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The generation and transport of mineral dust is strongly related to climate on seasonal, year-to-year, and glacialinterglacial timescales. The modern dust cycle is influenced by soil moisture, which is partly a function of drought duration and severity. The production and transport of dust can therefore be amplified by global and regional droughts, thereby moderating ecosystem vulnerability to disturbance through the influence of dust on nutrient delivery to ecosystems. In this work, we use strontium and neodymium isotopes in combination with trace element concentrations in modern dust samples collected in 2015 to quantify the role of regionally versus globally supplied dust in nutrient delivery to a montane ecosystem. The study sites lie along an elevational transect in the southern Sierra Nevada, USA, with samples spanning the dry seasons of 2014 (Aciego et al., 2017) and 2015 (this study), when the region was experiencing a historic drought. The goal of our research was to quantify the spatial and temporal variability and sensitivity of the dust cycle to short term changes at nutrientlimited sites. We find that, during the dry season of 2015, Asian sources contributed between 10 and 40% of dust to sites located along this elevational transect, and importantly increased in importance during the summer growing season compared to regional dust sources. These changes are likely related to the prolonged drought in Asia in 2015, highlighting both the sensitivity of dust production and transport to drought and the teleconnections of dust transport in terrestrial ecosystems.

Subsoil microbiomes play important roles in soil carbon and nutrient cycling, yet our understanding of the controls on subsoil microbial communities is limited. Here, we investigated the direct (mean annual temperature and precipitation) and indirect (soil chemistry) effects of climate on microbiome composition and extracellular enzyme activity throughout the soil profile across two elevation-bioclimatic gradients in central California, USA. We found that microbiome composition changes and activity decreases with depth. Across these sites, the direct influence of climate on microbiome composition and activity was relatively lower at depth. Furthermore, we found that certain microbial taxa change in relative abundance over large temperature and precipitation gradients only in specific soil horizons, highlighting the depth dependence of the climatic controls on microbiome composition. Our finding that the direct impacts of climate are muted at depth suggests that deep soil microbiomes may lag in their acclimation to new temperatures with a changing climate.

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<div> <p>Covalent Organic Frameworks (COFs) are crystalline, porous organic materials with promise for applications including catalysis, energy storage, electronics, gas storage, water treatment, and drug delivery. Conventional solvothermal synthesis approaches to COFs require elevated temperatures, inert reaction environments, and long reaction times. Here, we report that transition metal nitrates can catalyze the rapid synthesis of imine COFs. We tested a series of transition metal nitrates as catalysts for the synthesis of a model COF and found that all transition metal nitrates produced crystalline COF products for reactions conducted at ambient temperatures. The reactions were insensitive to the presence of oxygen. Fe(NO₃)₃·9H₂O was found to produce the most crystalline product, and by optimizing the catalyst loading we found that crystalline COF could be produced within 10 minutes. We further tested Fe(NO₃)₃·9H₂O as a catalyst for 6 different COF targets varying in linker lengths, substituents, and stabilities, and found that Fe(NO₃)₃·9H₂O effectively catalyzed the synthesis of all imine COFs tested. This work demonstrates a simple, low-cost approach for the synthesis of imine COFs and will significantly lower the barrier for the development of imine COFs for various applications. </p> </div>

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Elucidating climatic impacts on stream nutrient export and stoichiometry will improve the understanding of forest carbon (C) storage in a warmer world. We analyzed C, nitrogen (N), and phosphorus (P) cycles in four watersheds within a rain-snow transition site and another four within a higherelevation, snow-dominated site, in California's mixed-conifer zone. We used these two sites in a space-for-time substitution to assess the potential warming impacts on nutrient cycles in currently snow-dominated areas that will become more raindominated. During a non-drought period (water year (WY) 2004-2011), mean annual stream exports of C and N in particulate forms at the transition site were twice that at the snow-dominated site, suggesting sediment-associated nutrient losses may increase with warming. The transition site had 12% lower N but twice P content in mineral horizons, lower N:P mass ratios in organic horizons, and lower stream export of dissolved inorganic N than the snow-dominated site. These differences suggest montane forests may have lower inputs of available N relative to P with warming.