Jan-Erik Nylund

5 Ergosterol Analysis as a Means of Quantifying Mycorrhizal Biomass

Publisher Summary This chapter describes the ergosterol analysis as a means of quantifying mycorrhizal biomass. A fundamental problem concerns the concept of fungal biomass: while the chitin content may be assumed to be roughly proportional to the total amount of cell wall, the amount of cell wall is certainly not proportional to the amount of cytoplasm, which is normally concentrated at the tips, leaving the bulk of the hyphae highly vacuolated. Another fungus-specific compound, ergosterol, is a principal component of membranes, and should therefore provide a better correlation with the metabolically active biomass of a fungus. The chapter briefly discusses development and current procedure technique. The chapter also evaluates the methods—namely, sensitivity and replicability, variation in ergosterol levels within the same species, and applications in mycorrhiza research. The basic shortcomings of the method are those of variation in the ergosterol content depending on growing conditions, and interspecies variation.

The regulation of mycorrhiza formation— carbohydrate and hormone theories reviewed

Two “classical” theories, both originating in Elias Melins laboratory in Uppsala, have tried to explain the regulation of ectomycorrhiza formation. The carbohydrate theory, formulated by E. Bjorkman in 1942, identifies root carbohydrate concentrations as regulatory, while these are in turn considered to be strongly influenced by plant mineral nutrition and light conditions. The hormone theory, expounded by V. Slankis in the 1960s, claims auxin of fungal origin to be the key regulator, influencing root carbohydrate status, while the fungus itself may, to some extent, be affected by mineral nutrition. Both theories have been subject to much discussion and have led to further work, without ever having been conclusively proven experimentally. Recent results in Uppsala and elsewhere have shed new light on several of the key issues. The development of research in this field since 1942 is critically reviewed in light of later data, and a unifying theory is sketched on the basis of E. Hacskaylos proposal from 1...

Does liquid fertilization affect fine root dynamics and lifespan of mycorrhizal short roots

We studied effects of nitrogen, other nutrients and water (liquid fertilization; LF) on fine root dynamics (production, mortality) and life span of mycorrhizal short roots in a Norway spruce stand, using minirhizotrons. Data were collected and analyzed during a two-year period at depths of 0–20 cm, 21–40 cm and 41–85 cm, six years after the start of treatment. Relative to control (C), root production was lower in LF plots at depth 0–20 cm. Root production increased significantly at depth 41–85 cm. Fine root mortality in LF plots was higher at all depths. Life span of mycorrhizal short roots in LF plots was significantly lower than C plots and at the end of the study no mycorrhizal short roots were alive. It is suggested that the water and nitrogen input lower longevity of mycorrhizal short roots and promote fine root production at deeper soil layers.

Seasonal variation in protein, ergosterol and chitin in five morphotypes of Pinus sylvestris L. ectomycorrhizae in a mature Swedish forest

Abstract Pine ectomycorrhizae were collected from bedrock and moraine sites in a mature Pinus sylvestris L. forest in the vicinity of Uppsala, Sweden, on four occasions over the period of a year. Ectomycorrhizae were examined microscopically and five characteristic types (Piloderma, tuberculate, Lactarius-like, Russula-like and an unidentified pink) were described and used for further biochemical assays. Total protein, ergosterol and chitin extractions were performed in sequence for each sample of distinct mycorrhizal morphotype. Differences between sites (bedrock moss vs moraine) from which the morphotypes originated were small, except for an increase in protein in Piloderma and tuberculate mycorrhizae on moraine sites in July and January. However, there were significant variations in protein and chitin concentrations and in the ergosterol-to-chitin ratio, both between seasons and mycorrhizal types. Protein concentrations were significantly higher in the winter samples for Piloderma, tuberculate and pink mycorrhizae and were at a minimum in the early summer. Chitin concentrations peaked in both early summer and winter for all morphotypes, significantly so for Piloderma and tuberculate mycorrhizae, but remained low during mid-summer and fall. Although the seasonal differences in ergosterol concentrations were small, a significant correlation was found between chitin and ergosterol for Piloderma mycorrhizae. For all morphotypes, the ergosterol-to-chitin ratio varied seasonally from low January values increasing to high values in October, the end of the season of maximum fungal growth. The small seasonal variation in ergosterol and development of the ergosterol-to-chitin ratio suggests that ergosterol remains a better indicator of vital fungal biomass than chitin or other available measures.

Effects of N-free fertilization on ectomycorrhiza community structure in Norway spruce stands in Southern Sweden

The application of N-free fertilizer (i.e. lime combined with nutrients such as P, Ca, K and Mg) has been suggested as one way of compensating for nitrogen-caused eutrophication and losses of base cations due to atmospheric pollution. To study the effects of such a treatment on mycorrhizal fungi, fine-root samples were collected from the LFH-layer in four Norway spruce stands in southern Sweden. One stand was part of a larger experiment (Skogaby) and had four replicates. It was fertilized twice in 1988–89 (P:K:Ca:Mg:S 48:43:218:46:75 kg ha-1), and sampling was carried out once yearly during 1991–93. The other three stands were fertilized once in 1988–89 (P:K:Ca:Mg:S|25:62:33:12:54 kg ha-1) and sampled in 1992.Ectomycorrhizal fine-roots were classified into morphotypes on the basis of the structure and colours of their external hyphae and fungal mantle. The fungal biomass was estimated in 1992 using ergosterol analysis. In Skogaby, N-free fertilizer had no apparent effects on fungal biomass or on the total number of ECM types. Similar results were obtained for the other three stands. Previously reported 50% reductions in sporocarp production on the fertilized plots at Skogaby can probably be explained by a decrease in carbon allocation to the roots and by a decline in the abundance of a single morphotype which accounted for 3% of the total number of root tips, but ca. 30% of the sporocarp biomass in the control plots in the present study. It is concluded that moderate levels of N-free fertilization are not likely to drastically affect the community structure of the dominating ectomycorrhizal fungi. This result should be interpreted with some caution, however, since it remains to be determined whether the fertilizer treatments affect the function of the nutrient-absorbing soil mycelium of the mycorrhizal fungi.

Ectomycorrhizae in coastal miombo woodland of Tanzania

SummaryEctomycorrhizae were found in root samples of the treesAfzelia quanzensis Welw. andBrachystegia spiciformis Benth. (Caesalpiniaceae), collected in the coastal miombo type woodland 50 km west of Dar-es-Salaam, Tanzania. Root nodules with a structure resembling that of nitrogen-fixing root nodules of other leguminous plants were observed in theA. quanzensis material. The climate of the locality is rather dry, and strongly seasonal. In the tropics, ectomycorrhizae have previously been found only in humid or rain forest climate zones.

Ectomycorrhiza and nitrogen effects on root IAA: results contrary to current theory

SummaryIndole-3-acetic acid (IAA) concentrations of mycorrhizal and non-mycorrhizal Scots pine roots under moderate and high-nitrogen nutrition were assayed using mass spectrometry with an internal standard. Contrary to current theory, IAA was lower in mycorrhizal roots than in the controls, and higher during highnitrogen nutrition.

Methods for Studying Species Composition of Mycorrhizal Fungal Communities in Ecological Studies and Environmental Monitoring

Descriptions of the species composition of mycorrhizal communities has up to recent times almost exclusively been made using fruitbody inventories (Vogt et al. 1991). However, recent studies (Dahlberg & Stenlid, 1994) have shown that sporocarp biomass constitutes only a few percent of the total (annual accumulative) biomass of ectomycorrhiza (Taylor and Alexander, 1990; Danielson and Visser, 1989). More importantly, sporocarps only poorly reflect the composition of the mycorrhizal community. Efforts have been made to use morphotyping of mycorrhizal roots in order to better describe ectomycorrhizal communities (ECM), but this has had only limited application and success (Egli et al., 1993). Compared to the advances of plant ecology, our knowledge of the fungal communities, both mycorrhizal and saprophytic, is rudimental.

Cell wall penetration and papilla formation in senescent cortical cells during ectomycorrhiza synthesis in vitro

Abstract During experiments on the synthesis of mycorrhizae in vitro, with the host Picea abies and Pinus sylvestris, and the ectomycorrhizal fungi Piloderma croceum and Pisolithus tinctorius, it was found that the fungi regularly produced intracellular penetration in senescent and dead cortical cells, while they were strictly intercellular in living parts of the cortex of short roots. Senescent host cells occasionally produced papillae as a response to infection. The penetration was considered to be enzymatic, in spite of the fact that no cell wall lytic enzymes were demonstrated in these fungi.

Root respiration data and minirhizotron observations conflict with root turnover estimates from sequential soil coring

Abstract The turnover of fine roots in northern coniferous forests has conventionally been assumed to be rapid, in line with results from sequential coring in the late 1970s in a Swedish Scots pine stand (SWECON project) where a rate of 7.4 year−1 was estimated. New quantifications of the root respiration in other stands motivated a recalculation of the SWECON data; an indirect estimation of the turnover rate was much slower, about 2.1 year−1. As a consequence, fine-root production is considered to be much lower than in previous estimates. Furthermore, direct observations of Norway spruce fine roots (<1 mm) from minirhizotrons in Sweden, including a site close to the SWECON site, indicated a slower estimate, with fine-root turnover rate of 0.9 year−1.