MOLECULAR DIVERSITY OF FOLIAR FUNGAL ENDOPHYTES IN RELATION TO DEFENSE STRATEGIES AND DISEASE IN WHITEBARK PINE

An invasive fungal pathogen, Cronartium ribicola (the causative agent of white pine blister rust) infects and kills whitebark pine (Pinus albicaulis) throughout the western US. Blister rust has decreased whitebark pine populations by over 90% in some areas. Whitebark pine, a keystone species, has been proposed for listing under the Endangered Species Act in the U.S., and the loss of this conifer is predicted to have severe impacts on forest composition and function in high elevations. Hundreds of asymptomatic fungal species live inside whitebark pine tissue, and recent studies suggest that these fungi can influence the frequency and severity of pathogens such C. ribicola. I used molecular methods to characterize the fungal community in whitebark pine seedlings from 21 half-sibling seed families, sourced throughout the Pacific Northwest, and grown in a common garden. I characterized endophyte communities before and after experimental inoculation with blister rust and compared community composition in susceptible vs. resistant seedlings. I also explored the defensive chemistry of these same seedlings in relation to the fungal community and overall disease severity. Seed family was the biggest driver of endophyte community composition in our common garden, but I also observed shifts in fungal communities in response to blister rust infection. Seed family identity also influenced defensive chemistry, with terpene concentration differing in resistant and susceptible seedlings. In addition, both defensive chemistry and endophyte community were correlated with characteristics of disease severity. Endophyte communities and defensive chemistry in whitebark pine that can predict disease severity may act as biomarkers of disease resistance for future breeding programs. These results suggest that the resistance to white pine blister rust observed in natural whitebark pine populations may be a combination of genetics, endophytes, and terpene composition in needle tissue, where initial interactions between the pathogen endophytes, the host take place

Combining biogeographical approaches to advance invasion ecology and methodology

Understanding the causes of plant invasions requires that parallel field studies are conducted in the native and introduced ranges to elucidate how biogeographical shifts alter the individual performance, population success and community-level impacts of invading plants. Three primary methods deployed in in situ biogeographical studies are directed surveys, where researchers seek out populations of target species, randomized surveys and field experiments. Despite the importance of these approaches for advancing biogeographical research, their relative merits have not been evaluated. We concurrently deployed directed surveys, randomized surveys and in situ field experiments for studying six grassland plant species in the native and introduced ranges. Metrics included plant size, fecundity, recruitment, abundance and invader impact, as well as soil properties and root associations with putative fungal mutualists and pathogens. Consistent with key invasion hypotheses, Bromus tectorum experienced increased size and fecundity in the introduced range linked to population increases and significant invader impacts, along with altered fungal associations. However, performance differences did not predict population increases and invader impacts across species. A notable finding was that disturbance facilitated greater recruitment in the introduced range for most species, thereby playing a crucial, though underappreciated, role in driving invader success. Directed surveys consistently generated information on plant performance and fungal associations. However, soil sampling suggested that directed surveys may have been biased towards disturbed conditions for half the species. Randomized surveys generated robust data for population comparisons and impact, but generally failed to produce performance metrics for species that were uncommon or flowered outside the peak sampling window. Field experiments controlled for bias and confounding factors and provided rare information on recruitment and disturbance effects, but poor recruitment in the native range and ethical constraints on growing invaders in the introduced range hindered comparisons of performance and plant–fungal interactions. Synthesis. Each method had strengths and weaknesses. However, when combined they provided complementary information to paint the most complete biogeographical picture to date for several introduced plants. We propose a hybrid approach to optimize biogeographical studies.Fil: Pearson, Dean. University of Montana; Estados Unidos. United States Forest Service. Rocky Mountain Research Station; ArgentinaFil: Eren, Ozkan. Adnan Menderes Universitesi; TurquíaFil: Ortega, Yvette K.. United States Forest Service. Rocky Mountain Research Station; ArgentinaFil: Hierro, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Karakuş, Birsen. Adnan Menderes Universitesi; TurquíaFil: Kala, Sascha. University of Montana; Estados UnidosFil: Bullington, Lorinda. Mpg Ranch; Estados UnidosFil: Lekberg, Ylva. University of Montana; Estados Unidos. Mpg Ranch; Estados Unido

Effects of Short- and Long-Term Variation in Resource Conditions on Soil Fungal Communities and Plant Responses to Soil Biota

Soil biota can strongly influence plant performance with effects ranging from negative to positive. However, shifts in resource availability can influence plant responses, with soil pathogens having stronger negative effects in high-resource environments and soil mutualists, such as arbuscular mycorrhizal fungi (AMF), having stronger positive effects in low-resource environments. Yet the relative importance of long-term vs. short-term variation in resources on soil biota and plant responses is not well-known. To assess this, we grew the perennial herb Asclepias speciosa in a greenhouse experiment that crossed a watering treatment (wet vs. dry treatment) with a manipulation of soil biota (live vs. sterilized soil) collected from two geographic regions (Washington and Minnesota) that vary greatly in annual precipitation. Because soil biota can influence many plant functional traits, we measured biomass as well as resource acquisition (e.g., root:shoot, specific leaf area) and defense (e.g., trichome and latex production) traits. Due to their important role as mutualists and pathogens, we also characterized soil fungal communities in the field and greenhouse and used curated databases to assess fungal composition and potential function. We found that the experimental watering treatment had a greater effect than soil biota origin on plant responses; most plant traits were negatively affected by live soils under wet conditions, whereas responses were neutral or positive in live dry soil. These consistent differences in plant responses occurred despite clear differences in soil fungal community composition between inoculate origin and watering treatments, which indicates high functional redundancy among soil fungi. All plants grown in live soil were highly colonized by AMF and root colonization was higher in wet than dry soil; root colonization by other fungi was low in all treatments. The most parsimonious explanation for negative plant responses in wet soil is that AMF became parasitic under conditions that alleviated resource limitation. Thus, plant responses appeared driven by shifts within rather than between fungal guilds, which highlights the importance of coupling growth responses with characterizations of soil biota to fully understand underlying mechanisms. Collectively these results highlight how short-term changes in environmental conditions can mediate complex interactions between plants and soil biota

Invasive plant-derived dissolved organic matter alters microbial communities and carbon cycling in soils

Plant invaders often exhibit substantially higher productivity than the communities they replace. However, little is known about interactions among invaders and microbial decomposers responsible for converting organic nutrients into plant-available forms to fuel this productivity. We performed two laboratory incubations with soil and plant material collected from five-year-old experimental plantings to assess if four grassland invaders (Bromus tectorum, Centaurea stoebe, Euphorbia esula and Potentilla recta) or native plant mixtures (including Pseudoroegneria spicata and Penstemon strictus) changed microbial community composition and function (experiment 1), and if plant-derived dissolved organic matter (DOM) contributed to these changes (experiment 2). We measured respiration responses throughout the 39-day incubations and assessed soil bacterial communities with 16S rRNA high-throughput sequencing at 0 and 48 h. Overall, we found bacterial community composition and function differed among plant communities. Two invaders in particular, B. tectorum and E. esula, generated dissimilar DOM with corresponding differences in bacterial composition and function. Soil bacteria accustomed to B. tectorum DOM (high carbon to nitrogen, C:N) harbored more oligotrophs and generated slow but large cumulative responses to a resource pulse. By contrast, soil bacteria accustomed to E. esula DOM (low C:N) harbored more copiotrophs and generated quicker respiration responses. Finally, we found a single pulse of invader-derived DOM shifted bacterial composition in soil associated with native plants. Our findings indicate invaders can differ substantially in interactions with microbial decomposers and these differences are, at least in part, driven by differences in DOM. While increased productivity and accelerated nutrient cycling may be common across invaders, our findings indicate that the underlying mechanisms driving these increases may be specific to each invader

Data from: Effects of short- and long-term variation in resource conditions on soil fungal communities and plant responses to soil biota

Data files include fungal sequence data (SSU and ITS2) from the field sampling and greenhouse experiment, percent colonization by AMF on plant roots, and plant trait data measured in the greenhouse experiment.<div><br></div