Soil Organic Carbon Preservation Research Articles

Variable responses of mineral-bound soil organic carbon to land cover change in southern China’s coastal wetlands

The formation of mineral-bound organic carbon (OC) complexes is important for the long-term preservation of soil organic carbon (SOC) in wetlands. Many coastal wetlands globally have been threatened by plant invasion and land development, but information on the effects on mineral-bound OC is limited. We measured the soil contents of Ca-OC, Fe(Al)–OC and residual OC across 21 coastal wetlands in southern China that have gone through the same sequence of land cover change, from native mudflats (MFs) to Spartina alterniflora marshes (SAs) then to earthen aquaculture ponds (APs). Residual-OC was the main component of SOC (74.1–78.2 %), followed by Fe(Al)–OC (18.4–22.8 %) and Ca-OC (<3.5 %). All three components in the soil increased when MFs were converted to SAs, but decreased in subsequent conversion of SAs to APs. Land cover change affected Fe(Al)–OC the most, but SOC storage increased more strongly with increasing Ca-OC. Nitrogen supply in the form of NH4+-N and clay content both positively affected the changes in mineral-bound OC. Our results suggest that different land cover change scenarios had different effects on the amounts of mineral-bound OC and their liability to microbial turnover, resulting in different degrees of SOC preservation and carbon emissions.

How does national SOC monitoring on agricultural soils align with the EU strategies? An example using five case studies

AbstractSoil functioning contributes to the delivery of a vast range of ecosystem goods and services, and ecosystem health is therefore reflected by the capacity of the soil to perform underlying functions. Soil organic carbon (SOC) is a key indicator for soil quality as it is an integral driver of many soil functions and associated ecosystem services. Across the globe, SOC stocks are declining due to expanding agriculture and unsustainable practices. Awareness of the fact that soil is a non‐renewable resource and its functioning important for all life on Earth is increasing, especially among policymakers. As such, goals for the preservation and restoration of SOC are formulated in policies under the European Green Deal. However, the evaluation of these goals at the European level is hampered by a non‐harmonized diversity in national SOC monitoring strategies. While some SOC indicators can be useful for the evaluation of most policy goals (i.e., baseline and potential SOC stocks), additional and contrasting SOC data are often required for the evaluation of the goals formulated by the different EU directives. This study provides an overview of five ongoing SOC monitoring programmes across Europe and discusses how national programmes may be aligned to evaluate goals at the EU level. Five countries with very different soil monitoring programmes were included in a case study to illustrate the potential for harmonization and standardization of SOC assessment. Based on this study, we conclude that SOC monitoring strategies can be harmonized, but not standardized. We further suggest five sampling strategies that have potential for harmonization under the proposed Directive on Soil Monitoring and Resilience.

Preservation of Soil Organic Carbon (SOC) through Ecosystems’ Soil Retention Services in China

Preservation of Soil Organic Carbon (SOC) through Ecosystems’ Soil Retention Services in China

Organic Carbon and Lignin Protection by Metal Oxides Versus Silicate Clay: Comparative Study Based on Wetland and Upland Soils

AbstractMineral binding of organic carbon (OC) is one of the key mechanisms promoting soil organic carbon (SOC) persistence, which is vital for the long‐term sequestration of atmospheric carbon dioxide into soils. However, the relative importance of two main types of soil minerals ‐ metal oxides and silicate clay—in SOC protection remains unclear, hampering our ability to predict and protect this important pool of persistent SOC. Here, we analyzed OC bound to metal oxides (OCmetal) versus silicate clay (OCclay) in soils from contrasting environments (i.e., wetlands and uplands) using sequential dissolution by dithionite and hydrofluoric acid. We found that OCmetal% was higher than OCclay% in both wetlands and uplands, indicating the dominance of metal oxides in SOC protection. The sum of OCmetal% and OCclay% constituted a higher fraction of SOC in wetlands than uplands, suggesting an underappreciated role of mineral (in particular, metal oxide) protection in wetland SOC preservation. Furthermore, using lignin phenol analysis in tandem, ∼23% of lignin phenols were additionally released after the removal of silicate clay, providing a potential means to assess “hidden” lignin in mineral matrices. Given the wide use of lignin phenols as tracers for terrestrial plant‐derived OC, our results suggest that the contribution of terrestrial or plant‐derived carbon to sedimentary carbon stocks or mineral‐protected SOC deserves reassessment. These findings highlight the differential role of various soil minerals in the protection of SOC and its components in contrasting terrestrial environments, which warrants better recognition for understanding the distribution and dynamics of mineral‐protected SOC.

Microbial carbon use efficiency promotes global soil carbon storage

Soils store more carbon than other terrestrial ecosystems1,2. How soil organic carbon (SOC) forms and persists remains uncertain1,3, which makes it challenging to understand how it will respond to climatic change3,4. It has been suggested that soil microorganisms play an important role in SOC formation, preservation and loss5–7. Although microorganisms affect the accumulation and loss of soil organic matter through many pathways4,6,8–11, microbial carbon use efficiency (CUE) is an integrative metric that can capture the balance of these processes12,13. Although CUE has the potential to act as a predictor of variation in SOC storage, the role of CUE in SOC persistence remains unresolved7,14,15. Here we examine the relationship between CUE and the preservation of SOC, and interactions with climate, vegetation and edaphic properties, using a combination of global-scale datasets, a microbial-process explicit model, data assimilation, deep learning and meta-analysis. We find that CUE is at least four times as important as other evaluated factors, such as carbon input, decomposition or vertical transport, in determining SOC storage and its spatial variation across the globe. In addition, CUE shows a positive correlation with SOC content. Our findings point to microbial CUE as a major determinant of global SOC storage. Understanding the microbial processes underlying CUE and their environmental dependence may help the prediction of SOC feedback to a changing climate.

Rice–fish coculture system enhances paddy soil fertility, bacterial network stability and keystone taxa diversity

High-input, modern rice farming (MRF) has caused severe soil degradation worldwide, necessitating a transition towards more sustainable practices. The traditional rice–fish coculture (RFC) and manure fertilization (Manure) may provide valuable insights to this transition. However, it remains elusive how long-term agricultural conversion influences microbial community structure, soil fertility, and food supply. Here, we performed six-year conversions of MRF to either RFC or Manure in a hilly area of Sichuan (China). We found that agricultural conversions exerted a greater impact than rice growing stages on bacterial community structure. The RFC bacterial network exhibited the highest modularity and robustness, but also harbored the most diverse keystone taxa, followed by Manure. In contrast, MRF displayed network properties that are characteristic of unstable communities. Importantly, RFC also exhibited the greatest capability in improving the preservation of soil organic carbon, nitrogen, and phosphorus, and has significantly increased soil pH (> 1.5 units). Yet, adopting traditional practices, particularly Manure, decreased rice yields, but fish harvested in RFC could offset the decrease in rice yield. Our field study highlights bacterial network structure and keystone taxa diversity as possible indicators for agriculture sustainability, but also incentivizes the integration of traditional RFC in developing novel sustainable agricultural practices.

The crop residue conundrum: Maintaining long-term soil organic carbon stocks while reinforcing the bioeconomy, compatible endeavors?

Crop residues are a key bulk feedstock for supplying renewable carbon for bioenergy production and the broader bioeconomy without compromising food security. However, it is frequently advised to harvest no more than half of this potential to ensure the preservation of soil organic carbon (SOC) stocks. In this study, we challenge this recommendation and demonstrate that the crop residue potential allowing to maintain long-term SOC stocks is spatially differentiated and strongly dependent upon the bioeconomy conversion pathway for which it is intended. We assessed the interaction between the residues' usage for the bioeconomy and the maintenance of SOC stocks over 100 years by considering the coproduct return to soils from five bioeconomy pathways: pyrolysis, gasification, hydrothermal liquefaction, anaerobic digestion, and lignocellulosic ethanol production. To compare the long-term SOC changes from these scenarios against a reference where crop residues are unharvested, we developed a novel framework, applicable to any site or region, by coupling a SOC model that includes recalcitrant organic matter deriving from a bioeconomy calculation module. The adapted SOC model considers the recalcitrance to degradation of each coproduct, while the bioeconomy module determines the share of carbon from the crop residues ending in the coproducts. The framework was tested and applied with a high spatial resolution (>60,000 simulation units) to the context of French croplands over the period of 2020–2120, with state-of-the-art sensitivity analyses. The case study results revealed, among others, that an additional crop residue potential equivalent to 71–225 PJ (pathway-dependent) could be available for the French bioeconomy without SOC decreases, compared to applying a stringent removal limit of 31.5%.

Faster accumulation and greater contribution of glomalin to the soil organic carbon pool than amino sugars do under tropical coastal forest restoration.

Microbial metabolic products play a vital role in maintaining ecosystem multifunctionality, such as soil physical structure and soil organic carbon (SOC) preservation. Afforestation is an effective strategy to restore degraded land. Glomalin-related soil proteins (GRSP) and amino sugars are regarded as stable microbial-derived C, and their distribution within soil aggregates affects soil structure stability and SOC sequestration. However, the information about how afforestation affects the microbial contribution to SOC pools within aggregates is poorly understood. We assessed the accumulation and contribution of GRSP and amino sugars within soil aggregates along a restoration chronosequence (Bare land, Eucalyptus exserta plantation, native species mixed forest, and native forest) in tropical coastal terraces. Amino sugars and GRSP concentrations increased, whereas their contributions to the SOC pool decreased along the restoration chronosequence. Although microaggregates harbored greater microbial abundances, amino sugars and GRSP concentrations were not significantly affected by aggregate sizes. Interestingly, the contributions of amino sugars and GRSP to SOC pools decreased with decreasing aggregate size which might be associated with increased accumulation of plant-derived C. However, the relative change rate of GRSP was consistently greater in all restoration chronosequences than that of amino sugars. The accumulation of GRSP and amino sugars in SOC pools was closely associated with the dynamics of soil fertility and the microbial community. Our findings suggest that GRSP accumulates faster and contributes more to SOC pools during restoration than amino sugars did which was greatly affected by aggregate sizes. Afforestation substantially enhanced soil quality with native forest comprising species sequestering more SOC than the monoculture plantation did. Such information is invaluable for improving our mechanistic understanding of microbial control over SOC preservation during degraded ecosystem restoration. Our findings also show that plantations using arbuscular mycorrhizal plants can be an effective practice to sequester more soil carbon during restoration.

Preservation of soil organic carbon in coastal wetlands promoted by glomalin–iron–organic carbon ternary system

AbstractIron‐bound soil organic carbon (Fe‐bound SOC) and microbial residues are vital for SOC preservation, a process crucial for drawdown of anthropogenic carbon. However, the relative importance of Fe‐bound SOC in coastal wetlands, and its interaction with microbial residues remain poorly understood. Here, we used glomalin as a proxy for microbial residues, with the goal of determining microbial residues binding to Fe and Fe‐bound SOC across a 1000 km coastline of China including seven typical mangrove wetlands. As hypothesized, it was found that the glomalin fraction was strongly associated with and likely bound to Fe‐bound SOC complexes, which accounted for 21.4% ± 1.6% of mangrove SOC. Mean level of Fe‐bound glomalin was 1.2 ± 0.1 mg cm−3, accounting for 40.6% ± 1.5% of total glomalin and 35.4% ± 3.2% of Fe‐bound SOC in the top 10 cm mangrove soil layer at regional scale. Due to the growing realization that Fe may be a crucial factor of glomalin cycling, we performed multiple chemical characterization techniques to identify the association between Fe and glomalin. Our results suggested that association to Fe was a main stabilization mechanism of glomalin in soils, and glomalin served as organic ligands in the formation of Fe‐bound SOC. We also found that the bulk glomalin extracts were a glomalin–Fe–OC ternary complex, which constituted an important proportion of mangrove SOC. These findings highlight the important effect of glomalin bound to Fe as a major mechanism of SOC persistence in coastal wetlands.

Forest conversion effects on soil organic carbon are regulated by soil aggregate stability and not by recalcitrance: Evidence from a reforestation experiment

Preservation of biochemically recalcitrant organic matter and protection within soil aggregates are two important mechanisms of soil organic carbon (SOC) preservation, but their relative importance remains unclear. In this study, we converted part of a mature secondary forest to two young plantation forests (Castanopsis carlesii and Chinese fir) and an assisted naturally regenerated (ANR) forest in 2012. The three young forests (five years old at the time of study) and the remaining mature secondary forest constitute a soil disturbance intensity gradient ideal for exploring effects of forest conversion on soil aggregate size classes and stability as well as SOC concentration and chemical composition. Taking advantage of the disturbance gradient, we examined the relative importance of physical protection versus recalcitrance in SOC preservations. We found that the young ANR forest conserved a similar amount of SOC to that of the mature secondary forest, which was 18 %–21 % higher than those retained in the two young plantations. Compared with the mature secondary forest, the young ANR forest retained 87 % of >2 mm aggregates, whereas the two young forest plantations retained only 45 %–53 %. Compared to the mature secondary forest, aggregate mean weight diameter (MWD) decreased by 10 % in the young ANR forest and 37 %–43 % in the two young plantations. Moreover, the young Castanopsis carlesii plantation had proportionally more recalcitrant aromatic carbon (C) and less labile O-alkyl C compared to the mature secondary forest. Total SOC was positively related to >2 mm aggregates mass percent, soil aggregate MWD, and labile O-alkyl C, but not with recalcitrant alkyl and aromatic C. Our results indicate that SOC preservation is more related to soil aggregate stability than recalcitrant C abundance, and advocate that reducing soil disturbance is key to future forest management aiming to maximize C sequestration.

The Soil Aggregates and Associated Organic Carbon across the Greater Khingan Mountains: Spatial Patterns and Impacting Factors

(1) Background: The preservation of soil organic carbon (SOC) by soil aggregates (SA) is a key mechanism for the stability of the soil carbon (C) pool. (2) Methods: Soil samples were collected at a 0–20 cm depth from 75 sites across the forest regions of the Greater Khingan Mountains, China, and were fractionated as SA of 0.25–2 mm, 0.053–0.25 mm, and &lt;0.053 mm by a wet-sieving method. The spatial patterns of SA and associated organic C (OC) were investigated, as well as their associations with environmental factors. (3) Results: The predominant SA was the SA fraction (SAF) of 0.25–2 mm. The spatial pattern of SA, with moderate spatial autocorrelation, was found to be associated with aggregate size. SOC was mainly accumulated in the 0.25–2 mm SAF, accounting for 50.39% of the total content of aggregate SOC; the total SOC content in all SAF showed strong spatial autocorrelations without significant differences. No significant correlations were found between temperature and SA variables. Precipitation presented significantly positive and negative correlations with the SAF of &lt;0.053 mm and 0.053–0.25 mm, respectively. SOC was favorably associated with macroaggregate, geometric mean diameter (GMD), and mean weight diameter (MWD); however, the correlation between SOC and aggregate SOC lessened as particle size decreased. The aggregate SOC contents were significantly linked with NH4+-N, AK, and TP, while 0.25–2 mm SA content was negatively related with pH. (4) Conclusions: Precipitation was helpful for the development of clay aggregates (&lt;0.053 mm), i.e., increasing rainfall-induced aggregate disruption. SOC encourages small SA cementing to large SA, which improves SA stability. OC associated with the SAF of 0.25–2 mm and 0.053–0.25 mm was positively correlated with soil nutrients such as nitrogen, phosphorus, and potassium, suggesting that the formation of aggregates was conducive to the preservation of soil nutrients.

The regulators of soil organic carbon mineralization upon lime and/or phosphate addition vary with depth

Knowledge of the key factors regulating soil organic carbon (OC) mineralization in response to fertilizers and lime application is essential to understanding the effects of agricultural land management on soil OC preservation. Microbial community composition and OC availability to microorganisms have been proposed as the two most imperative factors controlling soil OC mineralization, although their relative importance is still under debate. Here we performed a laboratory incubation in combination with high-throughput sequencing and structural equation modeling to examine the mechanisms underlying the responses of OC mineralization in the topsoil and the subsoil of a volcanic soil (an Andosol) to the additions of lime and/or phosphate. Results showed that lime and/or phosphate additions induced distinct shifts in the microbial community composition and functional profiles in the topsoil and the subsoil. We found that OC mineralization relied on microbial community composition and functionality in the topsoil but was strongly related to the quality and quantity of the water-extractable OC (indicative of the OC availability) in the subsoil. These data suggest that the key regulator controlling the response of OC mineralization to lime and/or P additions shifts from microbial community composition to OC availability as soil depth increases in the Andosol. Our findings highlight the central role of mechanisms controlling soil OC mineralization in regulating the responses of mineralization to intensive agricultural management practices.

Visualizing Mineral-Associated Organic Matters in Long-Term Fertilization Treated Soils by NanoSIMS and SR-FTIR

Formation of mineral-associated organic matters is essential for long-term soil organic carbon preservation. However, the regulation pathways of mineral-associated organic matters in soils remains largely undescribed, especially at the submicron scale. Using a well-controlled long-term (32 years) field experiment at the Jiangxi Institute of Red Soils, Jinxian, China, we showed that long-term manure fertilization significantly (P &amp;lt; 0.05) increased the available Al and Fe concentrations over one order of magnitude in soil water dispersible colloids compared to no fertilization and chemical fertilization. Nano-scale secondary ion mass spectrometry (NanoSIMS) images and region of interest (ROI) analysis provided direct evidence demonstrating that long-term manure fertilization increased the 27Al16O−/12C−, 27Al16O−/12C14N−, 56Fe16O−/12C−, and 56Fe16O−/12C14N− ratios compared to no fertilization and chemical fertilization. This finding revealed that long-term manure fertilization may potentially enhance the stability of organic carbon and nitrogen. Synchrotron radiation based FTIR spectromicroscopy further supported that secondary minerals (&amp;lt;950 cm−1) were co-localized with amines, lipids, and proteins in the long-term manure fertilization, but only co-localized with proteins in the no fertilization and chemical fertilization. To summarize, our findings highlight the importance of manure inputs in increasing formation of mineral-associated organic matters and thus potentially increasing soil carbon persistence.

Mechanisms of soil organic carbon stability and its response to no-till: A global synthesis and perspective.

Mechanisms of soil organic carbon (SOC) stabilization have been widely studied due to their relevance in the global carbon cycle. No-till (NT) has been frequently adopted to sequester SOC; however, limited information is available regarding whether sequestered SOC will be stabilized for long term. Thus, we reviewed the mechanisms affecting SOC stability in NT systems, including the priming effects (PE), molecular structure of SOC, aggregate protection, association with soil minerals, microbial properties, and environmental effects. Although a more steady-state molecular structure of SOC is observed in NT compared with conventional tillage (CT), SOC stability may depend more on physical and chemical protection. On average, NT improves macro-aggregation by 32.7%, and lowers SOC mineralization in macro-aggregates compared with CT. Chemical protection is also important due to the direct adsorption of organic molecules and the enhancement of aggregation by soil minerals. Higher microbial activity in NT could also produce binding agents to promote aggregation and the formation of metal-oxidant organic complexes. Thus, microbial residues could be stabilized in soils over the long term through their attachment to mineral surfaces and entrapment of aggregates under NT. On average, NT reduces SOC mineralization by 18.8% and PE intensities after fresh carbon inputs by 21.0% compared with CT (p<.05). Although higher temperature sensitivity (Q10 ) is observed in NT due to greater Q10 in macro-aggregates, an increase of soil moisture regime in NT could potentially constrain the improvement of Q10 . This review improves process-based understanding of the physical and chemical mechanism of protection that can act, independently or interactively, to enhance SOC preservation. It is concluded that SOC sequestered in NT systems is likely to be stabilized over the long term.

Distribution Characteristics of SOC, STN, and STP Contents Along a Slope Aspect Gradient of Loess Plateau in China

In this study, the effects of slope aspects and depths on soil organic carbon (SOC), soil total nitrogen (STN), and soil total phosphorus (STP) were quantified in disturbed restoration regions of Gaolan County, located in the Gansu Province of semi-arid loess Plateau of China. Soil samples were collected at 0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm on southern, southwestern, western, northwestern, and northern slope aspects of three hills. A total of 75 soil profiles and 450 soil samples were analyzed. Results showed that the SOC, STN, and STP content varied from 1.65 to 12.87 g/kg, 0.45 to 1.53 g/kg, and 0.07 to 0.78 g/kg, and the SOCD, STND, and STPD at 0–100 cm varied from 3.9 to 9.5 kg/m2, 0.58 to 1.35 kg/m2, and 0.33 to 0.56 kg/m2, which increased from the southern to northern slope aspects. The SOC, STN, and STP contents and SOCD, STND, and STPD were mainly in the 0–60 and 60–100 cm soil layers. The vertical descent rate was γSOC &amp;gt; γSTN &amp;gt; γSTP for both content and density. For a single soil nutrient, the decline rate of its content and density on the northern slope aspect was greater than that on the southern slope aspect, that is γN &amp;gt; γ All &amp;gt; γS. The correlation degree between soil properties and SOC and STN content were above 0.6, the overall correlation with STP content was &amp;lt;0.6. These results confirmed that topography (slope aspects) was the most significant factor controlling the distribution patterns of SOC, STN, and STP in hill ecosystems. Overall, the northern slope aspect (vs. southern slope aspect) was more favorable to the preservation of SOC, STN, and STP. Accordingly, in the Loess Plateau and similar fragile environments, soil nutrient protection and vegetation restoration are selective to some extent.

The trajectory of soil development and its relationship to soil carbon dynamics

It has been postulated that the amount of soil organic carbon (SOC) associated with soil minerals exhibits a threshold relationship in response to effective soil moisture (estimated as precipitation less evapotranspiration). To better characterize the role of moisture in influencing mechanisms of SOC storage during pedogenesis, we compare soils from two different chronosequence sites: the Santa Cruz and Mattole River marine terraces that together form a soil age-by-climate gradient (i.e., climo-chronosequence). Our results demonstrate how variation in the effective soil moisture may drive soil development along divergent pedogenic trajectories, resulting in variations in the form and depth distribution of secondary weathering products. In particular, the residual metals Fe and Al are directly related to the type of secondary minerals that accumulate during weathering, and these variations are coupled to differences in the storage and long-term preservation of SOC both within and between soils. Over time, these differences in soil development may lead to ‘pedogenic thresholds’ that further differentiate soil characteristics and influence SOC dynamics. In this case, the pedogenic threshold takes the form of clay-rich argillic horizons that once formed, inhibit aqueous transport, decouple shallow and deep soil environments, and potentially limit SOC inputs and increase microbial recycling in deep soils. Our data suggest argillic horizon development is favorable in the drier Santa Cruz soils, where kaolinite is the dominant secondary weathering product. In contrast, greater available moisture in soils of the Mattole chronosequence drive a different weathering trajectory characterized by the accumulation of more amorphous secondary minerals. As a result, the Mattole soils and do not exhibit argillic horizon development but are instead characterized by greater accumulation of SOC across all depths sampled. Overall, our results illustrate how the interaction of climate (i.e., moisture) and time may shape the trajectory of soil development and the dynamics of SOC storage and preservation.

Microbial metabolic response to winter warming stabilizes soil carbon.

Current consensus on global climate change predicts warming trends with more pronounced temperature changes in winter than summer in the Northern Hemisphere at high latitudes. Moderate increases in soil temperature are generally related to faster rates of soil organic carbon (SOC) decomposition in Northern ecosystems, but there is evidence that SOC stocks have remained remarkably stable or even increased on the Tibetan Plateau under these conditions. This intriguing observation points to altered soil microbial mediation of carbon-cycling feedbacks in this region that might be related to seasonal warming. This study investigated the unexplained SOC stabilization observed on the Tibetan Plateau by quantifying microbial responses to experimental seasonal warming in a typical alpine meadow. Ecosystem respiration was reduced by 17%-38% under winter warming compared with year-round warming or no warming and coincided with decreased abundances of fungi and functional genes that control labile and stable organic carbon decomposition. Compared with year-round warming, winter warming slowed macroaggregate turnover rates by 1.6 times, increased fine intra-aggregate particulate organic matter content by 75%, and increased carbon stabilized in microaggregates within stable macroaggregates by 56%. Larger bacterial "necromass" (amino sugars) concentrations in soil under winter warming coincided with a 12% increase in carboxyl-C. These results indicate the enhanced physical preservation of SOC under winter warming and emphasize the role of soil microorganisms in aggregate life cycles. In summary, the divergent responses of SOC persistence in soils exposed to winter warming compared to year-round warming are explained by the slowing of microbial decomposition but increasing physical protection of microbially derived organic compounds. Consequently, the soil microbial response to winter warming on the Tibetan Plateau may cause negative feedbacks to global climate change and should be considered in Earth system models.

The State of Soil Organic Carbon in Vineyards as Affected by Soil Types and Fertilization Strategies (Tri Morave Region, Serbia)

Due to specific soil properties and management practices, soils in vineyards are sensitive to degradation. The aims of this study were to examine (i) the state of soil organic carbon (SOC) in vineyards compared to other agricultural land, (ii) the influence of different fertilization strategies and soil type on SOC content and (iii) the rate of SOC change over time and potential of deep tillage for SOC preservation in subsoil. The study was carried out at 16 representative vineyard locations of the Tri Morave region, which represents the largest vine growing region in Serbia. The analyzed area included 56 vineyard plots. Results showed that SOC stocks in the topsoil and subsoil were lower than the average for agricultural land in Serbia. The soil type was an important predictor of carbon storage in the topsoil. An adequate application of inorganic fertilizers or green manure combined with farmyard manure initially resulted in the highest SOC contents. Continuous application of inorganic fertilizer without organic amendments has led to a decrease of SOC in topsoil. High rates of SOC stock change in topsoil accompanied a rapid reduction of SOC in the earlier stage of cultivation. In all investigated subsoils, SOC increased, except for unfertilized vineyards. Deep tillage has the potential to preserve SOC in the deeper soil layer and prevent carbon loss from the topsoil. More attention should be paid to the soil conservation practices to meet environmental sustainability of viticulture.

Spatial and temporal patterns in soil organic carbon, microbial biomass and activity under different land-use types in a long-term soil-monitoring network

Preservation of soil organic carbon (SOC) requires knowledge concerning the quantity and quality of both the SOC and the SOC-decomposing microbial community. In northern Germany, this information is assessed as part of Schleswig-Holstein’s long-term soil-monitoring programme, in which topsoils have been analysed since 1995. In this study, we evaluated long-term data from Schleswig-Holstein’s monitoring sites and compared the content of SOC and microbial biomass carbon (MBC) among croplands, grasslands and forests. We distinguished the microbial fractions as total MBC (chloroform fumigation extraction method) and glucose-responsive MBC, and we used the MBC/SOC ratio and soil basal respiration (SBR) to obtain a qualitative view of the SOC and its turnover potential. Additionally, we performed a temporal comparison for SOC and MBC between the periods 1995–2002 and 2005–2015. The results showed that median SOC content is the highest in forest soils (41 g kg−1), followed by grasslands (33 g kg−1), and croplands (12 g kg−1). Different ascending orders occurred for the total MBC (cropland < forest < grassland), however, and for the glucose-responsive MBC (forest < cropland < grassland), indicating differences in SOC quality and the microbial community structure. The different ratios between MBC and SOC showed that SOC in croplands and grasslands is characterised as easily degradable, but more stable in grasslands under no-till conditions. Forest SOC appears almost non-degradable, and thus is most stable in the long term. We concluded that land-use-specific carbon characteristics, including the functional microbial community structure, are beneficial for evaluation of SOC preservation potential. From the temporal perspective, a significant increase (45–114 %) was observable for the total MBC on cropland and grassland sites, whereas the changes in SOC were not significant. The remarkable growth of the total MBC in relation to the glucose-responsive MBC indicates shifts in the microbial community towards a K-strategy metabolism.

Soil parent material controls organic matter stocks and retention patterns in subtropical China

The influence of parent material on soil organic carbon (SOC) retention remains largely unstudied. Here, we aimed to reveal the role of soil parent material on SOC stocks and elucidate the underlying SOC retention patterns for soils derived from limestone, quaternary red earth, granite, basalt, and tertiary red sandstone in subtropical China. The study assessed 110 topsoils (0–20 cm) under two land uses (forest and cultivated), but with similar topography. We compared soil properties (pH, oxides, multivalent cations, texture, aggregates) and SOC stocks, total SOC concentration as well as three organic C fractions (active, slow, and passive C). Factors influencing SOC concentration were explored using a combination of stepwise multiple regression analysis and redundancy analysis. Topsoil SOC stocks and SOC concentration varied significantly among the five parent materials, with the greatest values all observed in limestone-derived soils and the lowest in tertiary red sandstone–derived soils. While parent material significantly influenced both quantity and quality of SOC, there was no land use effect on the proportion of organic C fractions. Our results have also shown that parent material mediates land use impacts on SOC. The SOC stocks and SOC concentration in limestone, quaternary red earth, and basalt-derived soils were significantly higher in forest than in arable soils, while no significant land use effect was found for soils derived on granite and tertiary red sandstone. Soil aggregates, texture, content of Fe oxides, and multivalent cations accounted for 67.8% of the variation in SOC concentration, and both SOC stocks and SOC concentration were more closely related to aggregation and soil texture. The major influencing factors for SOC retention differed with parent material, with Ca2+/Mg2+-mediated interactions between organic matter and mineral surfaces being the main regulating processes for limestone-derived soils and oxide-mediated mechanisms to form stable aggregates being the likely SOC protecting patters for quaternary red earth and basalt-derived soils. Due to the coarse texture and low aggregate stability, the soils derived from granite and tertiary red sandstone lacked the properties for SOC preservation, with pH the main predictor for SOC concentration. Macroaggregates (> 2 mm) played especially important role in shaping SOC stocks. Parent material exerts an influence on SOC stocks and retention patterns, and should be used in determining SOC storage potential for soils.