Abstract Forests north of 45°N are vital carbon sinks, but increasing wildfire frequency and intensity threaten their carbon sequestration capacity. This study assesses post‐fire aboveground carbon (AGC) accumulation rates in boreal and temperate forests north of 45°N to better understand carbon recovery patterns. We employed a space‐for‐time substitution approach, integrating remote sensing data and field observations within 1‐degree grid cells, and modeled AGC accumulation over time using the Chapman‐Richards growth function. Our results indicate that during the early recovery period (1–30 years), the mean AGC accumulation rates averaged 0.93 ± 0.53 Mg C ha −1 yr −1 , with European forests exhibiting the highest rates at 1.63 ± 0.38 Mg C ha −1 yr −1 . Recovery times to reach 85% of old‐growth biomass averaged 87 ± 17 years, varying significantly among regions. Random Forest analysis identified mean annual temperature as a primary driver of AGC accumulation rates, followed by the proportion of mixed forests and summer precipitation. Climate change projections under the SSP1‐2.6 and SSP5‐8.5 scenarios suggest an overall increase in AGC accumulation rates, particularly under the high‐emission pathways. Regional variations are pronounced, with North America predicted to experience significant increases, while Europe may decline due to drought stress. These findings underscore the critical roles of climate and vegetation composition in post‐fire AGC accumulation and highlight the complex interplay of factors influencing forest regrowth. Our spatial estimates provide region‐specific benchmarks for prioritizing post‐fire monitoring and restoration planning in areas with slow or climate‐sensitive carbon recovery and for improving regional carbon accounting.
Abstract Soil acidification caused by increased nitrogen (N) inputs has emerged as a global environmental concern that threatens ecosystem functioning and food security worldwide. However, how background soil pH influences the extent and mechanism of N‐induced acidification remains poorly understood. By assembling a global data set of field N addition experiments, we showed that the degree of acidification was most pronounced in neutral soils (pH 5.98–7.95), followed by acidic (pH ≤ 5.98) and alkaline (pH > 7.95) soils. In acidic soils, ammonia‐oxidizing archaea continuously released protons during the nitrification process, and the relatively weak buffering capacity exacerbated acidification. In neutral soils, N inputs increased the abundance of ammonia‐oxidizing bacteria (AOB) as well as nirS‐ and nirK‐harboring denitrifiers. These microbes exhibited strong N transformation capabilities, resulting in severe soil acidification due to the marked decline in buffering cations such as calcium (Ca 2+ ) and magnesium (Mg 2+ ). In alkaline soils, the high buffer capacity provided by carbonates (CO 3 2− ) initially mitigated acidification. However, high background pH promoted the growth of AOB and nirK denitrifiers after N inputs, potentially initiating acid‐generating reactions and gradually depleting the soil's CO 3 2− buffer capacity. Our study suggests that N‐induced soil acidification is strongly regulated by background soil pH, with the microbial N transformation process and soil buffer capacity playing crucial mediating roles. These findings have important implications for developing sustainable soil management strategies under continued N enrichment.
Abstract In regions far removed from major atmospheric dust sources, such as the South Pacific and Southern Ocean, boundary exchange processes play a dominant role in regulating the supply of trace elements and their isotopes (TEIs) to the upper ocean, with important consequences for ecological stoichiometry and productivity. Here, we use radium (Ra) isotopes ( 223 Ra, 226 Ra, 228 Ra) as tracers of boundary exchange along the US GEOTRACES GP17‐OCE Pacific and Southern Ocean transect, providing the first full ocean‐basin section of excess 223 Ra. Activities of 228 Ra exhibit a prominent subsurface maximum (mean ≈0.21 dpm/100 L) between 20°S and 55°S that persists to ≈800 m. Hydrographic context and GLORYS12 velocity fields link this maximum to Subantarctic Mode Water sourced over the shallow Campbell Plateau. We infer source activities of 0.22–0.31 dpm/100 L, implying ventilation and export on sub‐annual to 2‐year timescales. Near‐bottom inventories of 228 Ra and excess 223 Ra reveal spatially variable benthic fluxes, and zonal integration of 228 Ra indicates that fluxes in the North and South Pacific are similar (2.8 × 10 16 and 3.5 × 10 16 dpm/yr, respectively), and comparable in magnitude to coastal 228 Ra inputs to the Pacific Ocean. Above the Pacific–Antarctic Ridge, elevated excess 223 Ra, 224 Ra, and 228 Ra, together with activity ratios, indicate entrainment of low‐temperature hydrothermal fluids that are weeks to a month old. Collectively, these results identify mode waters formed over the Campbell Plateau as a dominant conveyor of shelf‐derived Ra—and associated TEIs—to the South Pacific interior and document an active Pacific–Antarctic Ridge hydrothermal contribution that is underrepresented in current TEI models.
Abstract Canopy is a critical interface influencing atmospheric nitrogen (N) inputs into forest soils. Ammonium (NH 4 + ) is a major chemical form of N deposition. However, the fluxes of precipitation‐canopy NH 4 + exchange processes and their environmental responses remain unclear, which impairs the assessment of N deposition effects on forest biodiversity and functions. By collecting and synthesizing the flux and N isotope ( δ 15 N) data, we quantified the actual input of NH 4 + by comparing the differences in bulk precipitation and throughfall NH 4 + fluxes. We then constructed a novel model based on δ 15 N to identify the sources contributing to elevated throughfall NH 4 + fluxes and to elucidate the NH 4 + interactions between atmosphere and canopy. Results showed that throughfall had generally higher NH 4 + fluxes (by 26% and 74%) and δ 15 N values than bulk precipitation. Throughfall gained total 67% of NH 4 + (5.6 ± 6.5 and 6.0 ± 8.4 kg‐N/ha/yr) from canopy particulates and mineralization, while canopy retained 59% and 41% of precipitation NH 4 + (4.1 ± 4.4 and 2.2 ± 4.0 kg‐N/ha/yr) in broadleaved and coniferous forests, respectively. In addition, we identified that the fluxes of precipitation‐canopy NH 4 + exchange processes increased with NH 4 + deposition levels. These results revealed that dry deposition and microbial mineralization in canopy are important NH 4 + replenishment to throughfall and atmospheric NH 4 + loading would stimulate precipitation‐canopy NH 4 + exchanges. Our findings enrich the knowledge of forest N biogeochemistry and are useful for evaluating forest N deposition effects.
A technology-resolved bottom-up model is used to quantify the current state of global anthropogenic methane emissions and the scope for limiting these in a 2030 to 2050 timeframe. Findings show that with current legislation and “middle-of-the-road” developments in global energy and agricultural systems, anthropogenic methane emissions continue on an upward trend in the next decades. With full implementation of current national plans for methane mitigation, emissions decline between 2020 and 2030, but not enough to meet the Global Methane Pledge target of a joint global reduction by 30%. The pledge target can be met through full implementation of existing technology, with 70% of mitigation potential in the energy sector. Maintaining low methane emissions beyond 2030, requires also investments into improved waste and wastewater systems and measures to control emissions from livestock and rice cultivation, combined with demand-side measures to phase-down fossil fuels and shifts to more sustainable consumption patterns.
