Carbon Cycle Research Articles

Evolution of unexpected diversity in a putative mating type locus and its correlation with genome variability reveals likely asexuality in the model mycorrhizal fungus Rhizophagus irregularis

BackgroundArbuscular mycorrhizal fungi (AMF) form mutualistic partnerships with approximately 80% of plant species. AMF, and their diversity, play a fundamental role in plant growth, driving plant diversity, and global carbon cycles. Knowing whether AMF are sexual or asexual has fundamental consequences for how they can be used in agricultural applications. Evidence for and against sexuality in the model AMF, Rhizophagus irregularis, has been proposed. The discovery of a putative mating-type locus (MAT locus) in R. irregularis, and the previously suggested recombination among nuclei of a dikaryon R. irregularis isolate, potentially suggested sexuality. Unless undergoing frequent sexual reproduction, evolution of MAT-locus diversity is expected to be very low. Additionally, in sexual species, MAT-locus evolution is decoupled from the evolution of arbitrary genome-wide loci.ResultsWe studied MAT-locus diversity of R. irregularis. This was then compared to diversification in a phosphate transporter gene (PTG), that is not involved in sex, and to genome-wide divergence, defined by 47,378 single nucleotide polymorphisms. Strikingly, we found unexpectedly high MAT-locus diversity indicating that either it is not involved in sex, or that AMF are highly active in sex. However, a strongly congruent evolutionary history of the MAT-locus, PTG and genome-wide arbitrary loci allows us to reject both the hypothesis that the MAT-locus is involved in mating and that the R. irregularis lineage is sexual.ConclusionOur finding shapes the approach to developing more effective AMF strains and is highly informative as it suggests that introduced strains applied in agriculture will not exchange DNA with native populations.

Root exudates facilitate the regulation of soil microbial community function in the genus Haloxylon

IntroductionRoot exudates act as the "language" of plant-soil communication, facilitating crucial interactions, information exchange, and energy transfer between plants and soil. The interactions facilitated by root exudates between plants and microorganisms in the rhizosphere are crucial for nutrient uptake and stress resilience in plants. However, the mechanism underlying the interaction between root exudates and rhizosphere microorganisms in desert plants under drought conditions remains unclear, especially among closely related species.MethodsTo reveal the ecological strategies employed by the genus Haloxylon in different habitats. Using DNA extraction and sequencing and UPLC-Q-Tof/MS methods, we studied root exudates and soil microorganisms from two closely related species, Haloxylon ammodendron (HA) and Haloxylon persicum (HP), to assess differences in their root exudates, soil microbial composition, and interactions.ResultsSignificant differences were found in soil properties and root traits between the two species, among which soil water content (SWC) and soil organic carbon (SOC) in rhizosphere and bulk soils (P < 0.05). While the metabolite classification of root exudates was similar, their components varied, with terpenoids being the main differential metabolites. Soil microbial structure and diversity also exhibited significant differences, with distinct key species in the network and differential functional processes mainly related to nitrogen and carbon cycles. Strong correlations were observed between root exudate-mediated root traits, soil microorganisms, and soil properties, although the complex interactions differed between the two closely relative species. The primary metabolites found in the network of HA include sugars and fatty acids, while HP relies on secondary metabolites, steroids and terpenoids.DiscussionThese findings suggest that root exudates are key in shaping rhizosphere microbial communities, increasing microbial functionality, fostering symbiotic relationships with hosts, and bolstering the resilience of plants to environmental stress.

Emergent constraints on future Amazon climate change-induced carbon loss using past global warming trends

Reducing uncertainty in the response of the Amazon rainforest, a vital component of the Earth system, to future climate change is crucial for refining climate projections. Here we demonstrate an emergent constraint (EC) on the future response of the Amazon carbon cycle to climate change across CMIP6 Earth system models. Models that overestimate past global warming trends, tend to estimate hotter and drier future Amazon conditions, driven by northward shifts of the intertropical convergence zone over the Atlantic Ocean, causing greater Amazon carbon loss. The proposed EC changes the mean CMIP6 Amazon climate-induced carbon loss estimate (excluding CO2 fertilisation and land-use change impacts) from −0.27 (−0.59–0.05) to −0.16 (−0.42–0.10) GtC year−1 at 4.4 °C warming level, reducing the variance by 34%. This study implies that climate-induced carbon loss in the Amazon rainforest by 2100 is less than thought and that past global temperature trends can be used to refine regional carbon cycle projections.

Sustainable Production of Biofuels from Biomass Feedstocks Using Modified Montmorillonite Catalysts.

The rampant exploitation of fossil fuels has led to the significant energy scarcity and environmental disruption, affecting the sound momentum of development and progress of human civilization. To build a closed-loop anthropogenic carbon cycle, development of biofuels employing sustainable biomass feedstocks stands at the forefront of advancing carbon neutrality, yet its widespread adoption is mainly hampered by the high production costs. Montmorillonite, however, has garnered considerable attention serving as an efficient heterogeneous catalyst of ideal economic feasibility for biofuel production, primarily due to its affordability, accessibility, stability, and excellent plasticity. Up to now, nevertheless, it has merely received finite concerns and interests in production of various biofuels using montmorillonite-based catalysts. There is no timely and comprehensive review that addresses this latest relevant progress. This review fills the gap by providing a systematically review and summary in controllable synthesis, performance enhancement, and applications related to different kinds of biofuels including biodiesel, biohydrogenated diesel, levulinate, γ-valerolactone, 5-ethoxymethylfurfural, gaseous biofuels (CO, H2), and cycloalkane, by using montmorillonite catalysts and its modified forms. Particularly, this review critically depicts the design strategies for montmorillonite, illustrates the relevant reaction mechanisms, and assesses their economic viability, realizing sustainable biofuels production via efficient biomass valorization.

Dissolved ammonia catalyzes proto-dolomite precipitation at Earth surface temperature

Marine carbonate rocks are the major reservoir of carbon through CaCO3 and CaMg(CO3)2 precipitation extracting CO2/HCO3- from the atmosphere/oceans; hence dolomite is one of the major sinks in the global carbon cycle. Most ancient dolomite has been considered as mainly precipitated under Earth surface conditions. Previous studies have demonstrated that microbes can mediate dolomite formation. However, the “microbial dolomite” model is not sufficient to explain the dolomite that shows no or little evidence of a microbial origin. Although attempted for decades, the synthesis of inorganically-produced dolomite at normal temperatures (<50 °C) has been relatively unsuccessful. Hence, this "dolomite enigma" has been one principal research focus this century. Here we demonstrate that NH3 catalyzes proto-dolomite precipitation inorganically with higher Mg/Ca molar ratios and CO32- activity at normal temperatures of 30 °C and 40 °C. NH3 dissolution increases the alkalinity of the solution and transformes into NH4+ ions, which prefer to bond with H2O on Mg[(H2O)6]2+ rather than free H2O, thus releasing Mg2+ to facilitate proto-dolomite nucleation. Furthermore, the low dielectric constant and low dipole moment allow NH4+ absorbed on crystal surfaces to lower the energy barrier of Mg[(H2O)6]2+ dehydration, promoting proto-dolomite nucleis growth. The system for proto-dolomite precipitation in our experiments closely simulates the natural aqueous environment. This study brings new insights to understanding the mechanisms of dolomite precipitation in natural waters.

Forest Canopy Height Estimation Combining Dual-Polarization PolSAR and Spaceborne LiDAR Data

Forest canopy height data are fundamental parameters of forest structure and are critical for understanding terrestrial carbon stock, global carbon cycle dynamics and forest productivity. To address the limitations of retrieving forest canopy height using conventional PolInSAR-based methods, we proposed a method to estimate forest height by combining single-temporal polarimetric synthetic aperture radar (PolSAR) images with sparse spaceborne LiDAR (forest height) measurements. The core idea of our method is that volume scattering energy variations which are linked to forest canopy height occur during radar acquisition. Specifically, our methodology begins by employing a semi-empirical inversion model directly derived from the random volume over ground (RVoG) formulation to establish the relationship between forest canopy height, volume scattering energy and wave extinction. Subsequently, PolSAR decomposition techniques are used to extract canopy volume scattering energy. Additionally, machine learning is employed to generate a spatially continuous extinction coefficient product, utilizing sparse LiDAR samples for assistance. Finally, with the derived inversion model and the resulting model parameters (i.e., volume scattering power and extinction coefficient), forest canopy height can be estimated. The performance of the proposed forest height inversion method is illustrated with L-band NASA/JPL UAVSAR from AfriSAR data conducted over the Gabon Lope National Park and airborne LiDAR data. Compared to high-accuracy airborne LiDAR data, the obtained forest canopy height from the proposed approach exhibited higher accuracy (R2 = 0.92, RMSE = 6.09 m). The results demonstrate the potential and merit of the synergistic combination of PolSAR (volume scattering power) and sparse LiDAR (forest height) measurements for forest height estimation. Additionally, our approach achieves good performance in forest height estimation, with accuracy comparable to that of the multi-baseline PolInSAR-based inversion method (RMSE = 5.80 m), surpassing traditional PolSAR-based methods with an accuracy of 10.86 m. Given the simplicity and efficiency of the proposed method, it has the potential for large-scale forest height estimation applications when only single-temporal dual-polarization acquisitions are available.

Green manure (Ophiopogon japonicus) cover promotes tea plant growth by regulating soil carbon cycling

IntroductionIn mountainous tea plantations, which are the primary mode of tea cultivation in China, issues such as soil erosion and declining soil fertility are particularly severe. Although green manure cover is an effective agricultural measure for restoring soil fertility, its application in mountainous tea plantations has been relatively understudied.MethodsThis study investigated the effects of continuous green manure cover using the slope-protecting plant Ophiopogon japonicus on tea plant growth and soil microbial community structure. We implemented three treatments: 1 year of green manure coverage, 2 years of coverage, and a control, to study their effects on tea plant growth, soil physicochemical properties, and soil bacterial and fungal communities.ResultsResults demonstrate that green manure coverage significantly promote the growth of tea plants, enhanced organic matter and pH levels in soil, and various enzyme activities, including peroxidases and cellulases. Further functional prediction results indicate that green manure coverage markedly promoted several carbon cycling functions in soil microbes, including xylanolysis, cellulolysis, degradation of aromatic compounds, and saprotrophic processes. LEfSe analysis indicated that under green manure cover, the soil tends to enrich more beneficial microbial communities with degradation functions, such as Sphingomonas, Sinomonas, and Haliangium (bacteria), and Penicillium, Apiotrichum, and Talaromyce (fungi). In addition. Random forest and structural equation models indicated that carbon cycling, as a significant differentiating factor, has a significant promoting effect on tea plant growth.DiscussionIn the management practices of mountainous tea plantations, further utilizing slope-protecting plants as green manure can significantly influence the soil microbial community structure and function, enriching microbes involved in the degradation of organic matter and aromatic compounds, thereby positively impacting tea tree growth and soil nutrient levels.

Season-Dependent Effect of Fire-Derived Charcoal on Above- and Belowground Litter Decomposition in Boreal Forests

Fire-derived charcoal (charcoal) is a stable byproduct of forest fires that accumulates in the litter layer and soils of boreal forests. Therefore, decomposition of litter and roots, as one of the key processes in the carbon cycle, in the soils of northern forests almost everywhere go in the presence of charcoal. To date, there are extremely scarce data on the influence of charcoal on decomposition in boreal forests, and most of them do not consider the cold period, which lasts on average half a year in this zone. The purpose of this work was to determine the seasonal influence of charcoal on the decomposition of plant litter of different quality (larch needles, birch leaves, grasses, and mixtures of these species of litter) on the surface of the soil and the roots of these same species in the soil. In “litterbag” experiment it was found that charcoal accelerated decomposition of litter and that its effect was species-specific. The acceleration of mass loss in the presence of charcoal occurred for recalcitrant litter (needles) and all types of roots during the cold period. In the warm period, acceleration of decomposition in the presence of charcoal was observed only for needles and was not observed for roots. Thus, our study shows a greater influence of charcoal on intra-soil decomposition especially in the cold period. Seasonal influence of charcoal was established for the first time and should be taken into account as an important factor of humus formation and carbon dynamics in soils of boreal forests.

Natural forest colonisation as a management strategy to restore soil functioning of abandoned agricultural lands

Abstract Land abandonment promotes forest expansion into abandoned agricultural lands in Europe. This process leads to changes that affect several ecosystem services, but it is considered a low‐cost strategy to restore soil functions in past agricultural lands. Soil microbial communities play a key role in restoring functions. However, the relationship among forest expansion, microbial communities, and soil functioning is unclear. In this study, we used a Juniperus thurifera expansion gradient on abandoned agricultural lands in Alto Tajo National Park (Spain) to discover the changes elicited by the soil microbial communities and their functions along this gradient considering two microhabitats, under the canopy and open areas. Specifically, our objectives were (i) to analyse how soil properties (organic matter and pH), microbial communities (using PLFAs‐NFLAs) and enzymatic activities (related to C, N and P cycling) varied along the forest expansion gradient and between microhabitats and (ii) to decipher the pathways by which soil properties control the carbon and nutrient cycling in soils. The forest expansion gradient had a direct negative effect on phosphatase activity. The microhabitat showed a positive direct effect on organic matter content, pH, actinomycetes and arbuscular mycorrhizal fungi biomass and on soil C and P cycling. Moreover, the biomass of gram‐positive bacteria determined the biomass of other microbial groups. Synthesis and Applications: Though its effectiveness is variable, passive restoration can be more effective than active restoration. Our research indicates that passive tree colonisation of past agricultural land is enough to achieve soil functionality similar to a mature forest for most variables studied. However, some variables would need more time to reach mature forest levels, such as total microbial biomass and organic matter content. Therefore, to support ecosystem recovery, the management of this applied forest ecology strategy requires continuous monitoring of newly established trees and soil to elucidate the time needed to achieve mature soil properties.

Influence of Rivers, Tides, and Tidal Wetlands on Estuarine Carbonate System Dynamics

AbstractVariations in estuarine carbonate chemistry can have critical impacts on marine calcifying organisms, yet the drivers of this variability are difficult to quantify from observations alone, due to the strong spatiotemporal variability of these systems. Terrestrial runoff and wetland processes vary year to year based on local precipitation, and estuarine processes are often strongly modulated by tides. In this study, a 3D-coupled hydrodynamic-biogeochemical model is used to quantify the controls on the carbonate system of a coastal plain estuary, specifically the York River estuary. Experiments were conducted both with and without tidal wetlands. Results show that on average, wetlands account for 20–30% of total alkalinity (TA) and dissolved inorganic carbon (DIC) fluxes into the estuary, and double-estuarine CO2 outgassing. Strong quasi-monthly variability is driven by the tides and causes fluctuations between net heterotrophy and net autotrophy. On longer time scales, model results show that in wetter years, lower light availability decreases primary production relative to biological respiration (i.e., greater net heterotrophy) resulting in substantial increases in CO2 outgassing. Additionally, in wetter years, advective exports of DIC and TA to the Chesapeake Bay increase by a factor of three to four, resulting in lower concentrations of DIC and TA within the estuary. Quantifying the impacts of these complex drivers is not only essential for a better understanding of coastal carbon and alkalinity cycling, but also leads to an improved assessment of the health and functioning of coastal ecosystems both in the present day and under future climate change.

Fertilization and tillage influence on soil organic carbon fractions: A global meta-analysis

Soilorganic carbon(SOC), as the largest terrestrial carbon pool, plays an important role in global carbon cycling, which is significantly impacted by agricultural practices. However, our ability to accurately detect and predict the impacts of fertilization and tillage onSOC dynamicsis still limited. Investigating the effects of fertilization and tillage on different SOC fractions [i.e. mineral-associated organic carbon (MAOC), particulate organic carbon (POC), free POC (frPOC), occluded POC (oPOC), coarse POC (cPOC), and fine POC (fiPOC)]can aid in the understanding of overall SOC accumulation and stabilization. To this end, we evaluated the fertilization and tillage influences on SOC fractions through a global meta-analysis. We also quantified the role of environmental and agronomic factors in modulating these effects. Fertilization increased SOC fractions by mean percent change (MPC)13 %-77 %, while tillage decreased by MPC 4 %-63 %. Among them, cPOC was the most sensitive to fertilization, while frPOC had the highest sensitivity to tillage. MAOC was the least sensitive to both practices. The application of organic fertilizer increased MAOC, SOC, and POC the most (MPC 20 %-77 %), while mineral-organic fertilizer increased frPOC, oPOC, fiPOC, and cPOC the most (MPC 81 %-126 %). Fertilization in alkaline soils with warm and humid (MAT=16–24 °C, MAP>1000 mm) climate could maximally increase SOC contents from various fractions in surface layer (<20 cm depth), particularly when the altitude was 500–1000 m. However, tillage in acidic soils with low temperatures and rainy climate (MAT=8–16 °C, MAP>1000 mm) reduced the contents of SOC fractions the most in deep layer (>40 cm depth), especially at altitudes greater than 2000 m. Whether under fertilization or tillage, POC (occupying 62 %-74 %) consistently contributed more to SOC than MAOC (26 %-38 %). Overall, we suggest that SOC fractions should be prioritized over total SOC when evaluating the effects of site-specific management strategies on carbon sequestration in agricultural lands.

Carbon Sequestration Capacity after Ecological Restoration of Open-Pit Mines: A Case Study in Yangtze River Basin, Jurong City, Jiangsu Province

Open-pit mining seriously damages the original vegetation community and soil layer and disturbs the carbon cycle of vegetation and soil, causing instability in the mining ecosystem and decrease in the carbon sequestration capacity of the mining area. With the deepening of environmental awareness and the influence of related policies, the ecological restoration of open-pit mines has been promoted. The mining ecosystem is distinct owing to the disperse distribution of mines and small scale of single mines. However, the carbon sequestration capability of mines after ecological restoration has not been clearly evaluated. Therefore, this study evaluated the carbon sequestration capacity of restoration mines, taking the mines of the Yangtze River Basin in Jurong City, Jiangsu Province as the research objects. Firstly, the visual effects of the vegetation and soil in their current status were determined through field investigation, the methods for sampling and data collection for the vegetation and soil were selected, and the specific laboratory tests such as the vegetation carbon content and soil organic carbon were clarified. Meanwhile, the evaluation system consisting of three aspects and nine evaluation indexes was established by using the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE). The process of evaluation included the following: the establishment of the judgment matrix, calculation of the index weight, determination of the membership function, and establishment of the fuzzy membership matrix. Finally, the evaluation results of the restoration mines were determined with the ‘excellent, good, normal and poor’ grade classification according to the evaluation standards for each index proposed considering the data of the field investigation and laboratory tests. The results indicated that (1) the evaluation results of the mines’ carbon sequestration capacity were of excellent and good grade at a proportion of 62.5% and 37.5%, which was in line with the field investigation results and demonstrated the carbon sequestration capacity of all the restored mines was effectively improved; and (2) the weights of the criterion layer were ranked as system stability &gt; vegetation &gt; soil with the largest value of 0.547, indicating the stability of the system is the main factor in the carbon sequestration capacity of the mines and the sustainability of the vegetation community and the stability of soil fixation on the slope. The proposed evaluation system effectively evaluates the short-term carbon sequestration capability of the restoration mining system according to the visual effects and the laboratory testing results, objectively reflecting the carbon sequestration capacity via qualitative assessment and quantitative analysis. The evaluation method is relatively applicable and reliable for restoration mines and can provide a reference for similar ecological restoration engineering.

Hyperexpansion of genetic diversity and metabolic capacity of extremophilic bacteria and archaea in ancient Andean lake sediments

BackgroundThe Andean Altiplano hosts a repertoire of high-altitude lakes with harsh conditions for life. These lakes are undergoing a process of desiccation caused by the current climate, leaving terraces exposed to extreme atmospheric conditions and serving as analogs to Martian paleolake basins. Microbiomes in Altiplano lake terraces have been poorly studied, enclosing uncultured lineages and a great opportunity to understand environmental adaptation and the limits of life on Earth. Here we examine the microbial diversity and function in ancient sediments (10.3–11 kyr BP (before present)) from a terrace profile of Laguna Lejía, a sulfur- and metal/metalloid-rich saline lake in the Chilean Altiplano. We also evaluate the physical and chemical changes of the lake over time by studying the mineralogy and geochemistry of the terrace profile.ResultsThe mineralogy and geochemistry of the terrace profile revealed large water level fluctuations in the lake, scarcity of organic carbon, and high concentration of SO42--S, Na, Cl and Mg. Lipid biomarker analysis indicated the presence of aquatic/terrestrial plant remnants preserved in the ancient sediments, and genome-resolved metagenomics unveiled a diverse prokaryotic community with still active microorganisms based on in silico growth predictions. We reconstructed 591 bacterial and archaeal metagenome-assembled genomes (MAGs), of which 98.8% belonged to previously unreported species. The most abundant and widespread metabolisms among MAGs were the reduction and oxidation of S, N, As, and halogenated compounds, as well as aerobic CO oxidation, possibly as a key metabolic trait in the organic carbon-depleted sediments. The broad redox and CO2 fixation pathways among phylogenetically distant bacteria and archaea extended the knowledge of metabolic capacities to previously unknown taxa. For instance, we identified genomic potential for dissimilatory sulfate reduction in Bacteroidota and α- and γ-Proteobacteria, predicted an enzyme for ammonia oxidation in a novel Actinobacteriota, and predicted enzymes of the Calvin–Benson–Bassham cycle in Planctomycetota, Gemmatimonadota, and Nanoarchaeota.ConclusionsThe high number of novel bacterial and archaeal MAGs in the Laguna Lejía indicates the wide prokaryotic diversity discovered. In addition, the detection of genes in unexpected taxonomic groups has significant implications for the expansion of microorganisms involved in the biogeochemical cycles of carbon, nitrogen, and sulfur.EPcqnK6xUD66cr6MUL2q3UVideo

Prediction and spatial–temporal changes of soil organic matter in the Huanghuaihai Plain by combining legacy and recent data

Soil organic matter (SOM) is critical for soil fertility, crop growth, and plays an important role in the global carbon cycle and climate change. Therefore, spatial prediction of SOM is important to rational soil resource utilization, agricultural production, and ecological environment management. However, large-area SOM mapping research heavily relies on legacy soil data, and large-scale recent SOM mapping may not be possible or have lower accuracy due to limited or less recent data availability. In this study, we aimed to improve SOM prediction and mapping accuracy by combining legacy data with limited recent data. Three models, namely, partial least squares regression (PLSR), random forest (RF), and one-dimensional convolutional neural network (1D-CNN), were applied and compared. The results showed that combining legacy and recent data effectively improved SOM prediction accuracy compared to using only recent data. Among the three modeling methods, 1D-CNN exhibited superior performance, with an averaged determination coefficient of the prediction (R2) of 0.58, a root mean square error (RMSE) of 4.56 g/kg, and a ratio of performance to interquartile distance (RPIQ) of 2.05. The predicted SOM content for both legacy (1980 s) and recent (2010 s) periods showed similar spatial distribution patterns throughout the Huanghuaihai Plain. Generally, there was a noticeable trend of increasing SOM content from northwest to southeast, with higher values observed in Jiangsu and lower values concentrated in Henan, Hebei, and Shandong regions within the study area. Over time, SOM contents in the Huanghuaihai Plain showed an increasing trend, with an average increase of 5.90 g/kg from legacy to recent period. This study provides a promising approach for improving SOM prediction and mapping accuracy at large scales, particularly when recent data availability is limited.

Bacterial community and dissolved organic matter networks in urban river: The role of human influence

Human activities have significantly altered the biogeochemical cycles of carbon, nitrogen, and sulfur in aquatic ecosystems, leading to ecological problems.This study utilized 16S rRNA gene high-throughput sequencing and excitation-emission matrix parallel factor analysis (EEM-PARAFAC) to evaluate the bacterial community composition and dissolved organic matter structure in the upstream (less impacted) and downstream (severely impacted) sections of the river, with a focus on the interactions between bacterial diversity and dissolved organic matter (DOM) characteristics.Results indicated significant spatial diversity in bacterial communities, with a higher α-diversity upstream compared to the more polluted downstream sections. Environmental parameters, particularly total phosphorus (TP) and dissolved oxygen (DO), were found to significantly influence the distribution and composition of bacterial phyla through redundancy analysis. The pattern of bacterial community assembly has shifted from predominantly deterministic to predominantly stochastic as a result of human activities. The analysis of DOM through EEM-PARAFAC identified three main fluorescent components, reflecting varied sources and interactions with bacterial communities. Upstream, microbial activities predominantly contributed to autochthonous DOM, while downstream, increased inputs of allochthonous DOM from human activities were evident. Furthermore, the study revealed that through the introduction of various organic pollutants and nutrient loads that shift microbial metabolic functions towards increased degradation and transformation of complex organic compounds downstream. Structural equation modeling (SEM) revealed that upstream human activities primarily affected bacterial communities indirectly by altering DOM properties. In contrast, downstream activities had both direct and indirect effects due to higher pollutant loads and more complex environmental conditions. These interactions underline the profound effect of anthropogenic factors on riverine ecosystems and emphasize the importance of managing human impacts to preserve microbial biodiversity and water quality.

The Analysis of NPP Changes under Different Climatic Zones and under Different Land Use Types in Henan Province, 2001–2020

Net Primary Productivity (NPP) is a crucial indicator of ecological environment quality. To better understand the carbon absorption and carbon cycling capabilities of Henan Province, this study investigates the trends and driving factors of NPP across different climatic zones and land use types. The Theil–Sen Median trend analysis method and the Mann–Kendall trend test are employed to monitor NPP changes from 2001 to 2020. The average annual NPP in Henan Province during this period was 414.61 gC·m−2·year−1, showing a significant increasing trend with a growth rate of 3.73 gC·m−2·year−1. Spatially, both the annual average NPP and its increase rate were higher in the western part of Henan compared to the eastern part, and NPP variability was more stable in the southern region than in the northern region. By classifying climatic zones and using the Geodetector method to assess NPP sensitivity to natural factors, the results show that climate and vegetation factors jointly influence NPP variations, with annual precipitation being the primary natural factor affecting NPP trends in Henan Province from 2001 to 2020. By analyzing the NPP gain and loss matrix, the impact of land use changes on NPP was evaluated. Forests had the highest average annual NPP at 483.52 gC·m−2·year−1, and the conversion of arable land to urban areas was identified as the primary land change type leading to NPP reductions. In the subtropical zone of Henan, forests, croplands, and grasslands exhibited higher NPP values and increase rates compared to those in the warm belt. This study provides new insights into the spatial variation of NPP caused by changes in climatic zones and land use types.

Extreme trophic tales: deciphering bacterial diversity and potential functions in oligotrophic and hypereutrophic lakes

BackgroundOligotrophy and hypereutrophy represent the two extremes of lake trophic states, and understanding the distribution of bacterial communities across these contrasting conditions is crucial for advancing aquatic microbial research. Despite the significance of these extreme trophic states, bacterial community characteristics and co-occurrence patterns in such environments have been scarcely interpreted. To bridge this knowledge gap, we collected 60 water samples from Lake Fuxian (oligotrophic) and Lake Xingyun (hypereutrophic) during different hydrological periods.ResultsEmploying 16S rRNA gene sequencing, our findings revealed distinct community structures and metabolic potentials in bacterial communities of hypereutrophic and oligotrophic lake ecosystems. The hypereutrophic ecosystem exhibited higher bacterial α- and β-diversity compared to the oligotrophic ecosystem. Actinobacteria dominated the oligotrophic Lake Fuxian, while Cyanobacteria, Proteobacteria, and Bacteroidetes were more prevalent in the hypereutrophic Lake Xingyun. Functions associated with methanol oxidation, methylotrophy, fermentation, aromatic compound degradation, nitrogen/nitrate respiration, and nitrogen/nitrate denitrification were enriched in the oligotrophic lake, underscoring the vital role of bacteria in carbon and nitrogen cycling. In contrast, functions related to ureolysis, human pathogens, animal parasites or symbionts, and phototrophy were enriched in the hypereutrophic lake, highlighting human activity-related disturbances and potential pathogenic risks. Co-occurrence network analysis unveiled a more complex and stable bacterial network in the hypereutrophic lake compared to the oligotrophic lake.ConclusionOur study provides insights into the intricate relationships between trophic states and bacterial community structure, emphasizing significant differences in diversity, community composition, and network characteristics between extreme states of oligotrophy and hypereutrophy. Additionally, it explores the nuanced responses of bacterial communities to environmental conditions in these two contrasting trophic states.

Exploring the Influencing Factors of Net Ecosystem Productivity (NEP) Based on Random Forest and SHAP

As global climate change intensifies, Net Ecosystem Productivity (NEP) serves as a crucial indicator for measuring the carbon absorption and release of ecosystems, playing a vital role in understanding the carbon cycle and shaping climate policy. The Northwestern region of China, characterized as a typical inland arid and semi-arid area, is particularly sensitive to global changes. Understanding the environmental drivers of NEP in this region is critical for both regional ecological protection and global environmental management. This study utilized environmental data from five provinces in Northwestern China, applying the Random Forest (RF) model and SHapley Additive exPlanation (SHAP) method to analyze the primary environmental factors influencing NEP. The research integrated climatic data (including temperature, precipitation, wind speed, and solar radiation), soil characteristics such as pH, organic carbon content, and soil texture, topographic attributes elevation and slope, and a Human Footprint. The RF model identified significant environmental factors impacting NEP, and SHAP values were used to explain the specific contributions of these factors. Furthermore, multiple linear regression analysis revealed interactions among environmental factors. The results indicate that solar radiation (Srad), precipitation, topsoil reference bulk density (T_REF_BULK), temperature, and the topsoil clay fraction (T_CLAY) significantly influence NEP. Notably, interactions between aspect and T_CLAY, aspect and T_REF_BULK, as well as the human footprint (HFP) and Srad, also show significant impacts on NEP. This study confirms that solar radiation, precipitation, soil characteristics, and human activities are the primary environmental drivers of NEP in the Northwest region of China, with solar radiation playing the most critical promotional role. The findings not only provide a scientific basis for the management of ecosystems in Northwestern China but also offer references for formulating global climate change mitigation strategies and estimating the global carbon budget. Future research should further explore the specific mechanisms and interactions of these drivers across different ecosystems to more comprehensively understand and predict the trends in NEP changes.

Re-discovering macerating Posidonia oceanica bottoms: Characterization of meiofaunal community inhabiting a peculiar Mediterranean habitat

The highly efficient carbon storage capacity of beds formed by Posidonia oceanica, an endemic Mediterranean seagrass species, has been widely recognized. Recently, the supra-littoral deposits of leaf litter (i.e., banquettes) have been investigated in terms of their nutrients, biomass and associated community. Nevertheless, an overlooked fraction of the P. oceanica detritus never reaches the shore and sinks far away to deeper seafloor. Additionally, part of the supra-littoral deposit goes back to the sea during winter swells. This deep detrital compartment, mainly composed of sediment mixed with dead leaves and rhizomes coming from P. oceanica beds, has only been described once by Pères in 1953, who focused on the macrofaunal component. Here, we investigated for the first time the meiofaunal community inhabiting sediments characterized by P. oceanica detritus in a deposit located at 65−80 m depth off the Ischia Island (Gulf of Naples, Italy, Tyrrhenian Sea). Our results show that the meiofaunal community appears highly diversified and strongly dominated by nematodes (from 85% to 93%). Differences in meiobenthic assemblage structures were significant only when rare taxa were considered (i.e. taxa found in low abundances and characterized by a sporadic distribution in the study area). The nematode community revealed a very high biodiversity (number of families and genera: 31 and 104, respectively), with a clear prevalence of selective and non-selective deposit feeders that suggest the key role of this habitat in the benthic detrital food web. The richness of meiofauna and the taxonomic and functional diversity of the nematode assemblages account for a “good” to “moderate” ecological quality status. These findings support the high ecological value of the macerating seagrass bottoms, an overlooked component of the blue carbon cycle that deserves to be further investigated.

Effects of LDPE and PBAT plastics on soil organic carbon and carbon-enzymes: A mesocosm experiment under field conditions

Although the effects of plastic residues on soil organic carbon (SOC) have been studied, variations in SOC and soil carbon-enzyme activities at different plant growth stages have been largely overlooked. There remains a knowledge gap on how various varieties of plastics affect SOC and carbon-enzyme activity dynamics during the different growing stages of plants. In this study, we conducted a mesocosm experiment under field conditions using low-density polyethylene and poly (butylene adipate-co-terephthalate) debris (LDPE-D and PBAT-D, 500–2000 μm (pieces), 0%, 0.05%, 0.1%, 0.2%, 0.5%, 1%, 2%), and low-density polyethylene microplastics (LDPE-M, 500–1000 μm (powder), 0%, 0.05%, 0.1%, 0.5%) to investigate SOC and C-enzyme activities (β-xylosidase, cellobiohydrolase, β-glucosidase) at the sowing, seedling, flowering and harvesting stages of soybean (Glycine Max). The results showed that SOC in the LDPE-D treatments significantly increased from the flowering to harvesting stage, by 12.69%–13.26% (p < 0.05), but significantly decreased in the 0.05% and 0.1% LDPE-M treatments from the sowing to seedling stage (p < 0.05). However, PBAT-D had no significant effect on SOC during the whole growing period. For C-enzyme activities, only LDPE-D treatments inhibited GH (17.22–38.56%), BG (46.7–66.53%) and CBH (13.19–23.16%), compared to treatment without plastic addition, from the flowering stage to harvesting stage. Meanwhile, C-enzyme activities and SOC responded nonmonotonically to plastic abundance and the impacts significantly varied among the growing stages, especially in treatments with PBAT-D (p < 0.05). These risks to soil organic carbon cycling are likely mediated by the effects of plastic contamination and degradation soil microbe. These effects are sensitive to plastic characteristics such as type, size, and shape, which, in turn, affect the biogeochemical and mechanical interactions involving plastic particles. Therefore, further research on the interactions between plastic degradation processes and the soil microbial community may provide better mechanistic understanding the effect of plastic contamination on soil organic carbon cycling.