The growth of the extramatrical mycelium of ectomycorrhizal fungi and the growth response of Pinus sylvestris L.

Abstract

SUMMARYNine ectomycorrhizal fungi bave been studied for their effect on the growth oi Pinus syhestris L. seedlings. Tbe plants were kept growing for six months in root chambers witb a changeable volume. Al! seedlings were cultivated under conditions of low substrate nutrient concentrations and they became strongly infected within a short time. We demonstrated the existence of an important negative correlation between tbe extent of the fungal development and the growth of tbe host plants. In most studies tbis reduced growth is attributed to an energy drain by tbe fungus. Fungi producing large amounts of fungal tissue are more energy consuming than species wbicb only develop a sparse mycelium. However we suggest that also nitrogen acquisition by tbe plants might be altered by the fungus. Certain fungi probably retain a considerable amount of nitrogen for tbeir own growth, thus reducing the amount transported to the host plant. A decreased N transport finally results in a slower growtb. In tbis study the extramatrical mycelium in the rooting substrate was determined by wet oxidation and by nitrogen determination. This component of the fungal biomass showed the biggest variation a.inong the different tnycohiont species. Tbe results are discussed in relation to the culture technique employed.

Outcome of interactions between genets of two Suillus spp. and different Pinus sylvestris genotype combinations: identity and distribution of ectomycorrhizas and effects on early seedling growth in N‐limited nursery soil

“…This is likely, since the former genet possessed the highest in vitro growth rates, 3-6 and 2-9 mm d~-^ on MMN and HA respectively, in a comparison of genets from different Scots pineforest stands (Sen, 1990a). Considerable differences between extramatrical mycelium growth rates of different S. bovinus genets on the same pine species has been reported by Colpaert, Van Assche & Luijtens, (1992), and in vitro growth rates of other fungal species were shown to correlate with colonization success of Scots pine root in a related microcosm study (Erland & Finlay, 1992).…”

Susceptibility of ectomycorrhizal and non‐mycorrhizal Scots pine (Pinus sylvestris) seedlings to a generalist insect herbivore, Lygus rugulipennis, at two nitrogen availability levels

“…Wallander & Nylund (1991) found that mycorrhizal colonization reduced the sugar concentrations both in pine shoots and roots. Reductions in plant growth due to mycorrhizal formation have been recorded previously in young seedlings (Colpaert, Van Assche & Luijtens, 1992 ;Nylund & Wallander, 1989). Mycorrhizal infection did not improve N uptake into shoots.…”

“…This could imply that developing mycorrhizas retained N. Higher mycorrhizal infection level together with decreased root growth in mycorrhizal seedlings at lower N level (expt 2) support this suggestion. Colpaert et al (1992) concluded that the degree of N reduction in shoots after mycorrhizal establishment was species dependent and linked with the fungal biomass. Higher mycorrhizal infection in pine roots in expt 2 at lower N availability did not increase total phenolics concentration in roots.…”

Mycorrhizal fungi have a potential role in soil carbon storage under elevated CO2 and nitrogen deposition

“…This measure might be an appropriate index for nutrient transfer to the host plant (in AM fungi the presence of internal structures such as arbuscules implies transfer of P). However, because extraradical hyphae account for a large portion of fungal biomass (30-87% of ECM fungi ; Colpaert et al, 1992 ;, cited by Ekblad et al, 1995), direct measures of hyphal length are a valuable indicator of the mycorrhizal C pool (Rillig & Allen, 1999). Furthermore, root colonization does not necessarily increase linearly with hyphal biomass, and environmental changes might alter relationships between the two variables.…”