Ecosystem Stocks Research Articles

Modelling the spatiotemporal dynamics of blue carbon stocks in tidal marsh under Spartina alterniflora invasion

Spatial quantification of blue carbon ecosystem stocks is crucial for developing policies to mitigate climate change, especially in regions experiencing ongoing wetland disturbance from biological invasions. We integrated multiple machine learning models with the space-for-time substitution method to quantify the spatiotemporal impact of Spartina alterniflora invasion on tidal marsh sediment blue carbon (soil organic carbon – 'SOC') stocks at 100 cm depth in the Yangtze Estuary. Our results show that the invasive S. alterniflora contributed more than half of the total SOC stocks (2,056 ± 379 Gg C, 1 Gg = 106 kg) in the 27,600 ha tidal marshes of the Yangtze Estuary, which were estimated to be 1,107 ± 176 Gg C. S. alterniflora increased the SOC stocks in the Yangtze Estuary within the first 15 years, but this gain was not sustained in the long term, with a gradual decline (by 13.14 Mg C/ha) observed after 15 years of S. alterniflora growth. We found that sediment salinity, tidal range, and human accessibility were strong indicators for modeling and predicting SOC stocks, with Random Forest providing the best simulation of tidal marsh SOC stocks (R2 = 0.894, RMSE=7.646 Mg C/ha, and MAPE=9.469 %). Our study provides much needed information on blue carbon stocks in the Yangtze Estuary under biological invasion stress, and offers guidance for targeted S. alterniflora management actions in the future.

Ecosystem carbon stock and annual sequestration rate from three genera-dominated mangrove zones in Benoa Bay, Bali, Indonesia

Abstract. Sugiana IP, Prartono T, Rastina, Koropitan AF. 2024. Ecosystem carbon stock and annual sequestration rate from three genera-dominated mangrove zones in Benoa Bay, Bali, Indonesia. Biodiversitas 25: 287-299. The mangrove ecosystem is an ecologically productive wetland system that serves as a carbon sink. However, various factors have contributed to the variation in values when calculating ecosystem carbon stock and the sequestration rate in the mangrove ecosystem. The presence of varying environmental conditions has resulted in the categorizing different species of mangroves, which may lead to variations in ecosystem carbon stock and sequestration rates. In this study, we aim to assess the ecosystem carbon stock and sequestration rate of the mangrove ecosystem in Benoa Bay, Bali, Indonesia. The ecosystem has been categorized into three zones based on the dominant genera: Bruguiera, Rhizophora, and Sonneratia. This research aimed to investigate the influence of mangrove zoning on the variability of carbon stock values and sequestration rates within the ecosystem. The allometric calculation technique and net primary productivity and soil organic carbon percentage values obtained using the Loss on Ignition (LOI) method are used to estimate each zone's ecosystem carbon stock and sequestration rate. The findings of our study indicate that there are notable variations in the carbon stock of ecosystems across different zones. However, we did not observe any substantial changes in the annual carbon sequestration rates. The Sonneratia zone exhibits the maximum value of ecosystem carbon stock and sequestration rate (1,570.9±248.0 tCO2ha-1 and 81.8 tCO2ha-1yr-1), while the Bruguiera zone demonstrates the lowest values (1,029.6±130.9 tCO2ha-1 and 75.6 tCO2ha-1yr-1). The three zones' average carbon stock and sequestration rate are estimated as 338.2 tCha-1 (1239.9 tCO2ha-1) and 21.5 tCha-1yr-1 (78.9 tCO2ha-1yr-1), respectively. In total, the carbon storage and absorption capacity of Benoa Bay amounts to 421,149 tC (equivalent to 1.5 million tCO2), with an annual rate of 25,769.4 tCyr-1 (equivalent to 94,573.6 tCO2yr-1). We recommended that future ecosystem carbon stock evaluations consider mangrove-type zoning characteristics due to significant value fluctuations in various mangrove zones found.

Middle-aged forests in the Eastern U.S. have significant climate mitigation potential

Middle-aged forests in the Eastern U.S. are broadly defined to consist of forests between the regeneration phase following harvest or disturbance, and an older phase with forests composed of large trees, complex structure, and increasing natural mortality. Study objectives were to develop new carbon accumulation curves based on recent inventory data that represent the actual growth rates of forests as they advance beyond middle age; quantify the projected carbon sink from reducing or increasing harvest of middle-aged forests; and disseminate credible estimates of future carbon stocks in ecosystems and harvested wood products to support policies designed to enhance the role of forests in removing carbon dioxide from the atmosphere and storing it securely. We found that middle-aged Eastern U.S. forests could continue to accumulate carbon for many decades or several centuries in the absence of harvesting, with relatively low risk of natural disturbances. Compared with a recent study that estimated a potential increase in biomass of only 22%, and some analyses that anticipate significant increases in risks from natural disturbances, our results indicate a potential increase of about 100% over current biomass stocks by 2100. Temperate Continental forests have greater potential to increase carbon stock over longer time periods than Subtropical Humid forests. Results from scenario analyses showed that in the near term of 20–40 years, reducing harvest will yield the greatest reduction in net greenhouse gas emissions compared with business as usual. Under an extreme “no-harvest” scenario, C sequestration could increase by about 20 TgC yr−1 in Temperate Continental forests by 2050, and by about 30 TgC yr−1 in Subtropical Humid forests over the same time period. In contrast, a scenario of tripling harvest would increase C emissions by 30 and 60 TgC yr−1 in the Temperate Continental and Subtropical Humid ecozones by 2050, respectively. In the longer term of 80 or so years, all scenarios and “business as usual” converge toward similar impacts on greenhouse gas emissions, nearing neutrality in the Subtropical Humid ecozone but separated by about 30 TgC yr−1 in the Temperate Continental ecozone. Our estimated annual emission reduction from stopping harvest over the 73 million ha of middle-aged forests amounts to 117 Mg CO2 per year in 2050, equivalent to about 7% of the emissions from using fossil energy in the two ecozones. Increasing harvest would have the opposite effect of increasing emissions by a similar magnitude in 2050. How middle-aged forests in the Eastern U.S. are managed can clearly affect their contribution to achieving net-zero GHG emissions by 2050 and beyond.

Scale variance in the carbon dynamics of fragmented, mixed-use landscapes estimated using model–data fusion

Abstract. Many terrestrial landscapes are heterogeneous. Mixed land cover and land use generate a complex mosaic of fragmented ecosystems at fine spatial resolutions with contrasting ecosystem stocks, traits, and processes, each differently sensitive to environmental and human factors. Representing spatial complexity within terrestrial ecosystem models is a key challenge for understanding regional carbon dynamics, their sensitivity to environmental gradients, and their resilience in the face of climate change. Heterogeneity underpins this challenge due to the trade-off between the fidelity of ecosystem representation within modelling frameworks and the computational capacity required for fine-scale model calibration and simulation. We directly address this challenge by quantifying the sensitivity of simulated carbon fluxes in a mixed-use landscape in the UK to the spatial resolution of the model analysis. We test two different approaches for combining Earth observation (EO) data into the CARDAMOM model–data fusion (MDF) framework, assimilating time series of satellite-based EO-derived estimates of ecosystem leaf area and biomass stocks to constrain estimates of model parameters and their uncertainty for an intermediate complexity model of the terrestrial C cycle. In the first approach, ecosystems are calibrated and simulated at pixel level, representing a “community average” of the encompassed land cover and management. This represents our baseline approach. In the second, we stratify each pixel based on land cover (e.g. coniferous forest, arable/pasture) and calibrate the model independently using EO data specific to each stratum. We test the scale dependence of these approaches for grid resolutions spanning 1 to 0.05∘ over a mixed-land-use region of the UK. Our analyses indicate that spatial resolution matters for MDF. Under the community average baseline approach biological C fluxes (gross primary productivity, Reco) simulated by CARDAMOM are relatively insensitive to resolution. However, disturbance fluxes exhibit scale variance that increases with greater landscape fragmentation and for coarser model domains. In contrast, stratification of assimilated data based on fine-resolution land use distributions resolved the resolution dependence, leading to disturbance fluxes that were 40 %–100 % higher than the baseline experiments. The differences in the simulated disturbance fluxes result in estimates of the terrestrial carbon balance in the stratified experiment that suggest a weaker C sink compared to the baseline experiment. We also find that stratifying the model domain based on land use leads to differences in the retrieved parameters that reflect variations in ecosystem function between neighbouring areas of contrasting land use. The emergent differences in model parameters between land use strata give rise to divergent responses to future climate change. Accounting for fine-scale structure in heterogeneous landscapes (e.g. stratification) is therefore vital for ensuring the ecological fidelity of large-scale MDF frameworks. The need for stratification arises because land use places strong controls on the spatial distribution of carbon stocks and plant functional traits and on the ecological processes controlling the fluxes of C through landscapes, particularly those related to management and disturbance. Given the importance of disturbance to global terrestrial C fluxes, together with the widespread increase in fragmentation of forest landscapes, these results carry broader significance for the application of MDF frameworks to constrain the terrestrial C balance at regional and national scales.

The time value of carbon storage

Widespread concern about the risks of global climate change is increasingly focused on the urgent need for action, and natural climate solutions are a critical component of global strategies to achieve low temperature targets. Yet to date, the full potential of natural systems to store carbon has not been leveraged because policymakers have required long-term contracts to compensate for permanence concerns, and these long-term contracts substantially raise costs and limit deployment. In this paper, we lay out the rationale that our time preference for early action leads to the conclusion that multiple tons of short-term storage of carbon in ecosystem stocks can be considered to have equal value – as measured by the social cost of carbon – as 1 ton of carbon sequestered permanently. This equivalence can be used to quantify the value of short-term carbon storage, thereby removing one of the most significant barriers to participation in the carbon market and enabling the full climate mitigation potential of the land sector to be realized.

Effects of whole-tree and stem-only clearcutting on forest floor and soil carbon and nutrients in a balsam fir (Abies balsamea (L.) Mill.) and red spruce (Picea rubens Sarg.) dominated ecosystem

Intensive harvesting of forest biomass for bioenergy has the potential to degrade forest soils and productivity if ecosystem carbon and other nutrients are depleted faster than replenished naturally or by management inputs. Climate change mitigation potential associated with bioenergy may be threatened if forest management operations reduce soil carbon stocks. Research reported here was initiated in 1979 to determine the effects of whole-tree harvesting on long-term site productivity and ecosystem carbon and nutrient pools and fluxes in a northeastern North American temperate balsam fir-red spruce forest. A sequence of harvesting and silvicultural treatments were applied from 1981 to 1993 using a paired-watershed experimental design. Treatments included whole-tree clearcutting, stem-only harvesting, simulated by return of chipped or lopped delimbing residue, conifer release by applying herbicide, and pre-commercial thinning and fertilizer application. Quantitative samples of the forest floor were excavated in 2016. Quantitative soil pits were sampled in 2017 to a depth of 50 cm below the forest floor, where possible; the basal till subsoil was sampled to a depth of 100 cm with an auger. Forest floor samples were analyzed for total carbon, nitrogen, phosphorus, potassium, calcium, magnesium and aluminum. Organic and mineral soil layer samples from the quantitative pits were analyzed for pH, short and long-lived soil carbon via 13C cross polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR), total carbon and nitrogen and extractable phosphorus, potassium, calcium, magnesium and aluminum. Forest floor carbon and nitrogen on whole-tree harvested plots 35 years after harvest were about 50% of the amount on the unharvested watershed. Stem-only harvesting partially mitigated the reduction, and gross losses were apparently offset by increases in the mineral soil solum to depth 50 cm, suggesting that downward translocation of soil organic matter was a significant ecosystem process during the 35 years since harvest. Accumulated forest floor and mineral soil stock of total carbon and nitrogen and extractable nutrients to depth 100 cm did not differ significantly between the harvested and unharvested watershed. A corresponding similarity in mineral soil pools of extractable phosphorus and non-acid cations in the two watersheds suggests that inputs from atmospheric deposition, primary and secondary mineral weathering, organic matter mineralization and litterfall balanced exports including leaching and plant uptake. Ecosystem stocks of extractable phosphorus, base cations, and total organic carbon and nitrogen were maintained 35 years after whole-tree harvesting of a primary spruce-fir forest.

Applying ecosystem accounting to develop a risk register for peatlands and inform restoration targets at catchment scale: a case study from the European region

Combining natural capital accounting tools and ecosystem restoration approaches builds on existing frameworks to track changes in ecosystem stocks and flows of services and benefits as a result of restoration. This approach highlights policy‐relevant benefits that arise due to restoration efforts and helps to maximize opportunities for return on investment. Aligning the System of Environmental Economic Accounting–Ecosystem Accounting (SEEA EA) framework with risk assessment tools, we developed a risk register for peatlands in two contrasting catchments in Ireland, based on available information relating to peatland stocks (extent and condition) and flows (services and benefits), as well as knowledge of pressures. This approach allowed for identification of areas to target peatland restoration, by highlighting the potential to reduce and reverse negative trends in relation to provisioning, regulating, and cultural services, flows relating to non‐use values, as well as abiotic flows. We also highlighted ways to reduce and reverse the effects of historical and ongoing pressures through restoration measures, aligning our approach with that outlined in the SER International Principles and Standards for the Practice of Ecological Restoration. Building on the synergies between the SEEA EA and the SER Standards is highlighted as a means to develop transdisciplinary collaboration, to assist in setting and achieving targets set out under the UN Decade on Ecosystem Restoration as well as integrating regional policy targets set under the EU Biodiversity Strategy for 2030, and the related EU Habitats and EU Water Framework Directives.

Developing peatland ecosystem accounts to guide targets for restoration

The United Nations System of Environmental and Economic Accounting - Ecosystem Accounting (SEEA EA) is a geospatial approach, whereby existing data on ecosystem stocks and flows are collated to show changes over time. The framework has been proposed as a means to track and monitor ecosystem restoration targets across the EU. Condition is a key consideration in the conservation assessment of habitats protected under the EU Habitats Directive and ecosystem condition accounts are also integral to the SEEA EA. While SEEA EA accounts have been developed at EU level for an array for ecosystem types, condition accounts remain the least developed. Collating available datasets under the SEEA EA framework, we developed extent and rudimentary condition accounts for peatland ecosystems at catchment scale in Ireland. Information relating to peatland ecosystem sub-types or habitat types was collated for peatland habitats listed under Annex I of the EU Habitats Directive, as well as degraded peatlands not included in EU nature conservation networks. While data relating to peatland condition were limited, understanding changes in ecosystem extent and incorporating knowledge of habitat types and degradation served as a proxy for ecosystem condition in the absence of more comprehensive data. This highlighted the importance of the ecosystem extent account, which underpins all other accounts in the SEEA EA framework. Reflecting findings at EU level, drainage, disturbance and land conversion were identified as the main pressures affecting peatland condition. We highlighted a number of options to gather data to build more robust, time-series extent and condition accounts for peatlands at varying accounting scales. Overall, despite the absence of comprehensive data, bringing information under the SEEA EA framework is considered a good starting point, with the integration of expert ecological opinion considered essential to ensure development of reliable accounts, particularly when working at ecosystem sub-type (habitat type) and catchment scale.

Carbon Polygons and Carbon Offsets: Current State, Key Challenges and Pedological Aspects

Russia holds the largest store of carbon in soils, forests and permafrost grounds. Carbon, stored in a stabilized form, plays an important role in the balance of the global biogeochemical cycle and greenhouse gases. Thus, recalcitrance of soil organic matter to mineralization results in a decrease in current emissions of carbon dioxide into the atmosphere. At the same time, stabilization of organic matter in the form of humus due to organo–mineral interactions leads to the sequestration of carbon from the atmosphere into soils and biosediments. Thus, global carbon balance is essentially determined by soil cover state and stability. Currently, Russia is faced with a set of problems regarding carbon offsets and the carbon economy. One of the methods used to evaluate carbon stocks in ecosystems and verify offsets rates is carbon polygons, which are currently being organized, or are under organization, in various regions of Russia. This discussion addresses the current issues surrounding the methods and methodology of carbon polygons and their pedological organization and function.

Biotic and abiotic drivers of carbon, nitrogen and phosphorus stocks in a temperate rainforest

Forest ecosystems are recognized for their large capacity to store carbon (C) in their aboveground and belowground biomass and soil pools. While the distribution of C among ecosystem pools has been extensively studied, less is known about nitrogen (N) and phosphorus (P) pools and how these stocks relate to each other. There is also a need to understand how biotic and abiotic ecosystem properties drive the magnitude and distribution of C-N-P stocks. We studied a temperate rainforest in southern South America to answer the following questions: 1) how are C-N-P total stocks distributed among the different ecosystem pools?, 2) how do C:N, C:P and N:P ratios vary among ecosystem pools?, and 3) which are the main biotic and abiotic drivers of C-N-P stocks? We established 33 circular plots to estimate C, N, and P stocks in different pools (i.e. trees, epiphytes, understory, necromass, leaf litter, and soil) and a set of biotic (e.g., tree density and richness) and abiotic variables (e.g., air temperature, humidity and soil depth). We used structural equation modeling to identify the relative importance of environmental drivers on C-N-P stocks. We found that total ecosystem stocks (mean ± SE) were 1062 ± 58 Mg C ha−1, 28.8 ± 1.5 Mg N ha−1, and 347 ± 12.5 kg P ha−1. The soil was the largest ecosystem pool, containing 68%, 92%, and 73% of the total C, N, and P stocks, respectively. Compared to representative temperate forests, the soil of this forest contains the largest concentrations and stocks of C and N. The low P stock and wide soil C:P and N:P ratios suggest that P may be limiting forest productivity. The ecosystem C-N-P stocks were mainly driven by abiotic properties measured in the study area, however for N stocks, variables such as plant diversity and canopy openness were also relevant. Our results provide evidence about the importance not only of understanding the differences in C, N, and P stocks but also of the factors that drive such differences. This is key to inform conservation policies related to preserving old-growth forests in southern South America, which indeed are facing a rapid land-use change process.

Socio-ecological drivers of long-term ecosystem carbon stock trend: An assessment with the LUCCA model of the French case

• Land-use change are driven by socio-ecological processes affecting carbon fluxes. • We assess these drivers and fluxes based on a long-term modelling approach. • Carbon stocks in ecosystem increased by 32 % of in France from 1850 to 2015. • The main drivers are first change in land use intensity and second land conversion. • However, carbon emissions by fossil fuel are 9 times the sink in ecosystems. Land ecosystems can play a crucial role in climate-change mitigation by acting as sinks for carbon. Legacy effects of past land use, including land conversion and changes in land-use intensity, influence the capacity for future ecosystem carbon sequestration. These effects are hard to quantify, however, and the influence of changes in land-use intensity are still largely overlooked. This study assessed the long term dynamics (1850–2015) of the terrestrial carbon budget in France. We developed a new dynamic model: LUCCA (Land Use Change & Conversion Accounting) that robustly quantifies the dynamics of carbon stocks and fluxes. It allows disentanglement of land conversion from land management effects following a socio-ecological perspective. Carbon stocks in terrestrial ecosystems in France increased from 3.5 GtC in 1850 to 4.8 GtC in 2015 as a result of contrasting regional land-use trajectories. Based on five counterfactual scenarios, we unravel that changes in land-use intensity explained 46 % of the observed carbon stock changes since 1850, while land conversion was responsible for 30 %, and the rest can be attributed to changes in forest growth rates induced by both environmental and management changes. The effects of land conversion and changes in land-use intensity on carbon stock accumulation, however, would have been hardly possible in the absence of agricultural intensification and release of harvest pressure following wood-fuel substitution by fossil fuel. In fact, carbon emissions induced by fossil fuel consumption in France from 1850 to 2015 were 9 times the carbon sink in terrestrial ecosystems. These figures highlight the importance of considering long-term trajectories of ecosystem carbon fluxes and their relationship with emissions from other processes for climate action strategies.

Effects of afforestation with different species on carbon pools and soil and forest floor properties

Land use and land use change are factors that affect carbon and nutrient stocks in ecosystems. The aim of this research was to determine the effects of forest land use types on carbon pools and soil and forest floor features. This study was conducted in areas afforested with black pine (Pinus nigra Arn. subsp. pallasiana Lamb. Holmboe) and Scots pine (Pinus sylvestris L.) and on adjacent bare land within the Akdağ Nature Park, which is located in the West-Central Anatolia Region of Turkey. Three 20 × 20 m sample plots were selected within each forest land use, and the diameters at breast height and heights of all trees were measured. Tree biomass and carbon stocks in the unit areas were calculated using tree biomass equations, and carbon conversion factors were developed for two tree species. Within each sample plot, disturbed and core soil samples and forest floor samples were taken at three points at depths of 0–10, 10–20 and 20–30 cm. The physical and chemical properties of the soil and forest floor samples were determined in the laboratory and measurements were converted to a unit area using volume values. The data were evaluated using independent sample t-tests and analysis of variance. The results showed that the ecosystem carbon (C) stocks differed significantly with forest land use type; black pine plantations, Scots pine plantations and bare land accumulated 235.2 t C ha−1, 206.1 t C ha−1 and 37.4 t C ha−1, respectively. We found that in addition to the positive effect of afforestation on soil, black pine had a greater impact on some forest floor and soil characteristics in the region than Scots pine. Thus, we suggest that priority should be given to black pine in afforestation of the region and in other ecosystems with similar climates. Additionally, our results reveal the importance of afforestation on bare lands for reducing the impact of global climate change.

Global quantitative synthesis of ecosystem functioning across climatic zones and ecosystem types

AbstractAimProviding a quantitative overview of ecosystem functioning in a three‐dimensional space defined by ecosystem stocks, fluxes and rates, across major ecosystem types and climatic zones.LocationGlobal.Time period1966–2019.Major taxa studiedEcosystem‐level measurements (all organism types).MethodsWe conducted a global quantitative synthesis of a wide range of ecosystem variables related to carbon stocks and fluxes. We gathered a total of 4,479 values from 1,223 individual sites (unique geographical coordinates) reported in the literature (604 studies), covering ecosystem variables including biomass and detritus stocks, gross primary production, ecosystem respiration, detritus decomposition and carbon uptake rates, across eight major aquatic and terrestrial ecosystem types and five broad climatic zones (arctic, boreal, temperate, arid and tropical). We analysed the relationships among variables emerging from the comparisons of stocks, fluxes and rates across ecosystem types and climates.ResultsWithin our three‐dimensional functioning space, average ecosystems align along a gradient from fast rates–low fluxes and stocks (freshwater and pelagic marine ecosystems) to low rates–high fluxes and stocks (forests), a gradient that we hypothesize results mainly from variation in primary producer characteristics. Moreover, fluxes and rates decrease from warm to colder climates, consistent with the metabolic theory of ecology. However, the strength of climatic effects differs among variables and ecosystem types, resulting, for instance, in opposing effects on net ecosystem production between terrestrial and freshwater ecosystems (positive versus negative effects).Main conclusionsThis large‐scale synthesis provides a first quantified cross‐ecosystem and cross‐climate comparison of multivariate ecosystem functioning. This gives a basis for a mechanistic understanding of the interdependency of different aspects of ecosystem functioning and their sensitivity to global change. To anticipate responses to change at the ecosystem level, further work should investigate potential feedbacks between ecosystem variables at finer scales, which involves site‐level quantifications of multivariate functioning and theoretical developments.

Carbon dynamics in three subtropical forest ecosystems in China.

The carbon sequestration capacity of the forest ecosystem normally increases overage due to the carbon dynamic in below canopy and soil. The carbon dynamic is reflective of the forest characteristics and their interactions with climate, topographic, and soil conditions. In this study, we measured the carbon content and carbon density of canopy, shrub, understory vegetation, litter, and soil, and assessed carbon dynamics in three forest ecosystems (Cunninghamia lanceolate, Pinus massoniana, and Evergreen broad-leaved forests) with a combination of data from Fujian Provincial forest resource inventory. This study showed that the carbon content of the canopy layers increased over time, and the carbon content of the topsoil (0-30cm) in the young forests was significantly higher than that in other age groups in Cunninghamia lanceolata forest and Pinus massoniana forest. Due to the carbon differences in the soil layer, the carbon stocks of the C. lanceolata forest and the P. massoniana forest declined from 1996 to 2007, but the carbon stocks of Evergreen broad-leaved forest increased. Besides, using the traditional carbon content coefficient (0.5) might underestimate the carbon sequestration potential of these forest ecosystems, especially for the mature forests. The coniferous forests displayed a short-term reduction in the carbon stocks of ecosystems between 10 and 20years after afforestation, and the decline cannot be ignored in the carbon budget.

Mikania micrantha invasion enhances the carbon (C) transfer from plant to soil and mediates the soil C utilization through altering microbial community

Exotic plant invasion alters the structure and coverage of terrestrial vegetation and affects the carbon (C) stocks in ecosystems. Previous studies have shown the increases in the C stocks with increasing invasive plants, but these results remain contentious. Soil microbial communities are usually altered by plant invasion, which potentially influences the C cycling underground. We hypothesized that the plant invasion-caused dynamic changes in soil microbes would lead to the corresponding change in soil C accumulation. Using greenhouse experiments we simulated different invader intensities through varying the relative abundance of invasive species Mikania micrantha and its co-occurring native species Paederia scandens. By analyzing 13C-phospholipid fatty acid we found the invasive M. micrantha assimilated more 13C and transferred faster the fixed 13C through different tissues to soils, as compared to native P. scandens. Soil microbial components, i.e., i15:0, 16:0, 10Me16:0, 18:1w9c and 18:2w6,9 were mainly using the photo-assimilated 13C. In addition, we found a hump-shaped relationship between soil net 13C accumulate rate and rhizosphere microbial biomass, indicating that the soil C accumulation may be either enhanced or reduced in invaded ecosystems, depending on microbe abundance.

Carbon and Nitrogen Sequestration of Melaleuca Floodplain Wetlands in Tropical Australia

Wetlands of Melaleuca spp. in Australia form large forests that are highly threatened by deforestation and degradation. In America, Melaleuca has invaded large areas of native wetlands causing extensive damage. Despite their status as an endangered native ecosystem and as a highly invasive one, little is known about their C and N dynamics. In this study, we sampled five Melaleuca wetlands and measured their C and N ecosystem stocks (aboveground biomass and soil), tree accumulation rates, sedimentation rates, and soil stability. Melaleuca wetlands were highly heterogeneous, but most have large ecosystem C [mean ± SE (range); 360 ± 100 (80–670) Mg C ha−1] and N [8100 ± 1900 (1600–13,000) kg N ha−1] stocks. Tree accumulation rates were 5.0 ± 2.1 Mg C y−1 and 26 ± 14 kg N y−1, and surface soil accumulation rates were 0.6 ± 0.2 Mg C ha−1 y−1 and 39 ± 1 kg N y−1. We found evidence of long-term C and N accumulation in the soil, but also of some level of organic decomposition. Overall, we found that Melaleuca wetlands store and accumulate large amounts of C, especially in their trees, and large amounts of N in their soils, suggesting an important role in coastal biogeochemical cycles.

The effects of land cover change on carbon stock dynamics in a dry Afromontane forest in northern Ethiopia

BackgroundForests play an important role in mitigating global climate change by capturing and sequestering atmospheric carbon. Quantitative estimation of the temporal and spatial pattern of carbon storage in forest ecosystems is critical for formulating forest management policies to combat climate change. This study explored the effects of land cover change on carbon stock dynamics in the Wujig Mahgo Waren forest, a dry Afromontane forest that covers an area of 17,000 ha in northern Ethiopia.ResultsThe total carbon stocks of the Wujig Mahgo Waren forest ecosystems estimated using a multi-disciplinary approach that combined remote sensing with a ground survey were 1951, 1999, and 1955 GgC in 1985, 2000 and 2016 years respectively. The mean carbon stocks in the dense forests, open forests, grasslands, cultivated lands and bare lands were estimated at 181.78 ± 27.06, 104.83 ± 12.35, 108.77 ± 6.77, 76.54 ± 7.84 and 83.11 ± 8.53 MgC ha−1 respectively. The aboveground vegetation parameters (tree density, DBH and height) explain 59% of the variance in soil organic carbon.ConclusionsThe obtained estimates of mean carbon stocks in ecosystems representing the major land cover types are of importance in the development of forest management plan aimed at enhancing mitigation potential of dry Afromontane forests in northern Ethiopia.

干旱区沙漠化逆转过程植被–土壤碳储量的恢复演变规律研究

碳汇作用是陆地生态系统的重要生态功能之一，也是生态修复关注的重要方面。以地带性植被区为对照，应用空间代替时间的方法，在石羊河中游选择流动沙丘及造林恢复5年、15年和25年沙化土地样地，研究了沙漠化逆转过程沙地生态系统植被–土壤有机碳储量的恢复演变过程、规律及其影响因素。结果表明：固沙植被碳储量随沙漠化逆转过程先增加后降低，造林恢复25年平均固碳速率仅达到0.05 Mg/hm2•a。尽管沙漠化逆转过程的不同恢复阶段地上植被碳储量大，但是造林恢复5年、15年和25年沙化土地地下植被总碳储量也仅占到地带性植被的22.6%、54.9%和45.3%。0~1 m土壤和生态系统有机碳储量均随沙漠化逆转过程持续增加，造林恢复25年平均固碳速率分别达到0.48 Mg/hm2•a和0.53 Mg/hm2•a，远远高于固沙植被的固碳速率，而且0~5 cm表层土壤是有机碳储量为增长最快的层次。土壤有机碳储量所占比例均在87.5%以上，是沙漠化逆转不同恢复阶段沙化土地和地带性植被区的主要碳库。上述结果证明，固沙造林加速了沙漠化逆转过程，快速提高了沙化土地植被和表层土壤的碳储量，是固定大气CO2于沙地植被和土壤中的有效途径。但是，造林恢复25年沙化土地碳储量与地带性植被间依然存在明显差距，特别是地下植被和深层土壤有机碳储量还存在较大的增长潜力。 Carbon sequestration is one of the important ecological functions of land ecosystem, and it is also an important aspect of ecological restoration. An unrestored shifting sand dune and three formerly shifting sand dunes that had been afforested for 5, 15 and 25 years were selected in the middle reaches of Shiyang River to study restoration changes in biomass carbon (BC) and soil organic carbon (SOC) stocks of the desertified lands in the reversion process of desertification and their influence factors. Results showed that BC stocks of the desertified lands was increased and then reduced in the reversion process of desertification, and the average vegetation carbon se-questration rate reached only 0.05 Mg/hm2•a in 25 years. Total BC stocks of the desertified lands afforested for 5 years, 15 years and 25 years only accounted for 22.6%, 54.9% and 45.3% of native zonal vegetation, respectively. SOC in 0 - 1 m layer and ecosystem stocks increased gradually in the reversion process of desertification, and the average carbon sequestration rate reached 0.48 Mg/hm2•a and 0.53 Mg/hm2•a in 25 years, respectively. 0 - 5 cm topsoil was the fastest layer for restoration of SOC stocks. SOC stocks accounted for more than 87.5% of the ecosystem organic C stocks, and soil was major C stocks of the different restoration stages in the reversion process of desertification and native zonal vegetation. Therefore, sand-fixation afforestation not only promoted the reversal of desertification, but also increased BC and topsoil SOC stocks rapidly, which proved that sand-fixation afforestation was the effective way to fix atmospheric CO2 in the desertified lands. However, C stocks of the desertified lands at the different restoration stages were lower than native zonal vegetation obviously and there was still a growth potential for BC of underground vegetation and SOC stocks of deep soil of the desertified lands afforested for 25 years.

Sustainable Management of Soil for Carbon Sequestration

Mechanisms governing carbon stabilization in soils have received a great deal of attention in recent years due to their relevance in the global carbon cycle. Two thirds of the global terrestrial organic C stocks in ecosystems are stored in below ground components as terrestrial carbon pools in soils. Furthermore, mean residence time of soil organic carbon pools have slowest turnover rates in terrestrial ecosystems and thus there is vast potential to sequester atmospheric CO2 in soil ecosystems. Depending upon soil management practices it can be served as source or sink for atmospheric CO2. Sustainable management systems and practices such as conservation agriculture, agroforestry and application of biochar are emerging and promising tools for soil carbon sequestration. Increasing soil carbon storage in a system simultaneously improves the soil health by increase in infiltration rate, soil biota and fertility, nutrient cycling and decrease in soil erosion process, soil compaction and C emissions. Henceforth, it is vital to scientifically explore the mechanisms governing C flux in soils which is poorly understood in different ecosystems under anthropogenic interventions making soil as a potential sink for atmospheric CO2 to mitigate climate change. Henceforth, present paper aims to review basic mechanism governing carbon stabilization in soils and new practices and technological developments in agricultural and forest sciences for C sequestration in terrestrial soil ecosystems.

Changes in soil C and N stocks and C:N stoichiometry 21 years after land use change on an arable mineral topsoil

The sequestration of excess atmospheric C into resilient and long-lasting belowground pools is of increasing global importance to mitigate greenhouse gas emissions. One land use that is particularly amenable to this type of manipulation is agricultural land, which often has high sequestration potential. However, this capacity can depend on local factors such as cropping history, soil type and climate. Critically, it may also be limited by N availability. In this study we used the retrospective (repeated measures) methodology to assess the impact on previously arable land of land use change by either afforestation with two species of broadleaf trees planted at 800 or 1600stemsha−1 (T800 and T1600), or reversion to rough grassland (NT) for 21years. We quantified the concentration, distribution and total stocks of organic C and N in the upper 0–30cm of a common soil type found in NE Scotland and investigated the robustness of C:N to land use change. Finally we estimated ecosystem stocks of C and N, and how these were partitioned between plant and soil components. We found increases in the overall concentrations of soil C from 4.6% to 5.8%, and N from 0.32% to 0.43%. The increase in soil C stocks over the experiment was in the order NT>T800>T1600 and each treatment differed significantly. The same pattern was seen for increases in N stocks but here the increases in NT and T800 were significantly greater than for T1600. Overall, stocks were higher in the rough grassland plots than under trees by 35Mgha−1 for C and 2.2Mgha−1 for N. These increases in stocks were accompanied by a highly significant narrowing in C:N with time across all treatments from 14.6 to 13.6 and differences seen between upper and lower soil layers in 1991 had disappeared by 2012. From an average of 151Mgha−1 in 1991, the system C stock (soil+plants) had increased to between 202Mgha−1 (NT) and 221Mgha−1 (T1600) by 2012, with between 96% (NT) and 73% (T1600) of the C in the soil. Concurrently the system stock of N had increased to between 14.1Mgha−1 (NT) and 11.3Mgha−1 (T1600), from an average of 9.4Mgha−1 in 1991, with between 99% (NT) and 81% (T1600) of the system N in the soil. Although in 2012 there were significantly greater soil C stocks in NT, this was offset by C accumulation in the treatments containing trees, such that overall there were no treatment differences. However, this was not seen with system N stocks in 2012, which were significantly larger in the NT treatment than in those with trees. Mean annual rates of C and N accumulation in the systems were greatest in NT (2.7 and 0.22Mgha−1yr−1) and least in T1600 (0.7 and 0.08Mgha−1yr−1). These results are important in the context of land use strategies aimed at pollution mitigation, such as C sequestration and nitrate leaching. They are also relevant to the possible effects of land use change, especially reversion to agricultural use, of land previously taken out of production.