Ectomycorrhizal Sporophore Distributions in a Southeastern Appalachian Mixed Hardwood/Conifer Forest with Thickets of Rhododendron Maximum
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, Mycologia. 94(2), 2002, pp. 221-229. © 2002 by The Mycological Society of America, Lawrence, KS 66044-8897 Ectomycorrhizal sporophore distributions in a southeastern Appalachian mixed hardwood/conifer forest with thickets of Rhododendron maximum John F. WalkerI 1950, Phillips and Murdy 1985, Clinton et al 1994). Orson K. Miller, Jr. A previous study found that total ectomycorrhizal col Department of Biology, Virginia Polytechnic Institute onization of hemlock (Tsuga canadensis L.) seedlings and State University, Blacksburg, Virginia, 24061 was reduced inside of RmT, and that this depression of mycorrhization was correlated with decreased pro ductivity of the seedlings (Walker et al 1999). Fur Abstract: Sporophore abundance of putatively ec thermore, there was a shift in the proportion of ec tomycorrhizal fungi was compared in a mature mixed to mycorrhizal morpho types toward Cenococcum geo hardwood I conifer forest inside of ( +) versus outside phi/um Fr., a generalized, unspecialized, disturbance of (-) Rhododendmn maximum thickets (RmT). Ex tolerant ectomycobiont in RmTs. These observations perimental blocks (114 ha) were established inside beg the following question: Is the ectomycorrhizal of (3) and outside of (3) RmT at the Coweeta Hy fungus community negatively affected by the pres drologic Laboratory in Macon County, North Caro ence of RmT? lina, USA. Litter and organic layer substrates were The hypotheses addressed in this study were: (i) Is removed, composited and redistributed among 90 2 the assemblage of ectomycorrhizal fungi different X 2m plots within the blocks. Plots received either when examined inside of versus outside of RmT? (ii) +RmT or -RmT litter, and either +RmT or -RmT Are certain ectomycorrhizal fungus taxa indicators organic layers, or were unmanipulated for controls. with regard to RmT? (iii) Are there differences in the Sporophores of 67 putatively ectomycorrhizal species ability to re-colonizing manipulated soil substrates were collected from the blocks. Species diversity and from inside of versus outside of RmT among ecto overall community structure were similar inside of mycorrhizal fungus species? and (iv) Is there a strong and outside of RmTs, and no grouping was detected relationship between sporophore distributions and by substrate type. Differences within the ectomycor abiotic environmental parameters? rhizal fungus community were associated only weakly with environmental parameters, as indicated by or Sporophore sampling and ectomycorrhizal community dination. In light of these results, recent observations analyses.-Numerous studies have successfully used of ectomycorrhizal suppression and strong shifts in sporophore abundance (and or biomass) to assess ec the proportions of morpho types on tree seedlings in tomycorrhizal fungus community composition (e.g., side of RmT do not appear to be related to differ Miller 1982a, Bills et al 1986, Villeneuve et al 1989, ences in sporophore distributions. The changes in Nantel and Neumann 1992, Palmer et aI1994). The seedling mycobiont dominance in relation to RmT results produced by these studies appear to corre and the influence this has on seedling health should spond well with plausible explanations. For example, be examined directly from root tips. Nantel and Neumann (1992) found that the stron Key Words: ericoid mycorrhiza, fungal commu gest niche dimension of ectomycorrhizal communi nity, indicator species, ordination ties was stand composition, but within the range of a stand, fungal assemblages differed in relation to edaphic characteristics. However, we know of no pre vious studies comparing sporophore assemblages in INTRODUCrION relation to an ericoid subcanopy shrub in the south The important implications of spreading Rhododen-. eastern Appalachian Mountains. dron maximum L. thickets (RmT) in the southern Ap The relationship between sporophore abundance palachian Mountains are well documented (see Walk (or biomass) and the amount of mycelium below er et al 1999). Particularly, interest in this topic stems ground is dependent upon species-specific differenc from severe suppression of tree seedling regenera es in life history characteristics. Furthermore, sporo tion inside of RmT (e.g., Minkler 1941, Wahlenberg phore production in basidiomycetes can be influ enced strongly by environmental factors such as light Accepted for publication August 13, 200l. (Miller 1967). However, an allometric relationship I Corresponding author, Email: [email protected] between sporophore and mycelial biomass does ap- 221 222 MYCOLOGIA pear to hold for some species (Laiho 1970, Newell the experimental design can be found in Walker et al 1984, Cotter and Bills 1985) and for even a complete (1999) . community (Menge and Grand 1978). When a spo Sporophore sampling.-All sporophores of putative ectomy rophore is produced, we know that part of the indi corrhizal fungi (Miller 1983 and 1982b, Bills 1986, Molina vidual mycelial unit producing the sporophore is def et al 1992) were collected from the substrate manipulation initely present at that location. Sampling sporophore blocks throughout the fruiting season during 1996 and distributions therefore provides a valuable resource 1997. Collections were gathered once a week during all when evaluating ectomycorrhizal fungus communi peak fruiting periods. During periods of sparse sporophore ties. production, the plots were checked at least once every two weeks, and deteriorated, unidentifiable sporophores were It is known that sporophore abundance of a spe rarely observed. All sporophores were identified in the field cies is not tightly correlated with the abundance of or dried and examined microscopically in the laboratory in mycorrhizae in a given area (Gardes and Bruns 1996, cases when identification was ambiguous based solely on Dahlberg et al 1997). However, identifying ectomy macromorphology. Voucher collections, color photos of corrhizae from root cores, like sampling sporo fresh specimens, and detailed fresh descriptions were uti phores, provides only a point estimate of the pres lized for taxonomically difficult fungi. ence of an individual unit of mycelium below Analytical methods.-The abundance of sporophores pro ground. In addition, the process of mycorrhization, duced on a plot was estimated using the following catego like sporulation, is influenced by environmental and ries: (i) solitary, 1-2 sporophores, (ii) low abundance, ~5 biotic factors. Finally, root colonization can be vari sporophores, (iii) medium abundance, 6-10 sporophores, able seasonally. For these reasons, mycorrhizae pre iv) abundant, >10 sporophores. For all analyses, the plots sent in the root zone should still be compared with of the manipulation experiment were treated as sample sporophore samples for the purpose of identifying units, and the abundance class for each species/plot pair the pool of fungi potentially available to seedlings. was entered as a categorical variable (coded as 0 = absent With this in mind, an additional study is being con 1 = solitary, 2 = low abundance, 3 = medium abundance, ducted to examine distributions of ectomycorrhizae 4 = abundant). Abundance categories for all collection dates in the same year were summed prior to classifying the from root samples in relation to RmT gradients. abundance. For example, a taxon that produced two spo rophores one week and another three the next week on the same plot would be coded as medium abundance (category MATERIALS AND METHODS 1 + category 2 = category 3). Species that produced spo The study was conducted at the Coweeta Hydrologic Lab, rophores on an individual plot during both years of the on a site that is dominated by mature northern red oak study were placed in the higher abundance category plus (Quercus rubra L.), which also includes eastern hemlock one (e.g., 1996-category 2, 1997---category 2; coded as cat (Tsuga canadensis L.) and a variety of other taxa. All of the egory 3). blocks for this study were located on a single hillside with Categories were employed for abundance because the similar aspect and slope. It is likely that roots of individual types of analyses performed were designed for vegetation trees extend between the blocks; most of the tree species and depend on the abundance of individuals, not repro found on a particular block also occur in the forest sur ductive structures. Therefore use of absolute counts of spo rounding all the other blocks. Therefore, the ,composition rophores for abundance would over-represent the impor of the root zone in terms of canopy and subcanopy trees tance of taxa that produce copious numbers of small spo was treated as uniform across the blocks for this study. rophores. Because abundance was treated categorically, it is necessary to point out that the relative abundance values Plot layout and site preparation.-Three 1A ha blocks were presented in TABLE II are not based on absolute numbers. randomly located inside of dense RmTs (+ RmT) and three The groups used for all analyses were presence and ab blocks were randomly positioned outside of RmTs (-RmT). sence of RmT, and the substrate treatments applied to the Fifteen 2 X 2 m plots were systematically located within 2 X 2m plots. Substrate comparisons included all fungi col each block (90 plots total) and randomly assigned one of lected on the plots. Control plots and substrate treatment five treatments (3 plots/block X 6 blocks; 18 plots per treat plots were pooled for the inside versus outside ofRmT com