Global Change Biology最新文献

The sediments in mangrove forests play an important role in the global carbon cycle due to high inputs of organic matter (OM) and low decomposition rates, making them highly efficient at sequestering carbon. The balance between OM sequestration and decomposition in these systems is influenced by a complex interplay of environmental factors. However, there is a large amount of uncertainty surrounding decomposition rates from mangrove forests, particularly at regional scales. We used standardized decomposition assays of a labile and recalcitrant substrate in 30 estuaries, spanning a gradient in human land use intensity, to identify dominant drivers of OM decomposition in temperate mangrove forests. Our results reveal that, while labile OM decomposition is strongly driven by eutrophication, recalcitrant OM decomposition is primarily influenced by increases in the minimum sediment temperature. Furthermore, we demonstrate that nutrient enrichment from human land use, in combination with increased sediment temperature, synergistically accelerates the decomposition of labile OM, thereby threatening the carbon sequestration potential of these ecosystems. This suggests that coastal eutrophication can exacerbate the effects of warming on decomposition, leading to heightened vulnerability of carbon storage and potential feedbacks between local and global stressors.

Rapid Arctic warming is accelerating permafrost thaw and mobilizing previously frozen organic carbon (OC) into waterways. Upon thaw, permafrost-derived OC can become susceptible to microbial degradation that may lead to greenhouse gas emissions (GHG), thus accelerating climate change. Abrupt permafrost thaw (e.g., riverbank erosion, retrogressive thaw slumps) occurs in areas rich in OC. Given the high OC content and the increase in frequency of abrupt thaw events, these environments may increasingly contribute to permafrost GHG emissions in the future. To better assess these emissions from abrupt permafrost thaw, we incubated thaw stream waters from an abrupt permafrost thaw site (Duvanny Yar, Siberia) and additionally, waters from their outflow to the Kolyma River. Our results show that CO₂ release by volume from thaw streams was substantially higher than CO₂ emissions from the river outflow waters, while the opposite was true for CO₂ release normalized to the suspended sediment weight (gram dry weight). The CH₄ emissions from both thaw streams and outflow waters were at a similar range, but an order of magnitude lower than those of CO₂. Additionally, we show that nearshore riverbank waters differ in their biogeochemistry from thaw streams and Kolyma River mainstem: particles resemble thaw streams while dissolved fraction is more alike to the Kolyma River thalweg. In these waters dissolved OC losses are faster than in the river thalweg. Our incubations offer a first insight into the GHG release from permafrost thaw streams that connect exposed and degrading permafrost outcrops to larger river systems.

Brown bears across Europe are responding to the human footprint, with space use and movement behaviour strongly influenced by limited habitat connectivity. While natural food availability and habitat suitability remain important for bears, growing human pressure is increasingly constraining their ecological role. The picture was drawn by Andrea Gazzola.

Soil respiration, the main ecosystem process that produces carbon dioxide into the atmosphere, is sensitive to extreme climatic events. The immediate, usually negative effect of droughts on soil respiration has often been observed, but the recovery of soil respiration following drought is rarely documented. Soil respiration can be reduced beyond the drought year if drought-induced changes suppress soil activity. Alternatively, reduction in soil respiration may be overcompensated in the subsequent years due to increased substrate input and soil moisture, resulting from plant dieback during drought. In addition, post-drought weather patterns may also affect the recovery of soil respiration. In a full-factorial grassland experiment, we combined an extreme (5 months) summer drought in 2014 with four levels of post-drought precipitation regimes, including severe (2 months) droughts, moderate (1 month) droughts, ambient weather, and water addition (four large rain events) in summers of 2015 and 2016. We measured soil respiration monthly between May and November, from 2013 to 2016. The extreme drought had an immediate strong negative effect, decreasing soil respiration by 50.8% in 2014 compared to the control plots, and it had a negative legacy effect in 2015 (14.5% reduction), but not in 2016. This legacy effect was unaffected by the post-drought precipitation regime. Moderate drought decreased soil respiration by 12.1% and 18.6%, while severe drought decreased soil respiration by 18.3% and 27.3% in 2015 and 2016, respectively, while water addition had no effect. Since soil water content in extreme drought plots recovered by 2015, we hypothesize that changes in soil biota and reduced root activity are responsible for extreme drought's long-term negative effects. Overall, our results highlight that extreme droughts may have negative effects on soil respiration well beyond the event, and thus the full effect on carbon cycling may be much larger than what is estimated solely based on the immediate effects.

Drying river networks include non-perennial reaches that cease to flow or dry, and drying is becoming more prevalent with ongoing climate change. Biodiversity responses to drying have been explored mostly at local scales in a few regions, such as Europe and North America, limiting our ability to predict future global scenarios of freshwater biodiversity. Locally, drying acts as a strong environmental filter that selects for species with adaptations promoting resistance or resilience to desiccation, thus reducing aquatic α-diversity. At the river network scale, drying generates complex mosaics of dry and wet habitats, shaping metacommunities driven by both environmental and dispersal processes. By repeatedly resetting community succession, drying can enhance β-diversity in space and time. To investigate the transferability of these concepts across continents, we compiled and analyzed a unique dataset of 43 aquatic invertebrate metacommunities from drying river networks in Europe and South America. In Europe, α-diversity was consistently lower in non-perennial than perennial reaches, whereas this pattern was not evident in South America. Concomitantly, β-diversity was higher in non-perennial reaches than in perennial ones in Europe but not in South America. In general, β-diversity was predominantly driven by turnover rather than nestedness. Dispersal was the main driver of metacommunity dynamics, challenging prevailing views in river science that environmental filtering is the primary process shaping aquatic metacommunities. Lastly, α-diversity decreased as drying duration increased, but this was not consistent across Europe. Overall, drying had continent-specific effects, suggesting limited transferability of knowledge accumulated from North America and Europe to other biogeographic regions. As climate change intensifies, river drying is increasing, and our results underscore the importance of studying its effects across different regions. The importance of dispersal also suggests that management efforts should seek to enhance connectivity between reaches to effectively monitor, restore and conserve freshwater biodiversity.

Fungal communities are critical for leaf decomposition, a central ecosystem function in streams. A wide range of anthropogenic stressors can alter their structure and function (i.e., leaf decomposition). Additionally, fungal communities are subject to seasonal turnover due to natural processes. Despite this, seasonality in interaction with varying stressor exposure has rarely been studied in the context of leaf decomposition. We investigated fungal community composition and leaf decomposition over one agricultural growing season by deploying leaf bags at least impacted forest and viticultural sites of 10 streams. Additionally, we transplanted leaf bags that had been colonised at the forest sites to viticultural sites to investigate how changes in stressor exposure affect the structure and function of fungal communities. Leaf decomposition was repeatedly lower in the viticultural treatment than in the forest treatment, which was partly explained by the environmental variables. The decomposition of the transplanted leaves varied across the time points and was overall more similar to that of the forest treatment. The fungal communities in April were similar across treatments, whereas all exhibited different seasonal community turnover. At later time points (June, August and September), the fungal communities from the forest and transplant treatment remained similar, likely triggered by the priority effects of the location of colonisation (forest). The viticultural treatment, however, deviated at these time points, which coincided with the timing of fungicide application. Overall, we show that both community composition and function of leaf decomposition exhibit seasonal and stressor-related variability. Thus, our study demonstrates that seasonality and the actual stressor regime need to be considered and well described when investigating land use effects on leaf decomposition and associated fungal communities.

Coral reefs, known for their remarkable diversity, serve a pivotal function in modulating the global oceanic carbon cycle and act as natural barriers that protect coastlines from erosion and storm surges by dissipating wave energy. Despite their importance, their sensitivity to temperature fluctuations, sea-level shifts and anthropogenic changes in the future is highly unknown. In this study, we create a comprehensive documentation of coral growth, sedimentology and ecology spanning the middle to late Holocene in the Gulf of Eilat/Aqaba, northern Red Sea. We then integrate these findings with a reconstruction of the area's environmental conditions over time. The findings reveal a noticeable hiatus of reef growth between 4400 and 1000 years BP (Before Present; “present” being defined as 1950), aligning well with comparable observations made across various locations in the Southern Hemisphere. The coral diversity and abundance along the cores display surprisingly similar patterns before and after the hiatus. This implies that the distinctive coral community thriving during the initial growth phase reappeared nearly 4000 years later, presumably sourced from the deeper reefs. The results are evaluated in the context of a potential sea-level drop and the resilience of coral communities to perturbations of this magnitude. We conclude that the hiatus at this site is due to a combination of factors, including tectonic activity and glacio-eustatic sea-level changes. Our research highlights the critical importance of understanding and managing coral reef ecosystems' responses to sea-level fluctuations to mitigate future impacts on these vulnerable environments.

Droughts affect soil microbial abundance and functions—key parameters of plant–soil carbon (C) allocation dynamics. However, the impact of drought may be modified by the mean climatic conditions to which the soil microbiome has previously been exposed. In a future warmer and drier world, effects of drought may therefore differ from those observed in studies that simulate drought under current climatic conditions. To investigate this, we used the field experiment ‘Hohenheim Climate Change,’ an arable field where predicted drier and warmer mean climatic conditions had been simulated for 12 years. In April 2021, we exposed this agroecosystem to 8 weeks of drought with subsequent rewetting. Before drought, at peak drought, and after rewetting, we pulse-labelled winter wheat in situ with ¹³CO₂ to trace recently assimilated C from plants to soil microorganisms and back to the atmosphere. Severe drought decreased soil respiration (−35%) and abundance of gram-positive bacteria (−15%) but had no effect on gram-negative bacteria, fungi, and total microbial biomass C. This pattern was not affected by the mean precipitation regime to which the microbes had been pre-exposed. Reduced mean precipitation had, however, a legacy effect by decreasing the proportion of recently assimilated C allocated to the microbial biomass C pool (−50%). Apart from that, continuous soil warming was an important driver of C fluxes throughout our experiment, increasing plant biomass, root sugar concentration, labile C, and respiration. Warming also shifted microorganisms toward utilizing soil organic matter as a C source instead of recently assimilated compounds. Our study found that moderate shifts in mean precipitation patterns can impose a legacy on how plant-derived C is allocated in the microbial biomass of a temperate agroecosystem during drought. The overarching effect of soil warming, however, suggests that how temperate agroecosystems respond to drought will mainly be affected by future temperature increases.