Bacteria and fungi, representing two major soil microorganism groups, play an important role in global nutrient biogeochemistry. Biogeographic patterns of bacterial and fungal biomass are of ...fundamental importance for mechanistically understanding nutrient cycling. We synthesized 1323 data points of phospholipid fatty acid-derived fungal biomass C (FBC), bacterial biomass C (BBC), and fungi:bacteria (F:B) ratio in topsoil, spanning 11 major biomes. The FBC, BBC, and F:B ratio display clear biogeographic patterns along latitude and environmental gradients including mean annual temperature, mean annual precipitation, net primary productivity, root C density, soil temperature, soil moisture, and edaphic factors. At the biome level, tundra has the highest FBC and BBC densities at 3684 (95% confidence interval: 1678–8084) mg kg−1 and 428 (237–774) mg kg−1, respectively; desert has the lowest FBC and BBC densities at 16.92 (14.4–19.89) mg kg−1 and 6.83 (6.1–7.65) mg kg−1, respectively. The F:B ratio varies dramatically, ranging from 1.8 (1.6–2.1) in savanna to 8.6 (6.7–11.0) in tundra. An empirical model was developed for the F:B ratio and it is combined with a global dataset of soil microbial biomass C to produce global maps for FBC and BBC in 0–30 cm topsoil. Across the globe, the highest FBC is found in boreal forest and tundra while the highest BBC is in boreal forest and tropical/subtropical forest, the lowest FBC and BBC are in shrub and desert. Global stocks of living microbial biomass C were estimated to be 12.6 (6.6–16.4) Pg C for FBC and 4.3 (0.5–10.3) Pg C for BBC in topsoil. These findings advance our understanding of the global distribution of fungal and bacterial biomass, which facilitates the incorporation of fungi and bacteria into Earth system models. The global maps of bacterial and fungal biomass serve as a benchmark for validating microbial models in simulating the global C cycle under a changing climate.
•Fungal and bacterial biomass distribution showed clear biogeographical patterns.•Biomass of fungi and bacteria and their ratio are controlled by different factors.•Global biomass carbon budget is 12 PgC for fungi and 4 PgC for bacteria in topsoil.
The microbial metabolic quotient (MMQ), microbial respiration per unit of biomass, is a fundamental factor controlling heterotrophic respiration, the largest carbon flux in soils. The magnitude and ...controls of MMQ at regional scale remain uncertain. We compiled a comprehensive data set of MMQ to investigate the global patterns and controls of MMQ in top 30 cm soils. Published MMQ values, generally measured in laboratory microcosms, were adjusted on ambient soil temperature using long-term (30 yr) average site soil temperature and a Q₁₀ = 2. The area-weighted global average of MMQ_Soil is estimated as 1.8 (1.5–2.2) (95% confidence interval) μmol C·h⁻¹·mmol⁻¹ microbial biomass carbon (MBC) with substantial variations across biomes and between cropland and natural ecosystems. Variation was most closely associated with biological factors, followed by edaphic and meteorological parameters. MMQ_Soil was greatest in sandy clay and sandy clay loam and showed a pH maximum of 6.7 ± 0.1 (mean ± se). At large scale, MMQ_Soil varied with latitude and mean annual temperature (MAT), and was negatively correlated with microbial N:P ratio, supporting growth rate theory. These trends led to large differences in MMQ_Soil between natural ecosystems and cropland. When MMQ was adjusted to 11°C (MMQ_Ref), the global MAT in the top 30 cm of soils, the area-weighted global averages of MMQ_Ref was 1.5 (1.3–1.8) μmol C-mmol MBC⁻¹·h⁻¹. The values, trends, and controls of MMQ_Soil add to our understanding of soil microbial influences on soil carbon cycling and could be used to represent microbial activity in global carbon models.
Natural wetlands are critically important to global change because of their role in modulating atmospheric concentrations of CO₂, CH₄, and N₂O. One 4-year continuous observation was conducted to ...examine the exchanges of CH₄ and N₂O between three wetland ecosystems and the atmosphere as well as the ecosystem respiration in the Sanjiang Plain in Northeastern China. From 2002 to 2005, the mean annual budgets of CH₄ and N₂O, and ecosystem respiration were 39.40 ± 6.99 g C m⁻² yr⁻¹, 0.124 ± 0.05 g N m⁻² yr⁻¹, and 513.55 ± 8.58 g C m⁻² yr⁻¹ for permanently inundated wetland; 4.36 ± 1.79 g C m⁻² yr⁻¹, 0.11 ± 0.12 g N m⁻² yr⁻¹, and 880.50 ± 71.72 g C m⁻² yr⁻¹ for seasonally inundated wetland; and 0.21 ± 0.1 g C m⁻² yr⁻¹, 0.28 ± 0.11 g N m⁻² yr⁻¹, and 1212.83 ± 191.98 g C m⁻² yr⁻¹ for shrub swamp. The substantial interannual variation of gas fluxes was due to the significant climatic variability which underscores the importance of long-term continuous observations. The apparent seasonal pattern of gas emissions associated with a significant relationship of gas fluxes to air temperature implied the potential effect of global warming on greenhouse gas emissions from natural wetlands. The budgets of CH₄ and N₂O fluxes and ecosystem respiration were highly variable among three wetland types, which suggest the uncertainties in previous studies in which all kinds of natural wetlands were treated as one or two functional types. New classification of global natural wetlands in more detailed level is highly expected.
Approximately one-third of northern peatlands are within permafrost regions. Soil organic matter (SOM) and plant root biomass in permafrost peatlands are vulnerable to future global warming. However, ...previous studies have primarily focused on the response of SOM mineralization to increases in temperature without analysing the potential interaction effects of increased plant root biomass. This study investigated the influence of temperature and root additions on soil carbon and nitrogen mineralization as well as the mechanisms driving mineralization in a high latitude permafrost peatland in the Da Xing'an Mountains, Northeast China. We investigated changes in shallow soil (0–15 cm) and deep soil (15–30 cm) carbon mineralization, available N contents, microbial biomass carbon (MBC), dissolved organic carbon (DOC), and enzyme activities in response to increasing temperature and Eriophorum vaginatum root additions by using an incubation experiment. Our results indicate that elevated temperature significantly increased soil carbon mineralization. The Q10 values of the carbon mineralization rates in the shallow soil and deep soil were 3.95 and 2.91, respectively. In contrast, the soil MBC and DOC decreased significantly, confirming that labile carbon is the main driving force of microbial mineralization activities under warming conditions. Elevated temperature significantly increased the shallow soil net N mineralization rates and increased the net nitrification rates in both soil layers. At high temperatures, ammonification rates increased in the shallow soil but decreased in the deep soil. The increase in the incubation temperature resulted in significantly increased shallow soil β-glucosidase activity and decreased invertase activity. This suggests the increased production of complex substrate enzymes, and decreased production of simple substrate-acquiring enzymes. The root additions significantly increased the soil C mineralization and stimulated the secretion of invertase by soil microorganisms. These findings indicate that future climate warming in the northern high latitude will significantly stimulate soil carbon and nitrogen mineralization in permafrost peatlands. Furthermore, increases in plant roots will enhance C accumulation and may even enhance the response of soil C mineralization to temperature, significantly impact the soil C balance in high latitude permafrost peatlands.
•Peat soil labile C is the main driving force of microbial mineralization activity.•Soil C and N mineralization in peatland increase with elevated temperature.•Increasing temperature significantly decreases soil MBC and DOC in peatland.•Root additions increase soil C mineralization and stimulate soil invertase activity.
•Rising temperature accelerated the mineralization of SOC in permafrost peatlands.•Q10 of SOC mineralization ranged from 2.24 to 4.22 among 7 permafrost peatlands.•SOC mineralization positively ...correlated with soil DOC, NH4+-N, NO3−-N contents.•Substrate availability and microbe drive SOC mineralization in permafrost peatlands.
Permafrost peatlands are important pools of soil carbon. Soil organic carbon (SOC) mineralization and its temperature sensitivity in permafrost peatlands are crucial for predictions of soil carbon-climate feedback. However, little is known about the changes in SOC mineralization and its mechanism in response to environmental change in the permafrost peatlands of Northeastern China. We collected seven permafrost peatland soils from Greater and Lesser Khingan Mountains in Northeastern China to investigate how the responses of microbes and labile substrates control the mineralization of SOC in the laboratory incubation study. The results show that temperature and sampling sites affected the mineralization of SOC. Elevated temperatures significantly increased the rate of carbon mineralization across the peatland soils. The mean sensitivity of SOC mineralization to temperature (Q10 value) was 2.96. The increase in substrate availability and microbial abundance in parallel with the increase in temperature is responsible for the high rates of decomposition of the organic carbon pools. We found that the mineralization of soil carbon positively correlated with the concentrations of soil dissolved organic carbon (DOC), NH4+-N, NO3−-N, as well as the abundances of bacteria, fungi, methanotrophs and nirK denitrifiers. Moreover, the content of DOC positively correlated with the abundances of soil bacteria, methanotrophs and nirK denitrifiers, indicating that the influences of soil microbial abundances on carbon mineralization were strongly mediated by the availability of carbon substrates. Our findings provide novel insights into the effects of increasing temperatures on the relationship between microbial communities and labile substrates and their roles in carbon decomposition in permafrost peatlands.
Rapid and periodic assessment of the impact of land cover changes on ecosystem services at regional levels is essential to understanding services and sustainability of ecosystems. This study focused ...on quantifying and assessing changes of multiple ecosystem services in the Sanjiang Plain of China as a result of land cover changes over the period of 1992–2012. This region is important for its large area of natural wetlands and intensive agriculture. The ecosystem services that were assessed for this region included its regulating services (water yield and ecosystem carbon stocks), supporting services (suitable waterbird habitats), and provisioning services (food production), and the approach to the assessment was composed of the surface energy balance algorithms for land (SEBAL), soil survey re-sampling method and an empirical waterbird habitat suitability model. This large scale and integrated investigation represents the first systematic evaluation on the status of ecosystem carbon stocks in the Sanjiang Plain in addition to the development of an effective model for analysis of waterbird habitat suitability with the use of both remote sensing and geographic information systems (GIS). More importantly, the result from this study has confirmed trade-offs between ecosystem services and negative consequences to environment in this region. The trade-offs were typically manifested by increased water yield and significantly grown food production, which is in contrast with significant losses in ecosystem carbon stocks (−14%) and suitable waterbird habitats (−23%) mainly due to the conversion of land cover from wetland to farmland. This finding implies that land use planning and policy making for this economically important region should take ecosystem service losses into account in order to preserve its natural ecosystems in the best interest of society.
•We studied changes of multiple ecosystem services and their synergies and trade-offs.•We developed several methods to quantify ecosystem services in a spatially explicit manner.•Wetlands shrinkage, agriculture expansion and urban sprawl were observed during 1992–2012.•Provisioning services (food production) increased significantly during the 20years.•Large losses in ecosystem carbon stocks and suitable waterbird habitats were found.
•The decomposition of E. vaginatum litter is faster than that of Sphagnum.•Warming could promote decomposition of E. vaginatum and Sphagnum litter.•N addition promoted the decomposition of Sphagnum ...(low N) and vascular litter.•High N concentration inhibited the decomposition of Sphagnum litter.•Microorganisms regulated warming and N addition impacts on litter decomposition.
As one kind of the most important carbon (C) sink in the world, peatlands are sensitive to climate change. The decomposition of litter plays an important role in C fixation and nutrient utilization in peatlands. To reveal the mechanism of response of the litter decomposition to climate warming and the addition of nitrogen (N) in permafrostpeatlands, we selected two typical plants, Eriophorumvaginatum and Sphagnumpalustre, in the permafrost peatland of Da Xing’anling Mountains, China, as the research objects and conducted a 54-day litter decomposition experiment at 10 ℃ and 20 ℃. Three N addition treatments (CK: 0 mg N g−1, N1: 2.5 mg N g−1, and N2: 5 mg N g−1) were established. Our results showed that the E. vaginatum litter decomposed more quickly than that of Sphagnum, and an increase in temperature significantly promoted the litter decomposition and CO2 emission of E. vaginatum and Sphagnum. The addition of N promoted the decomposition of E. vaginatum litter, whereas the decomposition of Sphagnum litter was promoted by the N1 treatment but was inhibited by the N2 treatment. The enzyme activity in both types of litter was inhibited with the increase in temperature. The abundances of bacteria and fungi positively correlated with the decomposition constant and mean CO2 release rate by E. vaginatum and Sphagnum litter, indicating that the effects of temperature and N addition on the decomposition of plant litter were primarily regulated by microorganisms. This study provides a theoretical basis to understand and predict the effects of global climate change on the decomposition of plant litter in boreal peatlands.
•The equations for calculating the total grey water footprint of the basin are modified.•The principles of parameter determination in statistical method are clarified.•Hydrological models are ...suitable for calculating the basin grey water footprints.•Applicability of different grey water footprint accounting methods was compared.
The water footprint is a widely used indicator for water resource assessment, among which quantifying the grey water footprint (GWF) is essential in assessing the basin-scale water resources. Due to the lack of accurate data and parameters in calculating the GWF by statistical methods, a few studies have used the Soil and Water Assessment Tool (SWAT) model to assess the GWF. This study aims to explore the applicability of statistical and modeling methods for GWF accounting of a basin. The Fuzhou River basin (FRB) in Dalian, China, was used as a case study; the GWF in 2015 was assessed using the statistical and modeling methods, respectively. Results showed that the GWF calculated by the statistical method and the SWAT model were 4158.44 million m3 and 4494.62 million m3, respectively. Both spatially exhibited a rise from the upstream to the downstream reaches, and a decrease from the mainstream river to both sides of the river. In comparison, the modeling method lowered the difficulties of data acquisition and generated a more refined spatial distribution of GWF; whereas the statistical method can provide a more comprehensive analysis of the GWF from each pollution source. Furthermore, the water pollution level of FRB was calculated as 11.88 and 12.84, respectively, by the statistical method and the SWAT model, suggesting that the current water resources in the FRB are seriously polluted, which may threaten the sustainable use of local water resources.
•A model for remote estimation of surface and vertical SPM was established.•Spatiotemporal variation of SPM was mapped in the Liaohe estuary.•Vertical distribution types of SPM in the Liaohe estuary ...were discussed.•Impacts of natural factors and human activities on the SPM in the Liaohe estuary were discussed.
The estuary and its nearshore waters are of great ecological value. As one of the important water quality evaluation indicators, suspended particulate matter (SPM) is also relevant to the ecology of the estuary. However, the current research on SPM of surface water is quite well established. It is urgent to study the vertical distribution of SPM due to its significance for further studies of biogeochemical processes in the water column. This study developed remote estimation model of SPM for five different depth water layers in the Liaohe estuary based on in situ Rrs(λ) data and support vector regression (SVR) methods, and the model performed well (RMSE = 24.32 mg/L, MAPE = 26.11%, MAE = 18.37 mg/L, N = 115). After applying the model to 10,090 MODIS images collected in 2000–2021, results show that: (1) Vertical distribution of SPM concentration in the Liaohe estuary could be divided into three types: top-down decreasing type (Type Ⅰ), uniform type (Type Ⅱ) and top-down increasing type (Type III). (2) Seasonal distribution of SPM concentration in the Liaohe estuary is: medium in spring (76.30 ± 10.34 mg/L), low in summer (61.80 ± 6.98 mg/L) and high in autumn (82.28 ± 19.12 mg/L). There is a significant decreasing trend of SPM from 2000 to 2021 (p < 0.01). (3) Meteorological factors (wind speed and precipitation), water depth, human reforestation and reclamation activities are closely related to SPM concentration.
Over the past 4 decades, a number of numerical models have been developed to quantify the magnitude, investigate the spatial and temporal variations, and understand the underlying mechanisms and ...environmental controls of methane (CH4) fluxes within terrestrial ecosystems. These CH4 models are also used for integrating multi-scale CH4 data, such as laboratory-based incubation and molecular analysis, field observational experiments, remote sensing, and aircraft-based measurements across a variety of terrestrial ecosystems. Here we summarize 40 terrestrial CH4 models to characterize their strengths and weaknesses and to suggest a roadmap for future model improvement and application. Our key findings are that (1) the focus of CH4 models has shifted from theoretical to site- and regional-level applications over the past 4 decades, (2) large discrepancies exist among models in terms of representing CH4 processes and their environmental controls, and (3) significant data–model and model–model mismatches are partially attributed to different representations of landscape characterization and inundation dynamics. Three areas for future improvements and applications of terrestrial CH4 models are that (1) CH4 models should more explicitly represent the mechanisms underlying land–atmosphere CH4 exchange, with an emphasis on improving and validating individual CH4 processes over depth and horizontal space, (2) models should be developed that are capable of simulating CH4 emissions across highly heterogeneous spatial and temporal scales, particularly hot moments and hotspots, and (3) efforts should be invested to develop model benchmarking frameworks that can easily be used for model improvement, evaluation, and integration with data from molecular to global scales. These improvements in CH4 models would be beneficial for the Earth system models and further simulation of climate–carbon cycle feedbacks.
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