Valentin Furlan

Growth responses of several plant species to mycorrhizae in a soil of moderate P-fertility

SummaryThe growth of twenty plant species was compared under field conditions in a methyl bromide fumigated and non-fumigated soil. The non-fumigated soil had a wild endomycorrhizal flora and contained 100 μg/g of available phosphorus. No phosphorus was added to the soil but both fumigated and non-fumigated plots received a basal fertilization of 100 kg/ha N−NH4NO3 and 100 kg/ha K−KCl. Based on plant growth responses, three groups of plants were distinguishable. Plants from group I were mycorrhizal and had better growth in non-fumigated than in the fumigated soil. This group was the most important, including sixteen plant species. Stunting of plants from group I following soil fumigation was mainly attribuable to the destruction of mycorrhizae. Plants from group II (oat and wheat) grew equally well in non-fumigated and fumigated soils. For these plants which were mycorrhizal in the non-fumigated plots, the P-content of the soil was sufficient for growth and therefore no stunting was observed in the absence of mycorrhizae. Plants from group III (cabbage and garden beet) grew better in fumigated than in non-fumigated soil. Their better growth in fumigated soil was tentatively attributed to the destruction of soil-borne pathogens. They did not form mycorrhizae in non-fumigated soil.A new method of calculating mycorrhizal dependency is proposed, and the value calculated was named relative field mycorrhizal dependency (RFMD) index. It is also proposed that the acronym RFMD receive a superscript representing in μg/g the quantity of available P in the soil. Carrot with its characteristic root systems had the highest RFMD100 index (99.2%), but other plants with high phosphorus requirements for normal growth had a wide range of RFMD100 index values.

Growth responses of several plant species to mycorrhizae in a soil of moderate P-fertility: II. Soil fumigation induced stunting of plants corrected by reintroduction of the wild endomycorrhizal flora

SummaryA greenhouse experiment was carried out comparing the growth of various plant species in non-fumigated, fumigated, and fumigated-inoculated soils. The soil used contained numerous pieces of root of Broom-Corn Millet (Panicum miliaceum L.) that were found intensely colonized by indigenous endomycorrhizal fungi. The soil was fumigated with methyl bromide and the inoculum used was a mixture of VA mycorrhizal root fragment from plants grown in the field from which the soil was collected. Plants used were cabbage (Brassica oleracea L. var Copenhagen Market), carrot (Daucus carota L. var. Nantaise), leek (Allium porrum L. var. American Flag), marigold (Tagetes patulus L. var. Golden Boy), tomato (Lycopersicum esculentum Mill. var. Michigan Ohio), sweet corn (Zea mays L. var. Span Cross) and wheat (Triticum aestivum L. var. Glenlea). No phosphorus was added to the soil which contained 93 μg/g of available P (bray II). All plants tested formed mycorrhizae except cabbage. Generally, values of the root endomycorrhizal colonization (REC) index were higher in fumigated-inoculated soil than in non-fumigated soil. Cabbage grew equally well in fumigated and fumigated-inoculated soil, but better than in non-fumigated soil. Cabbage did not form VA mycorrhizae and its better growth in fumigated soil was tentatively attributed to the destruction of soil-borne pathogens and the absence of competition. Wheat grew equally well in the three treatments, because 93 μg/g of available P is sufficient for wheat growth and thus the mycorrhizae were not efficient. The five other plant species used were severely stunted in fumigated soil and the inoculation permitted the reestablishment of normal growth as in non-fumigated soil. Growth stimulation is attributed to the efficiency of VA mycorrhizae since these plants were mycorrhizal in non-fumigated soil and in fumigated-inoculated soil. Stunting of these plants in fumigated soil was due to the destruction of VA mycorrhizae since results show that this stunting cannot be attributed to methylbromide residues in the soil. Moreover soil pH and nutrient content were not markedly changed after fumigation.

Effect of soil K, Ca and Mg saturation and endomycorrhization on growth and nutrient uptake of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated with high exchangeable Mg levels in soils relative to soil K and Ca. A greenhouse experiment was set up to test the hypothesis that the equilibrium between soil exchangeable K, Ca, and Mg ions influences the growth and nutrient status of sugar maple seedlings. Also tested was whether endomycorrhization can alter nutrient acquisition under various soil exchangeable basic cations ratios. Treatments consisted of seven ratios of soil exchangeable K, Ca, and Mg making up a total base saturation of 58%, and a soil inoculation treatment with the endomycorrhizal fungus Glomus versiforme (control and inoculated), in a complete factorial design. Sugar maple seedlings were grown for 3 months in the treated soils. Plant shoot elongation rate, dry biomass and nutrient concentrations in foliage were influenced by the various ratios of soil cations. The predicted plant biomass and foliar K concentration were highest at a soil Ca saturation of 38%, a soil K saturation of 12%, and a soil Mg saturation of 8%. Potassium concentration in foliage was dependent on the level of Ca and Mg saturation in the soil when soil K saturation was close to 12%. Foliar Ca and Mg levels were more dependent on their corresponding levels in soil than foliar K. Colonization by G. versiforme did not influence seedling growth and macronutrient uptake. The results confirm that growth and nutrition of sugar maple are negatively affected by imbalances in exchangeable basic cations in soils.

Colonization potential of in vitro-produced arbuscular mycorrhizal fungus spores compared with a root-segment inoculum from open pot culture

Abstract A reliable inoculum, free from other microorganisms, to produce arbuscular mycorhizal (AM) plants is of the greatest importance when studying the interaction between AM plants and soil microorganisms. We investigated the colonization of leeks from monoxenic in vitro-produced Glomus intraradices spores. The isolated spores were produced using a two-compartment in vitro growth system previously described. A spore suspension was used as inoculum and was compared to the inoculum potential of endomycorrhizal root segments of pot-grown leek (Allium porrum L.) plants. The leeks were grown in a controlled environment and two types of sterilized growth media were tested: calcined montmorillonite clay and a soil mix. Root colonization progressed faster in the soil mix than in the clay. However, in this medium, after an initial delay, root colonization from in vitro-produced spores was essentially the same as that observed with the root-segment inoculum, reaching 44% and 58% respectively, after 16 weeks. Leek roots colonized by the monoxenically-produced spores harbored only the studied AMF fungi while the roots colonized from the root segments were substantially contaminated by other fungi.