Global Change Biology最新文献

Nitrogen (N) and phosphorus (P) cycling are crucial for terrestrial ecosystem productivity and carbon sequestration. While biodiversity is known to regulate soil N and P availability, the mechanistic linkages between biodiversity and fundamental processes of nutrient cycles remain unclear. This knowledge gap limits our capacity to model ecosystem biogeochemical responses to biodiversity loss. Using a large-scale tree diversity experiment in subtropical China, we examined how tree species richness regulates ecosystem nutrient cycling in a region with N sufficiency but P limitation. We found that increased tree species richness enhanced N retention by boosting plant N stock and recycling, while reducing soil NO₃ ^- leaching and N₂O emissions. These shifts, coupled with a reduction in soil δ¹⁵N, demonstrate tighter N cycling. Concurrently, tree species richness increased soil acid phosphatase activity, foliar P resorption efficiency, and plant P storage, synergistically accelerating ecosystem P cycling. Our integrated findings provide direct experimental evidence that tree diversity regulates both N and P cycling, offering valuable insights into how plant diversity can mitigate nutrient imbalances and promote ecosystem resilience to nutrient limitations.

Alpine grasslands are vital for biodiversity and ecosystem service delivery, yet their responses to climate change remain a focus of intense scientific interest. While studies have examined separate ecological processes such as biodiversity changes or treeline shifts, broader ecosystem changes are not as well understood. Here, leveraging time series of high-resolution images from the Landsat satellite, we developed an automated method to track the shifts in the upper limits of alpine grasslands on the high and expansive Tibetan Plateau, a region of high ecological and climatic significance. Our analysis revealed modest upward boundary shifts of -0.55 to 0.99 m year^-1 (2nd-98th percentile; mean = 0.12 m year^-1) across the plateau over nearly four decades, from 1986 to 2023, with faster rates in wetter areas, yet drastically slower than the rapid climate-driven isotherm shifts of 3.35 to 12.04 m year^-1. This substantial lag, further confirmed by ≤ 3 m resolution satellite images, is potentially attributed to water scarcity, poor soil quality, and a lack of stable substrates beyond the current boundaries and geomorphological features. Consequently, the upward expansion of alpine grasslands on the Tibetan Plateau-attributed to the shift of the upper grassland boundary-was limited to approximately 6100 km². Notably, two high-spatial-resolution CMIP6 models simulated more rapid upward expansion of alpine grasslands and greater carbon sequestration than observed. These findings underscore the need to integrate local environmental nuances into future predictions. Our study elucidates the resilient yet vulnerable nature of alpine ecosystems, sparking new conversations regarding effective strategies to safeguard these extraordinary landscapes under changing climate.

Tropical peatland wildfire incidence has risen in recent decades, driven by drainage for land use and intensified by severe droughts with global climate change. These disturbances have altered vegetation structure, disrupted ecosystem functioning, and increased carbon emissions, particularly in Southeast Asia. However, the long-term history and characteristics of wildfires in tropical peatlands remain largely unknown. Here, we compiled fifty-eight macro-charcoal records from peatlands across the tropics, ranging from lowland forested to montane peatlands, to assess millennia-scale changes and controlling factors of tropical peatland burning. We divided the datasets into four main sub-regions: Neotropical, Afrotropical, Indomalayan and Australasian ecoregions to explore regional variability. Tropical peatlands had high burning levels between 0 and 850 ce, followed by a relatively low and stable period until a marked increase during the 20th century. The general trend in tropical peatland burning follows changes in global temperature, and climate variables that control the length and severity of drought events have a notable influence on peat burning before 1900 ce. During the 20th century, regional differences were observed, with declining fire trends in the Neotropical and Afrotropical regions and increasing fire trends in the Indomalayan and Australasian regions. This difference is likely attributable to human activities, and such intervention is also evident in palm swamps and hardwood swamps under similar wet, weakly seasonal climates. With the increase in anthropogenic pressures on peatlands and greater climate variability, future wildfires in peatlands are likely to become more frequent and widespread across all tropical ecoregions. Conservation and sustainable land-use practices could be used to mitigate and control peatland burning and protect these carbon-rich sinks.

Carbon efflux (C_efflux) makes up 20% of total greenhouse gases emitted globally. Accurate global C_efflux is critical for projecting and responding to future global warming. However, current C_efflux estimates remain incomplete due to the omission of C_efflux released from the dissolution of inorganic carbon in calcareous soils (C_{efflux-calcareous}) and dissolution of lime in acidic soils (C_{efflux-acidic}). Here, we present a global terrestrial C_efflux that incorporates C_{efflux-calcareous}, C_{efflux-acidic}, and soil respiration. Using 7562 field measurements from 2481 publications and machine learning, this study revealed that C_{efflux-acidic} and C_{efflux-calcareous} contributed 0.29% and 0.09%, respectively, to an overall C_efflux of 96.52 Pg C year^-1 (95% confidence interval, 91.2-101.9 Pg C year^-1). Previous estimates of C_efflux from soil respiration underestimated 0.4% of C_efflux. Structural equation modelling (SEM) revealed that C_efflux was directly driven by heterotrophic respiration, autotrophic respiration, dissolution of soil inorganic carbon and liming, while being regulated indirectly by land productivity (gross primary productivity, roots and litter), soil properties (soil acidity and soil inorganic carbon content), and anthropogenic activities (nitrogen fertiliser application). Soil acidification must be viewed as a dual challenge impacting both crop yields and global warming threats. Therefore, the study emphasises the need to incorporate neutralising soil acidity into soil carbon dynamics models, which was previously overlooked.