SUMMARY

Spores of twenty species of arbuscular mycorrhizal fungi (AMF) were isolated from putting greens located mostly in the northeastern US and Canada. Sand-based greens that were one or two years old had lower populations of AMF (spore abundance and species richness) than did older greens. The most frequently isolated AMF species were Glomus etunicatum, G. intraradices and G. mosseae. Possible means by which the fungi invade the greens are discussed.

INTRODUCTION

Arbuscular mycorrhizal fungi (AMF, formerly called vesicular-arbuscular mycorrhizal fungi [VAMF]) form symbiotic relationships with the majority of vascular plants (Harley & Smith 1983, Harley & Harley 1987). Most research on AMF has focused on their association with crop species, although the role of AMF in natural communities has received increasing attention (e.g. Francis & Read 1994, 1995). In contrast, the species of AMF associated with amenity turfgrasses have received almost no study despite the knowledge that the fungi may confer a variety of benefits (e.g. improved mineral nutrition, drought tolerance and possible protection from root pathogenic nematodes and fungi) to host plants (Harley & Smith 1983, Nelsen 1987, Allen 1991, Little & Maun 1996). Although an estimated 84% of grass species form arbuscular mycorrhizae (AM) (Newman & Reddel 1987, Trappe 1987), it is generally believed that AMF are of relatively little importance to plants with fine roots and abundant root hairs such as turfgrasses, to cool-season (C3) grasses, and to plants grown under conditions of high fertility and maintenance (e.g. Baylis 1975, Harley & Smith 1983, Miller et al. 1987, Hetrick et al. 1988, 1990, 1991, Smiley et al. 1992). However, some fine-rooted grasses, including turf species, respond with increased growth (Hayman 1983, Petrovic 1984, Gemma et al. 1997) and enhanced drought resistance (Koske et al. 1995, Gemma et al. 1997) when inoculated with AMF. The perception of the minor importance of AMF to turfgrasses appears to have discouraged researchers from sampling highly maintained turfs such as those of putting greens.

Because AMF are common inhabitants of nearly all soils in which plants are growing, putting greens that contain soil (in contrast to those composed only of sand and peat) will possess significant populations of AMF that soon colonize the roots of the turf. Greens turf grown in such soils is highly mycorrhizal, and more than twenty one species of AMF have been isolated from turf cultivated in loam (Herskowitz & Estey 1978, Rhodes & Larsen 1981, Petrovic 1984, Murakoshi et al. 1996, Koske et al. 1997). Recently, there has been a trend towards constructing soilless putting greens using a combination of 80% sand and 20% milled peat (Bengeyfield 1989). The medium used in such sand greens typically is lacking in AMF (unpubl. observ.), and there has been no study of the presence or identity of AMF that eventually invade these sites.

During a larger study of the effects of mycorrhizae on turfgrasses, we were able to survey a variety of newly constructed and older sand greens and estimate the population of AMF therein.

MATERIALS AND METHODS

Soil samples from nineteen golf putting greens in the eastern United States and Canada and from one green in California (Table 1) were examined for populations of AMF. The samples originally had been sent to one of us (NJ) for diagnosis of various turf problems. Routinely, a single sample was obtained from each green. All greens were composed of Agrostis palustris L. 'Penncross' (creeping bentgrass) growing in sand-based mixes. Some greens appeared to meet the US Golf Association Green Section Specification (12-14 in. of a mix of sand (80%) and milled Sphagnum peat (20%) overlying layers of coarse sand and gravel) (Bengeyfield 1989), while other greens were composed of the sand-peat mix that had been amended with soil. Greens were assigned to one of three categories: one-year-old, two-year-old, and mature (greater than two years old), but samples were not classified by the amount or type of soil amendment in the sand-peat mix or whether they had been fumigated prior to planting. At each site, a 10 cm cup cutter was inserted to a depth of 10 cm, and a plug of soil and roots was removed. Spores of AMF were extracted by wet-sieving and sucrose centrifugation (Walker et al. 1982) from a 50-100 ml sub-sample taken from the lower 4 cm of the plug. Spores were mounted in a polyvinyl alcohol solution (Koske & Tessier 1983) on microslides and were identified by comparison with authenticated specimens.

The total number of AMF species in each sample (species richness) was used to calculate an average richness for greens of different ages. Differences were assessed for significance using ANOVA and Duncan's multiple range test. Spore abundance values (spores l^-1) were not normally distributed, and differences between different-aged greens were investigated using Wilcoxson's test based on rankings. Median spore abundance values are given in the text in place of means because of the skewed distribution of the spore count data.

RESULTS

Spores of twenty species of AMF were recovered from the greens (Table 2). Four samples (from one- and two-year-old greens) lacked spores. The most frequently isolated species were Glomus etunicatum (in 50% of the greens), G. intraradices (40%), and G. mosseae (30%). Some undescribed species were recovered, and these are referred to by their collection numbers in Table 2.

Spores of up to seven AMF species were isolated from individual samples, and the average richness for all 20 samples was 2.55 ± 2.18 (s.d.). The abundance of spores varied from 0 to 6500 l^-1 soil (median = 72). Young greens had significantly lower spore abundance and species richness than did mature greens (Fig. 1). In the mature greens, the single sample (green No. 15) taken from the anaerobic black layer (Waddington 1992) was notable in having very few spores (24 l^-1) and a species richness of 1.

FIGURE 1. Species richness and abundance of spores of arbuscular mycorrhizal fungi isolated from sand-based putting greens of different ages. The mean is used for species richness, and the median is used for spore abundance values. Sites sharing the same letter did not differ significantly (p=0.05).

DISCUSSION

Despite intensive management practices and the sand-peat composition of the growth medium, the sampled putting greens supported populations of AMF similar (both in spore abundance and species richness) to those reported from other managed, cultivated and natural sites (e.g. Molina et al. 1978, Koske 1987, An et al. 1993, Koske et al. 1997).

The low number of spores in the sample from the black layer of a mature green probably resulted from the anaerobic conditions associated with formation of the layer. Waterlogging and anaerobosis routinely are correlated with reduced populations of AMF in soils (Gerdemann 1968), but more samples need to be examined to determine the significance of our single observation for putting greens.

The low species richness and spore abundance of AMF in the youngest greens is consistent with observations from other studies of newly planted areas. Spore populations built up slowly in sand dunes when plantings of Ammophila breviligulata Fern. (American beachgrass ) were made in long-barren (AMF-free) sites (Koske & Gemma 1997). Spores were not recovered from dune sites that had been planted with Ammophila for less than one year. After one year, spores of three species were present in an abundance of 4.2 l^-1. More were present after two years (four species, 7.3 spores l^-1) and five years (seven species, 686 l^-1). Similar results were reported in sand dunes of Florida planted with the warm-season grass Uniola paniculata L. (Sylvia & Will 1988).

A previous study of two putting greens (of unknown age) constructed with a loamy sand in Ohio (Rhodes & Larsen 1981) revealed spores of three species of AMF present (G. macrocarpum Tul. & Tul., G. microcarpum Tul. & Tul., and G. tenue (Greenhall) Hall), none of which was isolated from our sites. Herskowitz & Estey (1978) isolated spores of G. mosseae and G. geosporum (Nicol. & Gerd.) Walker from unidentified turf at a university campus in Quebec, and G. etunicatum and an identified Glomus species were found in the rootzones of A. paulstris 'Penncross' in Japan (Murakoshi et al. 1996).

The origin of AMF in the greens is unclear. If the greens have been prepared according to USGA specification, they will have been fumigated prior to seeding (Bengeyfield 1989) and AMF will be absent. However, in those greens that were not fumigated and contained soil in the sand-peat mix, the fungi may have been incorporated into the green at the time of construction. Spores and hyphae of AMF are ubiquitous in nearly all natural soils and thus are present in sites adjacent to the sand greens. The spores are formed underground near the roots, and any event that carries soil onto the green from adjacent areas may introduce the fungal propagules (spores, hyphae, mycorrhizal root fragments). In addition to flooding and wind-blown soil, earthworms and other soil invertebrates (e.g. Rabatin & Stinner 1988, 1989, Reddell & Spain 1991, Gange 1993) as well as birds (McIlveen & Cole 1976) and human activities (e.g. aeration, the wheels of equipment, foot traffic) may carry soil onto the green, introducing AMF to the sites.

Another means by which AMF may colonise a green is through the lateral spread of hyphae from native soil at the margins of the green. The reported rate of spread by this means in agricultural soils is only a few centimetres per week (Powell 1979, Mosse et al. 1982, Warner & Mosse 1982), but in concert with greens maintenance practices it may be a significant contributor.

Previous field and glasshouse experiments with 'Penncross' turf grown in the sand-peat medium have clearly demonstrated that AMF can enhance the rate of seedling establishment and growth and confer significantly increased drought resistance (Petrovic 1984, Koske et al. 1995, 1997, Gemma et al. 1997) when turf is fertilised every week or two with a full nutrient solution containing P at 7.5-11 mg l^-1. Outside of this range of P or with monthly applications, however, these mycorrhizal benefits may be lost or replaced by deleterious effects (e.g. growth depression and increased sensitivity to drought). The loss of the growth response of mycorrhizal plants in the presence of both low or high P levels is well known in a variety of non-turf species (e.g. Harley & Smith 1983, Habte 1995).

In addition to soil P levels, whether AMF will be beneficial or not will be determined by the nature and amount of fungicides and pesticides that are applied. Numerous reports clearly document the ability of some of these materials to significantly depress the population and lessen the benefits conferred by AMF in a variety of non-turf species (e.g. Menge 1982, Trappe et al. 1984, Klough et al. 1987, Dodd & Jefferies 1989, Sukarno et al. 1993). It appears that periodic use of certain fungicides (e.g. benomyl) can eliminate mycorrhizal benefits (e.g. Fitter & Nichols 1988). Rhodes & Larsen (1981) reported that spring applications of fungicides reduced the colonisation of roots of A. palustris 'Toronto' by AMF in greens, although no effect on the quality of the turf was mentioned. Nevertheless, fungicides remain an essential component of any greens management programme.

Based on the widespread occurrence of AMF in putting greens and the capacity of AMF to benefit or even to harm greens turf, further investigations on the effects of fertilisation rates and pesticides seem desirable.

ACKNOWLEDGEMENTS

This study was supported by the Greens Research Section of the US Golf Association to whom we are grateful for assistance, interest, and guidance.

REFERENCES

Allen, M.F. (1991). The Ecology of Mycorrhizae. Cambridge Univ. Press.

An, Z.Q., Guo, B.Z. & Hendrix, J.W. (1993). Populations of spores and propagules of mycorrhizal fungi in relation to the life cycles of tall fescue and tobacco. Soil Biol. Biochem. 25, 813-817.

Baylis, G.T.S. (1975). The magnolioid mycorrhiza and mycotrophy in root systems derived from it. In: Endomycorrhizas (Eds. F.E. Sanders, B. Mosse & P.B. Tinker), Academic Press, London, pp. 373-389.

Bengeyfield, W.H. (Ed.) (1989). Specifications for a Method of Putting Green Construction. United States Golf Association, Far Hills, New Jersey. R=14838

Dodd, J.C. & Jefferies, P. (1989). Effects of fungicides on the vesicular-arbuscular mycorrhizal fungi associated with winter wheat (Triticum aestivum L.). Biol. Fert. Soils 7, 120-128.

Fitter, A.H. & Nichols, R. (1988). The use of benomyl to control infection by vesicular-arbuscular mycorrhizal fungi. New Phytol. 110, 210-206.

Francis, R. & Read, D.J. (1994). The contribution of mycorrhizal fungi to the determination of plant community structure. Pl. Soil 159, 11-25. R=44193

Francis, R. & Read, D.J. (1995). Mutualism and antagonism in the mycorrhizal symbioses, with special reference to impacts on plant community structure. Can. J. Bot. 73 (Suppl.), S1301-S1309.

Gange, A.C. (1993). Translocation of mycorrhizal fungi by earthworms during early succession. Soil Biol. Biochem. 25, 1021-1026.

Gemma, J.N., Koske, R.E., Roberts, E.M. & Jackson, N. (1997). Enhanced establish-ment of bentgrasses by arbuscular mycorrhizal fungi. J. Turfgrass Science 73, in this volume. R=44641

Gemma, J.N., Koske, R.E., Roberts, E.M., Jackson, N. & De Antonis, K.M. (1997). Mycorrhizal fungi enhance drought resistance in creeping bentgrass. J. Turfgrass Science 73, in this volume. R=44658

Gerdemann, J.W. (1968). Vesicular-arbuscular mycorrhiza and plant growth. Ann. Rev. Phytopathol. 6, 397-418.

Habte, M. (1995). Dependency of Cassisa siamea on vesicular arbuscular mycorrhizal fungi. J. Plant Nutr. 18, 2191-2198.

Harley, J.L. & Harley, E.L. (1987). A check-list of mycorrhiza in the British flora. New Phytol 105, 1-102.

Harley, J.L. & Smith, S.E. (1983). Mycorrhizal Symbiosis. Academic Press, London.

Hayman, D.S. (1983). The physiology of vesicular-arbuscular endomycorrhizal symbiosis. Can. J. Bot. 61, 944-963. R=6761

Herskowitz, J.M. & Estey, R.H. (1978). Endogonaceae from Quebec soils. Can. J. Bot. 56, 1095-1098.

Hetrick, B.A.D., Kitt, D.G. & Wilson, G.W.T. (1988). Mycorrhizal dependency and growth habit of warm-season and cool-season tallgrass prairie plants. Can. J. Bot. 66, 1376-1380. R=12635

Hetrick, B.A.D., Wilson, G.W.T. & Todd, T.C. (1990). Differential response of C₃ and C₄ grasses to mycorrhizal symbiosis, P fertilization, and soil microorganisms. Can. J. Bot. 68, 461-467. R=17874

Hetrick, B.A.D., Wilson, G.W.T. & Leslie, J.F. (1991). Root architecture of warm- and cool-season grasses: relationship to mycorrhizal dependence. Can. J. Bot. 69, 112-118. R=18543

Klough, J.L., Gianinazzi-Pearson, V. & Gianinazzi, S. (1987). Depressed metabolic activity of vesicular-arbuscular mycorrhizal fungi after fungicide applications. New Phytol. 106, 707-715.

Koske, R.E. (1987). Distribution of VA mycorrhizal fungi along a latitudinal temperature gradient. Mycologia 79, 55-68.

Koske, R.E. & Gemma, J.N. (1997). Mycorrhizae and succession in plantings of beachgrass in sand dunes. Amer. J. of Bot. 84, in press.

Koske, R.E., Gemma, J.N. & Jackson, N. (1995). Mycorrhizal fungi benefit putting greens. USGA Green Section Record 33 (6), 12-14. R=36353

Koske, R.E., Gemma, J.N. & Jackson, N. (1997). Mycorrhizal fungi associated with three species of turfgrass. Can. J. Bot. 75, in press. R=39847

Koske, R.E. & Tessier, B. (1983). A convenient, permanent slide mounting medium. Mycol. Soc. Am. Newsl. 34(2), 59.

Little, L.R. & Maun, M.A. 1996. The "Ammophila problem" revisited: a role for mycorrhizal fungi. J. Ecol. 84, 1-7.

McIlveen, W.D. & Cole, H. (1976). Spore dispersal of Endogonaceae by worms, ants, wasps and birds. Can. J. Bot. 54, 1486-1489.

Menge, J.A. (1982). Effect of some fumigants and fungicides on vesicular arbuscular fungi. Phytopathol. 72, 1125-1132.

Miller, R.M., Jarstfer, A.G. & Pillai, J.K. (1987). Biomass allocation in an Agropyron smithii-Glomus symbiosis. Amer. J. Bot. 74, 114-122.

Molina, R.J., Trappe, J.M. & Strickler, G.S. (1978). Mycorrhizal fungi associated with Festuca in the western United States and Canada. Can. J. Bot. 56, 1691-1695. R=3840

Mosse, B., Warner, A. & Clarke, C.A. (1982). Plant growth responses to vesicular-arbuscular mycorrhiza. XIII. Spread of an introduced VA endophyte in the field and residual growth effects of inoculation in the second year. New Phytol. 90, 521-528.

Murakoshi, T., Tojo, M., Ueda, T. & Ichitani, T. (1996). Two Glomus species from rhizosphere soil of a bent grass nursery in Japan. Mycoscience 37, 233-235.

Nelsen, C. R. (1987). The water relations of vesicular-arbuscular mycorrhizal systems. In: Ecophysiology of VA Mycorrhizal Plants (Ed. G. R. Safir), CRC Press, Boca Raton, Florida, pp. 71-91.

Newman, E.I. & Reddel, P. (1987). The distri-bution of mycorrhizas among families of vascular plants. New Phytol. 106, 745-751.

Petrovic, A.M. (1984). Endomycorrhizal fungi: friend or foe. Proceedings of the 53rd Annual Northeastern Turfgrass Conference, Univ. of Massachusetts, Amherst, Massachusetts, pp. 18-20. R=9891

Powell, C.L. (1979). Spread of mycorrhizal fungi through soil. NZ J. Agric. Res. 22, 335-339. R=6802

Rabatin, S. & Stinner, B.R. (1988). Indirect effects of interactions between VAM fungi and soil-inhabiting invertebrates on plant processes. Agric. Ecosys. Environ. 24, 135-146.

Rabatin, S. & Stinner, B.R. (1989). The significance of vesicular-arbuscular mycorrhizal fungal-soil invertebrate interactions in agroecosystems. Agric. Ecosys. Environ. 25, 195-204.

Reddell, P. & Spain, A.V. (1991). Earthworms as vectors of viable propagules of mycorrhizal fungi. Soil Biol. Biochem. 23, 767-774.

Rhodes, L.H. & Larsen, P.O. (1981). Effects of fungicides on mycorrhizal development of creeping bentgrass. Pl. Dis. 65, 145-147. R=1397

Smiley, R.W., Dernoeden, P.H. & Clarke, B.B. (1992). Compendium of Turfgrass Diseases, 2nd edition, APS Press, St. Paul, Minnesota, USA. R=21874

Sukarno, N., Smith, S E. & Scott, E.S. (1993). The effect of fungicides on vesicular-arbuscular mycorrhizal symbiosis. I. The effects on vesicular-arbuscular mycorrhizal fungi and plant growth. Pl. Soil 125, 139-147.

Sylvia, D.M. & Will, M.E. (1988). Establish-ment of vesicular-arbuscular mycorrhizal fungi and other microorganisms on a beach replenishment site in Florida. Appl. Environ. Microbiol. 54, 348-352.

Trappe, J.M. (1987). Phylogenetic and ecologic aspects of mycotrophy in the angiosperms from an evolutionary standpoint. In: Ecophysiology of VA Mycorrhizal Plants (Ed. G.R. Safir), CRC Press, Boca Raton, Florida, pp. 5-26.

Trappe, J.M., Molina, R. & Castellano, M. (1984). Reactions of mycorrhizal fungi and mycorrhiza formation to pesticides. Ann. Rev. Phytopathol. 22, 331-359.

Waddington, D. V. 1992. Soils, soil mixtures, and soil amendments. In: Turfgrass (Eds. D.V. Waddington, R.N. Carrow & R.C. Shearman), Amer. Soc. Agronomy, Madison, Wisconsin, pp. 331-383. R=26028

Walker, C., Mize, C.W. & McNabb, H.S. (1982). Populations of endogonaceous fungi at two locations in central Iowa. Can. J. Bot. 60, 2518-2529.

Warner, A. & Mosse, B. (1982). Factors affecting the spread of vesicular-arbuscular mycorrhizal fungi in soil. I. Root density. New Phytol. 90, 529-536. R=3473

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