Soil signals of key mechanisms driving greater protection of organic carbon under aspen compared to spruce forests in a North American montane ecosystem

Selective transport of soil organic and inorganic carbon in eroded sediment in response to raindrop sizes and inflow rates in rainstorms

Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

Soil organic carbon (SOC) is the principal factor contributing to enhanced soil fertility and also functions as the major carbon sink within terrestrial ecosystems. Applying fertilizer is a crucial agricultural practice that enhances SOC and promotes crop yields. Nevertheless, the response of SOC, active organic carbon fraction and hay yield to nitrogen and phosphorus application is still unclear. The objective of this study was to investigate the impact of nitrogen-phosphorus interactions on SOC, active organic carbon fractions and hay yield in alfalfa fields. A two-factor randomized group design was employed in this study, with two nitrogen levels of 0 kg·ha-1 (N0) and 120 kg·ha-1 (N1) and four phosphorus levels of 0 kg·ha-1 (P0), 50 kg·ha-1 (P1), 100 kg·ha-1 (P2) and 150 kg·ha-1 (P3). The results showed that the nitrogen and phosphorus treatments increased SOC, easily oxidized organic carbon (EOC), dissolved organic carbon (DOC), particulate organic carbon (POC), microbial biomass carbon (MBC) and hay yield in alfalfa fields, and increased with the duration of fertilizer application, reaching a maximum under N1P2 or N1P3 treatments. The increases in SOC, EOC, DOC, POC, MBC content and hay yield in the 0-60 cm soil layer of the alfalfa field were 9.11%-21.85%, 1.07%-25.01%, 6.94%-22.03%, 10.36%-44.15%, 26.46%-62.61% and 5.51%-23.25% for the nitrogen and phosphorus treatments, respectively. The vertical distribution of SOC, EOC, DOC and POC contents under all nitrogen and phosphorus treatments was highest in the 0-20 cm soil layer and tended to decrease with increasing depth of the soil layer. The MBC content was highest in the 10-30 cm soil layer. DOC/SOC, MBC/SOC (excluding N0P1 treatment) and POC/SOC were all higher in the 0-40 cm soil layer of the alfalfa field compared to the N0P0 treatment, indicating that the nitrogen and phosphorus treatments effectively improved soil fertility, while EOC/SOC and DOC/SOC were both lower in the 40-60 cm soil layer than in the N0P0 treatment, indicating that the nitrogen and phosphorus treatments improved soil carbon sequestration potential. The soil layer between 0-30 cm exhibited the highest sensitivity index for MBC, whereas the soil layer between 30-60 cm had the highest sensitivity index for POC. This suggests that the indication for changes in SOC due to nitrogen and phosphorus treatment shifted from MBC to POC as the soil depth increased. Meanwhile, except the 20-30 cm layer of soil in the N0P1 treatment and the 20-50 cm layer in the N1P0 treatment, all fertilizers enhanced the soil Carbon management index (CMI) to varying degrees. Structural equation modeling shows that nitrogen and phosphorus indirectly affect SOC content by changing the content of the active organic carbon fraction, and that SOC is primarily impacted by POC and MBC. The comprehensive assessment indicated that the N1P2 treatment was the optimal fertilizer application pattern. In summary, the nitrogen and phosphorus treatments improved soil fertility in the 0-40 cm soil layer and soil carbon sequestration potential in the 40-60 cm soil layer of alfalfa fields. In agroecosystems, a recommended application rate of 120 kg·ha-1 for nitrogen and 100 kg·ha-1 for phosphorus is the most effective in increasing SOC content, soil carbon pool potential and alfalfa hay yield.

We conducted a 2-year field experiment which was comprised of five treatments, namely no straw returning (CK), straw mulching (SM), straw plowed into the soil (SP), and straw returned in granulated form (SG). The aim of this study was to investigate the effects of different straw returning modes on soil bacterial and fungal community structure and their relationships to soil organic carbon (SOC) fractions at three different soil depths (0-20, 20-40, and 40-60 cm) in a dryland under maize cultivation in Northeast (NE) China. SM, SP, and SG treatments significantly increased SOC content. Compared with SM and SP treatments, SG treatment significantly increased the content of SOC and easily oxidizable carbon (EOC) in the topsoil (0-20 cm depth), and increased dissolved organic carbon (DOC) and SOC content of the light fraction (LFOC) in the 20-40 cm layer. Meanwhile, SG treatment exhibited the highest microbial biomass C (MBC) content in all of the three soil depths. SG treatment also enhanced bacterial richness as well as fungal richness and diversity in the upper 40 cm of soil. In addition, SG treatment increased the relative abundance of Proteobacteria in all depths, and had the highest relative abundance of Basidiomycota in the first 20 cm of soil. SP treatment showed the lowest soil organic carbon content in all fractions and soil microbial community composition. SM treatment exhibited similar results to SG treatment in SOC, DOC, and LFOC contents, and bacterial diversity in the topsoil and subsoil. As a whole, treatment SG improved soil quality and maize yield, hence we recommend returning granulated straw as the most effective practice for enhancing labile SOC fractions as well as maintaining soil diversity and microbial richness of arid farmlands in NE China.

Precipitation patterns impact soil aggregates and organic carbon of an alpine wetland on the Qinghai-Tibetan Plateau

Spatial distribution of soil carbon in pastures with cow-calf operation: effects of slope aspect and slope position

Streams and rivers are important pathways for the export of atmospherically deposited mercury (Hg) from watersheds. Dissolved Hg (HgD) is strongly associated with dissolved organic carbon (DOC) in stream water, but the ratio of HgD to DOC is highly variable between watersheds. In this study, the HgD:DOC ratios from 19 watersheds were evaluated with respect to Hg wet deposition and watershed soil organic carbon (SOC) content. On a subset of sites where data were available, DOC quality measured by specific ultra violet absorbance at 254 nm, was considered as an additional factor that may influence HgD:DOC . No significant relationship was found between Hg wet deposition and HgD:DOC, but SOC content (g m−2) was able to explain 81% of the variance in the HgD:DOC ratio (ng mg−1) following the form: HgD:DOC=17.8*SOC−0.41. The inclusion of DOC quality as a secondary predictor variable explained only an additional 1% of the variance. A mathematical framework to interpret the observed power‐law relationship between HgD:DOC and SOC suggests Hg supply limitation for adsorption to soils with relatively large carbon pools. With SOC as a primary factor controlling the association of HgD with DOC, SOC data sets may be utilized to predict stream HgD:DOC ratios on a more geographically widespread basis. In watersheds where DOC data are available, estimates of HgD may be readily obtained. Future Hg emissions policies must consider soil‐mediated processes that affect the transport of Hg and DOC from terrestrial watersheds to streams for accurate predictions of water quality impacts.

Enclosure walls enhanced soil organic carbon storage in sloping croplands of the Yi ethnic minority region: evidence from the Anning River Basin (SW China).

Natural and regenerated saltmarshes exhibit different bulk soil and aggregate-associated organic and inorganic carbon contents but similar total carbon contents

Vegetation degradation along water gradient leads to soil active organic carbon loss in Gahai wetland

Peat swamp wetlands, crucial carbon pools in terrestrial ecosystems, significantly impact regional carbon cycling and climate change. In this study, the peat swamp wetland in the Altay Mountains was selected as the research object. In July 2023, soil samples were collected in situ from a depth of 0–80 cm of the peat swamp wetland. Subsequently, the contents of soil organic carbon (SOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and the physicochemical properties of the soil samples were determined. The distribution characteristics of soil organic carbon and its active carbon fractions at different soil depths and their influencing factors were investigated. The results demonstrate that (1) SOC, POC, and DOC concentrations were significantly higher in subsurface layers (20–80 cm) than in those of surface layers (0–20 cm), with SOC and POC peaking at 20–40 cm and DOC predominantly accumulating at 40–80 cm. (2) The concentrations of SOC, POC, and DOC reached minima at 0–10 cm, accounting for 17.25%, 16.91%, and 6.46% of the total 0–80 cm profile, respectively. POC represented 76.46% of SOC throughout the profile. (3) Available phosphorus (AP), total nitrogen (TN), ammonium nitrogen (NH4+N), and soil moisture (SM) accounted for an average of 68.94% of the variation in soil organic carbon and active carbon fractions at a depth of 0–80 cm. Higher levels of soil moisture and total nitrogen content emerged as the primary factors responsible for the reduction in soil organic carbon and active carbon fractions. In shallow soils (0–20 cm), an increase in the content of available phosphorus and ammonium nitrogen contributed to a decline in the soil’s active carbon fraction. Conversely, the situation was reversed in deeper soils. This study thus offers scientific insights into alpine peat bog wetland soil carbon dynamics and environmental responses.

Soil organic carbon (SOC) in arable topsoil is known to have beneficial effects on soil physical properties that are important for soil fertility. The effects of SOC content on soil aggregate stability have been well documented; however, few studies have investigated its relationship with the soil pore structure, which has a strong influence on water dynamics and biogeochemical cycling. In the present study, we examined the relationships between SOC and clay contents and pore size distributions (PSDs) across an arable field with large spatial variations in topsoil SOC and clay contents by combining X‐ray tomography and measurements of soil water retention. Additionally, we investigated the relationships between fractionated SOC, reactive Fe and Al oxide contents and soil pore structure. We found that porosities in the 0.2–720 μm diameter class were positively correlated with SOC content. A unit increase of SOC content was associated with a relatively large increase in porosity in the 0.2–5 and 480–720 μm diameter classes, which indicates that enhanced SOC content would increase plant available water content and unsaturated hydraulic conductivity. On the other hand, macroporosities (1200–3120 μm diameter classes) and bioporosity were positively correlated with clay content but not with SOC content. Due to strong correlations between soil texture, carbon‐to‐nitrogen ratios and reactive iron contents, we could not separate the relative importance of these soil properties for PSDs. Reactive aluminium and particulate organic carbon contents were poorer predictors for PSDs compared with clay and SOC contents. This study provides new insights on the relations between SOC and soil pore structure in an arable soil and may lead to improved estimations of the effects of enhanced SOC sequestration on soil water dynamics and soil water supply to crops.Highlights Relations between soil organic carbon (SOC) and pore size distribution (PSD) in an arable soil were explored. We used X‐ray tomography and soil water retention to quantify a wide range of PSD. There were positive correlations between SOC and porosities in 0.2–720 μm diameter classes. Porosities in 0.2–5 and 480–720 μm diameter classes were more strongly correlated with SOC than clay. Our results have implications for improved estimates of effects of SOC sequestration on soil water dynamics.

三江平原不同湿地类型土壤活性有机碳组分及含量差异

The capability of coastal wetland soils to store large amounts of organic carbon (OC) has been increasingly recognised. Stabilisation mechanisms (e.g. aggregation or mineral association) and stability of organic matter (OM) (recalcitrant vs. labile) are important features for the long-term storage of soil organic carbon (SOC). In estuarine marshes, SOC storage is dominated by a complex and dynamic interaction of abiotic conditions such as tidal inundation or changes in salinity. However, little is known on OC stabilisation and stability in these transitional ecosystems and how they are affected by system-specific characteristics. Therefore, our aim was to assess the effect of flooding and salinity on (i) OC stabilisation by aggregation and mineral association and (ii) the stability of the OC pool in estuarine marsh soils.We analysed topsoil (0 – 10 cm) and subsoil (10 – 30 cm) samples from 9 marsh zones along the salinity gradient (salt, brackish and freshwater) and flooding gradient (pioneer zone, low and high marsh) of the Elbe Estuary for their SOC contents, OC stabilisation mechanisms (density fractionation), OC stability (incubation with one- and two-compartment model fits) and dissolved organic carbon (DOC) concentrations.Total SOC contents were highest in the freshwater marsh and decreased towards topsoils with higher salinity. Flooding frequency had no uniform effect on SOC contents: While there was a positive tendency with decreasing flooding frequency, subsoils of the freshwater marsh showed the opposite trend. Total SOC contents were positively correlated with mineral-associated OC (CMAOM) and pedogenically unprotected particulate OM (CfPOM). The highest proportion of CMAOM was found in topsoils of freshwater marshes and it decreased towards higher salinities in topsoils of high marshes and pioneer zones. The OM protection by aggregation (CoPOM) increased in topsoils of high marshes. The proportion of CfPOM was less directly affected by salinity and flooding than by the CN ratio of the aboveground biomass (CNlitter). Furthermore, CfPOM correlated positively with the potential mineralisable C (Cpot) and labile C (Clabile) and negatively with the recalcitrant C pool (Crecalcitrant) that were derived from the one- and two-compartment models. Labile C, Cpot and Crecalcitrant were also strongly influenced by CNlitter. Moreover, Crecalcitrant was linked to the proportion of CMAOM. Concentrations of DOC increased with total SOC and Cpot but decreased with CoPOM.We conclude that SOC stabilisation in the Elbe Estuary is mainly related to mineral association of OM. With increasing terrestrial influence, physical protection in aggregates becomes more important. Besides these pedogenic stabilisation mechanisms, recalcitrance is strongly determined by vegetation characteristics.

Soil organic carbon (SOC) is a key player in global carbon cycling and has primary effects on soil quality and functioning. There is a general interest in modeling SOC content and understanding the factors controlling its accumulation and stability. The mid-IR spectra that provide fingerprints of soil chemical composition are well recognized in modeling and predicting SOC contents, which is generally done using different types of empirical multivariate analyses. This work suggests, for the first time, the decomposition of soil mid-IR spectra using nonnegative multivariate curve resolution (MCR) with an alternating least squares (ALS) algorithm [1]. The advantage of the nonnegative MCR-ALS decomposition is that it allows the expression of soil mid-IR absorbance in terms of contributions from chemically meaningful components, following the Beer-Lambert law. Hence, this combination of IR spectroscopy and the nonnegative MCR-ALS decomposition proposes a new analytical approach to decipher soil compositions and elucidate the components controlling soil functions. Potentially, the nonnegative MCR-ALS decomposition can identify chemically individual components or groups of constituents maintaining constant proportions in a series of samples. Based on this decomposition, a simple mechanistic model is developed to link the identified MCR-ALS components with their contribution to the whole SOC content [1]. This approach has been used to examine the SOC of soil samples collected in the north and south of Israel, from different depths and under different land uses. Four components including a carbonate-rich constituent and three others representing clay-organic matter associations were capable of quantitatively describing 99.7% of the variance of soil mid-IR spectra. SOC modeling using these four components suggested a SOC content threshold affecting modeling performance such that SOC content below 1.0 % w w-1 could be modeled with RMSD of 0.18% w w-1. The emergence of this threshold is currently related to mechanisms of how different SOC fractions become "mirrored" in mid-IR spectra. This threshold could be useful to distinguish between different types of SOC, i.e., those tending to tightly interact with mineral surfaces and those having weak connections with minerals, if at all. The perspectives in extending the whole approach for a wide range of SOC contents are also discussed.[1] Borisover, M., Lado, M., & Levy, G. J. (2025). Modeling Soil Organic Carbon Content Using Mid-Infrared Absorbance Spectra and a Nonnegative MCR-ALS Analysis. Soil & Environmental Health, 3(1) 100123.