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1. Dissolved and gaseous nitrogen losses in forests controlled by soil nutrient stoichiometry

   https://doi.org/10.1088/1748-9326/ac007b  

   Oulehle, Filip; Goodale, Christine L; Evans, Christopher D; Chuman, Tomáš; Hruška, Jakub; Krám, Pavel; Navrátil, Tomáš; Tesař, Miroslav; Ač, Alexandr; Urban, Otmar; et al (May 2021, Environmental Research Letters)

   Abstract Global chronic nitrogen (N) deposition to forests can alleviate ecosystem N limitation, with potentially wide ranging consequences for biodiversity, carbon sequestration, soil and surface water quality, and greenhouse gas emissions. However, the ability to predict these consequences requires improved quantification of hard-to-measure N fluxes, particularly N gas loss and soil N retention. Here we combine a unique set of long-term catchment N budgets in the central Europe with ecosystem 15 N data to reveal fundamental controls over dissolved and gaseous N fluxes in temperate forests. Stream leaching losses of dissolved N corresponded with nutrient stoichiometry of the forest floor, with stream N losses increasing as ecosystems progress towards phosphorus limitation, while soil N storage increased with oxalate extractable iron and aluminium content. Our estimates of soil gaseous losses based on 15 N stocks averaged 2.5 ± 2.2 kg N ha −1 yr −1 and comprised 20% ± 14% of total N deposition. Gaseous N losses increased with forest floor N:P ratio and with dissolved N losses. Our relationship between gaseous and dissolved N losses was also able to explain previous 15 N-based N loss rates measured in tropical and subtropical catchments, suggesting a generalisable response driven by nitrate (NO 3 − ) abundance and in which the relative importance of dissolved N over gaseous N losses tended to increase with increasing NO 3 − export. Applying this relationship globally, we extrapolated current gaseous N loss flux from forests to be 8.9 Tg N yr −1 , which represent 39% of current N deposition to forests worldwide. 

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2. A global FAOSTAT reference database of cropland nutrient budgets and nutrient use efficiency (1961–2020): nitrogen, phosphorus and potassium

   https://doi.org/10.5194/essd-16-525-2024  

   Ludemann, Cameron I.; Wanner, Nathan; Chivenge, Pauline; Dobermann, Achim; Einarsson, Rasmus; Grassini, Patricio; Gruere, Armelle; Jackson, Kevin; Lassaletta, Luis; Maggi, Federico; et al (January 2024, Earth System Science Data)

   Abstract. Nutrient budgets help to identify the excess or insufficient use of fertilizers and other nutrient sources in agriculture. They allow for the calculation of indicators, such as the nutrient balance (surplus if positive or deficit if negative) and nutrient use efficiency, that help to monitor agricultural productivity and sustainability across the world. We present a global database of country-level budget estimates for nitrogen (N), phosphorus (P) and potassium (K) on cropland. The database, disseminated in FAOSTAT, is meant to provide a global reference, synthesizing and continuously updating the state of the art on this topic. The database covers 205 countries and territories, as well as regional and global aggregates, for the period from 1961 to 2020. Results highlight the wide range in nutrient use and nutrient use efficiencies across geographic regions, nutrients, and time. The average N balance on global cropland has remained fairly steady at about 50–55 kg ha−1 yr−1 during the past 15 years, despite increasing N inputs. Regional trends, however, show recent average N surpluses that range from a low of about 10 kg N ha−1 yr−1 in Africa to more than 90 kg N ha−1 yr−1 in Asia. Encouragingly, average global cropland N use efficiency decreased from about 59 % in 1961 to a low of 43 % in 1988, but it has risen since then to a level of 55 %. Phosphorus deficits are mainly found in Africa, whereas potassium deficits occur in Africa and the Americas. This study introduces improvements over previous work in relation to the key nutrient coefficients affecting nutrient budgets and nutrient use efficiency estimates, especially with respect to nutrient removal in crop products, manure nutrient content, atmospheric deposition and crop biological N fixation rates. We conclude by discussing future research directions and highlighting the need to align statistical definitions across research groups as well as to further refine plant and livestock coefficients and expand estimates to all agricultural land, including nutrient flows in meadows and pastures. Further information is available from https://doi.org/10.5061/dryad.hx3ffbgkh (Ludemann et al., 2023b) as well as the FAOSTAT database (https://www.fao.org/faostat/en/#data/ESB; FAO, 2022a) and is updated annually. 

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3. A Meta‐Regression of 18 Wildfire Chronosequences Reveals Key Environmental Drivers and Knowledge Gaps in the Boreal Nitrogen Balance

   https://doi.org/10.1111/gcb.70398  

   Hupperts, Stefan F; Berninger, Frank; Chen, Han_Y H; Fenton, Nicole; Jean, Mélanie; Köster, Kajar; Larjavaara, Markku; Mack, Michelle C; Nilsson, Marie‐Charlotte; Palviainen, Marjo; et al (August 2025, Global Change Biology)

   ABSTRACT Climate change has increased the size and frequency of wildfires across the boreal biome. Severe wildfires in boreal forests have been found to trigger shifts from evergreen to deciduous canopies, which has cascading effects on carbon and nitrogen cycling. Ecosystem productivity and carbon uptake in boreal forests are strongly linked with nitrogen, and Earth system models increasingly depend on our understanding of the nitrogen balance to predict post‐fire carbon uptake. To investigate the post‐fire boreal nitrogen balance, we combined a mass balance approach and literature synthesis to estimate rates of nitrogen accumulation and nitrogen inputs across a network of 18 boreal wildfire chronosequences that varied in both wildfire regime and post‐fire canopy type, comprising 527 forest stands. We found that deciduous‐ or mixed‐dominance boreal forests establishing after severe, stand‐replacing fires had the highest nitrogen accumulation rates (15.7 ± 3.8 kg ha⁻¹ year⁻¹), while evergreen‐dominated forests establishing after surface‐ or mixed‐severity fires had the lowest nitrogen accumulation rates (1.4 ± 1.1 kg ha⁻¹ year⁻¹). Annual known inputs from nitrogen deposition and biological nitrogen fixation combined, estimated from published data, largely failed to explain the rate of nitrogen accumulation, particularly in deciduous or mixed‐dominance forests establishing after stand‐replacing fires, suggesting that the origins of most nitrogen in these forest types remain poorly understood. As the frequency of severe wildfires increases across the boreal biome and shifts toward deciduous canopies become more common, our study reveals a large knowledge gap in the resulting nitrogen balance that needs to be resolved in order to improve predictions of forest carbon uptake. 

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4. Arthropod rain in a lowland tropical forest

   https://doi.org/10.1111/icad.70046  

   Seiler, Andrew R; Stark, Alyssa Y; Yanoviak, Stephen P (December 2025, Insect Conservation and Diversity)

   Abstract In lowland tropical forests, “arthropod rain” (i.e., arthropods falling from the canopy to the understory), represents a potentially important terrestrial nutrient flux.We investigated the composition, abundance, biomass and environmental drivers of arthropod rain on Barro Colorado Island, Panama. Pairs of traps (pan traps and pole traps) placed 1 m above the ground, respectively, collected fallen arthropods and arthropods potentially climbing to the canopy.Average (±SE) arthropod biomass in pan traps was dominated by Hymenoptera (primarily ants; 0.501 ± 0.023 mg dry mass m⁻² day⁻¹) and Lepidoptera larvae (0.228 ± 0.001 mg m⁻² day⁻¹). Total dry biomass in pan traps was 0.891 ± 0.033 mg m⁻² day⁻¹; thus, ca. 27 kg of arthropod biomass rains into the understory per km²per month during the wet season in this forest. This equates to ca. 3 million mid‐sized ants falling from the canopy per day on BCI as a whole.Arthropod abundance in pan traps, especially ants and spiders, increased marginally with the increasing number of high‐wind events. By contrast, arthropod biomass showed no relationship with wind or rain.Arthropod abundance was higher in pole traps than in pan traps and was dominated by Collembola and Acari. Compositional overlap between pan and pole trap contents suggests that some fallen arboreal arthropods regularly return to the canopy.These findings illustrate an understudied pathway linking canopy and understory food webs within tropical forests, and the complex interactions between environmental conditions and arthropod rain. 

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5. Similarities in Storage and Transport of Sulfate in Forested and Suburban Watersheds, Despite Anthropogenically Elevated Suburban Sulfate

   https://doi.org/10.1029/2023JG007588  

   Cosans, C L; Gomes, M L; Marsh, M J; Moore, J; Harman, C J (January 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Sulfate is a potential pollutant and important nutrient linked with the nitrogen, carbon, and phosphorus cycles. The importance of different anthropogenic sulfate sources in suburban streams (septic systems, fertilizer, road salt, and infrastructure) is uncertain, and the temporal dynamics of stream export sparsely documented. We study sources and export dynamics of sulfate in suburban and forested headwater catchments. Stream baseflow discharge and sulfate concentrations were strongly positively correlated in both watersheds with the highest values in spring. Suburban concentrations and fluxes (2.48–7.5 mg/L or 25.8–78.1 μM, 16.6 kg/ha/yr) were consistently higher than forested (0.56–2.78 mg/L or 5.8–28.9 μM, 5 kg/ha/yr). Following precipitation, sulfate concentrations in both forested and suburban streams increased to concentrations above pre‐storm values and remained high after peak discharge. These dynamics suggest that both catchments have a large pool of sulfate that can be mobilized under wet conditions. Ridge‐top forest soil samples contained 210 kg/ha stored, extractable sulfate. Current atmospheric sulfate deposition rates (5–7 kg/ha/yr) are approximately in balance with sulfate export in the forested stream. In the suburban watershed, we estimated septic fields contribute up to 11 kg/ha/yr (about half from surfactants) and lawn care up to 4.3 kg/ha/yr and are the most likely sources of elevated stream sulfate. Sulfate sulfur (4.9–5.8‰ forested; 6.1–7.0‰ suburban) and oxygen isotope values (0.7–2.0‰ forested; −0.1–4.1‰ suburban) are consistent with this interpretation, but do not provide strong corroboration due to large variation and overlap in estimated source values. 

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