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Nitrogen (N) limitation to net primary production is widespread and influences the responsiveness of ecosystems to many components of global environmental change. Logic and both simple simulation (Vitousek and Fieldin in Biogeochemistry 46: 179–202, 1999) and analytical models (Menge in Ecosystems 14:519–532, 2011) demonstrate that the co-occurrence of losses of N in forms that organisms within an ecosystem cannot control and barriers to biological N fixation (BNF) that keep this process from responding to N deficiency are necessary for the development and persistence of N limitation. Models have focused on the continuous process of leaching losses of dissolved organic N in biologically unavailable forms, but here we use a simple simulation model to show that discontinuous losses of ammonium and nitrate, normally forms of N whose losses organisms can control, can be uncontrollable by organisms and can contribute to N limitation under realistic conditions. These discontinuous losses can be caused by temporal variation in precipitation or by ecosystem-level disturbance like harvest, fire, and windthrow. Temporal variation in precipitation is likely to increase and to become increasingly important in causing N losses as anthropogenic climate change proceeds. We also demonstrate that under the conditions simulated here, differentially intense grazing on N- and P-rich symbiotic N fixers is the most important barrier to the responsiveness of BNF to N deficiency.

BackgroundWest Nile virus (WNV) is the leading cause of mosquito-borne disease in humans in the United States. Since the introduction of the disease in 1999, incidence levels have stabilized in many regions, allowing for analysis of climate conditions that shape the spatial structure of disease incidence.ObjectivesOur goal was to identify the seasonal climate variables that influence the spatial extent and magnitude of WNV incidence in humans.MethodsWe developed a predictive model of contemporary mean annual WNV incidence using U.S. county-level case reports from 2005 to 2019 and seasonally averaged climate variables. We used a random forest model that had an out-of-sample model performance of R2=0.61.ResultsOur model accurately captured the V-shaped area of higher WNV incidence that extends from states on the Canadian border south through the middle of the Great Plains. It also captured a region of moderate WNV incidence in the southern Mississippi Valley. The highest levels of WNV incidence were in regions with dry and cold winters and wet and mild summers. The random forest model classified counties with average winter precipitation levels

Global declines in bird and arthropod abundance highlights the importance of understanding the role of food limitation and arthropod community composition for the performance of insectivorous birds. In this study, we link data on nestling diet, arthropod availability and nesting performance for the Coastal Cactus Wren (Campylorhynchus brunneicapillus sandiegensis), an at-risk insectivorous bird native to coastal southern California and Baja Mexico. We used DNA metabarcoding to characterize nestling diets and monitored 8 bird territories over two years to assess the relationship between arthropod and vegetation community composition and bird reproductive success. We document a discordance between consumed prey and arthropod biomass within nesting territories, in which Diptera and Lepidoptera were the most frequently consumed prey taxa but were relatively rare in the environment. In contrast other Orders (e.g., Hemiptera, Hymenoptera)were abundant in the environment but were absent from nestling diets. Accordingly, variation in bird reproductive success among territories was positively related to the relative abundance of Lepidoptera (but not Diptera), which were most abundant on 2 shrub species (Eriogonum fasciculatum, Sambucus nigra) of the 9 habitat elements characterized (8 dominant plant species and bare ground). Bird reproductive success was in turn negatively related to two invasive arthropods whose abundance was not associated with preferred bird prey, but instead possibly acted through harassment (Linepithema humile; Argentine ants) and parasite transmission or low nutritional quality (Armadillidium vulgare; "pill-bug"). These results demonstrate how multiple aspects of arthropod community structure can influence bird performance through complementary mechanisms, and the importance of managing for arthropods in bird conservation efforts.

Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecular tracking. However, concerns over toxicity in early types of FNPs, such as cadmium-containing quantum dots (QDs), may have prevented wide adoption. Recent developments, especially in non-Cd-containing FNPs, have alleviated toxicity problems, facilitating the use of FNPs for addressing ecological, physiological and molecule-level processes in biological research. Standardised protocols from synthesis to application and interdisciplinary approaches are critical for establishing FNPs in the biologists’ tool kit. Here, we present an introduction to FNPs, summarise their use in biological applications, and discuss technical issues such as data reliability and biocompatibility. We assess whether biological research can benefit from FNPs and suggest ways in which FNPs can be applied to answer questions in biology. We conclude that FNPs have a great potential for studying various biological processes, especially tracking, sensing and imaging in physiology and ecology.

Despite the tremendous importance of soil bacterial communities in biogeochemical cycles, the main functional variations developed by soil bacteria communities in-situ (as opposed to culture conditions) across the globe, and their environmental drivers has yet to be elucidated. Here we use shotgun metagenomes from all terrestrial biomes to characterize a genomic trait based soil bacteria’s functional spectrum, simplifying in two dimensions 53% of the global variation of their functional potential. Using machine learning, we show that soil pH, P content and climate (Precipitation patterns and temperature) predict 78% and 45% of the first and second dimension of the spectrum, respectively. The first dimension captures a continuum from small to large genomes associated with an increase of metabolism and resource acquisition complexity and versatility. Decrease in water stress and increased acidity drives this shift from small- to large-genome. The second dimension shows a continuum from microbial necromass and nutrient usage specialists to reactive degraders of simple carbons with more CAZy, rRNA and sigma factor genes. This shift to reactive bacteria was observed when climate restrains the growing window (low precipitation with high seasonality and extreme temperature) and pH becomes acidic. Overall, our study showed that metabolism versatility, reactivity and stoichiometry dominate soil bacteria functional spectrum across the globe.

The temperature sensitivity of soil processes is of major interest, especially in light of climate change. Originally formulated to explain the temperature dependence of chemical reactions, the Arrhenius equation, and related Q10 temperature coefficient, has a long history of application to soil biological processes. However, empirical data indicate that Q10 and Arrhenius model are often poor metrics of temperature sensitivity in soils. In this opinion piece, we aim to (a) review alternative approaches for characterizing temperature sensitivity, focusing on macromolecular rate theory (MMRT); (b) provide strategies and tools for implementing a new temperature sensitivity framework; (c) develop thermal adaptation hypotheses for the MMRT framework; and (d) explore new questions and opportunities stemming from this paradigm shift. Microbial ecologists should consider developing and adopting MMRT as the basis for predicting biological rates as a function of temperature. Improved understanding of temperature sensitivity in soils is particularly pertinent as microbial response to temperature has a large impact on global climate feedbacks.

Tropical montane cloud forests contain a large abundance and diversity of canopy epiphytes, which depend on canopy soil to retain water and nutrients. We lack an in depth understanding of how these soils contribute to ecosystem processes and soil diversity and how sensitive they may be to projected climate change. We compared canopy and ground soils in Monteverde, Costa Rica, to determine how these two soil types differ in their extracellular enzyme activity (EEA) and fungal communities. Samples were also collected along two elevation gradients to reveal if canopy soils differed in how EEA and fungal communities responded to elevation compared to ground soils. We found that canopy soils had higher EEA than ground soils. Fungal communities were less diverse and differed significantly between the two soil types. These differences were associated with higher relative abundances of yeasts and endophytes in canopy soils. The relative abundances of free-living filamentous fungi and yeasts shifted more dramatically with elevation in canopy soils compared to ground soils. Our study suggests that canopy soils may be a reservoir for endophytes. Epiphytes may invest in symbionts that promote stress tolerance over mycorrhizal fungi whose high resource demands are costly and less beneficial. Overall, soils harbor distinct fungal communities that may be altered under projected climate change.

Phenotypic plasticity of traits is commonly measured in plants to improve understanding of organismal and ecosystem responses to climate change but is far less studied for microbes. Specifically, decomposer fungi are thought to display high levels of phenotypic plasticity and their functions have important implications for ecosystem dynamics. Assessing the phenotypic plasticity of fungal traits may therefore be important for predicting fungal community response to climate change. Here, we assess the phenotypic plasticity of 15 fungal isolates (12 species) from a Southern California grassland. Fungi were incubated on litter at five moisture levels (ranging from 4–50% water holding capacity) and at five temperatures (ranging from 4–36 °C). After incubation, fungal biomass and activities of four extracellular enzymes (cellobiohydrolase (CBH), β-glucosidase (BG), β-xylosidase (BX), and N-acetyl-β-D-glucosaminidase (NAG)) were measured. We used response surface methodology to determine how fungal phenotypic plasticity differs across the moisture-temperature gradient. We hypothesized that fungal biomass and extracellular enzyme activities would vary with moisture and temperature and that the shape of the response surface would vary between fungal isolates. We further hypothesized that more closely related fungi would show more similar response surfaces across the moisture-temperature gradient. In support of our hypotheses, we found that plasticity differed between fungi along the temperature gradient for fungal biomass and for all the extracellular enzyme activities. Plasticity also differed between fungi along the moisture gradient for BG activity. These differences appear to be caused by variation mainly at the moisture and temperature extremes. We also found that more closely related fungi had more similar extracellular enzymes activities at the highest temperature. Altogether, this evidence suggests that with global warming, fungal biodiversity may become increasingly important as functional traits tend to diverge along phylogenetic lines at higher temperatures.

• Numerous field studies have measured mycorrhizal dynamics under additions of nitrogen (N), phosphorus (P), or atmospheric CO

Author(s): Treseder, KK; Allen, MF | Abstract: Since mycorrhizal fungi constitute an important component of the soil–plant interface, their responses to changes in nutrient availability may mediate shifts in ecosystem function. We tested the hypothesis that initial soil nutrient availability may determine effects of nitrogen (N) and phosphorus (P) additions on the growth and community of arbuscular mycorrhizal (AM) fungi. Extraradical hyphal lengths and degree of root colonization of AM fungi were measured in control and fertilized plots along a soil fertility gradient in Hawaii. Responses of individual AM genera were assessed through immunofluorescent labeling. The AM biomass was increased by N and P additions in the N- and P-limited sites, respectively, and reduced by P fertilization in the fertile site only. The abundance of Scutellospora was lower under N than under P fertilization, whereas the incidence of Glomus was higher in the fertile site than the N-limited site. Gigaspora and Acaulospora did not vary among sites or treatments. Our results indicate that a decrease in AM abundance following nutrient additions cannot be assumed to occur and the effects may differ among AM genera and ecosystems with varying soil nutrients. Limitation of N and P may be one possible explanation.

Author(s): Finks, SS; Weihe, C; Kimball, S; Allison, SD; Martiny, AC; Treseder, KK; Martiny, JBH | Abstract: Global changes such as increased drought and atmospheric nitrogen deposition perturb both the microbial and plant communities that mediate terrestrial ecosystem functioning. However, few studies consider how microbial responses to global changes may be influenced by interactions with plant communities. To begin to address the role of microbial–plant interactions, we tested the hypothesis that the response of microbial communities to global change depends on the plant community. We characterized bacterial and fungal communities from 395 plant litter samples taken from the Loma Ridge Global Change Experiment, a decade-long global change experiment in Southern California that manipulates rainfall and nitrogen levels across two adjacent ecosystems, a grassland and a coastal sage scrubland. The differences in bacterial and fungal composition between ecosystems paralleled distinctions in plant community composition. In addition to the direct main effects, the global change treatments altered microbial composition in an ecosystem-dependent manner, in support of our hypothesis. The interaction between the drought treatment and ecosystem explained nearly 5% of the variation in bacterial community composition, similar to the variation explained by the ecosystem-independent effects of drought. Unexpectedly, we found that the main effect of drought was approximately four times as strong on bacterial composition as that of nitrogen addition, which did not alter fungal or plant composition. Overall, the findings underscore the importance of considering plant–microbe interactions when considering the transferability of the results of global change experiments across ecosystems.

International audience; Atmospheric carbon dioxide concentration ([CO 2 ]) is increasing, which increases leaf-scale photosynthesis and intrinsic water-use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO 2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO 2]-driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO 2] (iCO 2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre-industrial times. Established theory, supported by experiments, indicates that iCO 2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO 2 responses are high in comparison to experiments and predictions from theory. Plantmortality and soil carbon iCO 2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2 , albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.

In this case study analysis, we identified fungal traits that were associated with the responses of taxa to 4 global change factors: elevated CO2, warming and drying, increased precipitation, and nitrogen (N) enrichment. We developed a trait-based framework predicting that as global change increases limitation of a given nutrient, fungal taxa with traits that target that nutrient will represent a larger proportion of the community (and vice versa). In addition, we expected that warming and drying and N enrichment would generate environmental stress for fungi and may select for stress tolerance traits. We tested the framework by analyzing fungal community data from previously published field manipulations and linking taxa to functional gene traits from the MycoCosm Fungal Portal. Altogether, fungal genera tended to respond similarly to 3 elements of global change: increased precipitation, N enrichment, and warming and drying. The genera that proliferated under these changes also tended to possess functional genes for stress tolerance, which suggests that these global changes—even increases in precipitation—could have caused environmental stress that selected for certain taxa. In addition, these genera did not exhibit a strong capacity for C breakdown or P acquisition, so soil C turnover may slow down or remain unchanged following shifts in fungal community composition under global change. Since we did not find strong evidence that changes in nutrient limitation select for taxa with traits that target the more limiting nutrient, we revised our trait-based framework. The new framework sorts fungal taxa into Stress Tolerating versus C and P Targeting groups, with the global change elements of increased precipitation, warming and drying, and N enrichment selecting for the stress tolerators.

The potential consequences of global warming for ecosystem carbon stocks are a major concern, particularly in high-latitude regions where soil carbon pools are especially large. Research on soil and plant carbon responses to warming are often based on short-term (' 10year) warming experiments. Furthermore, carbon budgets from boreal forests, which contain at least 10–20% of the global soil carbon pool, have shown mixed responses to warming. In this study, we measured carbon and nitrogen budgets (i.e., soil and understory vegetation carbon and nitrogen stocks) from a 13-year greenhouse warming experiment in an Alaskan boreal forest. Although there were no differences in total aboveground + belowground pools, the carbon in the moss biomass and in the soil organic layer significantly decreased with the warming treatment (− 88.3% and − 19.1%, respectively). Declines in moss biomass carbon may be a consequence of warming-associated drying, while shifts in the soil microbial community could be responsible for the decrease in carbon in the soil organic layer. Moreover, in response to warming, aboveground plant biomass carbon tended to increase while root biomass carbon tended to decrease, so carbon allocation may shift aboveground with warming. Overall these results suggest that permafrost-free boreal forests are susceptible to soil carbon loss with warming.

We compiled a coccidioidomycosis (Valley fever) case database for three states in the southwestern United States (US). Currently, county-level, monthly case counts are available from 2000–2015 for Arizona, California, and Nevada. We collected these data from each respective state public health agency. The Valley fever case database is available on GitHub, at https://github.com/valleyfever/valleyfevercasedata . This database may be used to examine relationships between the number of Valley fever cases and hypothesized explanatory variables such as environmental conditions, social determinants, human behavior, occupational activities, public policies, or other risk factors. We aim to provide regular updates to this database and include more states as data become available. Funding statement: M. E. Gorris received support from a Department of Defense (DoD), National Defense Science & Engineering Graduate Fellowship (32 CFR 168a). M. E. Gorris, L. A. Cat, and M. Matlock thank the UC Irvine Data Science Initiative for their funding and support. L. A. Cat acknowledges funding and support from the UC-Mexico Initiative. M. Matlock is also supported by Water UCI and the UCI Graduate Division. K. K. Treseder is supported by US NSF (EAR-1411942 and DEB-1457160) and the US Department of Energy, Office of Science, Office of Biological and Environmental Research (BER), under Award Numbers DE-PS02-09ER09-25 and DE-SC001641. J. T. Randerson received support from the Gordon and Betty Moore Foundation (GBMF#3269), NASA Soil Moisture and Interdisciplinary Science Program, and the U.S. Dept. of Energy Office of Science RUBISCO Science Focus Area. C. S. Zender acknowledges support from the Borrego Valley Endowment Fund and DOE ACME DE-SC0012998.

Atmospheric carbon dioxide concentration ([CO

© 2018 The US and Mexico share a common history in many areas, including language and culture. They face ecological changes due to the increased frequency and severity of droughts and rising energy demands; trends that entail economic costs for both nations and major implications for human wellbeing. We describe an ongoing effort by the Environment Working Group (EWG), created by The University of California's UC-Mexico initiative in 2015, to promote binational research, teaching, and outreach collaborations on the implications of climate change for Mexico and California. We synthesize current knowledge about the most pressing issues related to climate change in the US-Mexico border region and provide examples of cross-border discoveries and research initiatives, highlighting the need to move forward in six broad rubrics. This and similar binational cooperation efforts can lead to improved living standards, generate a collaborative mindset among participating universities, and create an international network to address urgent sustainability challenges affecting both countries.

Author(s): Treseder, KK; Allen, EB; Egerton-Warburton, LM; Hart, MM; Klironomos, JN; Maherali, H; Tedersoo, L | Abstract: Anthropogenic nitrogen (N) deposition is exposing plants and their arbuscular mycorrhizal fungi (AMFs) to elevated N availability, often leading to shifts in communities of AMF. However, physiological trade-offs among AMF taxa in their response to N enrichment vs the ability to acquire other soil nutrients could have negative effects on plant and ecosystem productivity. It follows that information on the functional traits of AMF taxa can be used to generate predictions of their potential role in mediating ecosystem responses to N enrichment. Arbuscular mycorrhizal fungi taxa that produce extensive networks of external hyphae should forage for N and phosphorus (P) more effectively, but these services incur greater carbon (C) costs to the plant. If N enrichment ameliorates plant nutrient limitation, then plants may reduce C available for AMF, which in turn could eliminate AMF taxa with large extensive external hyphae from the soil community. As a result, the remaining AMF taxa may confer less P benefit to their host plants. Using a synthesis of data from the literature, we found that the ability of a taxon to persist in the face of increasing soil N availability was particularly high in isolates from the genus Glomus, but especially low among the Gigasporaceae. Across AMF genera, our data support the prediction that AMF with a tolerance for high soil N may confer a lower P benefit to their host plant. Relationships between high N tolerance and production of external hyphae were mixed. Synthesis. If the relationship between N tolerance and plant P benefit is widespread, then shifts in arbuscular mycorrhizal fungi communities associated with N deposition could have negative consequences for the ability of plants to acquire P and possibly other nutrients via a mycorrhizal pathway. Based on this relationship, we predict that arbuscular mycorrhizal fungi responses could constrain net primary productivity in P-limited ecosystems exposed to N enrichment. This prediction could be tested in future empirical and modelling studies.

The magnitude and direction of carbon cycle feedbacks under climate warming remain uncertain due to insufficient knowledge about the temperature sensitivities of soil microbial processes. Enzymatic rates could increase at higher temperatures, but this response could change over time if soil microbes adapt to warming. We used the Arrhenius relationship, biochemical transition state theory, and thermal physiology theory to predict the responses of extracellular enzyme Vmax and Km to temperature. Based on these concepts, we hypothesized that Vmax and Km would correlate positively with each other and show positive temperature sensitivities. For enzymes from warmer environments, we expected to find lower Vmax , Km , and Km temperature sensitivity but higher Vmax temperature sensitivity. We tested these hypotheses with isolates of the filamentous fungus Neurospora discreta collected from around the globe and with decomposing leaf litter from a warming experiment in Alaskan boreal forest. For Neurospora extracellular enzymes, Vmax Q10 ranged from 1.48 to 2.25, and Km Q10 ranged from 0.71 to 2.80. In agreement with theory, Vmax and Km were positively correlated for some enzymes, and Vmax declined under experimental warming in Alaskan litter. However, the temperature sensitivities of Vmax and Km did not vary as expected with warming. We also found no relationship between temperature sensitivity of Vmax or Km and mean annual temperature of the isolation site for Neurospora strains. Declining Vmax in the Alaskan warming treatment implies a short-term negative feedback to climate change, but the Neurospora results suggest that climate-driven changes in plant inputs and soil properties are important controls on enzyme kinetics in the long term. Our empirical data on enzyme Vmax , Km , and temperature sensitivities should be useful for parameterizing existing biogeochemical models, but they reveal a need to develop new theory on thermal adaptation mechanisms.

Soil fungi and bacteria are the key players in the transformation and processing of carbon and nutrients in terrestrial ecosystems, yet controls on their abundance and activity are not well understood. Based on stoichiometric principles, soil microbial processes are expected to be limited by mineral nutrients, which are particularly scarce in often highly weathered tropical forest soils. Such limitation is directly relevant for the fate of soil carbon and global element cycles, but its extent and nature have never been assessed systematically across the tropical biome. Here, we address the relative importance of nitrogen, phosphorus and other nutrients in limiting soil microbial biomass and process rates in tropical forests. We conducted an in-depth literature review and a meta-analysis of the available nutrient addition experiments in tropical forests worldwide. Our synthesis showed predominant and general phosphorus limitation of a variety of microbial processes across tropical forests, and additional nitrogen limitation in tropical montane forests. The apparent widespread microbial phosphorus limitation needs to be accounted for in the understanding and prediction of biogeochemical cycles in tropical forests and their future functioning. Other mineral nutrients or carbon may modify the importance of phosphorus, but more experimental studies are urgently needed. This article is protected by copyright. All rights reserved.

Microorganisms are critical in terrestrial carbon cycling because their growth, activity and interactions with the environment largely control the fate of recent plant carbon inputs as well as protected soil organic carbon [1, 2]. Soil carbon stocks reflect a balance between microbial decomposition of organic carbon and stabilisation of microbial assimilated carbon. The balance can shift under altered environmental conditions [3], and new research suggests that knowledge of microbial physiology may be critical for projecting changes in soil carbon and improving the prognosis of climate change feedbacks [4–7]. Still, predicting the ecosystem implications of microbial processes remains a challenge. Here we argue that this challenge can be met by identifying microbial life history strategies based on an organism’s phenotypic characteristics, or traits, and representing these strategies in ecosystem models. What are the key microbial traits for soil carbon cycling under environmental change? Microbial growth and survival in soil are impacted by multiple traits that determine responses to varying resource availability and fluctuating abiotic conditions [8]. Cellular maintenance activities (those that do not produce growth) include production of extracellular enzymes to degrade and acquire resources, biomolecular repair mechanisms, maintenance of cellular integrity, osmotic balance, defence, antagonism, cell signalling and motility [9–11]. It is conceivable that microbial investment into maintenance activities would be generally high in soils, with their highly heterogeneous and temporally variable resource distribution and stressful abiotic conditions like extremes of moisture, temperature, pH and salinity [12, 13]. Selective pressures in suboptimal environmental conditions could lead to greater cellular-level physiological allocation to maintenance relative to growth traits (Fig. 1) thereby impacting soil carbon cycling processes. Open in a separate window Fig. 1 Schematic showing cellular C flux that includes depolymerisation, substrate uptake, assimilation, dissimilation, biomass synthesis and non-growth production. Extracellular enzyme production represents investment in resource acquisition, stress protein production is linked to stress tolerance mechanisms, and biomass production reflects higher growth yield. Forked arrows signify metabolic points where hypothesised tradeoffs in traits might occur. The expected empirical relationships among the key traits are also shown

Coccidioidomycosis (Valley fever) is a fungal disease endemic to the southwestern United States. Across this region, temperature and precipitation influence the extent of the endemic region and number of Valley fever cases. Climate projections for the western United States indicate that temperatures will increase and precipitation patterns will shift, which may alter disease dynamics. We estimated the area potentially endemic to Valley fever using a climate niche model derived from contemporary climate and disease incidence data. We then used our model with projections of climate from Earth system models to assess how endemic areas will change during the 21st century. By 2100 in a high warming scenario, our model predicts that the area of climate‐limited endemicity will more than double, the number of affected states will increase from 12 to 17, and the number of Valley fever cases will increase by 50%. The Valley fever endemic region will expand north into dry western states, including Idaho, Wyoming, Montana, Nebraska, South Dakota, and North Dakota. Precipitation will limit the disease from spreading into states farther east and along the central and northern Pacific coast. This is the first quantitative estimate of how climate change may influence Valley fever in the United States. Our predictive model of Valley fever endemicity may provide guidance to public health officials to establish disease surveillance programs and design mitigation efforts to limit the impacts of this disease., Key Points We created a niche model to estimate climate limits on the spatial extent of Valley fever endemicity in the United StatesFor a high warming scenario, the area of climate‐limited endemicity will more than double by 2100, expanding northward into dry western statesOur predictive model of Valley fever endemic regions may help mitigate disease impacts as the disease spreads into new regions

Fungi play many essential roles in ecosystems. They facilitate plant access to nutrients and water, serve as decay agents that cycle carbon and nutrients through the soil, water and atmosphere, and are major regulators of macro-organismal populations. Although technological advances are improving the detection and identification of fungi, there still exist key gaps in our ecological knowledge of this kingdom, especially related to function. Trait-based approaches have been instrumental in strengthening our understanding of plant functional ecology and, as such, provide excellent models for deepening our understanding of fungal functional ecology in ways that complement insights gained from traditional and -omics-based techniques. In this review, we synthesize current knowledge of fungal functional ecology, taxonomy and systematics and introduce a novel database of fungal functional traits (FunFun ). FunFun is built to interface with other databases to explore and predict how fungal functional diversity varies by taxonomy, guild, and other evolutionary or ecological grouping variables. To highlight how a quantitative trait-based approach can provide new insights, we describe multiple targeted examples and end by suggesting next steps in the rapidly growing field of fungal functional ecology.

Arbuscular mycorrhizal (AM) fungi can improve restoration outcomes by facilitating establishment of native plants. Yet, we know little about the effects of restoration methods on AM fungi. We examined how using herbicide and mowing to remove invasive Brassica nigra (black mustard) might alter AM abundance in a coastal sage scrubland. Black mustard is a non-mycorrhizal plant that produces allelochemicals that inhibit AM fungi. Although black mustard removal could potentially improve AM growth, herbicide and mowing might harm AM fungi. We measured black mustard cover, AM hyphal abundance, and native plant cover from plots exposed to either herbicide or mowing versus untreated controls. We found that both herbicide and mowing reduced black mustard cover. Furthermore, herbicide increased AM abundance in one field site, potentially because herbicide killed black mustard roots and reduced allelochemical production. However, neither restoration treatment improved native plant abundance over the course of our study. Overall, herbicide can deter black mustard invasion and help re-establish the AM community in certain ecosystems, but without a corresponding increase in native plants.

We tested the hypothesis that field applications of arbuscular mycorrhizal (AM) inocula would increase root colonization and plant performance in a coastal sage scrub (CSS) restoration project in Southern California. We applied commercial or native inocula (from nearby reference shrublands) as we seeded plots with native shrubs, forbs, and grasses. A control treatment was seeded but received no inocula. After 6 months, AM root colonization did not differ significantly among treatments. Likewise, neither inoculum type significantly altered shoot biomass of native shrubs and forbs at 6 months, or density of adult and seedling shrubs at 10 months. Notably, shoot height at 10 months was shorter in plots treated with commercial inoculum compared with the controls. In addition, flower and flower bud production by Salvia columbariae did not significantly respond to either inoculum type. Altogether, we found no evidence that AM inoculation improved restoration success in our CSS system.

In this commentary, I advocate for more detailed incorporation of arbuscular mycorrhizal (AM) fungi in Earth system models, to improve our projections of global climate change. Current Earth system models display relatively low predictability of soil C stocks, which limit our ability to estimate future climate conditions. A more explicit incorporation of microbial mechanisms can increase the accuracy of ecosystem-scale models that inform the larger-scale Earth system models. Of the numerous microbial groups that can influence soil C dynamics, AM fungi are particularly tractable for integration in models. Arbuscular mycorrhizal fungi are globally abundant and perform critical roles in C cycling, such as augmentation of net primary productivity and soil C storage. Moreover, AM communities exhibit relatively low diversity within ecosystems, compared with other microbial groups. In addition, global datasets of AM ecology are available for use in model development. Thus, AM communities can be readily simulated in next-generation trait-based models that link microbial diversity to ecosystem function. Altogether, we are well-poised to incorporate the dynamics of individual AM taxa in ecosystem models, which can then be coupled to Earth system models. Hopefully, these efforts would advance our ability to predict and plan for future climate change.

Southern California is an urban metropolis bordered by mountains to the north and east and the Pacific Ocean to the west. Its unique geography and climatological features lead to annual patterns in atmospheric aerosol content from natural and anthropogenic sources. Here we sought to determine the nitrogen (N, including NO3−, NH4+, and total N) content of Southern California particulate matter (PM2.5) collected in Orange County, CA, and to identify relevant sources and processes that affect PM2.5 abundance and chemistry in different seasons. PM2.5 carbon (C) and N isotopic compositions (δ13C and δ15N, respectively) suggested that the C content of the PM2.5 derived partly from the marine inversion layer that occurs in the months of May through July. The high N content and δ15N values of PM2.5 collected in summer suggest a contribution from anthropogenic emissions, which are likely trapped in the basin by the inversion layer. In contrast, winter PM2.5 had a lower N content per volume of air, and δ13C values indicated a greater terrestrial signal, consistent with easterly winds. This trend was particularly evident in samples collected during high velocity Santa Ana wind events, which bring terrestrial material from the Great Basin and mountainous regions to the east of Southern California. Based on these observations, we suggest that atmospheric deposition of N is more likely to affect terrestrial ecosystems in the summer, when N content is high and aerosols are trapped by the inversion layer, whereas coastal marine ecosystems are more likely to be affected in the winter when westward winds are more common.

Bacteria and fungi drive decomposition, a fundamental process in the carbon cycle, yet the importance of microbial community composition for decomposition remains elusive. Here, we used an 18-month reciprocal transplant experiment along a climate gradient in Southern California to disentangle the effects of the microbial community versus the environment on decomposition. Specifically, we tested whether the decomposition response to climate change depends on the microbial community. We inoculated microbial decomposers from each site onto a common, irradiated leaf litter within "microbial cages" that prevent microbial exchange with the environment. We characterized fungal and bacterial composition and abundance over time and investigated the functional consequences through litter mass loss and chemistry. After 12 months, microbial communities altered both decomposition rate and litter chemistry. Further, the functional measurements depended on an interaction between the community and its climate in a manner not predicted by current theory. Moreover, microbial ecologists have traditionally considered fungi to be the primary agents of decomposition and for bacteria to play a minor role. Our results indicate that not only does climate change and transplantation have differential legacy effects among bacteria and fungi, but also that bacterial communities might be less functionally redundant than fungi with regards to decomposition. Thus, it may be time to reevaluate both the role of microbial community composition in its decomposition response to climate and the relative roles of bacterial and fungal communities in decomposition.

© 2018 Elsevier Ltd and British Mycological Society Fungal metabolic rates could increase under climate warming but may be counteracted by mechanisms of physiological acclimation and evolutionary adaptation. We hypothesized that Vmax and Km parameters of Neurospora discreta extracellular enzymes would acclimate to warmer temperatures through compensatory mechanisms. We also predicted that evolution under warmer temperatures would alter enzyme parameters and fungal respiration through adaptive mechanisms. In contrast to these predictions, growth at higher temperature (22 °C versus 16 °C) increased the temperature-corrected Vmax of three enzymes. The carbon substrate used for fungal growth (lignin versus sucrose) had a much greater impact on enzyme Vmax than temperature. Following experimental evolution, the enzymatic parameters of Neurospora strains did not adapt to higher temperatures as hypothesized; rather, enzyme Vmax values were unaffected, and respiration rates increased. Together, these results suggest that physiological and evolutionary mechanisms are unlikely to counteract soil carbon losses driven by saprotrophic fungi under climate warming.

To better understand mechanisms of carbon (C) and nitrogen (N) dynamics under anthropogenic N enrichment, we examined frequencies of C- and N-targeting genes in litter fungi. In particular, we tested the hypothesis that N enrichment selects for C-targeting genes but against N-targeting genes, if fungi preferentially invest resources in acquisition of growth-limiting nutrients. We conducted a fully-factorial litter and microbial transplant in a N fertilization experiment in Southern California grassland. The transplant design enabled us to contrast direct effects of N fertilization in the environment, indirect effects of N-induced shifts in the microbial community, and indirect effects of N-induced changes in plant litter chemistry. For each treatment, we assessed frequencies of select well-annotated fungal functional genes: cellulose-targeting AA9 genes (for C acquisition) versus ammonium transporter genes and amino acid permease genes (for N acquisition). We found that our hypothesis was upheld only with regard to shifts in the microbial community. Specifically, when grown in the same environment and litter, fungi from the N-fertilized plots displayed greater frequencies of cellulose-targeting AA9 genes from basidiomycetes, but smaller frequencies of ammonium transporter genes and amino acid permease genes, when compared to fungi from the control plots. In contrast, N fertilization in the plot environment was associated with higher frequencies of amino acid permease genes and ammonium transporter genes. Likewise, plant litter from the N-fertilized plots selected for higher frequencies of ammonium transporter genes. Altogether, we found fairly inconsistent effects of N enrichment on fungal functional genes related to C and N acquisition. Even if the genetic capacity of the fungal community to acquire C versus N changes owing to shifts in the microbial community, direct effects of N fertilization and indirect effects of litter chemistry may offset the response.