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.