Ecosystem Carbon Budget Research Articles

Characteristics of Soil Profile Greenhouse Gas Concentrations and Fluxes of Alpine Grassland as Affected by Livestock Grazing

Previous research has investigated the effects of different grazing intensities on soil surface greenhouse gas (GHG) emissions, whereas the dynamics of GHG production and consumption within the soil profile and their responses to different grazing intensities remain unclear. In this study, a field experiment was conducted in 2017 and 2018 to evaluate the influences of three grazing intensities (none, light, heavy) on both soil surface and subsurface (0–60 cm) GHG fluxes estimated using chamber-based and concentration gradient-based methods, respectively. Results showed that soil at lower depths (30–60 cm) had higher carbon dioxide (CO2) concentrations but lower methane (CH4) concentrations. In contrast, soil profile nitrous oxide (N2O) concentration did not vary with depth, possibly resulting from the relatively low soil moisture in the semiarid grassland, which increased air diffusivity across the soil profile. Grassland soil acted as a source of N2O and CO2 production but as a sink for CH4 uptake, which mainly attributed to the topsoil (0–5 cm for N2O, and 0–15 cm for CO2 and CH4). The estimated soil surface GHG flux rates based on the concentration gradient method did not align well with those directly measured using the chamber method. Furthermore, the cumulative N2O flux over the study period was significantly higher for the concentration gradient method than the chamber method, whereas a contrary result was observed for CO2 emission and CH4 uptake. This study confirms that the grassland soil serves as an important source of CO2 and N2O emissions and a weak sink for CH4 consumption, playing a crucial role in the annual carbon budget of livestock-grazed grassland ecosystems.

Ecosystem productivity and carbon dynamics in Keibul Lamjao National Park, Manipur, India: a gray relational analysis perspective.

An in-depth understanding of carbon dynamics and ecosystem productivity is essential for conservation and management of different ecosystems. Ecosystem dynamics and carbon budget are assessed by estimating net ecosystem production (NEP) across different global ecosystems. An ecological productivity assessment of forest and floating meadow ecosystems in Keibul Lamjao National Park (KLNP), Manipur, North East India, was conducted using the multi-criteria decision-making process namely, gray relational analysis (GRA). The analysis was performed on 24 selected criterions classified either as "higher-the-better" or "lower-the-better" based on their degree of influence on the carbon budget. Floating meadows exhibited a higher production of aboveground and belowground biomass and a higher total mortality and decay. Furthermore, the study found that floating meadows exhibited a higher soil organic carbon (SOC) and net soil organic matter (SOM) than the forest ecosystem. The forest ecosystem showed higher total respiration (RT), heterotrophic respiration (RH), and autotrophic respiration (RA) than floating meadows. Floating meadows exhibited a higher net primary productivity (NPP) of 616.49 ± 33.87 gCm-2year-1 than the forest ecosystem, which has a NPP of 566.64 ± 65.26 gCm-2year-1. Similarly, floating meadows have higher NEP (495.25 ± 36.46 gCm-2year-1) than forest ecosystems (418.39 ± 65.76 gCm-2year-1). These characteristics have a significant influence on the carbon budget in floating meadows as compared to forest ecosystems, as shown by larger values of gray relational coefficient (GRC) in GRA. The floating meadows ecosystem (0.82) obtained 54.72% gain in gray relational grades (GRG) value with the forest ecosystem (0.53). This study might help in improving KLNP and other adjutant areas for conservation and management policies from the vital information given on the importance of wetlands in carbon dynamics and ecosystem productivity.

Rapid Increase in Soil Respiration and Reduction in Soil Nitrate Availability Following CO2 Enrichment in a Mature Oak Forest.

In the future, with elevated atmospheric CO2 (eCO2), forests are expected to increase woody biomass to capture more carbon (C), though this is dependent on soil nutrient availability. While young forests may access unused nutrients by growing into an unexplored soil environment, it is unclear how or if mature forests can adapt belowground under eCO2. Soil respiration (R s) and nutrient bioavailability are integrative ecosystem measures of below-ground dynamics. At Birmingham's Institute of Forest Research Free Air CO2 Enrichment (BIFoR FACE) facility, we investigated the effects of eCO2 (+150 ppm above ambient) on a mature oak forest during the first year of exposure. We observed an annual Rs increase of ∼21.5%; 996 ± 398 g C m-2 year-1 (ambient) to 1210 ± 483 g C m-2 year-1 (eCO2). The eCO2 impact was greater on belowground nutrient cycling, with monthly nitrate availability decreasing by up to 36%. These results show that high C uptake resulted in higher soil respiration with a concomitant decrease in the level of soil nitrate during the first year. These belowground responses and their long-term dynamics will have implications for the carbon budget of mature forest ecosystems in changing climate.

Optimizing water‐nitrogen regulation for enhanced carbon absorption and reduced greenhouse gas emissions in greenhouse tomato cultivation

AbstractTo study the impact of different water‐nitrogen regulation modes on the carbon cycle of greenhouse tomatoes and determine optimal irrigation and nitrogen application levels to enhance carbon absorption and minimize greenhouse gas emissions. This study employed three irrigation levels (100%, 80%, and 60% of ET0) and three nitrogen application levels (240, 192, and 144 kg·ha−1), along with a control group (W1N1, i.e., 100% ET0‐240 kg·ha−1). Gas‐chromatography methods were used to monitor CH4 and soil CO2 emissions, while assessing dry matter, carbon content, and carbon fixation capacity of tomato organs throughout the growth period. Additionally, a system for evaluating the net ecosystem carbon budget of facility tomatoes was developed based on net primary productivity. Results indicated reduced CH4 and soil CO2 emissions with decreased irrigation and nitrogen application. Dry matter, carbon content, and carbon fixation of tomato organs initially increased with reduced nitrogen and irrigation but then declined. The W2N2 (80% ET0‐192 kg·ha−1) treatment showed maximal values for dry matter, carbon content, carbon fixation, net primary productivity (NPP), and gross primary productivity (GPP). Findings suggest a positive net ecosystem carbon budget under reduced water and nitrogen conditions, indicating carbon absorption. Specifically, the W2N2 treatment outperformed others in net carbon absorption, highlighting its potential as an effective mode for enhancing carbon sequestration in the region.

Quantifying the Effects of Wind Turbulence on CO2 Flux Measurement in a Closed Chamber

This study aimed to investigate the effects of wind turbulence on CO2 transport within a medium and the extent of measurement errors in a closed chamber. Therefore, in a laboratory with controllable environmental conditions, the measurement performance of the closed chamber at various wind speeds was assessed using a soil respiration calibration apparatus and four types of porous media. The experimental results indicated that the closed chamber under the influence of wind turbulence exhibited varying degrees of underestimation, ranging from −51 to −6%. The effects of wind turbulence were more pronounced in sandy soils. As wind turbulence enhanced gas transport within the medium, the flux measurements of the closed chamber were biased, and this phenomenon was closely related to the medium’s particle size and surface wind speed. To address this issue, it is recommended to conduct long-term monitoring and eliminate errors by averaging repeated measurements, which will improve the accuracy of the ecosystem carbon budget.

Effects of the long-term rice expansion on ecosystem carbon budget in the typical agricultural area of Northeast China

Extensive rice expansion in northeast China has significantly altered land use and land cover (LULC) changes. However, the impact of long-term rice expansion on regional carbon budget dynamics remains unclear. A major obstacle in addressing this gap is the absence of agricultural LULC information with high spatiotemporal resolution. Here, we selected the Sanjiang Plain experienced dramatic rice expansion as the study area, presenting a framework that integrates high-resolution crop distribution data with a process-based model to quantify the impact of rice expansion on regional carbon budgets. Specifically, we employed a robust deep-learning network for crop mapping based on Landsat data, to reconstruct the spatiotemporal dynamics of rice expansion from 1985 to 2020. We then incorporated these long-term crop maps into the Denitrification-Decomposition (DNDC) model, to explore the effects of rice expansion on the regional carbon budget over this period. Analysis results showed that the rice planting area expanded by 708.64 km2/yr, resulting in more than a tenfold increase over the past 36 years. Spatially, rice planting expanded from the southwest to the northeast and from the interior to the exterior. This expansion has resulted in approximately 275 Mt. of CO2 and 6.92 Mt. of CH4 greenhouse gas emissions, altering the dynamics of the regional carbon budget and shifting the ecosystem from a carbon sink to a carbon source since 2016. Although the long-term expansion of rice increased soil respiration and CH4 emissions, it also enhanced soil carbon sequestration through agricultural management practices. These findings greatly enhance our understanding of the ecosystem carbon cycle's response to long-term agricultural LULC changes, providing more accurate data support and scientific evidence for developing low-carbon agricultural policies.

Anomalous wet summers and rising atmospheric CO2 concentrations increase the CO2 sink in a poorly drained forest on permafrost

At the northern high latitudes, rapid warming, associated changes in the hydrological cycle, and rising atmospheric CO2 concentrations, [CO2], are observed at present. Under rapid environmental changes, it is important to understand the current and future trajectories of the CO2 budget in high-latitude ecosystems. In this study, we present the importance of anomalous wet conditions and rising [CO2] on the long-term CO2 budget based on two decades (2003-2022) of quasicontinuous measurements of CO2 flux at a poorly drained black spruce forest on permafrost peat in interior Alaska. The long-term CO2 budget for the black spruce forest was a small sink of -53 ± 63 g C m-2 y-1. The CO2 sink increased from 49 g C m-2 y-1 for the first decade to 58 g C m-2 y-1 for the second decade. The increased CO2 sink was attributed to an 11.3% increase in gross primary productivity (GPP) among which 9% increase in GPP was explained by a recent increase in precipitation. Furthermore, a 3% increase in GPP in response to a 37-ppm increase in [CO2] was estimated from the data-model fusion. Our study shows that understanding the coupling between hydrological and carbon cycles and the CO2 fertilization effect is important for understanding the current and future carbon budgets of high-latitude ecosystems in permafrost regions.

Direct and Legacy Effects of Varying Cool-Season Precipitation Totals on Ecosystem Carbon Flux in a Semi-Arid Mixed Grassland.

In the semi-arid grasslands of the southwest United States, annual precipitation is divided between warm-season (July-September) convective precipitation and cool-season (December-March) frontal storms. While evidence suggests shifts in precipitation seasonal distribution, there is a poor understanding of the ecosystem carbon flux responses to cool-season precipitation and the potential legacy effects on subsequent warm-season carbon fluxes. Results from a two-year experiment with three cool-season precipitation treatments (dry, received 5th percentile cool-season total precipitation; normal, 50th; wet, 95th) and constant warm-season precipitation illustrate the direct and legacy effects on carbon fluxes, but in opposing ways. In wet cool-season plots, gross primary productivity (GPP) and ecosystem respiration (ER) were 103% and 127% higher than in normal cool-season plots. In dry cool-season plots, GPP and ER were 47% and 85% lower compared to normal cool-season plots. Unexpectedly, we found a positive legacy effect of the dry cool-season treatment on warm-season carbon flux, resulting in a significant increase in both GPP and ER in the subsequent warm season, compared to normal cool-season plots. Our results reveal positive legacy effects of cool-season drought on warm-season carbon fluxes and highlight the importance of the relatively under-studied cool-growing season and its direct/indirect impact on the ecosystem carbon budget.

Wildfire Emissions Offset More Permafrost Ecosystem Carbon Sink in the 21st Century

AbstractPermafrost ecosystems in high‐latitudes stock a large amount of carbon and are vulnerable to wildfires under climate warming. However, major knowledge gap remains in the effects of direct carbon loss from increasing wildfire biomass burning on permafrost ecosystem carbon sink. In this study, we used observation‐derived data sets and Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to investigate how carbon emissions from wildfire biomass burning offset permafrost ecosystem carbon sink under climate warming in the 21st century. We show that the fraction of permafrost ecosystem carbon sink offset by wildfire emissions was 14%–25% during the past two decades. The fraction is projected to be 28%–45% at the end of this century under different warming scenarios. The weakening carbon sink is caused by greater increase in wildfire emissions than net ecosystem production in permafrost regions under climate warming. The increased fraction of ecosystem carbon sink offset by wildfire carbon loss is especially pronounced in continuous permafrost region during the past two decades. Although uncertainties exist in simulations of wildfire emissions and ecosystem carbon budget, results from different models still show that wildfire emissions offset more permafrost ecosystem carbon sink in the 21st century. These findings highlight that carbon sink capacity of permafrost ecosystems is increasingly threatened by wildfires under the warming climate.

Reuse of straw in the form of hydrochar: Balancing the carbon budget and rice production under different irrigation management

Hydrochar is proposed as a climate-friendly organic fertilizer, but its potential impact on greenhouse gas (GHG) emissions in paddy cultivation is not fully understood. This two-year study compared the impact of exogenous organic carbon (EOC) application (rice straw and hydrochar) on GHG emissions, the net ecosystem carbon budget (NECB), net global warming potential (net GWP), and GHG emission intensity (GHGI) in a rice pot experiment using either flooding irrigation (FI) or controlled irrigation (CI). Compared with FI, CI increased ecosystem respiration by 23 – 44 % and N2O emissions by 85 – 137 % but decreased CH4 emissions by 30 – 58 % (p < 0.05). Since CH4 contributed more to net GWP than N2O, CI reduced net GWP by 16 – 220 %. EOC amendment increased crop yield by 5 – 9 % (p < 0.05). Compared with CK, hydrochar application increased initial GHG emission, net GWP and GHGI in the first year, while in the second year, there was no significant difference in net GWP and GHGI between CI–hydrochar and CK. Compared with straw addition, hydrochar amendment reduced net GWP and GHGI by 20 – 66 % and 21 – 66 %; and exhibited a lower net CO2 emission when considering the energy input during the hydrochar production. These findings suggest that integrated CI-hydrochar practices would be a sustainable and eco-friendly way for organic waste management in rice production as it holds potential to enhance the NECB and SOC sequestration of rice production, while also offsetting the extra carbon emissions from organic inputs.

Soil Health Intensification through Strengthening Soil Structure Improves Soil Carbon Sequestration

Intensifying soil health means managing soils to enable sustainable crop production and improved environmental impact. This paper discusses soil health intensification by reviewing studies on the relationship between soil structure, soil organic matter (SOM), and ecosystem carbon budget. SOM is strongly involved in the development of soil structure, nutrient and water supply power, and acid buffering power, and is the most fundamental parameter for testing soil health. At the same time, SOM can be both a source and a sink for atmospheric carbon. A comparison of the ratio of soil organic carbon to clay content (SOC/Clay) is used as an indicator of soil structure status for soil health, and it has shown significantly lower values in cropland than in grassland and forest soils. This clearly shows that depletion of SOM leads to degradation of soil structure status. On the other hand, improving soil structure can lead to increasing soil carbon sequestration. Promoting soil carbon sequestration means making the net ecosystem carbon balance (NECB) positive. Furthermore, to mitigate climate change, it is necessary to aim for carbon sequestration that can improve the net greenhouse gas balance (NGB) by serving as a sink for greenhouse gases (GHG). The results of a manure application test in four managed grasslands on Andosols in Japan showed that it was necessary to apply more than 2.5 tC ha−1 y−1 of manure to avoid reduction and loss of SOC in the field. Furthermore, in order to offset the increase in GHG emissions due to N2O emissions from increased manure nitrogen input, it was necessary to apply more than 3.5 tC ha−1y−1 of manure. To intensify soil health, it is increasingly important to consider soil management with organic fertilizers that reduce chemical fertilizers without reducing yields.

One–third substitution of nitrogen with cow manure or biochar greatly reduced N2O emission and carbon footprint in saline–alkali soils

The rapid expansion of farmland and long−term excessive nitrogen (N) application have caused huge environmental risks in fragile ecosystems facing global warming. Partially substituting N fertilizer with organic fertilizers offers an alternative field management strategy to alleviate the pressure of the ecological environment. To this end, the influence of one−third substitution of N fertilizer with cow manure or biochar field experiment was conducted under maize in Tarim River Basin since 2019. Five treatments with three replications were applied: CK (Fallow); no fertilization (0 N); conventional N fertilizer (N; N: 300 kg N ha−1, organic fertilizer: 0 kg N ha−1); one−third substitution of N with biochar (NB; N: 200 kg N ha−1, Biochar: 100 kg N ha−1) and one−third substitution of N with cow manure (NM; N: 200 kg N ha−1, Cow manure: 100 kg N ha−1) under maize season in saline−alkali soils. The greenhouse gas (GHG) emissions, net ecosystem carbon budget (NECB), soil organic carbon (SOC), maize yield, carbon footprint (CF), and yield carbon footprint (CFy) were analyzed from 2021 to 2022. The results showed that NB treatment decreased the average cumulative CO2 emissions by 21 %, while NM treatment showed no difference compared to N treatment. NB and NM treatments reduced the average cumulative N2O emissions (−61 %, −49 %), CF (−68 %, −10 %), CFy (−66 %, −19 %) and increased maize yield (+3 %, +2 %), SOC storage (+43 %, +6 %), NECB (+80 %, +24 %), and agronomic N use efficiency (ANUE) (+5 %, +3 %), compared to N treatment. NB treatment had the lowest emission factors (EF) (0.19 %) and the highest sustainability index (1.58) compared to NM treatment (0.26 %, 0.61) and N treatment (0.53 %, 0.84). To sum up, substituting one−third of N fertilizer with biochar or manure in saline−alkali soils was proved to be a multi−benefit strategy to increase yields and reduce GHG emissions and CF.

Carbon budget of paddy ecosystems in China simulated by denitrification‐decomposition model

AbstractQuantifying the carbon budget in rice paddy ecosystems is fundamental to understanding the role of paddy fields as carbon sinks or sources and to mitigating global climate change. This study used a process‐based model of the denitrification‐decomposition (DNDC) model to estimate greenhouse gas (GHG) emissions and carbon sinks in the paddy ecosystem across China. The simulation results showed that the GHG emissions were 0.147 Pg C‐equivalent year−1 and that the carbon sequestration in rice plants and soils reached 0.253 Pg C year−1 in 2016, indicating high carbon sequestration potential of the Chinese paddy ecosystem. Land management had a great influence on carbon budgets, among which straw residue incorporation rate and nitrogen fertilizer applications had a stronger influence on carbon budgets, particularly for double cropping rice. These results indicate that appropriate tillage practices can reduce GHG emissions and increase carbon sequestration of rice ecosystems while ensuring rice yields.

Estimating the Vertical Distribution of Biomass in Subtropical Tree Species Using an Integrated Random Forest and Least Squares Machine Learning Mode

Accurate quantification of forest biomass (FB) is the key to assessing the carbon budget of terrestrial ecosystems. Using remote sensing to apply inversion techniques to the estimation of FBs has recently become a research trend. However, the limitations of vertical scale analysis methods and the nonlinear distribution of forest biomass stratification have led to significant uncertainties in FB estimation. In this study, the biomass characteristics of forest vertical stratification were considered, and based on the integration of random forest and least squares (RF-LS) models, the FB prediction potential improved. The results indicated that compared with traditional biomass estimation methods, the overall R2 of FB retrieval increased by 12.01%, and the root mean square error (RMSE) decreased by 7.50 Mg·hm−2. The RF-LS model we established exhibited better performance in FB inversion and simulation assessments. The indicators of forest canopy height, soil organic matter content, and red-edge chlorophyll vegetation index had greater impacts on FB estimation. These indexes could be the focus of consideration in FB estimation using the integrated RF-LS model. Overall, this study provided an optimization method to map and evaluate FB by fine stratification of above-ground forest and reveals important indicators for FB inversion and the applicability of the RF-LS model. The results could be used as a reference for the accurate inversion of subtropical forest biomass parameters and estimation of carbon storage.

Effect of rice hull biochar treatment on net ecosystem carbon budget and greenhouse gas emissions in Chinese cabbage cultivation on infertile soil

Biochar, with its potential to enhance soil fertility, sequester carbon, boost crop yields and reduce greenhouse gas emissions, offers a solution. Addressing the challenges posed by climate change is crucial for food security and agriculture. However, its widespread adoption in agriculture remains in its infancy. This study assessed the effects of rice hull biochar on cabbage production and greenhouse gas emissions, especially nitrous oxide (N2O). A trial, employing a randomized block design in triplicate was conducted from September 13 to November 23, 2022, where "Cheongomabi" cabbage was cultivated with N-P2O5-K2O fertilization at 32-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}7.8-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-$$\\end{document}19.8 kg 10a−1. Additional fertilizer was applied twice post-sowing. The Biochar application rates were control = 0 ton ha−1, B1 = 1 ton ha−1, B3 = 3 ton ha−1, and B5 = 5 ton ha−1. The aboveground biomass of autumn cabbage harvested 82 days after sowing was 2.40–2.70 kg plant−1 in the control and biochar treatments (B1, B3, and B5), with no significant differences (p > 0.05). Cumulative CO2 emissions during cultivation varied across treatment groups, with initial and cumulative emissions of 10.40–17.94 g m−2 day−1 and 3.63–4.43 ton ha−1, respectively. N2O emissions decreased with higher biochar application: reductions of 2.9%, 25.4%, and 41.1% in the B1, B3, and B5 treatments, respectively, compared to the control. The biochar application had no significant impact on yield but curbed soil emissions, Net ecosystem carbon balance during cabbage cultivation ranged from 0.42 to 3.41 ton ha−1 for the B1, B3, and B5 treatments, respectively, compared to control. Overall, the study underscores biochar’s role in mitigating emissions and boosting soil carbon during cabbage cultivation in fall.

Short-term effect of the harvesting method on ecosystem carbon budget in hemiboreal Scots pine forest: Shelterwood cutting versus clear-cut

Shelterwood cutting (SC) has been highlighted as an alternative method to clear-cut (CC)-based even-aged forest management. However, compared to CC, the effect of SC on stand carbon (C) balance is still poorly understood at the ecosystem level. We examined the prompt effect of SC versus CC on ecosystem net primary production (NEP) on a short-term scale, using the C budgeting method combined with eddy covariance (EC) measurements in hemiboreal mature Scots pine stands.The early effect of SC on annual C budget after removing 30–40 % of the growing stock revealed diverse patterns in the studied stands; NEP varied from 0.62 to −1.3 t C ha−1 yr−1 for the C sink and the C source, respectively. However, C loss decreased already in the second post-thinning year and levelled out attaining −0.41 t C ha−1 yr−1, which is close to balance.Furthermore, C loss declined in the second post-harvesting year at the CC sites as a result of the increased production of the ground vegetation and the decreased soil heterotrophic respiration (Rh) flux. However, C loss from dry mesotrophic clear-cuts was almost −1.8 t C ha−1 yr−1 for both study sites. Since estimation of the individual C fluxes for C budgeting is associated with variability-induced errors, the estimated values of NEP contain uncertainties of various levels.The estimated annual cumulative Rh flux was significantly higher in the SC versus CC areas and the mean annual Rh values across the study sites were 3.57 ± 0.25 and 2.59 ± 0.09 t C ha−1 yr−1, respectively.Annual estimated NEE after SC was 1.8 ± 0.52 t C ha−1 yr−1, gross primary ecosystem production was 9.28 ± 0.97 and total ecosystem respiration was 7.47± 0.28 t C ha−1 yr−1. The discrepancy between the estimated values of NEE and NEP was 1.2 t C ha−1 yr−1.In the short term SC demonstrated some advantage over CC from the perspective of the C cycle, but the difference in NEP values between the SC and CC treatments was not convincingly overwhelming. Hence, SC allows to maintain the forest cover for a longer period and to avoid drastic changes in the landscape; still, after SC, C budget varied between the C sink and the C source.

Spatiotemporal variation and response of gross primary productivity to climate factors in forests in Qiannan state from 2000 to 2020

Accurate estimation of terrestrial gross primary productivity (GPP) is essential for quantifying the carbon exchange between the atmosphere and biosphere. Light use efficiency (LUE) models are widely used to estimate GPP at different spatial scales. However, difficulties in properly determining the maximum LUE (LUEmax) and downregulation of LUEmax into actual LUE result in uncertainties in the LUE-estimated GPP. The recently developed P model, a new LUE model, captures the adaptability of vegetation to the environment and simplifies parameterization. Site-level studies have proven the superior performance of the P model over LUE models. As a representative karst region with significant changes in forest cover in Southwest China, Qiannan is useful for exploring the spatiotemporal variation in forest GPP and its response to climate change for formulating forest management policies to address climate changes, e.g., global warming. Based on remote sensing and meteorological data, this study estimated the forest ecosystem GPP in Qiannan from 2000–2020 via the P model. This study explored the spatiotemporal changes in GPP in the study region over the past 20 years, used the Hurst index to predict future development trends from a time series perspective, and used partial correlation analysis to analyse the spatiotemporal GPP changes over the past 20 years in response to three factors: temperature, precipitation, and vapor pressure deficit (VPD). Our results showed that (1) the total amount of GPP and average GPP in Qiannan over the past 21 years (2000–2020) were 1.9 × 104 ± 2.0 × 103 MgC ha−1 year−1 and 1238.9 ± 107.9 gC m−2 year−1, respectively. The forest GPP generally increased at a rate of 6.1 gC m−2 year−1 from 2000 to 2020 in Qiannan, and this increase mainly occurred in the nongrowing season. (2) From 2000 to 2020, the forest GPP in Qiannan was higher in the southeast and lower in the northwest, indicating significant spatial heterogeneity. In the future, more than 70% of regional forest GPP will experience a weak increase in nonsustainability. (3) In Qiannan, forest GPP was positively correlated with both temperature and precipitation, with partial correlation coefficients of 0.10 and 0.11, respectively. However, the positive response of GPP to precipitation was approximately 70.47%, while that to temperature was 64.05%. Precipitation had a stronger restrictive effect on GPP than did temperature in this region, and GPP exhibited a negative correlation with VPD. The results showed that an increase in VPD inhibits GPP to some extent. Under rapid global change, the P model GPP provides new GPP data for global ecology studies, and the comparison of various stress factors allows for improvement of the GPP model in the future. The results of this study will aid in understanding the dynamic processes of terrestrial carbon. These findings are helpful for estimating and predicting the carbon budget of forest ecosystems in karst regions, clarifying the regional carbon absorption capacity, clarifying the main factors limiting vegetation growth in these regions, promoting sustainable regional forestry development and serving the “dual carbon goal.” This work has important guiding significance for policy formulation to mitigate climate change.

Canopy Heterogeneity and Environmental Variability Drive Annual Budgets of Net Ecosystem Carbon Exchange in a Tidal Marsh

AbstractTidal salt marshes are important ecosystems in the global carbon cycle. Understanding their net carbon exchange with the atmosphere is required to accurately estimate their net ecosystem carbon budget (NECB). In this study, we present the interannual net ecosystem exchange (NEE) of CO2 derived from eddy covariance (EC) for a Spartina alterniflora salt marsh. We found interannual NEE could vary up to 3‐fold and range from −58.5 ± 11.3 to −222.9 ± 12.4 g C m−2 year−1 in 2016 and 2020, respectively. Further, we found that atmospheric CO2 fluxes were spatially dependent and varied across short distances. High biomass regions along tidal creek and estuary edges had up to 2‐fold higher annual NEE than lower biomass marsh interiors. In addition to the spatial variation of NEE, regions of the marsh represented by distinct canopy zonation responded to environmental drivers differently. Low elevation edges (with taller canopies) had a higher correlation with river discharge (R2 = 0.61), the main freshwater input into the system, while marsh interiors (with short canopies) were better correlated with in situ precipitation (R2 = 0.53). Lastly, we extrapolated interannual NEE to the wider marsh system, demonstrating the potential underestimation of annual NEE when not considering spatially explicit rates of NEE. Our work provides a basis for further research to understand the temporal and spatial dynamics of productivity in coastal wetlands, ecosystems which are at the forefront of experiencing climate change induced variability in precipitation, temperature, and sea level rise that have the potential to alter ecosystem productivity.

The Application of Rice Straw with Reduced N Fertilizer Improves the Rice Yield While Decreasing Environmental N Losses in Southern China

To investigate the effects of straw residues with reduced nitrogen (N) fertilizer on greenhouse gas (GHG) and N losses in paddy fields, we conducted a field experiment during two growing seasons in paddy rice systems in southern China to evaluate the impacts of the application of straw residues with reduced N fertilizer on rice yield, GHG emissions, and ammonia (NH3) volatilization. The four treatments included N100 (conventional dose of N fertilizer), SN100 (conventional dose of N fertilizer + straw), N60 (60% of the conventional dose of N fertilizer), and SN60 (60% of the conventional dose of N fertilizer + straw). We found that the yield of the SN60 treatment was slightly reduced, but the partial factor productivity of applied N (PFPN) was significantly increased by 63.9% compared to the N100 treatment. At the same N application rate, the application of straw increased soil organic C (SOC), methane (CH4) emissions, carbon dioxide (CO2) emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), and net ecosystem carbon budget (NECB), but significantly decreased soil N2O emissions and NH3 volatilization. Compared with conventional fertilization (N100), straw residues with reduced N fertilization (SN60) reduced N2O emissions and NH3 volatilization by 42.1% and 23.9%, and increased GHGI and NECB by 11.1% and 18.3%, respectively. The results indicate that straw residues with reduced N fertilizer are a feasible strategy to reduce N losses in paddy fields while increasing carbon sequestration.

Amendment of straw with decomposing inoculants benefits the ecosystem carbon budget and carbon footprint in a subtropical wheat cropping field

The incorporation of straw with decomposing inoculants into soils has been widely recommended to sustain agricultural productivity. However, comprehensive analyses assessing the effects of straw combined with decomposing inoculants on greenhouse gas (GHG) emissions, net primary production (NPP), the net ecosystem carbon budget (NECB), and the carbon footprint (CF) in farmland ecosystems are scant. Here, we carried out a 2-year field study in a wheat cropping system with six treatments: rice straw (S), a straw-decomposing Bacillus subtilis inoculant (K), a straw-decomposing Aspergillus oryzae inoculant (Q), a combination of straw and Bacillus subtilis inoculant (SK), a combination of straw and Aspergillus oryzae inoculant (SQ), and a control with no rice straw or decomposing inoculant (Control). We found that all the treatments resulted in a positive NECB ranging between 838 and 5065 kg C ha−1. Relative to the Control, the S treatment increased CO2 emissions by 16%, while considerably enhancing the NECB by 349%. This difference might be attributed to the straw C input and an increase in plant productivity (NPP, 30%). More importantly, in comparison to that in S, the NECB in SK and SQ significantly increased by 27–35% due to the positive response of NPP to the decomposing inoculants. Although the combination of straw and decomposing inoculants yielded a 3% increase in indirect GHG emissions, it also exhibited the lowest CF (0.18 kg CO2-eq kg−1 of grain). This result was attributed to the synergistic effects of straw and decomposing inoculants, which reduced direct N2O emissions and increased wheat productivity. Overall, the findings of the present study suggested that the combined amendment of straw and decomposing inoculants is an environmentally sustainable management practice in wheat cropping systems that can generate win–win scenarios through improvements in soil C stock, crop productivity, and GHG mitigation.