Mycorrhiza Establishment Research Articles

Effects of Mycorrhizae on Establishment and Performance of Forage Species in Mine Spoil1

AbstractMine soil not containing topsoil usually lacks the normal endomycorrhizal fungi which improve the P uptake of many plants. The establishment of mycorrhizae might be useful for low‐cost, low‐maintenance revegetation of abandoned strip mines or other mineral wastes low in available P. The value of establishing endomycorrhizae to improve the growth of forage grasses and legumes on a low‐P strip mine spoil (Schlickig udispolent) was investigated using 1‐cm layers of field soil as mycorrhizal inoculum. In replicated l‐m2 field plots receiving lime but not fertilizer, yields of flatpea (Lathyrus sylvestris L.), crownvetch (Coronilla varia L.), and birdsfoot trefoil (Lotus corniculatus L.) after two seasons were 7, 13, and 18‐fold greater, respectively, in mycorrhizal treatments. Survival after two winters averaged 51 vs. 6% for nonmycorrhizal treatments. In 0.25 m2 plots receiving 0, 41, 81, and 162 kg/ha P or mycorrhizal inoculum at the two low rates of P, the yields of mycorrhizal and nonmycorrhizal plants converged as P was increased. The response of mycorrhizal trefoil improved over 2 years relative to nonmycorrhizal treatments receiving only initial applications of P. Growth of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) in 600‐ml pots in the greenhouse was not significantly improved by mycorrhizae. Mycorrhizal fungi from different sources varied in their adaptation to low‐pH mine spoil. The establishment of mycorrhizae in mining wastes is useful if indigenous inoculum is absent or nonadapted, if available P is low, and if the plant species used for revegetation responds to mycorrhizae. Under these conditions, mycorrhizal plants are more persistant and less affected by the immobilization of fertilizer P.

Effect of Early Mycorrhizal Infection on Nodulation and Nitrogen Fixation in Trifolium subterraneum L

Three experiments are described. Rapid establishment of vesicular-arbuscular mycorrhizas in roots of T. subterraneum cv. Mt Barker, using natural soil inoculum, was associated with improved nodulation, increased nitrogenase activity per plant (nmol C2H2 reduced per plant per hour) and increased nodule efficiency on the basis of nodule volume (nmol C2H2 reduced per mm� nodule per hour). In two experiments (on soil low in nutrients), this increase occurred before any positive growth response to mycorrhizal infection was apparent. In all experiments, mycorrhizal roots had a higher phosphorus concentration (%P) than did non-mycorrhizal roots. This difference, which was evident before any differences in total plant phosphorus were detected, was not accompanied by an increase in nodule phosphorus concentration, so that differences in nodule efficiency could not be attributed to differences in this parameter. In the third experiment (on soil with higher nutrient levels), establishment of mycorrhizas was also accompanied by increased growth, phosphorus and nitrogen contents within a 35-day experimental period. Phosphorus inflow into roots (moles P per cm root per second) was higher in mycorrhizal plants. Delay in formation of mycorrhizas (by reduction in the amount of inoculum in soil) was accompanied by lower inflow, and delay in both the establishment of high root phosphorus concentration and in the onset of enhanced nodulation and nitrogenase activity.

Synthesis of mycorrhiza on Pinus oocarpa

SUMMARYMycorrhiza was synthesized using Pinus oocarpa and Rhizopogon luteolus. After one year's successful growth in the laboratory, the seedlings raised were planted out in the field where the inoculated plants continued to grow normally. The uninoculated plants died after planting out. The results are believed to be significant in that a field establishment of mycorrhiza synthesized in controlled conditions is possible. The experiment also demonstrates the absence of suitable mycorrhizal fungi for pine establishment in Nigerian soils.

The Extractives of the Mycorrhizas and Roots of Pinus Radiata and Pseudotsuga Menziesii

The amounts of acetone extractives from mycorrhizas and their polyphenolic portion were variable over a 6�month period. During August the amounts of extrac� tives and polyphenols were higher in slow� than in fast-growing Pinus radiata seedlings. The amount of extractives in the roots were greater than those in the mycorrhizas but in the latter the polyphenols were concentrated in the outer layer. The composition of the mycorrhizal and root extractives of P. radiata were very similar and in addition to resin contained catechin, two components that are very similar to 3,5,3',4'.tetrahydroxystilbene and one of its glucosides, and leucocyanidin polymers. The mycorrhizas of Pseudotsuga menziesii contain 15 components, includ� ing catechin, epicatechin, leucocyanidin polymers, and a polyene. With the exception of the latter the roots of Ps. menziesii contained the same components and in addition poriolin, poriol, taxifolin, taxifolin-3�glucoside, and quercetin.3.glucoside. Evidence supports the view that the polyphenols are formed in situ and appear to be formed in enhanced amounts in the tannin layer of mycorrhizas. Their possible role in the establishment of mycorrhizas is discussed.

The establishment of vesicular-arbuscular mycorrhiza under aseptic conditions.

SUMMARY: The establishment of vesicular-arbuscular mycorrhizal infections by inoculation with germinated resting spores of an Endogone sp. was investigated under microbiologically controlled conditions; pure two-membered cultures were obtained for the first time. Seedlings were grown in a nitrogen-deficient inorganic salt medium; in these conditions the fungus failed to form an appressorium and to penetrate the plant roots unless a Pseudomonas sp. was also added. Adding soluble nitrogen to the medium completely inhibited root penetration, even in the presence of the bacteria. Various sterile filtrates could be used to replace the bacterial inoculum but these substitutes induced only few infections per plant. Mycorrhizal roots grew more vigorously than non-mycorrhizal roots of the same seedling. They were longer and more profusely branched. At first mycorrhizal infections were predominantly arbuscular, but many prominent vesicles developed as the seedlings declined, and then the fungus grew out of infected roots and colonized the agar. The fungus could not be subcultured without a living host. The possible interpretation of these results is considered with reference to the specialized nutritional conditions under which test plants were grown.