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SummaryPlants and mycorrhizal fungi form close mutualistic relationships that affect how resources flow between organisms and within ecosystems. Common mycorrhizal networks (CMNs) could facilitate preferential transfer of carbon and limiting nutrients but this preference remains difficult to predict. Do common mycorrhizal networks favor fungal growth at the expense of plant resource demands (a fungi-centric view), or are they passive channels through which plants regulate resource fluxes (a plant-centric view)? We used stable isotope tracers (13C and15N), plant traits, and fungal DNA, to quantify above- and belowground allocation and transfer of carbon and nitrogen between 18 plant species in restored prairie and introduced pasture systems in the Pacific Northwest, USA. We found that related plant species and connectivity with fungal communities did not predict resource flow. Instead, plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. Labeled “donor” plants assimilated isotopic tracers at similar rates; however, nitrogen was preferentially transferred to annual and forb “receiver” plants compared to perennial and grass receiver plants. This corresponded tissue stoichiometry differences. Our findings point to a simple mechanistic answer for long-standing questions regarding mutualism and transfer of resources between plants via mycorrhizal networks.

Arbuscular mycorrhizal (AM) symbioses between plants and fungi are essential to the functioning of terrestrial ecosystems through maintaining soil stability, controlling nutrient cycles (e.g. C, N, P and K), and influencing competitive dynamics in plant communities. Despite the importance of AM symbioses, the ecological coassembly patterns of AM fungi-plant partners are not well characterized across environmental gradients. Further, it is unclear whether fungi forming associations with several plants of the same or different species – forming common mycorrhizal networks (CMNs) – preferentially allocate limiting resources within natural plant communities at the local-scale. We used an experimental prairie-pasture grassland system in three sites along a latitudinal gradient ranging from cool/wet to warm/dry climates to investigate how environmental conditions, local plant diversity and drought shift AM fungal composition and plant-fungal coassembly patterns across spatial scales. We show that plant-AM fungal assembly patterns are hierarchically structured, with environmental variables driving differences in AM fungal communities at the largest spatial scale (across sites), and plant host identity and diversity governing AM assembly at the local scale (within plot). Bipartite interaction networks revealed evidence for preferential partner selection between plants and fungi, while there was no evidence for nested assembly of plant-fungal partners. At the plot-level, we applied stable isotopes (13C and15N) to illustrate CMN assembly and nutritional function. There was no significant correlation between increased resource transfer among plants in a plot that shared more AM fungal partners; however, we identified specific AM fungi that were indicator taxa for increased plant isotope enrichment. Further research integrating stable isotope probing of fungal DNA in plant roots is necessary to more clearly illustrate the form and function of CMNs in grasslands under different environmental and plant diversity conditions.

Does drought stress in temperate grasslands alter the relationship between plant structure and function? Here we report data from an experiment focusing on growth form and species traits that affect the critical functions of water- and nutrient-use efficiency in prairie and pasture plant communities. A total of 139 individuals of 12 species (11 genera and four families) were sampled in replicated plots maintained for three years across a 520 km latitudinal gradient in the Pacific Northwest, USA. Rain exclusion did not alter the interspecific relationship between foliar traits and stoichiometry or intrinsic water-use efficiency. Rain exclusion reduced intrinsic water-use efficiency in grasses, an effect was primarily species-specific, although leaf morphology, life history strategy, and phylogenetic distance predicted intrinsic water-use efficiency for all twelve species when analyzed together. Variation in specific leaf area explained most of the variation in intrinsic water-use efficiency between different functional groups, with annual forbs and annual grasses at opposite ends of the resource-use spectrum. Our findings are consistent with expected trait-driven tradeoffs between productivity and resource-use efficiency, and provide insight into strategies for the sustainable use and conservation of temperate grasslands.Plain language summaryScientists have previously shown that plant leaf form (e.g., shape, width, size) has a predictable relationship to leaf function (e.g., how it can perform biological processes). When we deprive plants of water, does this relationship break down? We grew prairie and pasture plants at three sites in Oregon and Washington, USA, spanning a broad range of climate and water availability. At each site, we built shelters over half our plots to keep out some of the rain, reducing how much water our plants received. Leaf form-function relationships did not change between plots with more or less water. However, each species had a different water use efficiency and nutrient content, and some grasses had an unusual response, that is, they became less efficient at using water under less rain. Overall, we were pretty good at predicting water and nutrient use based on leaf form, whether plants were annual or perennial, and how related they were. Our findings match expectations about leaf structure-function relationships and people who manage temperate grasslands can use our results to decide which plants will work best for using and conserving their systems.Key pointsFoliar structure-function relationships did not change under experimental drought.Leaf morphology, life history, and phylogenetics predicted resource-use for 12 species.

The projected increase in warming and drought severity (i.e., hotter and drier summers) in the U.S. Pacific Northwest (PNW) may negatively impact grassland plant composition and ecosystem function, with further implications for sustainable land management in the region. To test the vulnerability of Mediterranean grassland function to climate change, we quantified the response of grassland communities to multiannual warming (+2.5°C) and drought (−40% precipitation) by quantifying plant species diversity, legume cover, and biogeochemical controls on and patterns of soil asymbiotic nitrogen fixation (ANF). We hypothesized that the effects of warming on plant functional diversity would increase soil ANF inputs by decreasing legume cover and soil nitrogen availability. Given that asymbiotic N fixers can increase soil organic carbon (C) and nitrogen (N) availability under drought, we hypothesized that the effect of drought on grassland plant cover correlated with increased soil ANF. We surveyed the vegetation and collected composite soil samples from five co-located plots under control (ambient), drought and warming conditions during the fall and spring seasons. In control and drought plots, we quantified the moderator effect of plant composition by comparing low-diversity (unmanipulated plant composition) and high-diversity (manipulated composition) grassland plots. We used a point intercept technique to survey plot-level plant community composition and calculate Shannon’s diversity index and percent cover of legumes (members of Fabaceae according to the Integrated Taxonomic Information System). We measured ANF by incubating collected soils with N-labeled dinitrogen (15N2), and quantified total soil C, total and available N, available phosphorus (P) and iron (Fe) pools, pH, and soil water holding capacity. Plant species diversity decreased significantly with warming and along the drought severity gradient. ANF response to warming varied by season and site, with rates increasing along the drought severity gradient in the fall but decreasing in the spring. Total soil inorganic N was the strongest predictor of ANF response to warming in the spring but not in the fall. Soil ANF response to drought increased with drought intensity; while soil ANF increased nearly twofold in the southernmost (warm and dry) site, ANF decreased in the northernmost (cool and wet) site. ANF response to drought also varied depending on plant diversity, where low-diversity grasslands had more predictable response to drought than high-diversity grasslands. Soil P availability and pH were the most important variables explaining ANF variability across vegetation types and sites. Our study highlights the importance of using soil-plant-atmosphere interactions to assess grassland ecosystem resilience to drought and warming in the PNW.

Declines in grassland diversity in response to nutrient addition are a general consequence of global change. This decline in species richness may be driven by multiple underlying processes operating at different time-scales. Nutrient addition can reduce diversity by enhancing the rate of local extinction via competitive exclusion, or by reducing the rate of colonization by constraining the pool of species able to colonize under new conditions. Partitioning net change into extinction and colonization rates will better delineate the long-term effect of global change in grasslands. We synthesized changes in richness in response to experimental fertilization with nitrogen, phosphorus and potassium with micronutrients across 30 grasslands. We quantified changes in local richness, colonization, and extinction over 8–10 years of nutrient addition, and compared these rates against control conditions to isolate the effect of nutrient addition from background dynamics. Total richness at steady state in the control plots was the sum of equal, relatively high rates of local colonization and extinction. On aggregate, 30%–35% of initial species were lost and the same proportion of new species were gained at least once over a decade. Absolute turnover increased with site-level richness but was proportionately greater at lower-richness sites relative to starting richness. Loss of total richness with nutrient addition, especially N in combination with P or K, was driven by enhanced rates of extinction with a smaller contribution from reduced colonization. Enhanced extinction and reduced colonization were disproportionately among native species, perennials, and forbs. Reduced colonization plateaued after the first few (

With ongoing climate change, populations are expected to exhibit shifts in demographic performance that will alter where a species can persist. This presents unique challenges for managing plant populations and may require ongoing interventions, including in situ management or introduction into new locations. However, few studies have examined how climate change may affect plant demographic performance for a suite of species, or how effective management actions could be in mitigating climate change effects. Over the course of two experiments spanning 6 yr and four sites across a latitudinal gradient in the Pacific Northwest, United States, we manipulated temperature, precipitation, and disturbance intensity, and quantified effects on the demography of eight native annual prairie species. Each year we planted seeds and monitored germination, survival, and reproduction. We found that disturbance strongly influenced demographic performance and that seven of the eight species had increasingly poor performance with warmer conditions. Across species and sites, we observed 11% recruitment (the proportion of seeds planted that survived to reproduction) following high disturbance, but just 3.9% and 2.3% under intermediate and low disturbance, respectively. Moreover, mean seed production following high disturbance was often more than tenfold greater than under intermediate and low disturbance. Importantly, most species exhibited precipitous declines in their population growth rates (λ) under warmer-than-ambient experimental conditions and may require more frequent disturbance intervention to sustain populations. Aristida oligantha, a C4 grass, was the only species to have λ increase with warmer conditions. These results suggest that rising temperatures may cause many native annual plant species to decline, highlighting the urgency for adaptive management practices that facilitate their restoration or introduction to newly suitable locations. Frequent and intense disturbances are critical to reduce competitors and promote native annuals' persistence, but even such efforts may prove futile under future climate regimes.

Plant phenology will likely shift with climate change, but how temperature and/or moisture regimes will control phenological responses is not well understood. This is particularly true in Mediterranean climate ecosystems where the warmest temperatures and greatest moisture availability are seasonally asynchronous. We examined plant phenological responses at both the population and community levels to four climate treatments (control, warming, drought, and warming plus additional precipitation) embedded within three prairies across a 520 km latitudinal Mediterranean climate gradient within the Pacific Northwest, USA. At the population level, we monitored flowering and abundances in spring 2017 of eight range‐restricted focal species planted both within and north of their current ranges. At the community level, we used normalized difference vegetation index (NDVI) measured from fall 2016 to summer 2018 to estimate peak live biomass, senescence, seasonal patterns, and growing season length. We found that warming exerted a stronger control than our moisture manipulations on phenology at both the population and community levels. Warming advanced flowering regardless of whether a species was within or beyond its current range. Importantly, many of our focal species had low abundances, particularly in the south, suggesting that establishment, in addition to phenological shifts, may be a strong constraint on their future viability. At the community level, warming advanced the date of peak biomass regardless of site or year. The date of senescence advanced regardless of year for the southern and central sites but only in 2018 for the northern site. Growing season length contracted due to warming at the southern and central sites (~3 weeks) but was unaffected at the northern site. Our results emphasize that future temperature changes may exert strong influence on the timing of a variety of plant phenological events, especially those events that occur when temperature is most limiting, even in seasonally water‐limited Mediterranean ecosystems.

Spatial gradients in population growth, such as across latitudinal or elevational gradients, are often assumed to primarily be driven by variation in climate, and are frequently used to infer species’ responses to climate change. Here, we use a novel demographic, mixed‐model approach to dissect the contributions of climate variables vs. other latitudinal or local site effects on spatiotemporal variation in population performance in three perennial bunchgrasses. For all three species, we find that performance of local populations decreases with warmer and drier conditions, despite latitudinal trends of decreasing population growth toward the cooler and wetter northern portion of each species’ range. Thus, latitudinal gradients in performance are not predictive of either local or species‐wide responses to climate. This pattern could be common, as many environmental drivers, such as habitat quality or species’ interactions, are likely to vary with latitude or elevation, and thus influence or oppose climate responses.

This project aims to quantify the resiliency of prairie ecosystems in the U.S. Pacific Northwest (PNW) to climate change. Prairies in this region sustain over one million beef cows, and cow­-ca...

Three principal modes of civic involvement are volunteering, giving to charities, and participating in civic associations. The authors investigate how total effort is distributed in the Canadian population among these three behaviors. Their results show that in each area, there is a small group of individuals who is responsible for the majority of contributory effort. When activity in the three areas is considered all together, the authors find a remarkably high degree of concentration. Six percent of Canadian adults account for 35% to 42% of all civic involvement. This group of individuals represents the “civic core” in Canada. The implications of the existence of a small but dedicated civic core for the voluntary domain and for patterns of citizen engagement are discussed.

A detailed statistical portrait of the estimated 7.5 million Canadians who give more than the national median of 66 hours of their time each year as volunteers was produced using data on 18,301 Canadians from the 1997 National Survey of Giving, Volunteering, and Participating. This report profiles the most salient characteristics of active volunteers. At the national level, the key characteristic that universally sets active volunteers apart from others is their high level of involvement in a variety of other forms of contributing and participating, such as charitable giving, informal volunteering, social activity, and civic participation. They are also likely to have above-average educations and occupations and to have children younger than age 17 in a larger-than-average household. The study also reveals how active volunteers have different patterns of distinctive characteristics in different regions and communities of different size across the country.

In the mid-1940s, Le Chambon was an unremarkable village of 3000 souls in the mountains of south-east France, midway between Geneva and Marseille. During the four years of World War II when much of France was under the control of its German occupiers, a handful of Le Chambon’s residents performed an exceptional act: they secretly sheltered and provided safe passage for nearly five thousand Jews who would otherwise have been rounded up and sent to the camps in Germany and Poland, most to their deaths. The residents of Le Chambon who participated in this sustained act of courage did so at great risk to their own lives and without thought for personal advantage. This historical event prompts for many the question, why did they do it? What was it about these few people, and not the many others around them, and visibily no different from them, that energized such behavior? As Philip Hallie has recounted it in Lest Innocent Blood Be Shed (1979), a significant part of the answer can be found in the particular set of moral precepts and values they held in common as members of a small Protestant church congregation.

Comment l’engagement dans les activités bénévoles se définit-il comme pratique de la responsabilité sociale inscrite dans la logique du don ? Et comment varie-t-il au cours de la vie ? Voilà les questions qui guident l’analyse présentée dans cet article. En utilisant les données d’enquêtes effectuées par Statistique Canada en 1987, 1997 et 2000, les auteurs comparent les taux de participation des Canadiens aux activités bénévoles en fonction des groupes d’âge et des cohortes. À partir des résultats, il est possible de constater une influence entre les pratiques de responsabilité de la sphère privée et les pratiques de responsabilité sociale. Ainsi, les adultes vivant en union et (ou) les adultes ayant des enfants sont plus nombreux à faire du bénévolat. À l’opposé, les gens âgés de plus de 55 ans dont les obligations familiales et professionnelles diminuent avec le temps sont moins nombreux à faire du bénévolat, mais ils sont les plus généreux dans le nombre d’heures qu’ils offrent., This article analyses volunteering as an act involving social responsibility and giving, and its variations across the life cycle. Using Statistics Canada data from 1987, 1997 and 2000, the article compares rates of volunteering across age groups and age cohorts. The results reveal a link between responsibilities in private life and actions of social responsibility. Thus, adults living as a couple and adults with children are more likely to volunteer. Persons older than 55 and whose family and work responsibilities are less weighty are less likely to volunteer, but when they do they are more generous with their time.