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Abstract Land-use changes can alter soil carbon (C) contents, and in particular deforestation has been responsible for a large part of the cumulative human-induced greenhouse gas (GHG) emissions. This study aimed to determine the influence of land-use and land cover change on soil organic carbon (SOC) content, microbial biomass C (MBC) and microbial respiration (MR) in the Hyrcanian forests, north of Iran. We compared an agricultural field (AF), plantations of Alnus subcordata (AS), Acer velutinum (AV), Quercus castaneifolia (QC) and Cupressus sempervirens (CS), and a natural forest (NF). Soil samples were collected at three different depths (0–20, 20–40 and 40–60 cm). Results showed that different land covers significantly affected soil characteristics, and SOC increased by 25% and 1.11% after the conversion of NF to CS and AS plantations respectively, and decreased by 4%, 12.11% and 53% when NF was converted to QC, AV and AF respectively. In all treatments, MBC and MR were significantly higher (p < 0.05) in the 0–20 cm depth, and MR was also correlated positively with MBC and SOC. Microbial biomass was near the half in the agriculture field than in plantations and natural forest in the upper layer, but the effects of land use on microbial biomass C decreased with soil depth. However, we observed considerable amounts microbial biomass C in 40–60 cm depth. Also, results showed that topographical feature, altitude and slope, will affect SOC content. Our results indicated that forest plantation is a key measure to enhance SOC content and mitigate global CO 2 emission, especially when soils are degraded and have low soil C content. In particular, afforestation had a crucial effect on elevating SOC content in the Hyrcanian forest, but plantations of oak (QC) and maple (AV) were less effective in terms of soil C increase. Graphical abstract Unlabelled Image Highlights • SOC increased after the conversion of NF to CS and AS plantations. • SOC stock of the agricultural field was about 50% lower compared to the NF. • Half of SOC content in agriculture field is concentrated in 0–20 cm of soil. • MBC decrease with depth, but there was a considerable MBC in the 40–60 cm depth. • The effects of land use on microbial biomass C decrease with depth. [ABSTRACT FROM AUTHOR]

C-sequestration, as a function of soils, is known to help mitigate climate change. However, the potential of urban soils to be C-sinks or sources, is widely unknown. This study aims to understand the role and significance of urban soils in the C-balance of the region. It reveals several important findings about the C-balance capacities of urban soils and the multiple factors affecting this balance. This two-year study focused on soil organic carbon (SOC) stocks and CO 2 emissions of urban soils in the city of Kursk, located in the Central Chernozemic region of Russia, an area known to have some of the most fertile soils in the world. SOС stocks and emissions were studied in residential, recreational, and industrial functional zones and in comparison to corresponding natural reference soils to analyze the influence of urbanization on C turnover Urban soils were found to store 20 to 50 kg С m − 2 in 1.5 m layer; 10–30% less than in corresponding natural Luvic Chernozems and Chernic Phaeozems, but greater than what has been reported for many other cities. The urban soils with developed cultural layers stored more C in subsoil compared to the natural soils. Emissions of CO 2 in urban soils, however, were higher than from Chernic Phaeozems but comparable to those from Luvic Chernozems. The CO 2 /SOC stocks ratio in urban soils was two–three times higher than in natural soils. These outcomes point to the intensive C turnover and low sustainability of SOC stocks in urban soils. This study found evidence that the recent urbanization of the Chernozemic region has adversely affected the C balance. Natural soils in the region are important C sinks, however they can convert to C sources in result of urbanization. [ABSTRACT FROM AUTHOR]

The determination of the total carbon storage of peatlands is of high relevance in the context of climate-change mitigation efforts. This determination relies on data about stratigraphy and peat properties, which are conventionally collected by coring. Ground-penetrating radar (GPR) and electrical resistivity imaging (ERI) can support these point data by providing subsoil information in two-dimensional cross-sections. In this study, GPR and ERI were conducted at two groundwater-fed fen sites located in the temperate zone in north-east Germany. The fens of this region are embedded in low conductive glacial sand and are characterised by thick layers of gyttja, which can be either mineral or organic. The two study sites are representative of this region with respect to stratigraphy (total thickness, peat and gyttja types) and ecological conditions (pH-value, trophic condition). The aim of this study is to assess the suitability of GPR and ERI to detect stratigraphy and peat properties under these characteristic site conditions. Results show that GPR clearly detects the interfaces between (i) Carex and brown-moss peat, (ii) brown-moss peat and organic gyttja, (iii) organic- and mineral gyttja, and (iv) mineral gyttja and the parent material (glacial sand). These layers differ in bulk density and the related organic matter content. ERI, however, does not delineate these layers; rather it delineates regions of varying properties. At our base-rich site, pore fluid conductivity and cation exchange capacity are the main factors that determine peat electrical conductivity (reverse of resistivity), whereas organic matter and water content are most influential at the more acidic site. Thus the correlation between peat properties and electrical conductivity are driven by site-specific conditions, which are mainly determined by the solute load in the groundwater at fens. When the total organic deposits exceed a thickness of 5 m, the depth of investigation by GPR is limited due to increasing attenuation. This is not a limiting factor for ERI, where the transition from organic deposits to glacial sand is visible at both sites. Due to these specific sensitivities, a combined application of GPR and ERI meets the demand for up-to-date information on carbon storage of peatlands, which is, moreover, very site-specific because of the inherent variety of ecological conditions and stratigraphy between peatlands in general and between fens and bogs in particular. [ABSTRACT FROM AUTHOR]

[Display omitted] • Agriculture/climate relationship is one of the most important contemporary problems. • Agriculture is a significant source of GHG emissions and carbon sequestration. • Agriculture must minimize greenhouse gas emissions without reducing yields. • Integrating trees with agricultural landscapes is strategy in climate change mitigation. Agronomy has significant impacts on climate stability due to the emission of large amounts of greenhouse gases and C sequestration in soil and plants and can influence on reducing the negative impact of agronomy on climate does not need to result in a reduction in yield. Nevertheless, satisfying both goals require the implementation of new methods. The present assessment was based on over 190 scientific publications. Forecasts from the beginning of the 21st century showed that the increase in temperature and CO 2 concentration would improve the productivity of crops by extending the growing season and allow for the cultivation of new species. However, this beneficial effect may be limited by the increasing intensity of the extreme weather phenomena such as: rainstorm, droughts, early frosts, storms etc. Here, we review more recent studies which indicate, however, that this beneficial effect of climate change will not be permanent and, consequently, will significantly reduce crop yields. Climate change is forcing the agronomy sector to implement adaptive methods for minimizing possible crop losses consisting, inter alia, (i) using crop species/varieties that are less sensitive; (ii) optimizing water management; (III) improving pest, disease and weed control efficiency. The pressure on the agriculture sector to increase food production due to the increase in the human population and the present hunger in specific regions run counter to the need to reduce the adverse climate impacts of agriculture. The current state of knowledge indicates that despite the implementation of new technologies, agricultural measures will not be able to significantly reduce climate change. Indeed, these approaches will not replace the need to reduce greenhouse gas emissions in other sectors. However, without the participation of agronomy in reducing GHG emissions by increasing carbon sequestration, the goals of the 2015 UN Climate Change Conference in Paris will not be achieved. [ABSTRACT FROM AUTHOR]

• High sediment carbon burial in semi-enclosed mangrove habitat with high NPP. • Low carbon burial in aquaculture converted mangrove habitat. • Biological factors like litterfall and crab density act as primary controls. • Secondary controls were sediment accumulation rates and grain size. Tropical mangrove environments have high carbon sequestration potential and this ecosystem service is currently used in mitigating climate change. However, these environments are declining rapidly in developing countries, diminishing their carbon sequestration potential and may ultimately transforming them as carbon dioxide sources. This study investigated the carbon sequestration potential through sediment burial at three mangrove habitats of Cochin, South-West coast of India. High burial estimates were recorded at two mangrove stations (2.95 ± 0.79–10.41 ± 2.50 t C ha−1 yr−1), but consistent with other tropical mangrove areas. Lower burial rates were estimated at one station (0.57 ± 0.24 t C ha−1 yr−1). Eighty percent of the mangrove net primary productivity through litterfall (NPP L) was stored in the sediment at the station with the highest burial rate, which is demonstrative of a robust carbon sink. However, at a different site, which is subject to aquaculture, only 7.23 % of NPP L was buried in the sediment. A major portion of the fixed carbon at this site is presumably emitted back to the atmosphere or exported to adjacent water bodies. The median total regional mangrove carbon burial rate in this study was 2.95 t C ha−1 yr−1 and the organic carbon burial rate was 1.93 ± 0.75 t C ha−1 yr−1. Biological factors such as mangrove biomass, litterfall and crab density have played a major role in controlling the sediment carbon burial rate. Sediment texture and bulk sediment accumulation acted as secondary controlling factors. The carbon source characterisation in the sediment profile using stable isotope techniques revealed the organic carbon origin as mangrove litter. Gaining a better understanding of carbon sources, burial rates and their controlling factors in mangrove habitats aids in regional climate mitigation efforts and global efforts to increase the carbon sequestration potential of tropical mangrove systems. [ABSTRACT FROM AUTHOR]

• C org burial was evaluated in seagrass sediments at the northern Mexican Caribbean. • Thalassia testudinum seagrass meadows showed C org storage within ~ 40 to ~ 100 years. • C org stock increments were related with increasing sediment accumulation rates. • Seagrasses might be gradually impacted by population growth and land use changes. Carbon sequestration in seagrass meadows mitigates the currently rising CO 2 atmospheric levels, as these ecosystems are highly productive and preserve sediment organic carbon over long periods. Five 210Pb dated sediment cores, collected from seagrass meadows dominated by Thalassia testudinum in the northern Mexican Caribbean touristic corridor Cancun-Riviera Maya, were used to establish temporal trends of organic carbon (C org) content, burial rates and stock variation over the past 100 years. C org contents (0.17–1.94%) and burial rates (2.0–252 g m−2 yr−1) were generally within the lower end range reported for seagrass meadow sediments worldwide. C org stock gradually increased over the past decades, associated with increasing sediment accumulation, possibly caused by inland erosion promoted by agricultural and forestry activities and, in the recent decades, by a rapid increase of urban development due to a fast growth of the tourist industry and population, likely causing fertilization of coastal waters. Seagrass meadow sediments in the northern Mexican Caribbean coastline showed long-term C org storage and preservation, since ~ 40 to ~ 100 years depending on the core, which emphasizes the need to protect these ecosystems against impacts of global change, and their incorporation into climate change mitigation strategies should be considered. [ABSTRACT FROM AUTHOR]

• Organic carbon burial rates and sources were assessed across Papuan mangroves. • Organic carbon burial rates ranged between 0.21 and 1.19 Mg C ha−1 yr−1. • Soil organic carbon stocks in the top 50 cm varied between 62 and 179 Mg C ha−1. • Soil organic carbon stocks are sourced from autoch- and alloch-thonous sources. Mangrove organic carbon is primarily stored in soils, which contain more than two-thirds of total mangrove ecosystem carbon stocks. Despite increasing recognition of the critical role of mangrove ecosystems for climate change mitigation, there is limited understanding of soil organic carbon sequestration mechanisms in undisturbed low-latitude mangroves, specifically on organic carbon burial rates and sources. This study assessed soil organic carbon burial rates, sources and stocks across an undisturbed coastal mudflat and mangrove hydrogeomorphological catena (fringe mangrove and interior mangrove) in Bintuni Bay, West Papua Province, Indonesia. 210Pb radionuclide sediment dating, and mixing model of natural stable isotope signatures (δ 13C and δ15N) and C/N ratio were used to estimate organic carbon burial rates and to quantify proportions of allochthonous (i.e., upland terrestrial forest) and autochthonous (i.e., on-site mangrove forest) organic carbon in the top 50 cm of the soil. Burial rates were in the range of 0.21–1.19 Mg C ha−1 yr−1. Compared to the fringe mangroves, organic carbon burial rates in interior mangroves were almost twice as high. Primary productivity of C 3 upland forest vegetation and mangroves induced soil organic carbon burial in interior mangroves and this was consistent with the formation of the largest organic carbon stocks (179 ± 82 Mg C ha−1). By contrast, organic carbon stored in the fringe mangrove (68 ± 11 Mg C ha−1) and mudflat (62 ± 10 Mg C ha−1) soils mainly originated from upland forests (allochthonous origin). These findings clearly indicate that carbon sequestered and cycling in mangrove and terrestrial forest ecosystems are closely linked, and at least a part of carbon losses (e.g., erosion) from terrestrial forests is buried in mangrove ecosystems. [ABSTRACT FROM AUTHOR]