Soil Organic Carbon Budget Research Articles

Early- and later-stage priming effects induced by spruce root fractions are regulated by substrate availability, stoichiometry and C input

The priming effect (PE), referring to the change in the soil organic carbon (SOC) turnover induced by fresh C input, is crucial to the SOC budget. Temperate coniferous forests store a large SOC pool that can be influenced by litter C input. Root litter is a major source of belowground C input but much less studied than leaf litter. Nowadays, it is not clear how PEs are controlled by root litter input of different availability and stoichiometry in coniferous forests and what the underlying mechanisms are. We prepared soluble fraction (SF) and insoluble fraction (IF) from 13C-depleted spruce roots using hot-water extraction and incubated these fractions with spruce forest soils (Cambisols) to measure the PE. Labile and slow C pools were simulated using a first-order parallel model, whereas soils were harvested during and after the incubation to estimate microbial utilization of substrate-C and C use efficiency (CUE).The SF had higher substrate availability, greater C:N ratio, and smaller C quantity than the IF. The PE ranged from −0.71 ± 0.44 to 3.34 ± 1.31 mg C/g SOC. The addition of SF induced an immediate and short-lasting positive PE, whereas that of IF caused a gradual and long-lasting positive PE. The immediate PE was associated with abundant, substrate-derived labile C. This indicates that the early-stage PE was controlled by substrate availability. The long-lasting PE was accompanied by an accelerated decomposition of the slow C pool, reflecting that substrate stoichiometry (C:N ratio) and total C input control the later-stage PE by regulating the decomposition of the slow C pool. This can be further explained by a shift between stoichiometric decomposition and N-mining mechanisms of the PE due to changes in CUE, microbial utilization of substrate-C, and K- vs. r-strategists with substrate C:N ratios. Regarding net C budget, a smaller C accumulation induced by the SF addition corresponded to the higher substrate availability and C:N ratio due to the greater early-stage PE and lower CUE, respectively. We propose that in our studied soils: (1) substrate availability determines the early-stage PE through substrate-derived labile C; (2) substrate stoichiometry and total C input regulate the later-stage PE through microbial utilization of substrates; and (3) both substrate availability and stoichiometry control net C budget. Our study highlighted that the shift in PEs with incubation time was regulated by substrate availability, stoichiometry, and C input at the level of the C input in natural spruce forests.

Evaluating the effects of soil erosion and productivity decline on soil carbon dynamics using a model-based approach

Abstract. Sustained accelerated soil erosion alters key soil properties such as nutrient availability, water holding capacity, soil depth and texture, which in turn have detrimental effects on crop productivity and therefore reduce C input to soils. In this study, we applied a 1-D soil profile model that links soil organic carbon (SOC) turnover, soil erosion and biomass production. We used observational data to constrain the relationship between soil erosion and crop productivity. Assuming no change in effort, we evaluated the model performance in terms of SOC stock evolution using published observational data from 10 catchments across Europe and the USA. Model simulations showed that accounting for erosion-induced productivity decline (i) increased SOC losses by 37 % on average compared to a scenario where these effects were excluded, and (ii) improved the prediction of SOC losses when substantial soil truncation takes place. Furthermore, erosion-induced productivity decline reduced soil–atmosphere C exchanges by up to 30 % after 200 years of transient simulation. The results are thus relevant for longer-term assessments and they stress the need for integrated soil–plant models that operate at the landscape scale to better constrain the overall SOC budget.

Redistribution of Soil Organic Carbon Induced by Soil Erosion in the Nine River Basins of China

AbstractGlobal soil erosion redistributes a large amount of soil organic carbon (SOC) and is potential to significantly change the terrestrial carbon budget. However, there are large uncertainties in the redistribution of SOC within the terrestrial and aquatic ecosystems. Based on two national survey data sets on soil erosion and sediment measurements from hydrological stations, this study estimated the redistribution of sediment and SOC in the nine river basins of China during 1995–1996 and 2010–2012. Over these two periods, 3.55–4.50 Pg of soil and 68.42–77.32 Tg C of SOC were eroded each year. For the SOC budget, on average 57% and 47% of the eroded SOC was deposited over land, 25% and 44% was deposited in the channel, and 18% and 8% was delivered into the sea during 1995–1996 and 2010–2012, respectively. Compared with the corresponding magnitudes during 1995–1996, the eroded SOC, the SOC deposited over land, and the SOC discharged into the sea decreased during 2010–2012, and only the SOC deposited into the river channel increased (from 19.5 to 30.1 Tg C yr−1). The changes in SOC deposition in the channel of the Yangtze River and the Yellow River basins demonstrate that the influence of human activities is extensive. Our results show that the erosion‐induced redistribution of SOC alters the carbon budget of China.

Black Spruce Soils Accumulate More Uncomplexed Organic Matter than Aspen Soils

Improving knowledge on the dynamics and maintenance of the boreal soil's C pool is of particular importance in response to climate change concerns. We hypothesized that different forest types (black spruce, trembling aspen, and mixedwood) found on a similar site type differentially affect soil organic carbon (SOC) distribution among physical fractions. The surface mineral soil (0-15 cm) of 24 plots differing in forest composition was sampled in forested Hapludalfs of the Abitibi-James Bay region, Canada. The soil was first separated into three water-stable aggregate size fractions (> 1000, 1000-250, and mixedwood (41.9) > trembling aspen (34.7). While similar amounts of SOC (∼30 Mg C ha ―1 ) were found in the S&C, more SOC was found in the less protected fractions (i.e., uncomplexed organic matter, UOM: LF and iPOM) under black spruce than under trembling aspen, the mixedwood being intermediate. This higher accumulation of UOM under black spruce suggests a slower C turnover that is probably induced by the low-quality C inputs and environmental constraints to decomposition found in these forests. These differences in the amounts of SOC stored within soil physical fractions might have strong repercussions on the SOC budget of the boreal forest of eastern Canada under climate change.

Analysis of Spatial and Temporal Variation of Soil Organic Carbon Budget in Northern Kazakhstan

Farm-regional evaluation of soil organic carbon (SOC) dynamics for the chernozem zone in northern Kazakhstan is now vitally important for making agro-environmental policy. In this study, the author intends to evaluate spatial and temporal variation of the SOC budget and to seek alternative ways of sustainable land use in northern Kazakhstan. To achieve this final goal, this study established the following objectives: to (1) clarify the spatial patterns of soil organic matter content, (2) clarify the influence of land use on the dynamics of soil organic carbon in situ for the three differential soil classes, and (3) clarify spatial and temporal variability of SOC budget in farm-regional scale. The highest SOC content was found in the northern region and the lowest content in the southern region of the study area. Potentially mineralizable carbon (PMC) content, however, was highest in the midwestern region. Furthermore, fluctuations in CO 2 emission from the soils showed a similar pattern to temperature fluctuations. Using PMC, soil temperature, precipitation and/or dryness factor, 40-80% of the variation of CO 2 emission could be estimated. From farm-regional evaluation, it is concluded that the spatial and temporal variation of the SOC budget was significantly affected by the crop rotation system in the area. In addition, the fallow- and barley-based crop rotation systems accelerate SOC depletion in the study area.

Land cover change and soil organic carbon stocks in the Republic of Ireland 1851–2000

Using both historic records and CORINE land cover maps, we assessed the impact of land cover change on the stock of soil organic carbon (SOC) in the Republic of Ireland from 1851 to 2000. We identified ten principal land cover classes: arable land, forest, grassland, heterogeneous agricultural areas/other, nonvegetated semi-natural areas, peatland, suburban, urban, water bodies, and wetland. For each land cover class, the SOC stock was estimated as the product of SOC density and land cover area. These were summed to calculate a national SOC budget for the Republic of Ireland. The Republic of Ireland’s 6.94 million hectares of land have undergone considerable change over the past 150 years. The most striking feature is the decrease in arable land from 1.44 million ha in 1851 to 0.55 million ha in 2000. Over the same time period, forested land increased by 0.53 million ha. As of 2000, agricultural lands including arable land (7.85%), grassland (54.33%), and the heterogeneous agricultural areas/other class (7.91%) account for 70.09% of Irish land cover. We estimate that the SOC stock in the Republic of Ireland, to 1 m depth, has increased from 1,391 Tg in 1851 to 1,469 Tg in 2000 despite soil loss due to urbanization. This increase is largely due to the increase of forested land with its higher SOC stocks when compared to agricultural lands. Peatlands contain a disproportionate quantity of the SOC stock. Although peatlands only occupy 17.36% of the land area, as of 2000, they represented 36% of the SOC stock (to 1 m depth).

Influence of crop rotation system on the spatial and temporal variation of the soil organic carbon budget in northern Kazakhstan

To optimize regional crop rotation systems to mitigate soil organic carbon (SOC) depletion, monitoring the spatial and temporal variation of the SOC budget is of major importance. This study evaluated the influence of crop rotation and topography on the spatial and temporal variation of the SOC budget under cereal cropping in northern Kazakhstan using a geostatistical method, predicted equations of CO2 emission and Moderate Resolution Imaging Spectroradiometer satellite images. The study was carried out in large-scale upland fields (7,915 ha) located in Shortandy, Aqmorinskaya Oblast, from 2001 to 2005. Under the assumption that all crop residue was incorporated into the soil, average annual C input as plant residues in cereal and abandoned fields ranged from 1.0 to 1.6 Mg C ha−1 year−1, with higher values in wet years. Average annual CO2 emission in the cereal fields and the fallow fields ranged from 1.0 to 1.2 Mg C ha−1 year−1 and from 0.7 to 0.8 Mg C ha−1 year−1, respectively. In relation to topography, CO2 emission was higher on the north-facing slope than the south-facing slope, with the highest values on the higher plateau, and the average annual carbon budget ranged from –0.1 to 0.3 Mg C ha−1 year−1. It should be noted that all fallow fields consistently had a negative carbon budget. The 5-year carbon budget for different crop rotation systems ranged from –0.5 (fallow-based rotation) to 0.6 (wheat-based 5-year continuous cereal cropped) Mg C ha−1. These results have some uncertainly because of the low predictive ability of the regression; however, the results indicated that fallow-based and barley-based crop rotation systems were depletive and conversion of the wheat-fallow system to continuous wheat cropping would sequestrate 0.1–0.3 Mg ha−1 year−1 of carbon into the soil.

Soil organic carbon budget and fertility variation of black soils in Northeast China

AbstractBlack soils in Northeast China are characteristic of high soil organic carbon (SOC) density and were strongly influenced by human activities. Therefore, any change in SOC pool of these soils would not only impact the regional and global carbon cycle, but also affect the release and immobilization of nutrients. In this study, we reviewed the research progress on SOC storage, budget, variation, and fertility under different scenarios. The results showed that the organic carbon storage of black soils was 646.2 TgC and the most potential sequestration was 2887.8 g m−2. According to the SOC budget, the net carbon emission of black soils was 1.3 TgC year−1 under present soil management system. The simulation of CENTURY model showed that future climate change and elevated CO2 concentration, especially the increase of precipitation, would increase SOC content. Furthermore, fertilization and cropping sequence obviously influenced SOC content, composition, and allocation among different soil particles. Long‐term input of organic materials such as manure and straw renewed original SOC, improved soil structure and increased SOC accumulation. Besides, soil erosion preferred to transport soil particles with low density and fine size, decreased recalcitrant SOC fractions at erosion sites and increased activities of soil microorganism at deposition sites. After natural grasslands were converted into croplands, obvious variation of soil chemical nutrients, physical structure, and microbial activities had taken place in surface and subsurface soils, and represented a degrading trend to a certain degree. Our studies suggested that adopting optimal management such as conservation tillage in black soil region is an important approach to sequester atmospheric CO2 and to slow greenhouse effects.

Soil and soil organic carbon redistribution on the landscape

Patterns of soil organic carbon (SOC) vary widely across the landscape leading to large uncertainties in the SOC budget especially for agricultural landscapes where water, tillage and wind erosion redistributes soil and SOC across the landscape. It is often assumed that soil erosion results in a loss of SOC from the agricultural ecosystem but recent studies indicate that soil erosion and its subsequent redistribution within fields can stimulate carbon sequestration in agricultural ecosystems. This study investigates the relationship between SOC and soil redistribution patterns on agricultural landscapes. Soil redistribution (erosion and deposition) patterns were estimated in three tilled agricultural fields using the fallout 137Cesium technique. 137Cs and SOC concentrations of upland soils are significantly correlated in our study areas. Upland areas (eroding) have significantly less SOC than soils in deposition areas. SOC decreased as gradient slope increases and soils on concave slopes had higher SOC than soils on convex slopes. These data suggest that soil redistribution patterns and topographic patterns may be used to help understand SOC dynamics on the landscape. Different productivity and oxidation rates of SOC of eroded versus deposited soils also contribute to SOC spatial patterns. However, the strong significant relationships between soil redistribution and SOC concentrations in the upland soil suggest that they are moving along similar physical pathways in these systems. Our study also indicates that geomorphic position is important for understanding soil movement and redistribution patterns within a field or watershed. Such information can help develop or implement management systems to increase SOC in agricultural ecosystems.

Organic carbon storage in soils of the Basque Country (Spain): the effect of climate, vegetation type and edaphic variables

This study was performed to identify the environmental factors that control soil organic carbon (SOC) accumulation in the Basque Country (Northern Spain) and to evaluate the impact of land use change on SOC budget in this territory. A total of 30 samples of the organomineral horizon were taken under representative vegetation types including native forest, coniferous plantations, scrub, pasture and cultures. The edaphic variables measured were organic C content, pH, total N, available P, exchangeable H+ and Al3+, cation exchange capacity (CEC), texture, and carbonates. The substitution of the original forest with a pasture led to a significant increase in organic C content of the topsoil in all cases studied. Temperature was the main climatic factor affecting the organic C levels in soil, being the two variables negatively correlated. The CEC and texture were other key factors controlling the organic C content, which increased with CEC and decreased with total sand. Average organic C content of the organomineral horizon did not differ significantly (P <0.05) with base content of original substrate nor climate type, but it was more sensitive to climate change in the Atlantic soils than in the Mediterranean ones, where edaphic variables such as CEC and texture were important in regulating C sequestration.