Ectomycorrhizal Fungal Community Structure of Pinyon Pines Growing in Two Environmental Extremes

Abstract

We used molecular techniques to examine the ectomycorrhizal fungal community associated with pinyon pine (Pinus edulis) growing in two soil types in a semiarid region of northern Arizona: cinder soils low in nutrients and moisture, and sandy-loam soils with higher moisture and nutrient levels. Pinyon performance (e.g., growth, reproduction, water stress) has been shown to be markedly lower in cinder than in sandy-loam environments. Fungal community composition and richness were determined using RFLP (restriction fragment length polymorphism) analysis of ectomycorrhizal root tips collected from three sites within each soil type.Several patterns emerged from these analyses. First, communities in both cinder and sandy-loam soils were dominated by one or a few abundant ectomycorrhizal types, a species abundance pattern common to many plant and animal communities. Second, unlike the pattern for many other organisms, ectomycorrhizal fungal type (species) richness was not correlated with measures of ecosystem productivity such as soil nutrient and moisture levels; cinder and sandy-loam soils had similar numbers of ectomycorrhizal fungal types (range of 15-19 fungal types for both soil types). Third, soil type and fungal community composition were linked, as cluster analysis demonstrated greater similarity of fungal communities from sites within soil types than between them. Differential amplification using primers with enhanced specificity for basidiomycetes indicated that an average of 85% of the ectomycorrhiza found at the sandy-loam sites were members of the subphylum Basidiomycotina, whereas over half (mean ϭ 52%) of the ectomycorrhiza at the cinder sites were formed by members of other fungal groups, probably the subphylum Ascomycotina. Fourth, a preliminary survey of 14-45 ectomycorrhizal root tips from each of 20 trees at one cinder site indicated that trees were dominated by one or a few ectomycorrhizal RFLP types. However, the same RFLP types did not dominate on all trees, and dominant types showed considerable spatial variation. Fifth, the RFLP patterns of some fungal sporocarps matched those of ectomycorrhizal root tips, but many did not, indicating that many of the ectomycorrhizal fungi at these sites fruit infrequently, whereas other fungi with more abundant sporocarps may not form ectomycorrhiza. This emphasizes the need to characterize the ectomycorrhizal communities formed on the plant roots themselves, rather than characterization based on sporocarps alone, particularly in arid environments. Finally, the differences in ectomycorrhizal fungal communities we observed between soil types supported the concept that conserving fungal diversity requires conservation of host plant species over their entire range, not just typical sites. If future studies corroborate these patterns, our results suggest that abiotically stressful environments are important to include in these conservation efforts.

Influences of Established Trees on Mycorrhizas, Nutrition, and Growth of Quercus Rubra Seedlings

“…This is similar to the single-species dominance of infection described in Pinus edulis Engelm. by Gehring et al (1998). Near-Quercus seedlings generally had lower Berger-Parker index values than seedlings in the other two treatments.…”

Interactions With Juniper Alter Pinyon Pine Ectomycorrhizal Fungal Communities

“…The soils were composed of basaltic ash, cinders, and lava flows and belong in the U.S. Department of Agriculture Soil Taxonomic Sub-Group of Typic Ustorthents. These soils are relatively low in nutrients and water storage capacity (Gehring et al 1998). The mean annual precipitation in Arizona for the period 1998-2000 and 2001-2003 was 31.7 cm and 25.0 cm, respectively.…”

“…Prior to trenching (July 2000) and again two years after trenching (August 2002), we collected 50-80 root tips, at a depth of 5-20 cm on the west aspect of the drip line of each of the trenched (n ϭ 30 trees) and control (n ϭ 30) trees at least 1 m from the trench line. We standardized sampling because aspect and crown location can affect ectomycorrhizal (EM) community composition (Gehring et al 1998). Roots were taken back to the laboratory and scored for percentage EM colonization using the methods of Gehring and Whitham (1991).…”

“…The DNA from two to three of the saved root tips of each morphotype per tree was extracted and the internal transcribed spacer (ITS) region of the fungal genome, located between the 18S and 28S rRNA, was amplified using PCR (polymerase chain reaction) with the ITS1F and ITS4 primer pair (Gardes and Bruns 1993). Restriction-fragmentlength polymorphism (RFLP) data were obtained following the methods of Gehring et al (1998). The amplified ITS region was characterized using restriction enzyme digestion with HinfI and MboI, which have been used successfully to discriminate among fungal species in P. edulis (Gehring et al 1998, Swaty et al 2004.…”

“…First, there is little potential for aboveground interactions because closed canopies rarely form. Second, the soils of many pinyon-juniper woodland sites are nutrient poor and have low water-holding capacity, features that could intensify belowground interactions such as competition (Gehring et al 1998). Third, these woodlands have experienced severe drought conditions in recent years, potentially exacerbating the effects of belowground interactions.…”