Showing papers by "Catherine A. Gehring published in 1998"

Ectomycorrhizal fungal community structure of pinyon pines growing in two environmental extremes

Abstract: We used molecular techniques to examine the ectomycorrhizal fungal com- munity 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, repro- duction, 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 com- position were linked, as cluster analysis demonstrated greater similarity of fungal com- munities 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 Basid- iomycotina, whereas over half (mean 5 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 abun- dant sporocarps may not form ectomycorrhiza. This emphasizes the need to characterize the ectomycorrhizal communities formed on the plant roots themselves, rather than char- acterization based on sporocarps alone, particularly in arid environments. Finally, the dif- ferences 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.

Temporal variation in temperature and rainfall differentially affects ectomycorrhizal colonization at two contrasting sites

Abstract: summary We examined the roles that seasonal shifts in precipitation and temperature played in the ectomycorrhizal (ECM) colonization of pinyon pine (Pinus edulis Engelm.) at two contrasting sites in northern Arizona. Pinyons growing in ash and cinder soils experienced much greater water and nutrient stress than pinyons growing nearby in sandyloam soils. Over a one year period, we obtained monthly measurements of ECM colonization, root zone soil moisture and temperature, and air temperature and precipitation. Four major patterns emerged. Firstly, although climate as measured by ambient temperature and precipitation did not vary between the two sites, soil temperature was significantly higher and soil moisture significantly lower at the cinder site than at the sandy-loam site. Secondly, ECM colonization was significantly higher at the cinder site for 5 of 12 months. Thirdly, although nearly 70% of the variation in ECM colonization of pinyons growing in cinder soil was predicted by a combination of soil moisture and soil temperature, these same variables had little predictive power for pinyons growing in sandy-loam soils. Air temperature and precipitation were also significantly correlated with ECM colonization at the cinder site but not the sandy-loam site. Fourthly, a watering experiment showed that ECM colonization significantly increased with supplemental water at the cinder site, but not at the sandy-loam site. Thus, in two sites that did not dier in plant community or climate, ectomycorrhizas in cinder soils were far more sensitive to changes in moisture and temperature than ectomycorrhizas in sandy-loam soils.