Ecosystems最新文献

Animal carcass decomposition is an often-overlooked component of nutrient cycles. The importance of carcass decomposition for increasing nutrient availability has been demonstrated in several ecosystems, but impacts in arid lands are poorly understood. In a protected high desert landscape in Argentina, puma predation of vicuñas is a main driver of carcass distribution. Here, we sampled puma kill sites across three habitats (plains, canyons, and meadows) to evaluate the impacts of vicuña carcass and stomach decomposition on soil and plant nutrients up to 5 years after carcass deposition. Soil beneath both carcasses and stomachs had significantly higher soil nutrient content than adjacent reference sites in arid, nutrient-poor plains and canyons, but not in moist, nutrient-rich meadows. Stomachs had greater effects on soil nutrients than carcasses. However, we did not detect higher plant N concentrations at kill sites. The biogeochemical effects of puma kills persisted for several years and increased over time, indicating that kills do not create ephemeral nutrient pulses, but can have lasting effects on the distribution of soil nutrients. Comparison to broader spatial patterns of predation risk reveals that puma predation of vicuñas is more likely in nutrient-rich sites, but carcasses have the greatest effects on soil nutrients in nutrient-poor environments, such that carcasses increase localized heterogeneity by generating nutrient hotspots in less productive environments. Predation and carcass decomposition may thus be important overlooked factors influencing ecosystem functioning in arid environments.

Benthic macrofauna modifies carbon and nutrient retention and recycling processes in coastal habitats. However, the contribution of benthic consumers to carbon and nutrient storage and recycling shows variation over spatial scales, as the benthic community composition changes in response to differences in environmental conditions. By sampling both shallow sandy and deep muddy sediments across a land-to-sea gradient in the northern Baltic Sea, we explored if benthic community composition, stoichiometry and process rates change in response to alterations in environmental conditions and food sources. Our results show that benthic faunal biomass, C, N, and P stocks, respiration rate and secondary production increase across the land-to-sea gradient in response to higher resource quality towards the open sea. The seston δ¹³C indicated terrestrial runoff and δ¹⁵N sewage input at the innermost study sites, whereas more fresh marine organic matter towards the open sea boosted benthic faunal carbon storage, respiration rate, and secondary production, that is, the generation of consumer biomass, which are essential processes for carbon turnover in this coastal ecosystem. Also, biological factors such as increasing species richness and decreasing biomass dominance of the clam Macoma balthica were significant in predicting benthic faunal C, N, and P stocks and process rates, especially at sandy sites. Interestingly, despite the variation in food sources, the benthic faunal C:N:P ratios remained stable across the gradient. Our results prove that human activities in the coastal area can influence the important links between biodiversity, structure, and process rates of benthic communities by modifying the balance of available resources, therefore hampering the functioning of coastal ecosystems.

Soil organic matter (SOM) is a major global carbon (C) pool vulnerable to ongoing warming, as microbial SOM decomposition and CO₂ respiration are sensitive to temperature. We characterized the edaphic characteristics that explain variation in soil C concentration, cycling, and temperature sensitivity (Q₁₀) across two sites of differing elevation, forest community composition, and mineral parent material at Hopkins Memorial Forest, Williamstown, Massachusetts, USA. We found that the upper site maintained significantly higher surface soil C concentration, despite similar litterfall inputs across sites. We found large differences in the fraction of total soil C that is protected from microbial decomposition, with enhanced physical protection in macroaggregate-rich, upper site soils. Upper site plots maintain a higher relative abundance of plants producing lignin-rich litter, which may fuel aggregate formation and SOM protection. Experimental addition of glucose, vanillin, and lignin substrates produced broadly conserved respiratory responses across sites, suggesting that microbial communities maintain similar decomposition capacity, although lignin addition induced slightly elevated respiration responses in upper relative to lower site plots. Seasonal Q₁₀ of soil respiration was higher at the upper site and increased with soil potassium (K⁺) availability across plots, potentially reflecting K⁺ constraints on autotrophic and heterotrophic metabolic activity. Our findings suggest that variation in the extent of physical protection of soil C, particularly through macroaggregate formation, is an important mechanism for long-term soil C storage at the site. Despite enhanced SOM physical protection at the upper site, the higher temperature sensitivity of soil respiration may reduce soil C in the context of future warming.

Raised bogs are wetland ecosystems which, under the right climatic conditions, feature patterns of pool hollows and hummock ridges. The relative cover and the spatial arrangement of pool and ridge microforms are thought to be influential on peatland atmosphere carbon gas fluxes and plant biodiversity. The mechanisms responsible for the formation and maintenance of pools, and the stability of these features in response to warming climates, remain topics of ongoing research. We employed historical aerial imagery, combined with a contemporary uncrewed aerial vehicle survey, to study 61 years of changes in pools at a patterned raised bog in central Sweden. We used a pool inheritance method to track individual pools between image acquisition dates throughout the time series. These data show a rapid loss of open-water pool area during the study period, primarily due to overgrowth of open-water pools by Sphagnum. We postulate that these changes are driven by ongoing climate warming that is accelerating Sphagnum colonisation. Open-water pool area declined by 26.8% during the study period, equivalent to a loss of 1001 m² y⁻¹ across the 150-hectare site. This is contradictory to an existing theory that states pools are highly stable, once formed, and can only convert to a terrestrial state through catastrophic drainage. The pool inheritance analysis shows that smaller pools are liable to become completely terrestrialised and expire. Our findings form part of a growing body of evidence for the loss of open-water habitats in peatlands across the boreal and elsewhere.

The alpine meadow of the Qinghai–Tibetan Plateau is an essential terrestrial ecosystem that provides a livelihood for approximately 9.8 million local inhabitants and serves as a habitat for millions of livestock. Changing facets of the global environment, such as increased nitrogen deposition, have not only affected the abundance and quality of forgeable plants but have also increased the prevalence and severity of plant diseases caused by pathogens. However, whether or not and to what extent these pathogens affect the rangeland quality of the alpine meadow remains unclear. We conducted a factorial experiment with the exclusion of fungal and oomycete pathogens to investigate the impact of various pathogens on rangeland quality in an alpine meadow in the Qinghai–Tibetan Plateau. We measured forage production for each plant species, forage quality (including measurements of organic matter, crude protein, phosphorus, total phenolics, neutral detergent fiber (NDF), metabolizable energy, and digestibility) for 11 abundant species, and community composition. We found that fungal pathogen exclusion and the combination of fungal and oomycete pathogen exclusion primarily affected nutrient production by altering forage production rather than changing community composition or forage quality. Exclusion of both fungal and oomycete pathogens led to a significant increase in community forage production, although no significant effect was observed for individual exclusion of fungal or oomycete pathogens. Excluding either fungal pathogens alone or simultaneous exclusion of both fungal and oomycete pathogens significantly increased the metabolizable energy content of the community. In contrast, oomycete pathogen exclusion significantly decreased the forage metabolizable energy content of the community. The exclusion of both fungal and oomycete pathogens also considerably increased the yield of organic matter, total phenolics, NDF, digestible dry matter, and metabolizable energy. However, the direction and magnitude of the effect of fungal and oomycete pathogen exclusion varied widely across the different species studied. These results suggest that the interaction of fungal and oomycete pathogens constitutes an essential limiting factor in rangeland quality that has not been previously recognized. Greater attention should be placed on overall forage production rather than forage quality in the context of grassland pathogen control strategies. Furthermore, metabolizable energy content may serve as an effective indicator for predicting the impact of pathogenic activity on forage quality.

Drainage is known to reduce carbon sequestration in peatlands, but its effect on the stability of carbon pool and changes in recalcitrant organic carbon fractions remain relatively unknown, especially in temperate montane peatlands. We investigated the effect of drainage on physicochemical properties and organic carbon fractions of six peat cores from drained and near-pristine areas of Baijianghe peatland, NE China, basing on ²¹⁰Pb and AMS ¹⁴C dating. The vegetation biomass and biomass-C sequestration were also measured in both areas. The loss of total soil carbon accumulation due to drainage was 7.5 kg m⁻² (− 25%), equivalent to a complete consumption of carbon accumulated for nearly 170 years in the near-pristine area. Vegetation succession after drainage had a little positive effect on ecosystem carbon sequestration, with an increase of 0.26 kg m⁻², which compensated for only 3.5% of the peat soil carbon loss. Notably, over 80% of the total carbon loss after drainage was attributed to the loss of the recalcitrant carbon fraction. The study emphasizes the crucial impact of drainage on carbon sequestration in temperate peatlands. Our findings suggest that continuous water table drawdown induced by drainage, together with drought driven by climate warming, will further reduce carbon sequestration in drained peatlands. There is an urgent need to restore hydrology of peatlands in order to mitigate the long-lasting negative effect of drainage.

While climate change significantly influences nitrogen cycling and its related microbial diversity, the effects of warming on nitrate reduction processes and their related microbial communities and functional gene abundances in mangrove sediments are not fully understood. In this study, mangrove sediment slurry was incubated under six controlled temperatures for 28 days to simulate warming trends. Following the incubation, rates of denitrification (DNF), anaerobic ammonium oxidation (ANA), and nitrate decomposition reduction to ammonium (DNRA), and net nitrous oxide (N₂O) production, functional gene abundances, and the structure of functional microbial taxa were investigated using a ¹⁵N tracer method, high-throughput sequencing, and qPCR methods. DNF’s optimal temperature was 25 °C, but ANA’s ranged from 25 to 35 °C. The DNRA rates; nosZ, nirS, and nrfA gene abundances; nosZ/(nirK + nirS) ratios; and, in particular, net N₂O production in the mangrove sediment significantly increased with increasing temperature. Furthermore, DNRA’s contributions to nitrate reduction increased from 26.70% at 10 °C to 44.42% at 40 °C, suggesting that the DNRA process transforms more nitrate to ammonia and retains more nitrogen within mangrove sediments than the other processes do. Meanwhile, microbial taxa changed significantly in relation to DNRA, indicating that DNRA is enhanced as temperature increases. Also, temperature explained most of the variance in the dominant bacterial communities (68.3%), nitrate reduction functional genes (91.8%), and process rates (79.9%). Thus, warming promotes nitrogen conservation in mangrove sediments but stimulates N₂O emissions, which in turn exacerbates global warming.

Understanding the biotic mechanisms of community stability in variable environments has been a focal point of fundamental ecological research. A multitude of mechanisms, encompassing compensatory dynamics arising from negative species covariance, portfolio effect linked to species richness and evenness, and dominant species stability, have been found to collectively enhance community stability. However, it is not clear how their stabilizing effects change and contribute to the maintenance of community stability along environmental gradients. We performed a ten-year investigation in a large shallow lake with a eutrophic gradient across space. With the dataset, we quantified the role of the three stability mechanisms, and their changes in effect size along the eutrophic gradient to determine their relative importance in biomass stability. Our results showed that the biomass stability shifted from one stable state at eutrophic sites to another stable state at hypertrophic sites, and biomass stability was positively correlated with composition stability. In the relatively stable state, biomass stability exhibited a closely synchronized variation along with compositional stability in response to environmental changes. Conversely, in the unstable state, biomass stability displayed weaker sensitivity to environmental changes compared to compositional stability. The effect sizes of different biotic mechanisms of biomass stability varied across the eutrophic gradient. Compensatory dynamics emerged as the primary force governing biomass stability in eutrophic waters, overshadowing the relatively weak impact of the portfolio effect, which might help resist the shift from turbid state to clear state with decreasing nutrient concentrations. However, as nutrient levels increased, the primary force shifted from compensatory dynamics toward the dominant species stability. This study improves our understanding for the biotic mechanisms of phytoplankton community responding to nutrients mitigation in eutrophic waters, which might be one of the most important ecological components for managing communities to maintain ecosystem functioning.

Relatively unmanaged interstitial areas at the residential–wildland interface can support the development of novel woody plant communities. Community assembly processes in urban areas involve interactions between spontaneous and cultivated species pools that include native, introduced (exotic/non-native) and invasive species. The potential of these communities to spread under changing climate conditions has implications for the future trajectories of forests within and beyond urban areas. We quantified woody vegetation (including trees and shrubs) in relatively unmanaged “interstitial” areas at the residential–wildland interface and in exurban reference natural areas in six metropolitan regions across the continental USA. In addition, we analyzed soil N and C cycling processes to ensure that there were no major anthropogenic differences between reference and interstitial sites such as compaction, profile disturbance or fertilization, and to explore effects of novel plant communities on soil processes. We observed marked differences in woody plant community composition between interstitial and reference sites in most metropolitan regions. These differences appeared to be driven by the expanded species pool in urban areas. There were no obvious anthropogenic effects on soils, enabling us to determine that compositional differences between interstitial and reference areas were associated with variation in soil N availability. Our observations of the formation of novel communities in interstitial spaces in six cities across a very broad range of climates, suggest that our results have relevance for how forests within and beyond urban areas are assessed and managed to provide ecosystem services and resilience that rely on native biodiversity.