Ratio Of Soil Organic Carbon Research Articles

Long-term tillage and irrigation effects on aggregation and soil organic carbon stabilization mechanisms

Sustainable soil management practices are required in agriculture to enhance carbon sequestration and restore soil functions. Here, the aim was to investigate the effect of different tillage practices combined with or without irrigation on (i) soil organic carbon (SOC) content, (ii) fungal biomass and their relationships with aggregate size classes in the soil surface layer; further, (iii) the concept of soil particle saturation with SOC was tested to evaluate if a threshold was reached in a 14 year-experiment. Our hypothesis was that long-term irrigation, intensive tillage and their combination, would negatively affect soil aggregation and SOC stabilization. The experiment has started in 2003 on a research farm in Canterbury, New Zealand. The present work focused on two contrasting tillage practices –intensive tillage with 20–25 cm ploughing (IT) and direct drill (DD)– combined with sprinkler-irrigated and non-irrigated (hereafter called Rainfed) conditions in a split-plot experimental design. Soil samples (0–5 cm layer) were analyzed for pore size distribution, specific surface area and microbial biomass. Further, wet sieving was used to isolate large macroaggregates (LM, > 2000 μm), small macroaggregates (SM, 250–2000 μm), microaggregates (m, 53–250 μm), particle sized silt + clay fractions (s+c, < 53 μm) and Fine20 particles (<20 μm), followed by the analysis of aggregate morphology and SOC quantification in them. Results showed that both DD and Rainfed management increased total SOC content of the bulk soil. Only the LM fraction and the SOC therein (OC-LM) increased significantly in DD compared to IT, while m and s+c fractions and OC-m and OC-s+c did not differ between treatments. Macroaggregate breakdown processes and measured SOC therein had likely not reached steady-state conditions, as suggested by the lack of any SOC differences in the aggregate size classes < 250 µm. In contrast, the Fines20:SOC ratio differentiated between soils that had reached (i.e., DD) or not reached (i.e., IT) the saturation threshold. Finally, it was observed that a higher fungal:bacteria (F:B) ratio was generally accompanied by a greater LM fraction and mean weight aggregate diameter, highlighting the importance of fungi in the formation of LM. These results suggested that our hypothesis of detrimental effects on soil aggregation and SOC accumulation of both tillage and irrigation was not fully demonstrated yet. A longer study period would be required to better understand the effects of such practices of SOC storage.

Relationships between Soil Nematode Communities and Soil Quality as Affected by Land-Use Type

Researchers have used both soil nematode data and soil quality index (SQI) data as indicators of soil quality. However, the relationship between soil nematodes and soil quality index is poorly understood. This study explored the relationship between soil nematode properties and soil quality in different land-use types in a subtropical karst region of Southwest China. We selected the following five typical land-use types that differ in the degree of soil disturbance: cropland (maize and soybean), sugarcane, mulberry, forage grass, and forest. SQI was calculated on the basis of bulk density (BD), soil pH, the ratio of soil organic carbon to total nitrogen (C:N), the contents of soil water (SWC), soil total nitrogen (TN), soil organic carbon content (SOC), calcium (Ca), magnesium (Mg), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), ammonium nitrogen (AN), nitrate nitrogen (NN), bacteria, fungi, actinomycetes (ACT), and arbuscular mycorrhizal fungi (AMF). We found that the abundance, Simpson dominance index, and metabolic footprint of soil nematodes were highest in the forest, followed by sugarcane, cropland (maize and soybean), forage grass, and mulberry. The SQI was highest in the forest and lowest in the cropland. There was no significant difference observed among the other three regions. In addition, the SQI was positively correlated with the total nematode biomass and abundances of total nematodes, fungivores, and herbivores, the abundances of total nematodes biomass and total nematode abundance, fungivores, and herbivores. A random forest model revealed that the dominant nematode genera (i.e., Coomansus and Acrobeloides) and the rare genera (i.e., Heterocephalobus) were closely associated with soil quality. Our results suggest that the soil nematodes (especially keystone genera) may mediate the effects of ecosystem disturbance on soil quality. These findings increase our understanding of the relationships between soil organisms and soil quality.

Variation Characteristics of Soil Organic Carbon Storage and Fractions with Stand Age in North Subtropical Quercus acutissima Carruth. Forest in China

Soil labile organic carbon sensitively reflects subtle changes in the soil carbon pool and is an important aspect of forest soil carbon pool research. However, little is known regarding soil labile organic carbon storage and its dynamic changes during the development of Quercus acutissima Carruth. forests. Consequently, we investigated the dynamic changes in soil organic carbon and its labile organic carbon fraction stocks at soil depths of 0–10 cm, 10–20 cm, and 20–40 cm along a 17-year-old, 26-year-old, and 65-year-old chronosequence in Quercus acutissima forests. We found that stand age significantly impacted particulate organic carbon (POC), light fraction organic carbon (LFOC), and soil organic carbon (SOC). The POC, LFOC, and SOC contents at different soil depths exhibited an increasing trend with stand age, which could be described by simple linear regression. However, there was no noteworthy difference in the soil water-soluble organic carbon (WSOC) content between different stand ages. Moreover, the 17-year-old, stand had higher POC, LFOC, and WSOC to SOC ratios. Soil nutrients significantly affected organic carbon and fractions, which revealed that POC, LFOC, WSOC, and SOC were remarkably positively correlated with alkaline hydrolysis nitrogen (AN) and available phosphorus (AP) (p &lt; 0.05). Furthermore, WSOC, POC, LFOC, and SOC were significantly positively correlated with available potassium (AK) (p &lt; 0.05). POC, LFOC, and SOC storage in the 0–40 cm soil layer increased with stand development, while WSOC storage decreased at 65a. In addition, LFOC stocks accounted for the highest proportion of organic carbon stocks. Our results indicated that the development of Quercus acutissima forests was a process of carbon sink; however, the soil organic carbon activity was high, and the soil structure was unstable during the early development stage.

Evaluation of carbon mineralization and its temperature sensitivity in different soil aggregates and moisture regimes: A 21-year tillage experiment.

Characterizing soil organic carbon (SOC) mineralization and its temperature sensitivity (Q10) under different soil moisture in tillage systems is crucial for determining global carbon balance under climate warming and increasing precipitation. Aggregate protection can potentially govern SOC mineralization and its Q10. However, how tillage and aggregate sizes affect SOC mineralization and its Q10, especially under varying soil moisture, remains unclear. Soil samples (0-10 cm and 10-20 cm) were collected from a 21-year field study with four tillage treatments: conventional tillage (CT), reduced tillage (RT), no-tillage (NT), and subsoiling (SS). Bulk soil and dry-sieved aggregates were incubated at 15°C and 25°C at low, medium, and high moistures (i.e., 40%, 70%, and 100% water-holding capacity, respectively). Macro-aggregates (> 0.25 mm) had lower SOC mineralization relative to micro-aggregates (< 0.25 mm) across all soil temperatures, moistures, and depths (P < 0.01), which was attributed to their lower SOC quality (i.e., higher ratio of SOC to total nitrogen and lower ratio of dissolved organic carbon to SOC). Moreover, NT and SS promoted macro-aggregation relative to CT and RT, and thereby decreased mineralization (P < 0.001). However, Q10 was higher in macro-aggregates than in micro-aggregates at low and medium moistures. The Q10 was negatively correlated with the SOC quality in macro-aggregates (P < 0.05). The macroaggregate-associated SOC quality was lower under NT and SS than under CT and RT, which resulted in a greater Q10 under NT and SS at low and medium moistures, suggesting that NT and SS may accelerate SOC losses under global warming. Furthermore, increased soil moisture could lower Q10, and no differences among tillage practices were observed at high moisture levels (P > 0.05). Overall, our findings indicated that NT and SS decreased SOC mineralization but increased Q10 because of their large amounts of macro-aggregates with low SOC quality, and the improvement of Q10 was constrained by increasing soil moisture.

Evaluating indices of soil organic carbon stability. A case study for forest restoration projects near Beijing, China

Afforestation of degraded lands close to mega-urban areas such as Beijing may help to restore some of the original soil carbon stocks and hold the potential for ameliorating the rate of increase in atmospheric CO2. However, the determinants of the stability of different soil carbon pools and the utility of indices of stability remain poorly characterized near these highly anthropogenic areas. In the current study, we compared metrics of soil organic carbon (SOC) stability taking into account different soil types and plantation forest combinations (Quartisamment soil-poplar plantation–QP, Eutrochrepts soil-Chinese pine plantation–ECP, Haplustepts soils-East-Liaoning oak plantation–HEO), in an experimental sub-humid area close to a mega-urban area (Beijing, China). We evaluated the following relative stability indices sequence: respired carbon from incubations (RI) for several incubation days to respire 5% of initial SOC (D), aggregate stability index (ASI), the ratio of SOC to total nitrogen (C: N), water-soluble carbon (WSC), particulate organic carbon (POC) and microbial biomass carbon (MBC). We examined the indices by three repeated measurements on soil samples from four soil layers (0–40 cm) in three soil-forest types in a forest area close to the peri-urban area of Beijing. Our results showed that there are inconsistencies among the six SOC stability indexes. The contribution rates of different indexes to the SOC in three plantations were different, for QP the highest contributor is WSC (54.73%), and for ECP and HEO the highest contributor is RI, contribution rates are 34.85% and 36.382%, respectively. Respired carbon from incubations registered the largest contribution rate to SOC (69.79%), and the correlation between RI and soil physical and chemical properties was the highest. We conclude that a combination of indices and knowledge of soil and vegetation types are needed for assessing SOC stability in restoration and reforestation projects close to mega-urban areas.

Limiting resource and leaf functional traits jointly determine distribution patterns of leaf intrinsic water use efficiency along aridity gradients.

Intrinsic water use efficiency (iWUE) is a critical eco-physiological function allowing plants to adapt to water- and nutrient-limited habitats in arid and semi-arid regions. However, the distribution of iWUE in coexisting species along aridity gradients and its controlling factors are unknown. We established two transects along an aridity gradient in the grasslands of Losses Plateau (LP) and Inner Mongolia Plateau (MP) to elucidate the patterns and underlying mechanisms of iWUE distribution in coexisting species along aridity gradient. We determined leaf carbon (δ13C) and oxygen (δ18O) stable isotopes, functional traits related to carbon fixation, and limiting resources. Bulk leaf δ13C and δ18O were used as proxies for time-integrated iWUE and stomatal conductance (gs) during the growing season. Our results showed that variability in iWUE within transect was primarily controlled by species, sampling sites and an interactive effect between species and sampling sites. Mean values of iWUE (iWUEMean) increased and coefficient of variation (CV) in iWUE (iWUECV) decreased with an increase in aridity, demonstrating that increases in aridity lead to conservative and convergent water use strategies. Patterns of iWUEMean and iWUECV were controlled primarily by the ratio of soil organic carbon to total nitrogen in LP and soil moisture in MP. This revealed that the most limited resource drove the distribution patterns of iWUE along aridity gradients. Interspecific variation in iWUE within transect was positively correlated with Δ18O, indicating that interspecific variation in iWUE was primarily regulated by gs. Furthermore, relationship between iWUE and multi-dimensional functional trait spectrum indicated that species evolved species-specific strategies to adapt to a harsh habitat by partitioning limiting resources. Overall, these findings highlighted the interactive effects of limiting resources and leaf functional traits on plant adaptation strategies for iWUE, and emphasized the importance of considering biological processes in dissecting the underlying mechanisms of plant adaptation strategies at large regional scales.

Soil carbon quantity and form are controlled predominantly by mean annual temperature along 4000 km North-South transect of Eastern China

The forest ecosystem plays a key role in mitigating global climate change through carbon sequestration in its biomass and soils to limit the rising atmospheric concentration of CO2. However, the combined overall interaction of climate and forest type on the quantities and forms of soil carbon (organic vs. inorganic) has not yet been sufficiently investigated. In this study, the contents of soil total carbon (STC), soil organic carbon (SOC) and soil inorganic carbon (SIC) were measured along the 4000 km North-South Transect of Eastern China. We sampled 252 soil samples (6 replicates for each site, 3 depths for each site) from four long-term ecosystem experimental stations in Dinghushan, Shennongjia, Beijing and Changbaishan, along the transect from south to north, including 14 different forest types. The contents of STC, SOC, and SIC in the upper 60 cm soil layer varied in different types of forest with 34–107 g C kg−1, 31–104 g C kg−1, and 1.5–8 g C kg−1, respectively. The northern fir and birch forest, most notably in Changbaishan, had the highest STC and SOC contents. The higher SIC contents were found in the southern evergreen broad-leaved forests in Dinghushan and Shennongjia. The contents of STC, SOC and SIC differed significantly in terms of mean annual temperature (MAT), mean annual precipitation (MAP), forest type, and soil depth. In the upper 60 cm soil layer, the most significant correlations occurred between SOC (or STC) and MAT (R2SOC = −0.62, R2STC = −0.60) when compared with the correlation between SOC (or STC) and MAP (R2SOC = −0.45, R2STC = −0.45) or elevation (R2SOC = 0.48, R2STC = 0.48). The soil stratification ratio (SR) of STC and SOC were typically ∼2–3 in most forests and even reached 5– 7 in Changbaishan forest, indicating a well-functioning ecosystem overall. We concluded that on the near-continental scale (4000 km), forest soil carbon contents and forms (SOC, STC, SIC) were controlled most strongly by temperature (MAT). Therefore, an innovative selection of a specific forest type (fir or broad-leaved forest) within set temperature regimes can better contribute to maximizing soil carbon content and thus optimize its sequestration on the national to near-continental scale to mitigate climate change.

Compensatory growth and understory soil stoichiometric features of Hippophae rhamnoides at different stubble heights.

BackgroundThis study was aimed to explore the compensatory growth ability and influence mechanism of Hippophae rhamnoides at the decaying phase in feldspathic sandstone areas of Ordos, and clarify the stubble height when the compensatory growth ability of H. rhamnoides was the strongest.MethodsThe H. rhamnoides forests in the decaying phase from an exposed feldspathic sandstone zone of Ordos were chosen. The compensatory growth ability of H. rhamnoides at stubble height of 0 cm (S1), 10 cm (S2), 15 cm (S3), 20 cm (S4) and control (CK) was investigated with H. rhamnoides forests at the decaying stage in the exposed feldspathic sandstone areas of Ordos. Relationships of compensatory growth ability of H. rhamnoides and understory soil properties with understory soil stoichiometric features as well as the response mechanism to stubble height were explored.Results(1) Overcompensatory growth of H. rhamnoides in feldspathic sandstone areas occurred at all stubble heights. Especially, the plant height compensation index (1.45) and biomass compensation index (1.25) at the stubble height of 15 cm were both larger compared with other stubbling treatments. These results indicate the stubble height of 15 cm can well promote the growth of the ground part of H. rhamnoides. (2) All stubble heights significantly affected the contents and eco-stoichiometric ratios of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) in understory soils, but the influence rules differed. SOC, TN, and TP contents at all stubble heights were larger than those of the control, and maximized at the stubble height of 15 cm. The carbon(C): phosphorus(P) ratio, and nitrogen (N):(P) ratio after stubbling treatments were all lower compared with the control, and minimized to 19.52 and 1.84 respectively at the stubble height of 15 cm. (3) The understory C:N:P stoichiometric ratio of H. rhamnoides in feldspathic sandstone areas is jointly affected by compensatory growth, stubble height, and soil physicochemical properties. The total explanation rate determined from RDA is 93.1%. The understory soil eco-stoichiometric ratio of H. rhamnoides is mainly affected by soil moisture content (contribution of 87.6%) and total porosity (7.9%), indicating soil moisture content is the most influential factor. The findings will offer some new clues for eco-construction and theoretically underlie soil-water loss administration.

Enrichment of 13C with depth in soil organic horizons is not explained by CO2 or DOC losses during decomposition

Stable isotope ratios of soil organic carbon (SOC) are a potentially powerful, integrative tool for analyzing the soil C cycle. However, limited understanding of the mechanisms for C isotope fractionation in soil prevents their widespread application. Soil organic carbon (SOC) is progressively enriched in 13C with age and depth in the soil profile even though CO2 produced during soil respiration is typically enriched in 13C compared to SOC. This results in an apparent mass balance paradox. To resolve this paradox, we hypothesized that the loss of 13C-depleted DOC during soil diagenesis, the combination of microbial decomposition and abiotic processes such as leaching, can account for the increase in SOC δ13C with depth. We combined three independent approaches (field measurements, a laboratory incubation experiment, and seasonal sampling of DOC across a climate transect) to systematically evaluate the relationship between the δ13C of soil respiration, DOC, and the SOC it is derived from. However, DOC was not significantly depleted in 13C compared to SOC in any of the three approaches, and mass balance calculations indicated that the DOC flux cannot account for the full extent of 13C enrichment of SOC with depth in the soil profile. We suggest that vertical C transport by plant roots or fungi, rather than diagenesis, may be largely responsible for the observed C isotope profile. Future studies aimed at understanding these vertical transport processes should enable increased application of soil δ13C, enhancing soil biogeochemical studies.

Microbial regulation of net N mineralisation is driven by C, N, P content and stoichiometry

AbstractSoil net nitrogen mineralisation (Nt) is crucial for nitrogen availability and ecosystem productivity. However, the patterns and drivers of Nt remain unclear under different management practices. We examined the biotic and abiotic determinants of Nt, using 11 treatments in Northern China fluvo‐aquic soil under wheat–maize rotation. Biotic properties, for example, soil microbial community, were determined based on phospholipid fatty acid (PLFA) together with high‐throughput sequencing technologies. Abiotic properties were characterised by the content and stoichiometric ratios of soil nutrients. Animal manure applications (HNM, NM, M, FM) significantly increased the Nt (1.80–3.40 mg kg−1) and available phosphorus (Olsen‐P) (46.3–199.3 mg kg−1), compared with treatments with plant residues (NG, NS) incorporation. Fallow with animal manure (FM) had the highest Gram‐negative bacteria (G‐, 29.3 nmol g−1), arbuscular mycorrhizal fungi (AMF, 4.57 nmol g−1) abundance, which was also significantly higher than that of the NG and NS. Structural Equation Modelling revealed that the content of total nutrient, including soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) rather than biotic properties, such as microbial community (λ = −0.26) and enzyme activities (λ = −0.16), had the strongest direct effect on Nt (λ = 0.85). Stoichiometric ratios of C, N, and P controlled Nt indirectly by mediating enzyme activities. Specifically, high Nt was associated with low Dothideomycetes, Tectomicrobia abundance that negatively correlated with SOC, TN, TP, Olsen‐P, and BG activity. Random forest model indicated that SOC and Olsen‐P contents were top‐rated determinants of Nt. Our result indicated that the content and stoichiometric ratios of SOC and N, P directly drive Nt or via microbial ways. Our study highlighted the importance of P to improve Nt: animal manure was thus recommended for nitrogen availability.Highlights Animal manure significantly enhanced Nt rather than plant residue incorporation Nt is negatively correlated with the AN:Olsen‐P ratio and Dothideomycetes abundance Stoichiometric ratios of nutrients associated with enzymes activities regulate Nt SOC and Olsen‐P affected Nt as key factors under N enrichment conditions

Digital mapping of soil biological properties and wheat yield using remotely sensed, soil chemical data and machine learning approaches

Mapping of soil properties by using novel machine learning (ML) algorithms and optimized environmental covariates is of great importance for agricultural management to enhance crop production. This research aimed at evaluating ML algorithms to predict spatial distribution of soil biological properties and wheat yield in the Southwest of Iran. Topsoil samples (0–30 cm) were collected from a total of 60 sampling locations and wheat grain yield (plot 1 × 1 m) was recorded at each location. Soil properties including urease (Ur), alkaline phosphatase (AP), basal respiration (BR), microbial biomass carbon (MBC), soil organic carbon (SOC), MBC:SOC ratio, and metabolic quotient (qCO2) were measured. At the first step, Random Forest (RF) model was employed to predict soil biological properties by using terrain attributes, remote sensing indices and soil properties as covariates. In this step, both Variance Inflation Factor (VIF) and Pearson regression were applied to select the most important covariates in predicting soil biological properties and to decrease the dimension of the input space with considering no reduction in prediction accuracy. Secondly, wheat grain yield was modeled using six ML algorithms; they were optimized and evaluated in Caret package with 10-fold cross validation. Results showed the highest prediction accuracy for qCO2 (R2adj = 0.80) and the lowest for BR (R2adj = 0.23). Compared to environmental predictors, soil covariates had a greater effect in modeling Ur, qCO2, MBC and MBC:SOC ratio, while, for AP and BR, bands 6 and Chanel Network Base Level were the most important factors, respectively. In prediction of wheat grain yield, both Stochastic Gradient Boosting (SGB) and RF models outperformed with R2adj of 0.89 and 0.88, respectively. Results indicated that the Ur and AP played the major roles in predicting wheat grain yield and explaining its spatial variability. Our modeling results suggested that soil biological properties and yield can be estimated easily with reasonable accuracy. Overall, their high resolution maps may be useful for decision makers, stakeholders and applicants in agricultural management practices towards precision agriculture.

Global distribution, formation and fate of mineral‐associated soil organic matter under a changing climate: A trait‐based perspective

Abstract Soil organic matter (SOM) is the largest actively cycling reservoir of terrestrial carbon (C), and the majority of SOM in Earth's mineral soils (~65%) is mineral‐associated organic matter (MAOM). Thus, the formation and fate of MAOM can exert substantial influence on the global C cycle. To predict future changes to Earth's climate, it is critical to mechanistically understand the processes by which MAOM is formed and decomposed, and to accurately represent this process‐based understanding in biogeochemical and Earth system models. In this review, we use a trait‐based framework to synthesize the interacting roles of plants, soil micro‐organisms, and the mineral matrix in regulating MAOM formation and decomposition. Our proposed framework differentiates between plant and microbial traits that influence total OM inputs to the soil (‘feedstock traits’) versus traits that influence the proportion of OM inputs that are ultimately incorporated into MAOM (‘MAOM formation traits’). We discuss how these feedstock and MAOM formation traits may be altered by warming, altered precipitation and elevated carbon dioxide. At a planetary scale, these feedstock and MAOM formation traits help shape the distribution of MAOM across Earth's biomes, and modulate biome‐specific responses of MAOM to climate change. We leverage a global synthesis of MAOM measurements to provide estimates of the total amount of MAOM‐C globally (~840–1540 Pg C; 34%–51% of total terrestrial organic C), and its distribution across Earth's biomes. We show that MAOM‐C concentration is highest in temperate forests and grasslands, and lowest in shrublands and savannas. Grasslands and croplands have the highest proportion of soil organic carbon (SOC) in the MAOM fraction (i.e. the MAOM‐C:SOC ratio), while boreal forests and tundra have the lowest MAOM‐C:SOC ratio. Drawing on our trait framework, we then review experimental data and posit the effects of climate change on MAOM pools in different biomes. We conclude by discussing how MAOM is integrated into soil C models, and how feedstock and MAOM formation traits may be included in these models. We also summarize the projected fate of MAOM under climate change scenarios (Representative Concentration Pathways 4.5 and 8.5) and discuss key model uncertainties. Read the free Plain Language Summary for this article on the Journal blog.

Hydraulic mechanisms of the uneven enrichment of soil organic carbon in sediments during rain-induced overland flow.

Organic carbon (OC) can be unevenly enriched in different-sized sediment particles under low-intensity, rain-induced overland flows, but its hydraulic mechanisms are not completely understood. Hence, in this study, the hydraulic transport mechanisms of unevenly enriched OC between different-sized sediment particles were investigated through simulated rainfall experiments at gradients of 5°, 10°, and 15° and typical regional rainfall intensities of 45, 90, and 120 mm h−1. Results showed that the critical flow velocity of aggregate transport through loess soil was approximately 0.08 m s−1. When the flow velocity was larger than this critical value, the aggregate loss amount increased quickly and exponentially. Flow velocities lower than 0.08 m s−1 were determined to be essential conditions for uneven OC enrichment between sediment particles. At such velocities, even when the runoff depth was greater than 0.0018 m, the enrichment ratio of soil organic carbon (SOC; ERoc) values in all size classes of sediment particles was larger than 1.0. Small runoff depths caused preferential OC enrichment in silt and clay, whereas large runoff depths promoted OC enrichment in the >0.25 mm size class of sediment particles. The critical flow velocity and transport way differ between these high-OC-concentration clay and silt and large light organic particles. The interaction between flow velocity and runoff depth on ERocs in <0.05 mm particles was larger than that of >0.05 mm particles. Under the transport limit erosion, the flow velocity and stream power positively correlated with uneven ERocs in different size sediment particles through distinct laws. Slope and rainfall intensity could not be ignored in predicting uneven OC enrichment in sediments by interacting with hydraulic factor and effecting aggregate stripping, respectively. Hydraulic factors mainly affected the uneven OC enrichment by controlling particle selective detachment and transport process. Owing to the different hydraulic mechanisms of OC enrichment in different size particles, the obtained regression functions for uneven OC enrichment could be divided into two types. One was for calculating the OC concentrations in sediment particles with sizes of <2 mm (R2 > 0.844, P < 0.005), and the other was for calculating the OC concentrations in large macroaggregates (>2 mm; R2 = 0.805, P < 0.005). The findings provide an important reference for understanding SOC transport mechanisms and its mineralization potential under the effect of water erosion and improving SOC dynamic models.

滇南喀斯特断陷盆地土地利用方式对土壤有机碳及其活性组分的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 滇南喀斯特断陷盆地土地利用方式对土壤有机碳及其活性组分的影响 DOI: 10.5846/stxb202108112216 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42071127）；云南大学人才项目（C176220100083） Effects of land use types on soil organic carbon and soil labile organic carbon in karst faulted basin of southern Yunnan Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土地利用方式是影响土壤有机碳库的重要因素，为探究喀斯特断陷盆地土壤有机碳库对土地利用方式及环境因素的响应，以滇南喀斯特地区5种典型土地利用方式(耕地、草地、灌丛、人工林、天然林)为研究对象，分析不同土地利用方式土壤有机碳(SOC)及活性有机碳(LOC)组分，即可溶性有机碳(DOC)、易氧化性有机碳(EOC)及微生物量碳(MBC)的含量、储量及分配比例在土壤垂直剖面(0-60 cm)的变化特征。结果表明：5种土地利用方式的SOC含量随土层深度的增加逐渐降低，其储量依次为灌丛(191.77 t/hm2)、草地(166.86 t/hm2)、耕地(142.47 t/hm2)、人工林(134.31 t/hm2)和天然林(102.62 t/hm2)；EOC和MBC的平均含量及储量均以草地及灌丛最高、人工林及天然林次之，二者在土壤垂直剖面上与SOC含量的变化特征一致，但EOC和MBC含量在土层间的下降幅度大于SOC；土地利用方式和土层深度对DOC无显著影响(P>0.05)；活性有机碳的分配比例受土地利用方式及土层深度的显著影响(P<0.01)，其中人工林的EOC/SOC和MBC/SOC显著低于草地、灌丛及天然林。通径分析指出SOC和EOC主要受C/P比、全磷、砂粒和交换性钙的影响，砂粒和C/P比是影响MBC的主要因子。研究阐明在喀斯特断陷盆地地区EOC和MBC对土地利用方式的响应比SOC更敏感。另外，今后在土壤碳库的研究中应更多关注土壤磷和物理结构对其的影响。 Abstract:Land use types are important factor affecting soil organic carbon pool by regulating carbon fluxes between the terrestrial biosphere and atmosphere. Five typical land use types including farmland, grassland, shrubland, artificial forest and natural forest were selected to explore the responses of soil organic carbon pool to land use types and environmental factors in the karst faulted basin, China. The contents, stocks and distribution ratios of soil organic carbon (SOC) and labile organic carbon (LOC), namely dissolve organic carbon (DOC), easily oxidated carbon (EOC) and microbial biomass carbon (MBC), were analyzed along soil profiles (0-60 cm) under different land use types. The results showed that the SOC contents was 4.83-69.01 g/kg, which decreased with soil depths under the five land use types. The SOC stocks under five land use types were in descending order of shrubland (191.77 t/hm2), grassland (166.86 t/hm2), farmland (142.47 t/hm2), artificial forest (134.31 t/hm2) and natural forest (102.62 t/hm2). The contents and stocks of EOC and MBC were the highest in grassland and shrubland on average, followed by artificial forest and natural forest. The variation characteristics of EOC and MBC in the soil profile were consistent with SOC, but the decline rates of EOC and MBC contents in soil layers were obviously higher than SOC. Land use types and soil depths had no significant effects on DOC contents with a range of 0.84-1.62 g/kg under the five land use types. The ratios of labile organic carbon to soil organic carbon were affected by land use types and soil depths (P<0.01). The EOC/SOC and MBC/SOC ratios of artificial forest were lower than those of grassland, shrubland and natural forest. Pearson correlation analysis showed that SOC was positively correlated with LOC (P<0.01). In addition, SOC and LOC were positively correlated with total nitrogen, C/P ratio, C/N ratio, exchangeable calcium, soil water content, clay, sand and so on (P<0.05). Path analysis further identified that the variation in the SOC and EOC were significantly related to the changes of C/P ratio, total phosphorus, sand and exchangeable calcium and MBC was mainly influenced by sand and C/P ratio. These findings suggested that the land use types had significant effects on SOC, EOC and MBC contents and the responses of EOC and MBC to land use types were more sensitive than SOC in karst faulted basins. Moreover, more attention should be paid to soil physical structure and phosphorus availability in the future research on soil organic carbon pool. 参考文献 相似文献 引证文献

Effects of Different Grazing Disturbances on the Plant Diversity and Ecological Functions of Alpine Grassland Ecosystem on the Qinghai-Tibetan Plateau.

Grazing is one of the main human disturbance factors in alpine grassland on the Qinghai-Tibet Plateau (QTP), which can directly or indirectly influence the community structures and ecological functions of grassland ecosystems. However, despite extensive field grazing experiments, there is currently no consensus on how different grazing management approaches affect alpine grassland diversity, soil carbon (C), and nitrogen (N). Here, we conducted a meta-analysis of 70 peer-reviewed publications to evaluate the general response of 11 variables related to alpine grassland ecosystems plant diversity and ecological functions to grazing. Overall, the results showed that grazing significantly increased the species richness, Shannon–Wiener index, and Pielou evenness index values by 9.89% (95% CI: 2.75–17.09%), 7.28% (95% CI: 1.68–13.62%), and 3.74% (95% CI: 1.40–6.52%), respectively. Aboveground biomass (AGB) and belowground biomass (BGB) decreased, respectively, by 41.91% (95% CI: −50.91 to −32.88%) and 17.68% (95% CI: −26.94 to −8.52%). Soil organic carbon (SOC), soil total nitrogen (TN), soil C:N ratio, and soil moisture decreased by 13.06% (95% CI: −15.88 to −10.15%), 12.62% (95% CI: −13.35 to −8.61%), 3.27% (95% CI: −4.25 to −2.09%), and 20.75% (95% CI: −27.89 to −13.61%), respectively, whereas, soil bulk density and soil pH increased by 17.46% (95% CI: 11.88–24.53%) and 2.24% (95% CI: 1.01–3.64%), respectively. Specifically, moderate grazing, long-durations (>5 years), and winter grazing contributed to increases in the species richness, Shannon–Wiener index, and Pielou evenness index. However, AGB, BGB, SOC, TN, and soil C:N ratios showed a decrease with enhanced grazing intensity. The response ratio of SOC was positively associated with AGB and BGB but was negatively related to the Shannon–Wiener index and Pielou evenness index. Furthermore, the effects of grazing on plant diversity, AGB, BGB, SOC, and TN in alpine grassland varied with grazing duration, grazing season, livestock type, and grassland type. The findings suggest that grazing should synthesize other appropriate grazing patterns, such as seasonal and rotation grazing, and, furthermore, additional research on grazing management of alpine grassland on the QTP is needed in the future.

Assessment of changes in soil organic carbon fractions and enzyme activities under apple growing ecosystems in temperate North-Western Himalayas

For better understanding about the dynamics of soil organic carbon (SOC) and enzyme activities in soil health management under intense cropping and fluctuating climatic scenario, we examined quantitatively the spatial distribution and relationship pattern of SOC (potassium dichromate oxidizable C (KCr2O7 -C), total organic carbon (TOC or SOC stocks) and SOC pools of labile organic carbon (LBC), particulate organic carbon (POC) and microbial biomass carbon (MBC) as well as enzyme activities viz:- dehydrogenase (DHA), urease (URE) and phosphatase (PPTase) under apple growing ecosystems in north western temperate Himalayas, India. Descriptive statistics, Pearson’s correlation and spatial variability analysis of SOC attributes and enzyme activities were performed. Analysis of the results show consistent decline in SOC with depth and altitude exhibiting distinct spatial variability (CV = 15.7%–44.4%); representing significantly greater proportion in orchards of higher altitude by a margin of 346% and 295% and surface layers by 32% and 68% than sub-surface layers of those mid and lower altitudes. SOC stocks ranged from 32.1 to 94.6 Mg ha−1 with significant variation (CV = 18.0%–30.9%) between soil depths. Amongst labile carbon fractions, LBC observed significantly maximum spatial variability (CV = 15.0%–27.2%) followed by MBC (CV = 7.7%–20.6%) while as POC represents least non-significant variation (CV = 7.2%–15.5%). Although LBC (0.78 to 4.90 g kg−1) accounts for significant higher fraction (490%), MBC represents substantial reduction of 36% to 71% from surface to sub-surface layers. Decrease in microbial quotient (MQ) from an average value of 4.0% (surface) to 2.7% (sub-surface) indicates distinct spatial variability (CV = 7.5%–17.8%). The stratification ratio (SR) of SOC changed significantly amongst three altitudes varying from 2.75 to 3.96. For soil enzyme activities tested, DHA, URE and PPTase observed significant decline with depth showing maximum activity loss of 504% for URE followed by 470% for PPTase and 310% for DHA. Relationship studies recorded significantly positive correlation (p =0.05 and 0.01) for TOC with SOC and POC (0.752* and 0.814**) and between SOC and POC (0.675*), although SOC was best correlated with LBC (0.834**) and MBC (0.650**). All carbon fractions showed strong positive and significant (p = 0.05 and 0.01) relation with MBC and all enzymes (DHA, URE and PPTase) exhibited similar relationship with SOC (r = 0.638*), (r = 0.725*) and (r = 0.502**). Principal component analysis (PCA) summarized the spatial variation and relationship among SOC attributes and enzyme activities. These results of soil quality signature can be used to design and implement effective management measures in terms of addition of appropriate nutrients and effective carbon sequestration practices for soil health sustainability.

Increasing soil organic carbon content can enhance the long‐term availability of phosphorus in agricultural soils

AbstractThe stocks of phosphorus (P) in soil resulting from decades of over‐fertilisation can be used as a long‐term source of P provided that crop P bioavailability is ensured. This study was set up to identify to what extent soil organic matter (SOM) affects the long‐term availability of these stocks, the premise being that OM may limit irreversible P fixation in soil by blocking P sorption sites on sesquioxides. An ensemble of 42 agricultural soils, composed from experimentally amended soils (field and incubation trials) and soils with contrasting properties, was subjected to 288 days of P depletion with anion exchange membranes as a P sink; this method was previously shown to yield P pools with agronomic significance. Cumulative P desorption data were fitted with a two‐pool kinetic desorption model, yielding estimates for a fast (labile) and total desorbable P pool. On average, 42% of oxalate extractable P (Pox) associated with poorly crystalline iron (Fe) and aluminium (Al) (oxy)hydroxides (Feox and Alox) were desorbable and 25% of that fraction (i.e. 11% of Pox) was labile. That labile P pool matched well with the 24 h isotopically exchangeable P (E value) in these soils (R2 = 0.74). Both the fast and total desorbable fraction of Pox were larger at higher degrees of phosphorus saturation (DPS). In soils with a low DPS (&lt;0.30), the labile fraction of Pox increased as the ratio of soil organic carbon to Feox + Alox increased (R2 = 0.70; p &lt; 0.001), but soils with a higher DPS did not exhibit that trend. These results adhere to soil chemical views that enhanced SOM contents reduce fixation of P by competitive sorption and prevention of P diffusion into micropores. No such effects occur in more P saturated soils, probably because orthophosphate sorption and electrostatic effects outcompete effective SOM sorption. The findings suggest that simultaneous application of OM with P fertilisers could keep P better available in the long term, but that this OM application does not affect P fixation when soils are excessively dosed with P.Highlights Long‐term availability of P in soil was assessed in contrasting soils in a P depletion experiment. A high ratio of organic C to Fe and Al in soil enhances the P fraction that is readily available. The positive effect of organic matter on soil P availability is only found at low soil P saturation. Residual P in European soils can sustain adequate P for crops for 5–55 years depending on the soil.

Effects of organic mulching on soil aggregate stability and aggregate binding agents in an urban forest in Beijing, China

Urban forest soil is often disturbed by rapid urbanization. Organic mulching is effective for improving soil quality and aggregate stability. This study evaluated how soil binding agents changed aggregate stability through organic mulching in urban forest soils. Three treatments were applied in Jiufeng National Forest Park, Beijing: (1) no organic mulch (control); (2) wood chips alone (5 cm thickness); and, (3) wood chips + wood compost (This mulch was divided into two layers, the upper layer of wood chips (2.5 cm), the lower layer wood compost (2.5 cm)). Soil samples were collected from the surface 10- cm soil layer and fraction into four aggregates. Glomalin-related soil protein and soil organic carbon were measured in bulk soil and the four aggregates. The results show that wood chips + wood compost increased the proportion of large and small macroaggregates, mean weight diameter and geometric mean diameter. The total and easily extractable glomalin-related soil protein were higher in the wood chips + wood compost. However, soil organic carbon was lower in the wood chips alone application compared to the controls and wood chips + wood compost. Easily extractable / total glomalin-related soil protein and glomalin-related soil protein / soil organic carbon ratios of wood chips alone and wood chips + wood compost had increased trend compared to the controls but did not reach significant levels (p > 0.05). Mean weight diameter and geometric mean diameter correlated positively with total and easily extractable glomalin-related soil protein but were not positively correlated with soil organic carbon, the ratios of easily extractable and total glomalin-related soil protein, and the ratios of glomalin-related soil protein and soil organic carbon. Redundancy analysis revealed that total glomalin-related soil protein was the most important driver for soil aggregate stability, especially the total glomalin-related soil protein of small macroaggregates. The results suggest that wood chips + wood compost enhanced soil aggregate stability through the increase of glomalin-related soil protein. Wood chips alone cannot enhance soil aggregate stability in urban forests in the short term.

Soil organic carbon fractions and its association with water‐stable aggregates under different fertilization management practices

AbstractAgricultural soil organic carbon (SOC) plays a critical role in soil ecosystems, and SOC sequestration is a key ecosystem service. This study investigated the SOC fractions, including mineral‐incorporated organic carbon (MSC), intra‐particulate organic carbon (iPOC) and microbial biomass carbon (MBC), in bulk soil and water‐stable aggregates, as influenced by soil fertilization managements, using three treatments: no fertilizer (CK), chemical fertilizer (FR) and organic manure (OM). Fertilizer application significantly increased SOC content and its fractions (MSC, iPOC and MBC) compared to CK, and the effect of organic manure amendment had more impact on the SOC accumulation than chemical fertilizer. Macroaggregate (&gt;250 μm)‐associated SOC, MSC and iPOC (including fine and coarse iPOC) increased by 22%–283%, 18%–84% and 45%–232%, respectively, in FR and OM treatments compared with CK. In addition, the iPOC:MSC ratio values (%) within all size aggregates were all increased in the FR (about 84%–183%) and OM (about 103%–230%) treatments compared to CK (about 65%–146%). Meanwhile, MBC:SOC ratio values were the highest (about 2.16%–3.07%) in small macroaggregates (250–2000 μm), but decreased sharply (about 2%–2.35%) in large macroaggregates (&gt;2000 μm) in different treatments. Our findings suggested that macroaggregates were the main sites of carbon sequestration and that carbon became more unstable with the increase of SOC in aggregates. Furthermore, the microbial biomass showed obvious differentiation characteristics in macroaggregates (&gt;250 μm). Specifically, small macroaggregates (250–2000 μm) contained more microbial biomass, and large macroaggregates (&gt;2000 μm) were inclined to inhibit microbial activity.

Wheat Straw Incorporation Affecting Soil Carbon and Nitrogen Fractions in Chinese Paddy Soil

Soil organic carbon (SOC) and nitrogen (N) fractions greatly affect soil health and quality. This study explored the effects of wheat straw incorporation on Chinese rice paddy fields with four treatments: (1) a control (CK), (2) a mineral NPK fertilizer (NPK), (3) the moderate wheat straw (3 t ha−1) plus NPK (MSNPK), and (4) the high wheat straw (6 t ha−1) plus NPK (HSNPK). In total, 0–5, 5–10, 10–20, and 20–30 cm soil depths were sampled from paddy soil in China. Compared with the CK, the HSNPK treatment (p &lt; 0.05) increased the C fraction content (from 13.91 to 53.78%), mainly including SOC, microbial biomass C (MBC), water-soluble organic C (WSOC), and labile organic C (LOC) in the soil profile (0–30 cm), and it also (p &lt; 0.05) increased the soil N fraction content (from 10.70 to 55.31%) such as the soil total N (TN) at 0–10 cm depth, microbial biomass N (MBN) at 0–20 cm depth, total water-soluble N (WSTN) at 0–5 and 20–30 cm depths, and total labile N (LTN) at 0–30 cm depth. The primary components of soil LOC and LTN are MBC and MBN. Various soil C and N fractions positively correlated with each other (p &lt; 0.05). The HSNPK treatment promoted the soil MBC, WSOC, and LOC to SOC ratios, and also promoted MBN, WSTN, and LTN to soil TN ratios at a depth of 0–20 cm. To summarize, the application of HSNPK could maintain and improve rice paddy soil quality, which leads to increased rice grain yields.