Hallo Peter,
das folgende Zitat ist aus der ersten Datei: "Ein primärer Laubwaldbewohner, hat die Speise-Morchel eine deutliche Vorliebe für Eschen. Den Grund für diese Affinität betreffend, ist die Fachwelt geteilter Meinung. Einige vermuten eine Symbiose zwischen Pilz und Baum (Mykorrhiza), andere wiederum machen das kaliumreiche Bodenmilieu unter Eschen geltend. Hierfür spräche auch das relativ häufige Auftreten in alten Obstgärten, denn Fallobst zeitigt nach Jahrzehnten gleichfalls ein kaliumreiches Milieu. Die Wahrheit dürfte, wie so oft, in der Mitte liegen. Tatsächlich scheint es sich um einen sogenannten fakultativen Mykorrhizabildner zu handeln, einen Pilz also, der es sich quasi aussuchen kann, ob er sein Dasein lieber mit oder ohne Partner fristet."
Den folgenden Text habe ich aus der zweiten Datei auf die Schnelle rauskopiert:
"Morels were originally thought to be saprobic (decomposing dead organic matter) because tested cultures grow rapidly in pure culture on simple nutrients such as starches, sugars, and nitrates (Robbins and Hervey 1959) and can be induced to fruit without association with plant hosts. Mycorrhizal fungi, by contrast, grow more slowly in pure culture and do not fruit without forming a symbiosis with their host plants. Moser (1949) suggested that some morels might have the ability to form mycorrhizal symbioses with trees or at least to form mycorrhiza-like structures. Assuming that this relationship is optional for morels that also have saprobic abilities, this form of symbiosis has been called a “facultatively mycorrhizal” nutritional strategy.
Trappe (1996) discussed the nature of mycorrhizal symbioses and noted that both the structure and function of mycorrhizae are important characteristics. Each can vary with such factors as the species involved, their developmental stage, the nutrient status of each partner, seasonal shifts in their nutrient allocation patterns, and the specific soil environment. These factors create a shifting spectrum of relative advantages and disadvantages to the fungus and plant symbionts. Johnson and others (1997) provided a chart of relative benefits and costs to both fungus
and host along a spectrum from mutualism to parasitism, but recognized that net benefits and costs can change over time as circumstances change for each symbiont. Not only is it inappropriate to assume that both partners benefit equally, but the observable structure of a mycorrhiza does not necessarily correspond to its functions. We note these caveats because most tested morels have the saprobic abilities noted above, morel mycorrhizae sometimes exhibit weakly developed structural features,16 few studies have examined benefits to the trees, and some morels form a different type of association with the larger roots of some plants (see the following section on muffs). Buscot and Kottke (1990) and Buscot (1992a, 1992c) described ectomycorrhizae17 on Norway spruce associated with M. rotunda, M. esculenta, and M. elata. Subsequently, Buscot (1994) described seven types of morel mycorrhizae with Norway spruce. In these descriptions, Buscot noted that M. esculenta mycorrhizae featured minimal development of a Hartig net18 and suggested that other bacteria and fungi might be involved in facilitating the symbiosis (Buscot 1992c). With M. elata, Buscot (1992a) reported that morel mycorrhizae only formed as a “secondary” mycorrhizae after replacing previous mycorrhizae formed by other fungi. Harbin and Volk (1999) reported that M. esculenta and M. elata were facultatively mycorrhizal with apples, elms, and black spruces. They reported formation of typical ectomycorrhizae and noted that inoculated seedlings grew more than noninoculated control seedlings. Although apples and elms are not common hosts of ectomycorrhizal fungi, they can be (Molina and others 1992), and morels certainly fruit in proximity to these trees. Dahlstrom and others (2000) reported that mountain blond morels and natural black morels from the Pacific Northwest formed several typical mycorrhizal structures (ecto- and ectendomycorrhizal) with ponderosa pine, Douglas-fir, western larch, and lodgepole pine. To date, we know of no reports of
fire morels being tested for their ability to form mycorrhizae. Hobbie and others (2001) provided additional circumstantial evidence that morels might use both saprobic and mycorrhizal nutritional strategies. They studied isotope ratios in a variety of fungi noting that: “In general mycorrhizal fungi are enriched in 15N and depleted in 13C relative to saprobic fungi.” The Morchella
specimens they sampled yielded intermediate values. A not-yet-tested hypothesis is that morels, by forming mycorrhizae, might also be positioning themselves to rapidly decompose the fine root tips of trees when these roots senesce or the tree dies. Abundant morel fruiting following tree death could be facilitated by such a flush of nutrients (Dahlstrom and others 2000, Pilz
and others 2004, Vrålstad and others 1998)."
Grüße, Andreas