Báo cáo lâm nghiệp: "Interrelationship between vitality of ectomycorrhizae and occurrence of microfungi"

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Interrelationship between vitality of ectomycorrhizae and occurrence of microfungi F. Oberwinkler I. Kottke T. Ritter, G. Weber, I. Haug, Botanik und Auf der Universitat Tubingen, Institut fur Morgenstelle Mykologie, Biologie I, Spezielle 1, D-7400 Tubingen, F.R.G. slightly gleyic brown earth of red sandstone, a Introduction stand of 70-80 yr old Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) In connection with forest decline, root-soil is located. One part of the area was limed in interactions are frequently discussed. Up 1975 with 30 dtlha ’Hiittenkalk’. On the limed to now, it has been difficult to classify the plot, trees are generally healthy, whereas on the unlimed plot, severe yellowing and loss of vitality of ectomycorrhizae and less atten- needles can be observed. A characterization of tion has been paid to the microfungal flora the limed and unlimed plots is given in Table I. associated with the roots. Thus occurrence and species diversity of microfungi of the rhizoplane and the interior of the mycorrhi- Determination of mycorrhizal vitality zae have been investigated in two plots, Root samples were taken strictly related to de- which differed in their degree of canopy fined trees, i.e., one representative silver fir (A. damage. In parallel studies, the vitality of alba Mill.) and one representative Norway spruce (P abies (L.) Karst.) from each plot at ectomycorrhizae was evaluated by vital irregular time intervals between May 1985 and staining with fluorescein diacetate (FDA). August 1987. Vitality of ectomycorrhizae was ascertained under the fluorescence microscope after vital Materials and Methods staining with FDA. Since only living cells give a light green fluorescent response to FDA-vital staining (Rotman and Papermaster, 1966; Zieg- The sites ler et al., 1975), this technique provides detailed The testing ground Ziefle is situated in the information about the physiological status northern Black Forest near Alpirsbach. On
of ectomycorrhizae (Ritter et al., 1986). Based Results vital staining with FDA, 5 stages of ectomy- on corrhizal vitality could be differentiated (see below). The vitality of the mycorrhizae of dam- Vitality of mycorrhizae aged and healthy trees was compared by ana- lyzing a random sample of 120-150 mycorrhizal root tips per tree and date of sampling (see Stages of ectomycorrhizal vitality (Fig. 1) below). Stage 1. Entirely active mycorrhizae (+++): all regions (hyphal sheath, cortex including the Hartig net, vascular cylinder Isolation of microfungi and meristematic region) are active. Mycorrhizal roots of spruce were collected from the upper humus layer beneath the surface litter Stage 2. Largely active mycorrhizae (++): of the 2 sites at monthly intervals, during the 2 the outer cortical cells and a larger part of yr investigation period. Suitable sections of the hyphal sheath have lost vitality. The mycorrhizae were excised and subjected to a activity of the hiyphal sheath is preserved serial washing procedure, adapted from the around the apical meristem. methods of Harley and Waid (1955) and Gams and Domsch (1967}. For the isolation of fungi Stage 3. Mycorrhizae of reduced activity from the inner root, surface sterilization after (+): living cells only in the vascular cylin- washing was used. Root pieces were then plat- ed on MEA (2% malt extract-agar with 500 ppm der and the meristematic region. Dead of streptomycin sulfate) and CMC-agar cells of the cortex, as well as the hyphal (S6derstr6m and B 1978). The plates were dth, g sheath, are frequently colonized intracellu- incubated at 15°C for 2 wk in the dark, and for larly by fungi. at least another 4-6 wk at 21 °C in light. As fun- gal colonies became established, inocula were Stage 4. Dying mycorrhizae (+/-): de- transferred to suitable nutrient media and incu- of the vascular and meristematic crease bated at 21 °C for subsequent determination. at the apex and then tissues, starting back to the basis of the rootlet. moving Infection tests with spruce seedlings Dead mycorrhizae (-): all root Stage 5. cells intracellularly colonized by fungi. are Infection tests were carried out with spruce (P. abies (L.) Karst.) grown sterilely in Petri dishes on filter paper (for a detailed description, see Vitality of the m,ycorrhizal systems of trees Haug et al., 1988). Three week old spruce seedlings were inoculated with a fungus, Cryp- from the limed zind the unlimed plots tosporiopsis abietina Petrak, which was isolated Significant differences in mycorrhizal vitali- earlier with high frequency from surface-steri- lized roots. The experiment lasted 6 mo. observed between trees from the ty were
species number unlimed and the limed plots (Fig. 2). On Differences in the unlimed plot (Fig. 2b, d), the percent- From the mycorrhizae of the quite healthy age of ectomycorrhizae with full vitality spruces on the limed plot, more species (stage 1 ) as well as the percentage of were isolated than from the mycorrhizae dying and dead mycorrhizae (stages 4 of the heavily damaged spruces on the and 5) were higher compared to the limed non-limed plot (Fig. 3). plot (Fig. 2a, c). However, mycorrhizae of medium vitality (stages 2 and 3) could be Differences in species composition detected more often on the limed plot. The highest amounts of dying and dead very Differences in the flora from microfungal fine roots were found in the extremely root surfaces of spruce on the 2 plots damaged Norway spruce from the unlimed occurred not only in species number, but plot (Fig. 2b). also in species composition. A comparison of the dominant species from the 2 stands showed that, on mycorrhizae of the da- maged trees, 2 fungal species were do- Microfungi from the rhizoplane minant. Among them, certain strains are known as root pathogens, Cylindrocarpon destructans (Zinssm.) Scholten and Tri- Forty-four fungal species, belonging to 2 5 choderma viride Pers. ex Gray. These two isolated from the rhizo- were genera, species were also present in the rhizo- planes of mycorrhizae. The most abun- planes from the limed stand, but at a lower dant genera were Trichoderma, Cylindro- frequency (Fig. 4). carpon, Penicillium, Oidiodendron, Thy- sanophora and the form genus Mycelium Remarkable at this limed stand is the radicis atrovirens. dominance of two saprobe species,
septate and showed simple pores with Woronin bodies. They could thus be identified as Ascomycetes. No intracellular infection was found in mycorrhizae with light-colored root tips and living hyphal mantles. Isolation of pathogenic fungi and infection tests From 96 surface-sterilized mycorrhizae from the unlimed plot, 17 isolates of fungi with septate hyphae were made. Two spe- cies could be distinguished: Mycelium radicis atrovirens Melin and Cryptospo- riopsis abietina Petrak. Infection tests with Cryptosporiopsi,s abietina and spruce seedlings revealed severe infection of cor- tex and vascular tissues, resulting in a decline of the spruce seedlings. Quite Oidiodendron aff. griseum Robak and often the cell structure of cortex and vas- Thysanophora penicilloides (Roum.) Ken- cular tissues was destroyed and large drick, which showed an antagonistic be- areas of the roots were consumed by a havior against various Cylindrocarpon dense network of hyphae. Cryptospo- destructans strains in paired culture test riopsis abietina can thus be considered to series. be responsible for the intracellular infec- tion of the vascular tissue of the investi- gated spruce roots from the Ziefle site. the Microfungi in mycorrhizae Infection of mycorrhizae of the unlimed spruce stand (for figures see Haug et al., 1988) Examination of mycorrhizae with dark roots tips from the unlimed spruce stand by light and electron microscopy revealed a heavy intracellular fungal infection of cortex cells, vascular tissue and meristem. Hyphal mantle, cortex and Hartig net of infected mycorrhizae were dead. Within the vascular tissue, different stages of infection could be detected. At an early stage, only a few cells contained several hyphae. At a more advanced stage, hol- low spaces with large amounts of mycelia were found, surrounded by cells filled with tannins. The intracellular hyphae were
Discussion References In mature forest stands, only small incre- E. (1987) Elementgehalte im boden Aldinger ments of fine root biomass can be ob- und in nadein verschieden stark geschadigter fichten-tannen-bestdnde auf praxiskalkungsfla- served because, in the annual balance, chen im buntsandstein-schwarzwald. Disserta- fine root loss due to normal aging and fine tion Freiburg root production are almost in equilibrium Gams W. & Dornsch K.H. (1967) Beitrage zur (Grier et al., 1980). In the actual paper, the anwendung der bodenwaschtechnik fur die iso- dynamic equilibrium between young and lierung von bodenpilzen. Arch. Mikrobiol. 58, senescent fine roots is illustrated by the 134-144 distribution of the 5 stages of ectomycor- Grier C.C., Vogt K.A., Keyes M.R. & Edmonds rhizal vitality, since these stages represent R.L. (1980) Biomass distribution and above- phases in the process of aging of mycor- and below-ground production in young and mature Abies amabilis zone ecosystems of the rhizae (Ritter et al., 1989). The low per- Washington cascades. Can. J. For. Res. 11, centage of mycorrhizae of medium vitality 155-167 (’++’, ’+’) and the higher percentage of Harley J.L. & Waid J.S. (1955) A method of stu- dying and dead mycorrhizae (’+/-’, ’-’) dying active mycelia on living roots and other from trees on the unlimed plot indicate a surfaces in the soil. Trans. Br Mycol. Soc. 38, more rapid ageing and a higher turnover 104-118 rate of very fine roots of these trees. In Weber G. & Oberwinkler F. (1988) Haug I., contrast, from trees on the limed plot, the Intracellular infection by fungi in mycorrhizae of vascular and the meristematic tissues of damaged spruce trees. Eur. J. For. Pathol. 18, 112-120 mycorrhizae retained vitality for a relatively long time after the hyphal sheath (’++’) or Oberwinkler F. (1986) Ritter T., Kottke I. & the hyphal sheath and the Hartig net (’+’) mykorrhizen durch Nachweis der vitalitdt von FDA-vitalfluorochromierung. Biol. Zeit 16, 179- had died. 185 The increase of dying and dead mycor- Ritter T., Weber G., Kottke 1. & Oberwindkler F. rhizae (stages 4 and 5) was paralleled by (1989) Zur mykorrhizaentwicklung von fichten an increase of pathogenic fungal species und tannen in gesch5digten bestanden. Biol. from the rhizoplanes or inner root on the Zeit 19, 9-155 unlimed plot. One interpretation of this fact Rotman B. & Papermaster B.W. (1966) Mem- might be that, on the unlimed plot, the pro- brane properties of living mammalian cells as tective effect of mycorrhizae is reduced. studied by enzymatic hydrolysis of fluorogenic esters. Proc. Natl. Acad. Sci. USA 55, 134-141 As a result, pathogenic fungi can establish themselves more easily on the rhizoplane, S6derstr6m B.E. & B59th E. Soil fungi in (1978) three Swedish coniferous forests. Holartic resulting in an increased penetration of the Ecol. 1, 62-72 root tissue. Thus it can be concluded that Ziegler G.B., Ziegler E. & Witzenhausen R. there exists an interrelationship between (1975) Nachweis der stoffwechselaktivit von t d the vitality of the mycorrhizae, the root mikroorganismen durch vital-fluorochromierung mycoflora and the occurrence of patho- mit 3’,6’-diacetylfluorescein. Zentralbl. Bakte- gens of the rhizoplane and the interior of riol. Parasitenkd. Infektionskr. Hyg. Abt. 1 Orig. mycorrhizae. A 230, 252-264