Degree Of Mycorrhizal Infection Research Articles

Stand fine root biomass and fine root morphology in old-growth beech forests as a function of precipitation and soil fertility

Only very limited information exists on the plasticity in size and structure of fine root systems, and fine root morphology of mature trees as a function of environmental variation. Six northwest German old-growth beech forests (Fagus sylvatica L.) differing in precipitation (520 – 1030 mm year−1) and soil acidity/fertility (acidic infertile to basic fertile) were studied by soil coring for stand totals of fine root biomass (0–40 cm plus organic horizons), vertical and horizontal root distribution patterns, the fine root necromass/biomass ratio, and fine root morphology (root specific surface area, root tip frequency, and degree of mycorrhizal infection). Stand total of fine root biomass, and vertical and horizontal fine root distribution patterns were similar in beech stands on acidic infertile and basic fertile soils. In five of six stands, stand fine root biomass ranged between 320 and 470 g m−2; fine root density showed an exponential decrease with soil depth in all profiles irrespective of soil type. An exceptionally small stand fine root biomass (<150 g m−2) was found in the driest stand with 520 mm year−1 of rainfall. In all stands, fine root morphological parameters changed markedly from the topsoil to the lower profile; differences in fine root morphology among the six stands, however, were remarkably small. Two parameters, the necromass/biomass ratio and fine root tip density (tips per soil volume), however, were both much higher in acidic than basic soils. We conclude that variation in soil acidity and fertility only weakly influences fine root system size and morphology of F. sylvatica, but affects root system structure and, probably, fine root mortality. It is hypothesized that high root tip densities in acidic infertile soils compensate for low nutrient supply rates, and large necromasses are a consequence of adverse soil chemical conditions. Data from a literature survey support the view that rainfall is another major environmental factor that influences the stand fine root biomass of F. sylvatica.

Role of mycorrhizal fungi and phosphorus in the arsenic tolerance of basin wildrye.

Revegetation of arsenic (As)-rich mine spoils is often impeded by the lack of plant species tolerant of high As concentrations and low nutrient availability. Basin wildrye [Leymus cinereus (Scribner & Merr.) A. Löve] has been observed to establish naturally in soils with elevated As content and thus may be useful for the stabilization of As-contaminated soils. An experiment was conducted to evaluate how variable phosphorus (P) concentrations and inoculation with site-specific arbuscular mycorrhizal fungi influence As tolerance of basin wildrye. Basin wildrye was grown in sterile sand in the greenhouse for 16 weeks. Pots of sterile sand were amended to create one of four rates of As (0, 3, 15, or 50 mg As kg(-1)), two rates of P (3 or 15 mg P kg(-1)), and +/-mycorrhizal inoculation in a 2 x 4 x 2 factorial arrangement. After 16 weeks of growth, plants were harvested, shoots and roots thoroughly washed, and the tissue analyzed for total shoot biomass, total root and shoot As and P concentrations, and degree of mycorrhizal infection. Basin wildrye was found to be tolerant of high As concentrations allowing for vigorous plant growth at application levels of 3 or 15 mg As kg(-1). Arsenic was sequestered in the roots, with 30 to 50 times more As in the roots than shoots under low P conditions. Mycorrhizal infection did not confer As tolerance in basin wildrye nor did mycorrhizal fungi influence biomass production. Phosphorus concentrations of 15 mg kg(-1) effectively inhibited As accumulation in basin wildrye. Basin wildrye has the potential to be used for stabilization of As-rich soils while minimizing exposure to grazing animals following reclamation.

Fine roots of trees - a new perspective.

Fine roots of trees - a new perspective.

The effect of Kalmia angustifolia on the growth, nutrition, and ectomycorrhizal symbiont community of black spruce

Kalmia angustifolia L. is an ericaceous shrub that frequently invades black spruce ( Picea mariana Mill.) clear-cuts in central Newfoundland. Field observations suggest that on many sites where K. angustifolia grows, black spruce seedlings become chlorotic and stunted. Previous laboratory research has suggested that allelochemicals of K. angustifolia affect the growth and development of black spruce as well as the growth of certain ectomycorrhizal (ECM) fungi associated with black spruce. Black spruce seedlings close to (<1 m) and far from (>1 m) K. angustifolia were sampled from a clear-cut in central Newfoundland. The ECM community structure, degree of mycorrhizal infection, height, mass, root:shoot ratio, and the foliar concentrations of N, P, K, Ca, and Mg of spruce seedlings growing close to and far from K. angustifolia were examined. Seedlings close to K. angustifolia had significantly lower foliar concentrations of N and P, had a lower rate of mycorrhizal infection, and were more frequently associated with Phialocephala dimorphospora Kendrick, a potential root pathogen of black spruce, than seedlings growing far from K. angustifolia. There were positive linear relationships between black spruce foliar N concentration and total seedling height and biomass for seedlings growing away from K. angustifolia, but not for seedlings in close proximity to K. angustifolia. Hypotheses suggesting possible roles for nutrient competition, allelopathy, and K. angustifolia's ability to increase the occurrence of the pseudomycorrhizal P. dimorphospora on black spruce are proposed.

Mechanisms of interference between hay-scented fern and black cherry

Hay-scented fern (Dennstaedtiapunctilobula Michx.) interferes with establishment of black cherry (Prunusserotina Ehrh.) in the Allegheny hardwood forest of Pennsylvania. In stands where fern cover is dense, black cherry seeds germinate, but seedlings do not become established. Allelopathy was eliminated as the cause of interference in previous work; the present studies evaluated the resources of soil water, soil phosphorus, soil nitrogen, and light. The impact of hay-scented fern on the level of each resource, the availability of each resource to black cherry seedlings, and the growth response of black cherry seedlings to changes in resource availability were evaluated. Hay-scented fern had little effect on soil moisture levels, nor did it affect plant availability of soil water. The level of soil phosphorus was not reduced by the presence of hay-scented fern nor was phosphorus availability to black cherry seedlings less when they grew with fern. Both the speed and degree of mycorrhizal infection and the foliar phosphorus concentrations were similar in seedlings growing with or without fern cover. Hay-scented fern had no effect on rates of ammonium- or nitrate-nitrogen production nor was the soil concentration of ammonium affected. The presence of hay-scented fern significantly reduced the soil nitrate-nitrogen concentration in the first year after a shelterwood seed cut, but not in the second. Overstory tree roots were more important than hay-scented fern in removing soil nitrate. Availability of soil nitrogen was unaffected by the presence of hay-scented fern or overstory tree roots. Black cherry seedlings grew more where ferns were absent, regardless of whether overstory tree roots were present or absent. Competitive reduction in light was the key mechanism of fern interference with black cherry. Hay-scented fern caused dramatic reductions in both the photon flux density and the ratio of red to far-red light beneath it. Black cherry seedlings survived and grew poorly in the presence of fern foliage shade. Survival and growth similar to that above fern could be restored by restraining fern foliage, allowing light to reach black cherry seedlings from above.

Response of bean, broadbean and chickpea plants to inoculation with Glomus species

Eight different locally obtained Glomus species, including G. pallidum, G. mosseae, G. fasciculatum, G. etunicatum and G. monosporum, were inoculated into bean, broadbean and chickpea plants to examine their effect on plant growth. The most effective in growth stimulation for all these inoculated crops were G. fasciculatum 2 and G. mosseae 2 while G. mosseae 1 and 2 were the most effective in colonizing the roots of bean, broadbean and chickpea plants. Glomus mosseae 2 increased the shoot growth of beans, broadbeans and chickpeas by 52, 117 and 190%, respectively. No relation was found between shoot growth and the degree of mycorrhizal infection.

Effect of dual inoculation ofRhizobium and vesicular arbuscular mycorrhizal fungi onPisum sativum

The interaction of two symbionts,Rhizobium (a bacterium) andGigaspora calospora (a VAM fungus) was studied inPisum sativum (a nodulating legume).Pisum sativum plants inoculated with VA mycorrhizal fungi andRhizobium singly and in combination responded favourably as compared to uninoculated control. Characteristically dual inoculation exerted a higher beneficial effect on shoot and root dry mass, phosphorus and nitrogen uptake, nodule formation and degree of mycorrhizal infection than either inoculum alone.

Sulfur supply and the formation of vesicular-arbuscular mycorrhizas by Glomus fasciculatum on subterranean clover

Sulfur supply and the formation of vesicular-arbuscular mycorrhizas by Glomus fasciculatum on subterranean clover

FACTORS AFFECTING THE VESICULAR‐ARBUSCULAR INFECTION AND MYCORRHIZAL DEPENDENCY OF THIRTEEN WHEAT CULTIVARS

SUMMARYWheat cultivars inoculated with Glomus mosseae show different degrees of mycorrhizal infection and mycorrhizal dependency. Mycorrhizal dependency was affected by root and root/shoot (R/S) ratio dry wts, but neither mycorrhizal dependency nor mycorrhizal infection levels were directly affected by N, P, K, Ca or Mg concentrations in plant tissues.Absence of mycorrhizal infection in some wheat varieties was associated with lack of sugar exudation from the roots rather than with the sugar content of the roots. VA infection led to a decrease in the reducing and total sugar content of root extracts, and this effect was correlated with the degree of mycorrhizal infection.

CARBOHYDRATE PHYSIOLOGY OF MYCORRHIZAL ROOTS OF BEECH

SummaryThe presence of several classes of reducing substances in mycorrhizal roots of beech is demonstrated, throwing considerable doubt on the values of ‘easily soluble reducing substances’ which have been used for correlation with degree of mycorrhizal infection by several workers. The soluble sugars of beech mycorrhizas are glucose, fructose, sucrose and trehalose, together with the acyclic polyol, mannitol and two cyclic polyols, myo‐inositol and an unidentified inositol. Trehalose and mannitol are absent from uninfected roots showing their presence to be dependent on fungal infection. Methods for the individual assay of the soluble carbohydrates are presented. The main sugars obtained by acid hydrolysis of the insoluble residue of mycorrhizas are galactose, glucose, mannose, arabinose, xylose, fucose, ribose, rhamnose and a deoxypentose provisionally identified as deoxyribose. The mannose and deoxypentose polymers are absent from beech tissue and deoxyhexose polymers from the fungus. Much of the glucose is derived from fungal glycogen. Mycorrhizas accumulate principally trehalose and glycogen from exogenous glucose and trehalose, and mannitol from fructose and mannitol. The pattern of synthesis from exogenous sucrose is intermediate between glucose and fructose. The results are compared with those obtained for other fungi by other workers and a possible ecologically significant role for mannitol is suggested.

Soil pH and Mycorrhiza Development in Pinus

MYCORRHIZAS of Pinus will not develop profusely on trees growing in neutral or alkaline soils, and it has usually been assumed that this is so because the mycorrhizal fungi are acidophilic. During investigations of the fertility status of a nodular podzolic soil from the coastal lowlands of southern Queensland, I have found that formation of mycorrhiza in pine seedlings is not always inhibited by a rise in soil pH, and when it is, the effect can usually be explained in terms of host nutrition. The direct effect of alkalinity in restricting the growth of the fungus may be less important than was formerly thought. These results are derived from a series of pot experiments designed primarily to test for nutrient deficiencies, but also to study the effect of nutrient supply on the degree of mycorrhizal infection of seedlings. Comparison of relative mycorrhiza development was based on the number of mycorrhizas expressed as a percentage of the total number of short roots per seedling (‘mycorrhiza per cent’). The criterion of infection used was the presence of dichotomous branching or forking of the short roots. Since dichotomy of short roots of Pinus is not always associated with mycorrhizal infection, some care is necessary in accepting forked short roots as mycorrhizas. Experience has shown that it is possible to recognize mycorrhizas of Pinus on the basis of their external morphology. In the work reported here, counting was carried out initially under a stereo-microscope (× 12.5), and after experience had been gained in this way a binocular loupe was used.