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Selection on quantitative traits by heterogeneous climatic conditions can lead to substantial trait variation across a species range. In the context of rapidly changing environments, however, it is equally important to understand selection on trait plasticity. To evaluate the role of selection in driving divergences in traits and their associated plasticities within a widespread species, we compared molecular and quantitative trait variation in Populus fremontii (Fremont cottonwood), a foundation riparian distributed throughout Arizona. Using SNP data and genotypes from 16 populations reciprocally planted in three common gardens, we first performed QST‐FST analyses to detect selection on traits and trait plasticity. We then explored the environmental drivers of selection using trait‐climate and plasticity‐climate regressions. Three major findings emerged: (1) There was significant genetic variation in traits expressed in each of the common gardens and in the phenotypic plasticity of traits across gardens, both of which were heritable. (2) Based on QST‐FST comparisons, there was evidence of selection in all traits measured; however, this result varied from no effect in one garden to highly significant in another, indicating that detection of past selection is environmentally dependent. We also found strong evidence of divergent selection on plasticity across environments for two traits. (3) Traits and/or their plasticity were often correlated with population source climate (R2 up to.77 and.66, respectively). These results suggest that steep climate gradients across the Southwest have played a major role in shaping the evolution of divergent phenotypic responses in populations and genotypes now experiencing climate change. [ABSTRACT FROM AUTHOR]

Restoration treatments in Bromus tectorum (cheatgrass)‐invaded sagebrush habitat have often produced poor results. This is perhaps due to multifaceted ecological changes associated with cheatgrass invasion like reduced water availability, altered nutrient availability, and shifts in soil microbial communities. We tested whether suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes improved restoration success. We conducted field experiments in Idaho, Utah, and Arizona where we transplanted seedlings of Artemisia tridentata ssp. tridentata (basin big sagebrush) and Elymus elymoides (squirreltail). Growth and survivorship of both species were higher in sites with greater precipitation and lower cheatgrass abundance. Significant nutrient modification effects were seen in Utah, where cheatgrass abundance was highest and soil nutrients were most limiting. In Utah, we observed an increase of 14% in survivorship for squirreltail in response to carbon addition, and 119% increase in growth of sagebrush with phosphorus addition. Inoculating plants with sagebrush rhizosphere soil or a commercial arbuscular mycorrhiza at the time of planting did not significantly affect growth, survivorship, arbuscular mycorrhizal fungi colonization, or extraradical mycorrhizal hyphae length for either plant species. The largest effects on seedling growth (+384%) and survivorship (+262%) were observed in response to the suppression of cheatgrass using a weed barrier cloth and associated with increased water availability. Interactions between suppressing cheatgrass, altering nutrient availability, and inoculating with soil microbes were not significant. Direct reduction of cheatgrass was shown to be more effective than targeting soil legacy effects associated with cheatgrass with regards to restoration outplanting success. [ABSTRACT FROM AUTHOR]

The article presents a study on the effects of water, nitrogen cycling and forest thinning and burning on soil nitrogen pools and fluxes in ponderosa pine forests near Flagstaff, Arizona. The study used a nitrogen-15 depleted fertilizer and documented the distribution of nitrogen in soil N pools. It was found that thinning and burning in ponderosa pine forests will not increase resistance to changes in soil N dynamics resulting from increased atmospheric N deposition or increased precipitation due to climatic change.

Journal of Applied Ecology (2004) 41, 379 –388 [ABSTRACT FROM AUTHOR]

• We measured post-fire regenerating ponderosa pine growth and niche attributes. • Seedling diameter and terminal leader growth were higher in burned than unburned plots. • Seedling growth varied by overstory (−), soil PO 4 −3 (+), and coarse wood cover (+). • Cover of forbs (+), mountain muhly (+), and squirreltail (−) were associated with pine growth. Several recent studies have documented how fire severity affects the density and spatial patterns of tree regeneration in western North American ponderosa pine forests. However, less is known about the effects of fire severity on fine-scale tree regeneration niche attributes such as understory plant composition and cover, surface fuel abundance, and soil properties, or how these attributes in turn affect regenerating ponderosa pine growth. Using 1-m2 plots centered on 360 ponderosa pine seedlings that regenerated naturally after the Pumpkin Fire in 2000 in Arizona, we quantified regeneration niche attributes 13 years post-fire and measured their associations with seedling growth 11–16 years post-fire. Plots were established in a) unburned, b) moderate-severity, and two types of high-severity (100% tree mortality) burns, either c) adjacent to residual live forest edges (high-severity edge plots), or d) >200 m from any residual live trees (high-severity interior plots). We found that all burned plots had greater understory plant species richness, percent cover of forbs, exotic plants and coarse wood, as well as higher soil pH, sand and gravel content, and lower soil clay content compared to unburned plots. High-severity burn plots had the greatest total understory plant and shrub cover, the most herbaceous fine fuel biomass, and tended to have the highest soil nitrogen content compared to other burn severity classes. Ponderosa pine growth (i.e., stem diameter at root collar (DRC) and length of terminal leader) was lowest in the unburned compared to burned plots, and ponderosa pine terminal leader growth was consistently greater in the high-severity edge plots compared to other severities. Finally, niche characteristics such as overstory tree canopy cover (−), soil phosphate (+), and cover of coarse wood (+), forbs (+), and the native grasses, mountain muhly (+) and squirreltail (−), were important explanatory variables of ponderosa pine growth. Exotic plant cover did not have a negative association with ponderosa pine growth. These results suggest that if ponderosa pine seeds can disperse and germinate, and if seedlings can survive the first few critical years after germination, then low overstory canopy cover and abundant forbs or coarse wood may be associated with increased growth rates. Alternatively, forbs may be responding to the same site benefits as the seedling; and abundant forbs, coarse wood, and fine fuels might also put seedlings at increased risk of mortality from subsequent fire, at least until they are taller and more fire resistant. [ABSTRACT FROM AUTHOR]

Over the past three decades, wildfires in southwestern US ponderosa pine (Pinus ponderosa Lawson & C. Lawson) forests have increased in size and severity. These wildfires can remove large, contiguous patches of mature forests, alter dominant plant communities and increase woody debris, potentially altering fungal community composition. Additionally, post-fire conditions may shift dominant fungal functional groups from plant-symbiotic ectomycorrhizal (EM) fungi to more decomposer saprotrophic fungi. We investigated the long-term (13 years post-wildfire) effect of fire severity on 1) fungal sporocarp density, functional groups and community composition and 2) EM colonization and community composition from naturally regenerating ponderosa pine seedlings on the Pumpkin Fire that burned in 2000 in Arizona, USA. Plots were located in four burn severity classes: unburned, moderate-severity, and two high-severity (defined as 100% tree mortality) classes, either adjacent to residual live forest edges (edge plots), or >200 m from any residual live trees (interior plots). We found that high-severity burn plots had a unique sporocarp community composition, and a shift in dominant sporocarp functional groups, with 5–13 times lower EM sporocarp densities, and 4–7 times lower EM sporocarp species richness compared to unburned and moderate-severity plots. In contrast, saprotrophic sporocarp densities and richness were similar among burn severity classes, even with the large amount of coarse wood in the high-severity burn patches. Regenerating ponderosa pine seedlings had similar EM colonization and richness among severity classes, yet high-severity interior plots had a different community composition and a lower relative abundance of EM species compared to moderate-severity burn plots. Taken together, our results suggest that large patches of high-severity fire have long-term consequences for both EM sporocarp and root tip communities. Because EM fungal species vary in function, the limited species pool available in interior high-severity burn patches may influence pine recovery. • High-severity burns had a unique sporocarp community composition. • EM sporocarp densities were 5–13 times lower on high-severity vs. moderate burns. • Saprotrophic sporocarp density and richness were similar among treatments. • Pine seedlings >200 m from live trees had a different EM community composition. [ABSTRACT FROM AUTHOR]

Species of the genus Geopora are important ectomycorrhizal associates that can dominate the communities of some plant taxa, such as pinyon pine (Pinus edulis), a widespread tree of the western United States. Several members of the genus Geopora are known only from ectomycorrhizal root tips and thus have not been described formally. The sporocarps of some Geopora species occur infrequently because they depend on wet years for sporulation. In addition, Geopora sporocarps can be small and may be hypogeous at some developmental stage, limiting the opportunities for describing their morphology. Using molecular and morphological data, we have described a new species of fungus, Geopora pinyonensis, which produced ascocarps after unusually high precipitation at a northern Arizona site in summer 2012. Based on analysis of the ITS and nuLSU regions of the rDNA, G pinyonensis is a new species of Geopora. It has small sporocarps and ascospores relative to other members of the genus; however, these morphological features overlap with other species. Using rDNA data from sporocarps and ectomycorrhizal root tips, we show that the sporocarps correspond to an abundant species of ectomycorrhizal fungus associated with pinyon pines that is increasing in abundance in drought-affected landscapes and may promote drought tolerance., (© 2014 by The Mycological Society of America.)