Global Change Biology最新文献

Under global warming, spring phenology in northern ecosystems (tundra, boreal forests, temperate grasslands, coniferous forests) has advanced, yet the causes of regional disparities and nonlinear responses remain unclear. While temperature and precipitation are recognized primary drivers, the regulatory role of freeze–thaw cycles (FTCs) on the start of growing season (SOS) is largely overlooked. Integrating 20 years (2003–2022) of satellite phenology and climate reanalysis data, this study assesses FTCs frequency impacts on SOS dynamics across the pan-Northern Hemisphere. Despite SOS advancing 1.9 days/decade on average, over 28% of vegetated areas show stable or delayed trends, particularly in boreal forests, alpine regions, and tundra. This pattern is linked to the heterogeneous increase in FTCs frequency, which modulates SOS in biome-specific and nonlinear ways. Frequent FTCs advanced SOS in boreal forests by up to 7 days, likely due to cumulative thermal pulses that reduce dormancy depth. In contrast, desert and temperate forest systems experienced delays exceeding 20 days, associated with repeated low-temperature stress. Sensitivity analyses using ridge regression and generalized additive models revealed that FTCs accounted for up to 14.6% of SOS variability in temperate broadleaf forests—comparable to precipitation and radiation. However, SOS sensitivity to FTCs has declined over time, coinciding with shorter frozen seasons, while sensitivity to shortwave radiation increased. These shifts indicate a reorganization of climatic constraints on phenology. Biomes exhibited divergent sensitivity trajectories: forests and grasslands became more responsive to temperature and radiation, whereas FTCs influence declined in boreal systems but intensified in coniferous and shrub-dominated landscapes. Our findings highlight FTCs as dynamic regulators of phenology that can offset warming-driven advancement.

Dark CO₂ fixation (DCF) in soil is a carbon sink process, in which microorganisms reduce CO₂ to organic matter. This process occurs most at the oxygen-anoxia interface, where microorganisms oxidize reduced inorganic substrates to obtain metabolic energy. By synthesizing 215 observations from 27 peer-reviewed studies and one controlled condition study using ¹³C-, ¹⁴C-based approaches, we conducted a meta-analysis to quantify DCF rates and identify their controlling factors across soils. Soils have an average DCF rate of 0.26 ± 0.02 μg C g⁻¹ soil day⁻¹, with the highest rates in wetlands (0.48 μg C g⁻¹ soil day⁻¹). Across all observations, microbial biomass carbon emerged as the dominant factor of DCF, while soil depth, pH, and electron donors also contributed to its variation. DCF rates increased under higher microbial biomass and moderate alkalinity but declined with depth, reflecting the influence of microbial biomass and metabolic activity as well as substrate accessibility. Hydrological regimes modulated DCF, with wetter ecosystems and stronger redox oscillations stimulating chemoautotrophic processes. Land use and management are additional factors affecting DCF intensity. The optimal pH for DCF differed by land-use type, peaking at 6.9 in cropland soils and 4.8 in natural ecosystems. Agricultural management shaped DCF dynamics: tillage and mineral fertilization raised DCF rate, while organic amendments suppressed its activity. These patterns likely arise from distinct microbial CO₂ fixation pathways, where the Calvin-Benson-Bassham cycle dominates under oxic and moderately alkaline conditions, and the reductive tricarboxylic acid and Wood-Ljungdahl pathways prevail in anoxic environments. Overall, DCF represents an underappreciated but ecologically relevant microbial process contributing to organic carbon accrual in soil. Incorporating DCF mechanisms into terrestrial carbon models could improve the representation of microbial carbon inputs and their feedbacks to soil carbon dynamics.

Micro/nano-plastics (M/NPs) as emerging particulate pollutants pose significant risks to ecosystem health. Nitrogen (N) cycling plays a crucial role in biogeochemistry and largely depends on microbe-driven N transformation. However, how and why N cycling responds to M/NP exposure in different environmental media such as soil and sediment remains largely unknown. Herein, through a meta-analysis of 116 publications, we found that M/NP exposure significantly reduced soil NO₃⁻ concentrations (24.9%) and enhanced N₂O emissions (32.6%), while increasing sediment NH₄⁺ concentrations (21.6%) and N₂O emissions (38.1%). The dynamics of N and N₂O emissions were jointly regulated by M/NPs exposure characteristics and the environmental medium. Particularly, soil N₂O emissions increased when the exposure dose exceeded 0.2% or the exposure duration was within 34.7 days. In sediments, N₂O emissions were enhanced under a wider range of conditions: when the exposure dose was either between 0.003% and 0.5% or above 1%, the particle size was less than 398.8 μm, or the exposure duration ranged from 5.5 to 353.1 days. This broader responsiveness indicates that sediment ecosystems are more sensitive to M/NPs-induced N₂O emissions than soil ecosystems. The mechanistic basis for the media-dependent effects of M/NPs on N cycling lies in their distinct regulation of key microbial functional gene abundance. Specifically, in soils, N₂O emissions were driven by an increased abundance of genes encoding nitrate reductase (nar) and nitrite reductase (nir), stimulating the denitrification pathway. Conversely, in sediments, the upregulation of nitric oxide reductase (nor) genes enhanced the conversion of NO to N₂O. Overall, by revealing how M/NP properties and environmental media interact to govern N cycling, this work provides a scientific foundation for predicting and mitigating N₂O emissions from terrestrial and aquatic ecosystems under increasing M/NP pollution.

Grassland ecosystems play essential roles in global carbon cycling and biodiversity conservation, yet it remains unclear whether belowground productivity is less sensitive to environmental change than aboveground productivity. Previous studies have predominantly focused on aboveground net primary productivity (ANPP) stability, potentially overestimating ecosystem vulnerability by neglecting critical belowground processes. By synthesizing 1513 observations from 113 studies across 85 grassland ecosystems worldwide, we quantified the responses of productivity, temporal stability, and carbon allocation to nine global change drivers, including nutrient enrichment, altered precipitation, elevated CO₂, warming, mowing, and grazing. Our results reveal that belowground net primary productivity (BNPP) stability shows generally weaker responses to global change drivers than ANPP stability. In addition, variation in ANPP stability was most closely associated with broad-scale climatic indices of water supply (precipitation and aridity, used here as proxies for plant-available soil water), whereas BNPP stability was more closely associated with edaphic context (soil moisture-related and fertility-related properties). These distinct patterns suggest that broad-scale climatic variability is more strongly reflected in aboveground stability, whereas belowground stability is better captured by edaphic predictors related to water retention and nutrient availability. Moreover, variation in belowground carbon allocation was consistently associated with stronger coordination between above- and belowground responses and with the maintenance of BNPP stability under global-change perturbations, suggesting a potential allocation-related pathway linked to ecosystem resistance. Our findings challenge traditional ecological theories emphasizing unified above-belowground responses and suggest that previous research focusing solely on aboveground processes may have overestimated grassland vulnerability. This synthesis provides critical insights for predicting grassland ecosystem stability and functioning under ongoing global environmental changes.

Fates of atmospheric reactive nitrogen (N) mainly contain foliar absorption of gaseous N, deposition in emission regions, and transportation out of emission regions, which determines their eco-environmental and climatic effects. However, it has long been challenging to estimate fractions and fluxes of reactive N fates in the atmosphere. Here we quantified regional ammonium-N and nitrate-N deposition in North America, Europe, and East Asia based on moss N contents and natural N isotopes. In combination with regional N emissions and foliar absorption rates of N gases, we further constrained major fates (deposition, foliar absorption, and export) of N emissions in the above regions. We found that 72% ± 15%, 59% ± 8%, and 72% ± 11% of N emissions (15.7 ± 4.3, 25.5 ± 5.3, and 28.0 ± 6.1 kg-N/ha/year) deposited back to three study regions, respectively. Having larger N emissions and deposition, Europe and East Asia also had larger exports (5.9 ± 5.9 and 4.2 ± 6.4 kg-N/ha/year, respectively) than those of North America (0.6 ± 4.8 kg-N/ha/year). Adding the area-weighted N emissions in three regions together, about 2/3 of N emissions deposited back to land, 1/6 was absorbed by plant leaves, and the remaining 1/6 was transported out of three regions. This work provides a unique method for unlocking processes of land-air N exchanges and useful evidence for evaluating effects of regional atmospheric N pollution.

Mass coral bleaching has become a hallmark ecological signature of anthropogenic climate change, yet the structural mechanisms governing its spatial and temporal evolution remain poorly resolved. Traditional assessments emphasize surface thermal anomalies and strong El Niño phases but increasingly fail to explain the persistence of bleaching, its regional asymmetry, and the instability of ecological thresholds. Here, using long-term datasets (1993–2020) of ocean temperature, bleaching alerts, El Niño–Southern Oscillation (ENSO) indices, coral–algal cover, and subsurface thermal profiles, we identify a regime shift from episodic bleaching toward chronic thermal exposure. This shift reflects a reduced dependence of bleaching on ENSO intensity, as even moderate ENSO phases, including both El Niño and La Niña events, are now associated with widespread bleaching, suggesting progressive erosion of thermal thresholds under sustained ocean warming. We further propose a “Structure–Pathway–Response” framework to capture the structural reconfiguration of bleaching risk: (i) heat convergence along eastern continental margins (e.g., East Asian Seas, Caribbean); (ii) poleward transport and topographic retention of subsurface heat along continental slopes; and (iii) vertical accumulation through isotherm deepening that elevates bleaching risk. We identify two dominant heat-retention regimes: a current-deflection mode in the Northern Hemisphere and a thermal-stacking mode in the Southern Hemisphere. These patterns increase regional vulnerability by broadening the spatial extent and persistence of thermal anomalies, reflecting processes not fully captured by surface Sea Surface Temperature (SST) variability. Our findings highlight the limitations of surface-only monitoring systems and underscore the need for thermodynamically informed, region-specific early-warning frameworks. Protecting structural thermal refugia and managing heat pathways will be critical for sustaining coral reef resilience in a rapidly warming ocean.

Large soil organic carbon (SOC) stocks in alpine tundra play a critical role in the global carbon budget but are increasingly vulnerable to loss under climate warming. These losses are partly driven by vegetation shifts, such as the upward migration of herbaceous plants, which alter soil food web structure and influence SOC sequestration. Although interactive effects between these processes are expected, they remain largely unclear or hidden. Here, we conducted a ¹³C-labeled glucose tracing experiment in the alpine tundra of Changbai Mountain to investigate how upward migration of Deyeuxia angustifolia affects soil food web structure, energy flows, and ultimately SOC sequestration. Compared with soils without migration (NM), heavily herb-migrated (HM) soils showed intensified carbon fluxes within trophic cascade, increasing carbon transfer to higher trophic levels, including fungivores, omnivores-predators, plant-parasites, meso- and macrofauna. Predators in HM soils progressively increased ¹³C assimilation over the 30-day period, while microbivores showed a 5-day lag behind microbial ¹³C uptake. This predator-driven energy dissipation was 2–14 times greater in HM than in NM soils and constituted an inefficient carbon sequestration pathway that limited the formation of stable carbon pools. As a result, SOC turnover in HM soils was more than 50% lower than in NM soils, indicating a shift toward less stable organic matter forms and reduced net carbon accumulation. Overall, our findings demonstrate that soil food webs play a pivotal role in both “belowground shaping” and “aboveground feedback” processes during herbaceous plant migration and that strengthened trophic cascade effects redirect carbon flow toward inefficient pathways, thereby constraining SOC sequestration in alpine tundra ecosystems.

Arctic permafrost soils are increasingly subject to thermokarst that is, abrupt ground subsidence caused by thaw. Wetlands can form within these depressions, leading to changes in organic matter decomposition and gas fluxes (CO₂, CH₄, N₂O, NH₃). Thermokarst wetlands tend to be dominated by graminoids, while surrounding upland tussock tundra tends to be dominated by mixed communities of shrubs and graminoids. To investigate how thermokarst alters the land-atmosphere exchange of C and N gases in Arctic tundra, we analyzed soil, porewater, above- and belowground biomass, and measured gas fluxes across dominant plant functional types (PFTs) within a lowland thermokarst wetland and adjacent upland tussock tundra. Both locations were overall sinks of CO₂, sources of CH₄, and sources of both N₂O and NH₃. We found that thermokarst wetlands emitted enough CH₄ to generate a positive radiative forcing in CO₂ equivalents (+1.2 μmol m⁻² s⁻¹ CO₂-eq), counteracting the high CO₂ uptake. In contrast, the upland tussock tundra had a net negative radiative forcing (−1.2 μmol m⁻² s⁻¹ CO₂-eq). Differences in gas flux and soil chemistry between upland and lowland are primarily driven by flooded conditions present in thermokarst wetland. Additionally, root biomass from graminoids across both lowlands and uplands significantly correlated with CH₄ fluxes, supporting previous observations of plant-mediated transport of CH₄. Graminoid cover was correlated with increases in low molecular weight dissolved organic carbon, possibly associated with root exudates that fuel methanogenesis. Forb cover in the upland tussock tundra was significantly correlated with nine soil chemical variables, indicating that forbs may influence local soil chemistry or conversely, that soil chemistry controls where forbs grow. Overall, our findings indicate the variability in gas fluxes in the upland tussock tundra is partially controlled by PFT cover, while thermokarst wetlands emit enough CH₄ to counteract CO₂ uptake, with implications for carbon budget changes in Arctic systems.