Long term effects of fire on the soil greenhouse gas balance of an old-growth temperate rainforest

Effects of magnesium-modified biochar on soil organic carbon mineralization in citrus orchard

In order to investigate the carbon sequestration potential of biochar on soil, citrus orchard soils with a forest age of 5 years was taken as the research object, citrus peel biochar (OBC) and magnesium-modified citrus peel biochar (OBC-mg) were selected as additive materials, and organic carbon mineralization experiments were carried out in citrus orchard soil. OBC and OBC-Mg were applied to citrus orchard soils at four application rates (0, 1, 2, and 4%), and incubated at a constant temperature for 100 days. Compared with CK, the cumulative mineralization of soil organic carbon decreased by 5.11% with 1% OBC and 2.14% with 1% OBC-Mg. The application of OBC and OBC-Mg significantly increased the content of soil organic carbon fraction, while the content of soil organic carbon fraction was higher in OBC-Mg treated soil than in OBC treated soil. Meanwhile, the cumulative mineralization of soil organic carbon was significantly and positively correlated with the activities of soil catalase, urease and sucrase. The enzyme activities increased with the cumulative mineralization of organic carbon, and the enzyme activities of the OBC-Mg treated soil were significantly higher than those of the OBC treated soil. The results indicated that the OBC-Mg treatment inhibited the organic carbon mineralization in citrus orchard soils and was more favorable to the increase of soil organic carbon fraction. The Mg-modified approach improved the carbon sequestration potential of biochar for citrus orchard soils and provided favorable support for the theory of soil carbon sink in orchards.

Different variations in soil CO2, CH4, and N2O fluxes and their responses to edaphic factors along a boreal secondary forest successional trajectory

Forest succession is an important process regulating the carbon and nitrogen budgets in forest ecosystems. However, little is known about how and extent by which vegetation succession predictably affects soil CO₂, CH₄, and N₂O fluxes, especially in boreal forest. Here, a field study was conducted along a secondary forest succession trajectory from Betula platyphylla forest (early stage), then Betula platyphylla-Larix gmelinii forest (intermediate stage), to Larix gmelinii forest (late stage) to explore the effects of forest succession on soil greenhouse gas fluxes and related soil environmental factors in Northeast China. The results showed significant differences in soil greenhouse gas fluxes during the forest succession. During the study period, the average soil CO₂ flux was greatest at mid-successional stage (444.72 mg m^-2 h^-1), followed by the late (341.81 mg m^-2 h^-1) and the early-successional (347.12 mg m^-2 h^-1) stages. The average soil CH₄ flux increased significantly during succession, ranging from -0.062 to -0.036 mg m^-2 h^-1. The average soil N₂O flux was measured as 17.95 μg m^-2 h^-1 at intermediate successional stage, significantly lower than that at late (20.71 μg m^-2 h^-1) and early-successional (20.85 μg m^-2 h^-1) stages. During forest succession, soil greenhouse gas fluxes showed significant correlations with soil and environmental factors at both seasonal and successional time scales. The seasonal variations of soil GHG fluxes were mainly influenced by soil temperature and water content. Meanwhile, soil MBN and soil NO₃^--N content were also important factors for soil N₂O fluxes. Structural equation modelling showed that forest succession affected soil CO₂ fluxes by changing soil temperature and microbial biomass carbon, affected soil CH₄ fluxes mainly by changing soil water content and soil pH value, and affected soil N₂O fluxes mainly by changing soil temperature, microbial biomass nitrogen, and soil NO₃^--N content. Our study suggests that forest succession mainly alters soil nutrient and soil environment/chemical properties affecting soil CO₂ and N₂O fluxes and soil CH₄ fluxes, respectively, in the secondary forest succession process.

Disturbance alters relationships between soil carbon pools and aboveground vegetation attributes in an anthropogenic peatland in Patagonia

Anthropogenic‐based disturbances may alter peatland soil–plant causal associations and their ability to sequester carbon. Likewise, it is unclear how the vegetation attributes are linked with different soil C decomposition‐based pools (i.e., live moss, debris, and poorly‐ to highly‐decomposed peat) under grassing and harvesting conditions. Therefore, we aimed to assess the relationships between aboveground vegetation attributes and belowground C pools in a Northern Patagonian peatland of Sphagnum magellanicum with disturbed and undisturbed areas. We used ordination to depict the main C pool and floristic gradients and structural equation modeling (SEM) to explore the direct and indirect relationships among these variables. In addition, we evaluated whether attributes derived from plant functional types (PFTs) are better suited to predict soil C pools than attributes derived from species gradients. We found that the floristic composition of the peatland can be classified into three categories that follow the C pool gradient. These categories correspond to (1) woody species, such as Baccharis patagonica, (2) water‐logged species like Juncus procerus, and (3) grasslands. We depicted that these classes are reliable indicators of soil C decomposition stages. However, the relationships change between management. We found a clear statistical trend showing a decrease of live moss, debris, and poorly‐decomposed C pools in the disturbed area. We also depicted that plant diversity, plant height, and PFT composition were reliable indicators of C decomposition only under undisturbed conditions, while the species‐based attributes consistently yielded better overall results predicting soil C pools than PFT‐based attributes. Our results imply that managed peatlands of Northern Patagonia with active grassing and harvesting activities, even if small‐scaled, will significantly alter their future C sequestration capacities by decreasing their live and poorly‐decomposed components. Finally, aboveground vegetation attributes cannot be used as proxies of soil C decomposition in disturbed peatlands as they no longer relate to decomposition stages.

Howland Forest, ME, USA: Multi-Gas Flux (CO2, CH4, N2O) Social Cost Product Underscores Limited Carbon Proxies

Forest carbon sequestration is a widely accepted natural climate solution. However, methods to determine net carbon offsets are based on commercial carbon proxies or CO2 eddy covariance research with limited methodological comparisons. Non-CO2 greenhouse gases (GHG) (e.g., CH4, N2O) receive less attention in the context of forests, in part, due to carbon denominated proxies and to the cost for three-gas eddy covariance platforms. Here we describe and analyze results for direct measurement of CO2, CH4, and N2O by eddy covariance and forest carbon estimation protocols at the Howland Forest, ME, the only site where these methods overlap. Limitations of proxy-based protocols, including the exclusion of sink terms for non-CO2 GHGs, applied to the Howland project preclude multi-gas forest products. In contrast, commercial products based on direct measurement are established by applying molecule-specific social cost factors to emission reductions creating a new forest offset (GHG-SCF), integrating multiple gases into a single value of merit for forest management of global warming. Estimated annual revenue for GHG-SCF products, applicable to the realization of a Green New Deal, range from ~$120,000 USD covering the site area of ~557 acres in 2021 to ~$12,000,000 USD for extrapolation to 40,000 acres in 2040, assuming a 3% discount rate. In contrast, California Air Resources Board compliance carbon offsets determined by the Climate Action Reserve protocol show annual errors of up to 2256% relative to eddy covariance data from two adjacent towers across the project area. Incomplete carbon accounting, offset over-crediting and inadequate independent offset verification are consistent with error results. The GHG-SCF product contributes innovative science-to-commerce applications incentivizing restoration and conservation of forests worldwide to assist in the management of global warming.

Dynamics of methane and other greenhouse gases flux in forest ecosystems in China

The article examines an important problem of studying greenhouse gas emissions in forest ecosystems. The CH₄ emission and absorption dynamics in the soil have been studied based on the physical-chemical and microbiological analysis of forest products. The changes in forest methanogenesis in relation concerning the value of the hydrothermal coefficient have been examined. It was established that the most intensive emission of greenhouse gases was observed within the value of the hydrothermal coefficient (HTC) of 1.8 … 2. For soils with the HTC value of <1.3, almost no increase in greenhouse gases level was observed. It was found that fluctuations of methane levels in soil were seasonal. Statistical analysis of the obtained results showed sufficient convergence of the results. Thus, the determination coefficient of the obtained results was R² > 0.7, the Pearson criterion - χ² ∼ 1, and the Student's t-criterion >0.8. The results showed that methane is almost completely absorbed by forest soils, while CO₂ and N₂O are released into the atmosphere. Laboratory studies of soil's adsorption capacity relative to hydrocarbon under dynamic conditions have been performed and it has been established that soils with a high composition of organic matter showed significantly higher absorption capacity in comparison with sandy and clayey soils.