Mycorrhizae
Excerpt from the introduction of a paper entitled “The role of mycorrhizal and rhizobial symbioses in growth, mortality, and height of four native Minnesotan plant species”. In-text citations can be provided if necessary.
Mycorrhizae, a term derived from the Greek for “fungus root”, are a symbiotic relationship between soil-dwelling fungus and the roots of a plant. In this partnership, the fungus obtains carbon from the plant while facilitating the uptake of inorganic nutrients from the soil. The fungal hyphae increase the volume of soil that can be explored by the plant’s roots, increasing nutrient and water uptake and enhancing growth (Beringer et al. 1979). Ideally, the mycorrhizal symbiosis can cause the plant to become more vigorous and more tolerant of chronically low soil moisture, but the association between fungi and roots is easily disturbed. Mycorrhizae do not take well to disturbances, the use of pesticides, or excessive amounts of fertilizer. They are also highly specific with regard to the plants with which they associate.
Plants also associate with nitrogen-fixing bacteria collectively known as rhizobia. These bacteria form nodules on the roots of leguminous plants and convert atmospheric nitrogen into a form usable by the plant. Like mycorrhizae, rhizobia are highly specific to their host plant.
Both mycorrhizae and rhizobia are important in enhancing certain aspects of various species of plants. Under optimal conditions, these can augment growth (and by extension, reproductive capacity), enhance water uptake in low moisture soils, and increase absorption of inorganic nutrients. While the effect of these symbionts is well documented in commercial and agricultural practice, their effect on native plants is poorly studied.
“Pest Importance” section from a USDA APHIS document on Ophiostoma piceae (=O. quercus). In-text citations can be provided if necessary.
Sapstain is a blue, grey, or black discoloration of cut wood, caused mainly by several species of Ascomycete fungi in the genera Ophiostoma and Ceratocystis (Luck et al. 1990; Uzunovic et al. 1999). Melanized hyphae penetrate into the ray parenchyma, resin ducts, and cell lumens of affected wood, causing it to appear discolored (Seifert 1993, Uzunovic et al. 1999, Payne et al. 2000; Bruce et al. 2003). However, no actual staining of the cell walls occurs (Seifert 1993). Münch (1907) explains the discoloration as an “optical effect” of the fungal melanin granules in the cells. In trees and freshy cut logs, growth of fungal mycelia along the medullary rays causes a triangular or wedge-shaped stain in cross-section (Gibbs 1993).
Most sapstaining fungi metabolize non-structural components of the sapwood, such as sugars, proteins, and triglycerides while structural components like lignin and cellulose are left untouched (Gharibian et al. 1996, Abraham et al. 1998; Bruce et al. 2003). As a result, the damage to affected lumber is primarily cosmetic (Seifert 1993; Bruce et al. 2003). Gharibian et al. (1996) suggest that conifer damage attributed to sapstain by O. piceae may be related to the presence of nitrogen-rich “protein bodies” in the sapwood.
Sapstaining fungi cause significant worldwide economic losses in the forest products industry (Gagné et al. 2001, Kim et al. 2005). Stained wood is unsightly and may be rejected by the timber buyer and the end-user of the wood (Seifert 1993; Uzunovic et al. 1999; Payne et al. 2000). Many other fungi are known to grow alongside sapstain fungi on a single piece of wood, which may lead to discoloration as well as decay and loss of strength (Seifert 1993; Payne et al. 2000).
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