Growth and metabolic activity of the extramatrical mycelium of endomycorrhizal maize plants

Abstract

SUMMARYThe objective of this experiment was to quantify the extramatrical mycelium of the arbuscular mycorrhizal (AM) fungus Glomus etunicatum (Becker & Gerdemann) grown on maize (Zea mays L. var. Piranão) provided with various levels of phosphate fertilizer and harvested at 30, 60 and 90 days after planting (DAP). Total extramatrical mycelium (TEM) was extracted from soil using a modified membrane filtration method, followed by quantification using a grid intersection technique. Active extramatrical mycelium (AEM) proportion was determined using an enzymatic method which measured dehydrogenase activity by following iodonitrotetrazolium reduction. At low levels of added P, there was relatively less TEM than at high levels of added P, but the AEM proportion at low soil P availability was significantly greater than at high soil P.Index terms: arbuscular mycorrhizae, Glomus etunicatum, extramatrical hyphae, metabolically active mycelium.(

Phosphorus availability changes the internal and external endomycorrhizal colonization and affects symbiotic effectivenes

“…These results conflict with previous findings in which the AEM decreased with P increase (Nogueira & Cardoso, 2000) or remained stable (Cardoso-Filho et al, 1999;Nogueira & Cardoso, 2006) but corroborate another work in which the AEM increased, depending on the host plant (Melloni & Cardoso, 1999b). The amount of AEM, less than 2.0 m g -1 , was comparable to that found in citrus experiments (Melloni & Cardoso, 1999b), but lower than in experiments with maize (Cardoso-Filho et al, 1999), who found up to 12 m g -1 , depending on the P level and plant age. Probably the host plant exerts direct effect on the AEM production.…”

“…As a result, less metabolically active mycorrhizal mycelium would be formed. The amount of TEM found in this experiment was comparable to previous findings (Sylvia, 1988;Cardoso-Filho et al, 1999;Andrade et al, 2005;Nogueira & Cardoso, 2006). Other evaluations for hyphal lengths of filamentous fungi under natural conditions, however, reached even much higher values, up to more than 100 m cm -3 of soil (Miller et al, 1995).…”

“…Other evaluations for hyphal lengths of filamentous fungi under natural conditions, however, reached even much higher values, up to more than 100 m cm -3 of soil (Miller et al, 1995). Although the differentiation of mycorrhizal hyphae from that of other filamentous fungi in the soil is quite difficult (Sylvia, 1992), at least 35 to 70% of the total is expected to be from mycorrhizal fungi (Cardoso-Filho et al, 1999). Although at lower amount, some AEM and TEM were found in the control treatments (Figure 4A, 4B).…”

“…These results are exactly the opposite of others (CardosoFilho et al, 1999) in which the ratio between AEM to TEM decreased with P increase in the substrate. Many factors, such as initial P levels in the soil, P fixation in the soil, P sources and their solubilities, may affect the AEM/TEM proportion (Cardoso-Filho et al, 1999). Moreover, some factors such as host age and host and soil types probably also affect this proportion.…”

“…Andrade et al (2005) observed that increasing P levels reduced the mycorrhizal external hyphae. Nevertheless, several authors found exactly the opposite (Cardoso-Filho et al, 1999;Melloni & Cardoso, 1999b;Neumann & George, 2005). These contradictions may be caused by factors related to the host plant, endophyte, or environment.…”