300 Wiseman and Wells: Soil Inoculum Potential and AMF Colonization Our observation of 22% mean AMF hyphal frequency for forest red maple growing on clay and clay–loam soils is within the range of values reported in these studies. There are also few published estimates of AMF coloniza- tion in nursery-grown and/or transplanted maples. Mean AMF hyphal frequencies of 29% to 52% were reported for red maples growing in undisturbed loam soil at a selection of Tennessee nurseries (Klingeman et al. 2002). Post- transplant AMF hyphal frequencies of 9% to 17% were reported in a variety of maple species (Morrison et al. 1993; Appleton et al. 2003; Wiseman, unpublished data). Our observation of 3% AMF hyphal frequency in landscape red maples is lower than previously reported values for trans- planted maples, but differences in plant material and soil type limit comparisons with previous work. AMF Inoculum Potential of Forest and Landscape Soils The results of the greenhouse bioassay did not support the hypothesis that AMF inoculum potential is greater in native forest soil than in developed landscape soil. The inoculum potential of landscape soil mixtures was more than twice that of forest soil mixtures. This result was unexpected given that forest maples possessed greater AMF colonization than landscape maples. A number of factors may have contrib- uted to this result. First, fine root length densities of soil cores from the landscape sites were higher than those of soil cores from the forest sites (Wiseman, personal observation). As a conse- quence, bioassay soil mixtures created from the landscape soils contained more root material than mixtures created from the forest soils. AMF-colonized fine roots are a significant source of inoculum. Higher root length densities may have enhanced the inoculum potential of the landscape soil mixtures, despite the fact that hyphal frequency was lower in landscape roots. Second, it has been amply demonstrated that the extent of root colonization decreases as soil P availability increases in a variety of soils and plant species (Smith and Read 1997). Maples may have been actively limiting the extent of their mycorrhizal colonization in response to higher P availability on the landscape sites. In this case, it is not surprising that colonization correlated poorly with soil inoculum potential. Third, soil from the developed sites was collected up to three years after landscape installation. It may be that the landscape soils were initially deficient in AMF propagules, but that inoculum potential recovered through time. Evidence suggests that AMF inoculum potential can be quite resilient in the face of significant soil disturbance: the AMF propagule density and colonization of herbaceous cover crops recovered within 2 years after reclamation of Ken- tucky surface mine sites (Gould et al. 1996). In a separate study, 98% of the sampling points in an artificial strip-mine ©2005 International Society of Arboriculture site possessed enough AMF propagules to establish coloni- zation in AMF-dependent species (Boerner et al. 1996). Finally, we cannot exclude the possibility that AMF species present in the landscape sites were more readily able to colonize corn, the greenhouse bioassay plant, than those from the forest sites. While most AMF species have a remarkably broad host range, it is possible that landscape inoculum was enriched in species that colonized turfgrass from nearby lawns and was therefore more likely to infect closely related corn than distantly related red maple. It is interesting to note, however, that many commercial AMF inoculants are also prepared using monocot host plants such as sudangrass and sorghum. CONCLUSION Although forest red maples were more extensively colonized than landscape maples, the AMF inoculum potential of forest soils was actually lower than that of landscape soils. The extent of red maple AMF colonization was not related to soil inoculum potential but instead was strongly corre- lated with soil pH. We suggest that red maple may permit greater AMF colonization in response to low P availability on acidic soils. The results reported here do not support the assertion that all developed landscape soils require amendment with commer- cial AMF inoculants. While the landscape soils in our study may have experienced a transient decline in inoculum potential following disturbance, AMF populations appear to have reestablished rapidly. It is possible that other types of disturbed landscapes – particularly those treated with soil fumigants such as methyl bromide – may benefit from artificial inoculation to enhance degraded AMF populations. Much more data on the quantity and quality of AMF propagules in a variety of land- scape soils is needed before arborists can adequately evaluate the necessity of AMF inoculation. LITERATURE CITED Appleton, B., J. Koci, S. French, M. Lestyan, and R. Harris. 2003. Mycorrhizal fungal inoculation of established street trees. J. Arboric. 29(2):107–110. Boerner, R.E., B.G. DeMars, and P.N. Leicht. 1996. Spatial patterns of mycorrhizal infectiveness of soils long a successional chronosequence. Mycorrhiza 6:79–90. Brundrett, M.C., and B. Kendrick. 1988. The mycorrhizal status, root anatomy, and phenology of plants in a sugar maple forest. Can. J. Bot. 66:1153–1173. Brundrett, M., G. Murase, and B. Kendrick. 1990. Comparative anatomy of roots and mycorrhizae of common Ontario trees. Can. J. Bot. 68:551–578. Coughlan, A.P., Y. Dalpé, L. Lapointe, and Yves Piché. 2000. Soil pH-induced changes in root colonization, diversity, and reproduction of symbiotic arbuscular mycorrhizal
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