 33-1) and the highest yielding cultivar among the original nine (NFG 7), were grown and investigated for various P-mobilising properties and yield. The linear regression coefficient of pod yield on % VAMF infection was significant in both the experiments. Additionally, many of the correlation coefficients of pod yield and VAM dependent characteristics were positive and significant. From consideration of published evidence, it seems possible to breed for the desirable reinforcing effects of infestation, by VAMF and Rhizobium that can ultimately improve the productivity of groundnuts.     

Response of lettuce to pre- and post-transplant phosphorus and pre-transplant inoculation with a VA-mycorrhizal fungus

Pre-transplant inoculation of lettuce (Lactuca sativa L.) seedlings with the vesicular-arbuscular mycorrhizal fungusGlomus aggregatum (Smith and Schenck emend. Koske) increased P uptake and dry matter yields after transplanting into soil when the concentration of P in the soil solution was 0.02 mg L^–1 but had little affect in soil with 0.30 mg L^–1 solution P. Tissue P concentrations and dry matter yields after transplanting were increased by supplying adequate P prior to transplanting. Adequate levels of pre-transplant P appeared to be more important than maximum mycorrhizal infection of transplants for promoting post-transplant growth of the fast maturing lettuce crop.Journal Series No. 0000 of the Hawaii Institute of Tropical Agriculture and Human Resources.     

Manganese reduction in the rhizosphere of mycorrhizal and nonmycorrhizal maize

The influence of rhizosphere microorganisms and vesicular-arbuscular (VA) mycorrhiza on manganese (Mn) uptake in maize (Zea mays L. cv. Tau) plants was studied in pot experiments under controlled environmental conditions. The plants were grown for 7 weeks in sterilized calcareous soil in pots having separate compartments for growth of roots and of VA mycorrhizal fungal hyphae. The soil was left either uninoculated (control) or prior to planting was inoculated with rhizosphere microorganisms only (MO-VA) or with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol and Gerd.) Gerdemann and Trappe] (MO+VA). Mycorrhiza treatment did not affect shoot dry weight, but root dry weight was slightly inhibited in the MO+VA and MO-VA treatments compared with the uninoculated control. Concentrations of Mn in shoots decreased in the order MO-VA > MO+VA > control. In the rhizosphere soil, the total microbial population was higher in mycorrhizal (MO+VA) than nonmycorrhizal (MO-VA) treatments, but the proportion of Mn-reducing microbial populations was fivefold higher in the nonmycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The most important microbial group taking part in the reduction of Mn was fluorescent Pseudomonas. Mycorrhizal treatment decreased not only the number of Mn reducers but also the release of Mn-solubilizing root exudates, which were collected by percolation from maize plants cultivated in plastic tubes filled with gravel quartz sand. Compared with mycorrhizal plants, the root exudates of nonmycorrhizal plants had two fold higher capacity for reduction of Mn. Therefore, changes in both rhizosphere microbial population and root exudation are probably responsible for the lower acquisition of Mn in mycorrhizal plants.     

Categories of vesicular-arbuscular mycorrhizal dependency of host species

Summary Brassica nigra and selected species of Leucaena and Sesbania were used as indicator hosts in a greenhouse experiment designed to establish distinct categories of mycorrhizal dependence. The plants were grown in an oxisol with different concentrations of established soil solution P in the presence or absence of the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus aggregatum. The extent to which the plant species depended on the fungus for dry matter production diminished with increased concentrations of soil solution P, but the magnitude of this decrease varied from species to species. Five distinct mycorrhizal categories are proposed based on the differences observed, ranging from non-dependent to very highly dependent. The critical soil solution P concentrations that were useful for separating host species into distinct VAM-dependency groups were 0.02 and 0.2 mg/l. Species differing in their mycorrhizal dependency differed with respect to the soil solution P concentration required for the expression of maximum VAM effectiveness, the degree to which increasing concentrations of P depressed VAM infection and the pattern of immobile nutrient accumulation.Contribution from the Hawaii Institute of Tropical Agriculture and Human Resources Journal Series No. 3547     

Alteration of growth ofSolanum opacum andPlantago drummondii and inhibition of regrowth of hyphae of vesicular-arbuscular mycorrhizal fungi from dried root pieces by manganese

Addition of MnSO₄ or MnCl₂ to a fine sandy soil from South Australia had a negative effect on shoot growth and root elongation ofSolanum opacum in the absence of significant presence of vesicular-arbuscular mycorrhiza (VAM). VAM ameliorated the reduction of plant growth by Mn, even though mycorrhizal development was decreased. Mn inhibited infection of roots by a fine endophyte less than that by some coarse endophytes. High concentrations of available Mn inhibited growth of hyphae of VAM fungi from dried root pieces, a significant source of infection by mycorrhizal fungi in the soil used.     

Phosphorus (P) efficiencies and mycorrhizal responsiveness of old and modern wheat cultivars

A pot experiment was carried out in a growth chamber to investigate P efficiencies and mycorrhizal responsiveness of modern (Krichauff and Excalibur) and old (Khapstein, Bobin, Comeback and Purple Straw) wheat cultivars (Triticum aestivum). The arbuscular mycorrhizal fungus (AMF) used in this study was Glomus intraradices. The growth medium was a soil/sand mixture with NaHCO₃-extractable P of 9.4 mg P kg^–1 and no extra P was added. Plant P efficiencies (uptake, utilisation and agronomic) were found to differ significantly between cultivars, but no general trends of changes with the year of release of the cultivar were found. AMF colonisation was found to decrease plant growth under our experimental conditions with low light intensity. Mycorrhizal responsiveness (MR) was measured in terms of the improvement in plant P nutrition (shoot P concentrations). MR was found to be generally lower in modern cultivars than in old cultivars, indicating that modern breeding programs may have reduced the responsiveness of modern wheat cultivars to arbuscular mycorrhizal fungi. MR was also found to decrease in general with increased plant P utilisation efficiency.     

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.     

Influence of phosphorus level on VA Mycorrhizal colonization and growth of cowpea cultivars

Vesicular-arbuscular mycorrhizal (VAM) associations often vary according to the abundance of available soil phosphorus (P). Therefore, understanding the response of crop plants to colonization by VAM fungi necessitates the study of the response of colonized and noncolonized plants, from a range of cultivars, to differing levels of P. Cowpea is grown throughout the world, often on impoverished soils in which it can benefit from formation of mycorrhizae. The present study was conducted to determine the response of four cultivars of cowpea (Vigna unguiculata (L.) Walp.), varying in nitrogen fixation capacity, to inoculation withGlomus fasciculatum at four levels of added P in the rooting medium. In a greenhouse experiment, four cowpea cultivars, Mississippi Silver, Brown Crowder, Six Week Browneye and MI 35, were grown with and without the mycorrhizal fungus at four levels of added P, 0, 10, 20 and 30 ppm. Root colonization (%) was negatively correlated with P content of the growth medium and shoot P concentration. Intraspecific variability was shown for shoot dry weight and leaf area in response to inoculation withG. fasciculatum at different P levels. The range of P required in the growth medium which allowed benefit fromG. fasciculatum was identified for individual cultivars using shoot dry weight and leaf area, and collectively across cultivars for other parameters.     

The vesicular-arbuscular (VA) mycorrhiza and its effects on growth of vegetatively propagated Theobroma cacao L.

A greenhouse experiment was conducted to study the effects of mycorrhizal inoculation on growth and nutrient uptake of vegetatively propagated cocoa plants from the Sabah hybrid (NA 33 × PA 7) raised on unsterilized Munchong soils. Inoculation with mixed species of Scutellospora and Glomus, resulted in higher dry matter yield and stem diameter of mycorrhizal plants obtained through budding, air layering or marcotting (a form of asexual plant propagation using vegetative parts and the selection of a healthy branch and scraping off the bark at the lower end of the branch, forcing it to root by covering it with a ball of soil) and stem cutting. Budded and marcotted mycorrhizal plants gave a significant increase in P content of shoots. In contrast, only budded mycorrhizal plants (on both young and old rootstocks) gave a significantly higher Ca concentration in tops, compared to uninoculated plants.     

Benefit and cost analysis and phosphorus efficiency of VA mycorrhizal fungi colonizations with sorghum (Sorghum bicolor) genotypes grown at varied phosphorus levels

Sorghum [Sorghum bicolor (L.) Moench] was grown in a greenhouse in a low P (3.6 mg kg^-1) soil (Typic Argiudolls) inoculated with the vesicular-arbuscular mycorrhizal fungi (VMAF) Glomus fasciculatum and P added at 0, 12.5, 25.0, and 37.5 mg kg^-1 soil to determine the effects of VAMF-root associations on plant growth, benefit and cost analysis, and P efficiency (dry matter produced/unit P absorbed). Root colonization with VAMF and shoot growth enhancements decreased with increased soil P applications. Mycorrhizal plants were less P efficient than nonmycorrhizal plants. Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants were considered the benefit derived by plants from VAMF-root associations. Shoot dry matter differences between mycorrhizal and nonmycorrhizal plants with similar P concentrations were considered the costs paid by plants for VAMF-root associations. Values of benefit and cost analysis for VAMF-root associations were highest when soil P was lowest and decreased with increasing P applications. Genotypic differences for calculated costs were pronounced, but not benefits. Benefit and cost analysis.may be helpful to evaluate host plant genotypes and VAMF species to optimize efficiencies of VAMF symbiosis in different soil environments.     

Growth and arsenic uptake by Chinese brake fern inoculated with an arbuscular mycorrhizal fungus

A split-root experiment investigated the effects of inoculation with the arbuscular mycorrhizal fungus Glomus mosseae and arsenic (As) addition on As uptake by Pteris vittata L. Either part or all of the root system was inoculated with G. mosseae or exposed to As addition (50 ml 1000 μmol L⁻¹ As 1 week before harvest). Mycorrhizal colonization substantially increased frond and root dry weight and P and As contents irrespective of As addition. Frond As contents in mycorrhizal plants were highest when the whole root system was exposed to As. Frond As concentrations and contents were higher when inoculation and As addition were in the same parts of the root system than when spatially separate. There were positive effects of arbuscular mycorrhiza inoculation on plant growth and As uptake, and inoculation of part of the roots seemed to be as effective as inoculation of the whole root system.