Distribution Of Soil Organic Matter Research Articles

Effects of continuous nitrogen addition on microbial properties and soil organic matter in a Larix gmelinii plantation in China

Continuous increases in anthropogenic nitrogen (N) deposition are likely to change soil microbial properties, and ultimately to affect soil carbon (C) storage. Temperate plantation forests play key roles in C sequestration, yet mechanisms underlying the influences of N deposition on soil organic matter accumulation are poorly understood. This study assessed the effect of N addition on soil microbial properties and soil organic matter distribution in a larch (Larix gmelinii) plantation. In a 9-year experiment in the plantation, N was applied at 100 kg N ha−1 a−1 to study the effects on soil C and N mineralization, microbial biomass, enzyme activity, and C and N in soil organic matter density fractions, and organic matter chemistry. The results showed that N addition had no influence on C and N contents in whole soil. However, soil C in different fractions responded to N addition differently. Soil C in light fractions did not change with N addition, while soil C in heavy fractions increased significantly. These results suggested that more soil C in heavy fractions was stabilized in the N-treated soils. However, microbial biomass C and N and phenol oxidase activity decreased in the N-treated soils and thus soil C increased in heavy fractions. Although N addition reduced microbial biomass and phenol oxidase activity, it had little effect on soil C mineralization, hydrolytic enzyme activities, δ13C value in soil and C–H stretch, carboxylates and amides, and C–O stretch in soil organic matter chemistry measured by Fourier transform infrared spectra. We conclude that N addition (1) altered microbial biomass and activity without affecting soil C in light fractions and (2) resulted in an increase in soil C in heavy fractions and that this increase was controlled by phenol oxidase activity and soil N availability.

Artificial bee colony feature selection algorithm combined with machine learning algorithms to predict vertical and lateral distribution of soil organic matter in South Dakota, USA

ABSTRACTThe main purpose of this study, is to evaluate an advanced feature selection technique, artificial bee colony (ABC) algorithm; to reduce the number of auxiliary variables derived from a digital elevation model (DEM) and remotely sensed data (e.g. Landsat images). A combination of depth functions (e.g. power, logarithmic and spline) and data miner methods (artificial neural network: ANN and support vector regression: SVR) were applied for three-dimensional mapping of soil organic matter (SOM) in Big Sioux River watershed, South Dakota, USA. Unsurprisingly, the ABC feature selection algorithm indicated that remote sensing data (e.g. NDVI) are powerful predictors at soil surface, however, with the increasing soil depth, the terrain parameters (e.g. wetness index) became more relevant. Our findings from this study demonstrated that both the spatial models generally performed well. The mean R2 values calculated by 10-fold cross validation suggested that SVR and ANN models could explain approximately 50 and 57% of total SOM variability, respectively. However, predictive power of both models increased when ABC feature selection algorithm applied, particularly when it combined with the ANN model. Results showed that DSM approaches are very important and powerful tool to explain the 3D spatial distribution of SOM across the study watershed.

Soil aggregation and soil organic matter in conventionally and organically farmed Austrian Chernozems / Bodenaggregation und organische Substanz in konventionell und biologisch bewirtschafteten österreichischen Tschernosemböden

Summary In order to study the soil aggregate distributions and soil organic matter (SOM), we sampled top- and subsoils in four intensively farmed croplands (two organic (Org-OB and Org-LA), and two conventional (Con-OB and Con-LA)) on Haplic Chernozems located in Marchfeld in the east of Vienna (Austria). Soil structure and SOM quantity, quality and distribution between free and occluded particulate organic matter and aggregate size fractions (<20 µm, 20-250 µm, 250-5000 µm) were studied by following a density fractionation procedure with low-energy ultrasound treatment. The relation of the soil physicochemical (e.g., particle size distribution, pH, organic carbon, total nitrogen) and biological properties (e.g., fungal biomass, active fungi) with stable soil aggregate size fractions and SOM was studied. The mean weight diameter (MWD) showed no significant difference between all studied sites and was between 3.8 mm and 10.0 mm in topsoils and between 6.7 mm and 11.9 mm in subsoils. In topsoils, the contents of calcium-acetate-lactate (CAL)-extractable P, active fungal biomass, dithionite-extractable Fe and sand were significantly positively correlated with the amount of the macroaggregates and with the MWD. We observed that most soil organic carbon, depending on soil texture, was stored in the microaggregate size classes <20 µm and 20-250 µm.

Thermal alteration of soil organic matter properties: a systematic study to infer response of Sierra Nevada climosequence soils to forest fires

Abstract. Fire is a major driver of soil organic matter (SOM) dynamics, and contemporary global climate change is changing global fire regimes. We conducted laboratory heating experiments on soils from five locations across the western Sierra Nevada climosequence to investigate thermal alteration of SOM properties and determine temperature thresholds for major shifts in SOM properties. Topsoils (0 to 5 cm depth) were exposed to a range of temperatures that are expected during prescribed and wild fires (150, 250, 350, 450, 550, and 650 °C). With increase in temperature, we found that the concentrations of carbon (C) and nitrogen (N) decreased in a similar pattern among all five soils that varied considerably in their original SOM concentrations and mineralogies. Soils were separated into discrete size classes by dry sieving. The C and N concentrations in the larger aggregate size fractions (2–0.25 mm) decreased with an increase in temperature, so that at 450 °C the remaining C and N were almost entirely associated with the smaller aggregate size fractions ( < 0.25 mm). We observed a general trend of 13C enrichment with temperature increase. There was also 15N enrichment with temperature increase, followed by 15N depletion when temperature increased beyond 350 °C. For all the measured variables, the largest physical, chemical, elemental, and isotopic changes occurred at the mid-intensity fire temperatures, i.e., 350 and 450 °C. The magnitude of the observed changes in SOM composition and distribution in three aggregate size classes, as well as the temperature thresholds for critical changes in physical and chemical properties of soils (such as specific surface area, pH, cation exchange capacity), suggest that transformation and loss of SOM are the principal responses in heated soils. Findings from this systematic investigation of soil and SOM response to heating are critical for predicting how soils are likely to be affected by future climate and fire regimes.

Does 20 Years of Tillage and N Fertilization Influence Properties of a Claypan Soil in the Eastern Great Plains?

Core Ideas Claypan soil properties were minimally affected by tillage and N fertilization after 20 years. Soil organic matter distribution was affected by tillage, but with no apparent net difference. Long‐term tillage and N fertilization did not affect soil bulk density or penetration resistance. Subtle long‐term soil changes may not influence producer choices for tillage and N fertilization. Tillage and nitrogen (N) fertilization systems may affect soil chemical and physical properties, especially long term. This study's objective was to examine the effect of three tillage systems (conventional tillage, reduced tillage, and no‐till) with four N fertilizer treatments on properties of a claypan soil in the eastern Great Plains after 20 yr of cropping. Soil chemical and physical properties were little affected by long‐term tillage and N fertilization. The lack of tillage to distribute soil phosphorus (P) and potassium (K) nutrients within no‐till treatments resulted in lower P and K values below the surface. In no‐till, the accumulation of organic matter in the surface soil (0 to 7.5 cm) was countered by lower organic matter in the 7.5‐ to 15 ‐cm zone, resulting in no net increase compared with the other two tillage systems. Soil bulk density and penetration resistance in the surface 30 cm were unaffected by tillage or N fertilization.

Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

Abstract. The spatial distribution and accessibility of organic matter (OM) to soil microbes in aggregates – determined by the fine-scale, 3-D distribution of OM, pores and mineral phases – may be an important control on the magnitude of soil heterotrophic respiration (SHR). Attempts to model SHR on fine scales requires data on the transition probabilities between adjacent pore space and soil OM, a measure of microbial accessibility to the latter. We used a combination of osmium staining and synchrotron X-ray computed tomography (CT) to determine the 3-D (voxel) distribution of these three phases (scale 6.6 µm) throughout nine aggregates taken from a single soil core (range of organic carbon (OC) concentrations: 4.2–7.7 %). Prior to the synchrotron analyses we had measured the magnitude of SHR for each aggregate over 24 h under controlled conditions (moisture content and temperature). We test the hypothesis that larger magnitudes of SHR will be observed in aggregates with (i) shorter length scales of OM variation (more aerobic microsites) and (ii) larger transition probabilities between OM and pore voxels. After scaling to their OC concentrations, there was a 6-fold variation in the magnitude of SHR for the nine aggregates. The distribution of pore diameters and tortuosity index values for pore branches was similar for each of the nine aggregates. The Pearson correlation between aggregate surface area (normalized by aggregate volume) and normalized headspace C gas concentration was both positive and reasonably large (r = 0.44), suggesting that the former may be a factor that influences SHR. The overall transition probabilities between OM and pore voxels were between 0.07 and 0.17, smaller than those used in previous simulation studies. We computed the length scales over which OM, pore and mineral phases vary within each aggregate using 3-D indicator variograms. The median range of models fitted to variograms of OM varied between 38 and 175 µm and was generally larger than the other two phases within each aggregate, but in general variogram models had ranges < 250 µm. There was no evidence to support the hypotheses concerning scales of variation in OM and magnitude of SHR; the linear correlation was 0.01. There was weak evidence to suggest a statistical relationship between voxel-based OM–pore transition probabilities and the magnitudes of aggregate SHR (r = 0.12). We discuss how our analyses could be extended and suggest improvements to the approach we used.

Estimating soil organic matter using interpolation methods with a electromagnetic induction sensor and topographic parameters: a case study in a humid region

Soil organic matter (SOM) is a key indicator of soil quality although, usually, detailed data for a given area is difficult to obtain at low cost. This study was conducted to evaluate the usefulness of soil apparent electrical conductivity (ECa), measured with an electromagnetic induction sensor, to improve the spatial estimation of SOM for site-specific soil management purposes. Apparent electrical conductivity was measured in a 10-ha prairie in NW Spain in November 2011. The ECa measurements were used to design a sampling scheme of 80 locations, at which soil samples were collected from 0 to 20 cm depth and from 20 cm to the boundary of the A horizon (ranging from 25 to 48 cm). The SOM values determined at the two depths considered were weighted to obtain the results for the entire A Horizon. SOM distribution maps were obtained by inverse distance weighting and geostatistical techniques: ordinary kriging (OK), cokriging (COK), regression kriging either with linear models (LM-RK) or with random forest (RF-RK). SOM ranged from 46.3 to 78.0 g kg−1, whereas ECa varied from 6.7 to 14.7 mS m−1. These two variables were significantly correlated (r = −0.6, p < 0.05); hence, ECa was used as an ancillary variable for interpolating SOM. A strong spatial dependence was found for both SOM and ECa. The maps obtained exhibited a similar spatial pattern for SOM; COK maps did not show a significant improvement from OK predictions. However, RF-RK maps provided more accurate spatial estimates of SOM (error of predictions was between four and five times less than the other interpolators). This information is helpful for site-specific management purposes at this field.

Application of solid surface fluorescence EEM spectroscopy for tracking organic matter quality of native halophyte and furrow-irrigated soils

Solid surface fluorescence excitation-emission matrix (EEM) is developed a potential method to characterize soil organic matter (SOM). Solid surface EEM spectroscopy with parallel factor analysis (PARAFAC) and hierarchical cluster analysis (HCA) is used to extract fluorescent components, to seek latent factors, and to investigate spatial distribution of SOM. Soil samples were collected from four native halophyte and two furrow-irrigated soil profiles, i.e. Comm. Salicornia europaea (CSE), Comm. Suaeda glauca (CSG), Comm. Kalidium cuspidatum (CKC), Comm. Sophora alopecuroides (CSA), corn fields (CFD), and wheat fields (WFD). SOM contained six fluorescent components: microbial/terrestrial fulvic-like fluorescent components (C1), tryptophan-like/lignin-derived phenol fluorescent components (C2), terrestrial humic-like fluorescent component (C3), lignin oxidative degradation by-products (C4 and C5), and amino acids (C6). The C 4 and C5 were the representative components of SOM within the CSE, CSG, CKC, CSA and CFD soil profiles, while the C2 and C6 were dominated within the WFD soil profile. The C4, C5, C1 and C2 were latent factors, and they could roughly distinguish SOM within the whole saline soil profiles except the CFD. A humification index (H/L) deduced from the fluorescent components, was very suitable to indicate humification levels of SOM. Humification levels of SOM within the halophyte soil profiles decreased with soil depth, but the opposite trends within the furrow-irrigated soil profiles. The H/L was closely correlated with exchangeable sodium percentage (ESP), and humification levels increased with the decreasing ESP. Soil surface EEM may not only indicate organic matter fractions of saline soils, but may be transferred to other types of landscape.

The vertical distribution of soil organic matter predicted by a simple continuous model of soil organic matter transformations

New modification of the simple continuous model of soil organic matter (SOM) transformation is proposed. The modification allows to convert a SOM distribution over humification rate to a SOM distribution over depth and vice versa. Qualitative correspondence of calculated curve patterns of SOM vertical distributions to observed ones for different soil types is shown.

Revealing the scale-specific controls of soil organic matter at large scale in Northeast and North China Plain

Soil organic matter (SOM) plays an important role in terrestrial ecosystem functioning and is closely related to soil fertility and soil health. Better understanding on the spatial distribution of SOM is vital to agriculture and C-cycle management. With the advancement of digital soil mapping framework and data mining technology, selection of environmental covariates become critical to identify the controls of SOM spatial distribution at different scales and were rarely discussed in previous studies. The objectives of this study were to separate the scale-specific variations in SOM and their dominant controls at those scales along two transects from Northeast and North China Plain. Spatial distribution of SOM was separated into seven scale components (six details, D1 through D6 and one approximation, A6) along each transect using the discrete wavelet transform. The largest variations in SOM were separated in A6 (>1280km) along the northeast transect (91.2% of the total) and D5 (320–640km) along the north transect (40.6% of the total). Unlike the northeast transect, considerable amount of variations was also separated in other scale components of the north transect. There were no significant correlations between the scale-components of SOM and terrain factors along both the transects. While a relatively stronger correlation was observed between SOM and climatic and vegetation factors along the northeast transect, no significant correlation was observed along the north transect at large scales. This may be due to the long-term cultivation in the Northern China Plain. Principal components 1 and 3 identified from the proximally sensed visible and near infrared (vis–NIR) spectra had strong correlation with SOM along the north transect while the principle component 2 was highly correlated with SOM along the northeast transect. The scale-specific controlling factors at different locations may help in selecting environmental factors in digital soil mapping at different scales for improving mapping accuracy.

长白山原始阔叶红松林土壤有机质组分小尺度空间异质性

PDF HTML阅读 XML下载 导出引用 引用提醒 长白山原始阔叶红松林土壤有机质组分小尺度空间异质性 DOI: 10.5846/stxb201503310626 作者: 作者单位: 1 山西大学环境与资源学院;2中国科学院地理科学与资源研究所，生态系统网络观测与模拟重点实验室,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,山西大学环境与资源学院,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金委青年项目，重大和国际合作项目（31400460，31290221，31420103917） Small-scale spatial heterogeneity of soil organic matter fractions within an original broad-leaved korean pine forest in Changbai Mountain, China Author: Affiliation: 1 Shanxi University; 2 Key Laboratory of Ecosystem Network Observation and Modeling, Chinese Academy of Sciences (CAS); Institute of Geographic Sciences and Natural Resources Research,Institute of Geographic Sciences and Natural Resources Research, CAS,,,,,, 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:土壤有机质（SOM）对于维持生态系统生产力具有非常重要的意义，有机质的组成、空间分布和空间关联性是影响和控制诸多生态系统过程的重要因素。应用地统计学方法，对长白山原始阔叶红松林局部尺度内0-20 cm土壤有机质与活性有机质的空间异质性进行了研究，并通过交叉半方差分析探讨了二者之间的相关性。研究结果表明：（1）总体上来说，土壤有机碳（SOC）、全氮（TN）、颗粒态有机碳（POC）和颗粒态有机氮（PON）空间异质性较小；而土壤微生物量碳（MBC）、微生物量氮（MBN）和表层（0-10 cm）溶解性有机碳（DOC）的空间异质性较大；（2）SOC、TN、MBC、DOC、POC和PON随着深度的增加空间自相关性增加；而溶解性有机氮（DON）的空间自相关性随深度的增加变化不大；（3）SOC与TN在表层和下层（10-20 cm）均存在空间上的正相关关系；（4）SOC、TN在表层和下层分别与MBC、MBN、DOC、DON和POC呈空间上的正相关性，但是与PON之间的空间相关关系较差；（5）不同土层深度的土壤活性有机质之间的相关关系存在差异。在表层，除POC，PON外，其余土壤活性有机质组分在空间上两两相关；但是随着土壤深度的增加，活性有机质变量之间在空间上两两相关。研究结果表明土壤有机质组分在长白山原始阔叶红松林小尺度内存在不同空间异质性和空间关联性，这为人们更好的理解森林生态系统功能（如土壤养分循环）提供了重要的理论依据。 Abstract:Soil organic matter (SOM) plays an important role in the maintenance of ecosystem productivity. In particular, the fractions, spatial distribution, and spatial dependency of SOM are important factors influencing multiple ecosystem processes including nutrient cycling, retention, and availability for plant growth. In the present study, geostatistical approaches were used to study the spatial variability of total and labile SOM fractions from the soil at a depth of 0-20 cm, in a Broad-Leaved Korean Pine forest in Changbai Mountain, China. Furthermore, the dependency between total SOM and labile organic matter was analyzed by calculating the cross-variogram. The results showed that:(1) The spatial heterogeneity of soil organic carbon (SOC), total nitrogen (TN), particulate organic carbon (POC), and particulate organic nitrogen (PON) was smaller than soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and the dissolved organic carbon (DOC) in the surface horizon (0-10 cm); (2) With increased soil depth, the autocorrelation of SOC, TN, MBC, DOC, POC, and PON increased, but remained unchanged for dissolved organic nitrogen (DON); (3) SOC and TN were positively correlated in space within both the 0-10 cm and 10-20 cm soil layers; (4) SOC and TN were both spatially correlated to MBC, MBN, DOC, DON, and POC, respectively, but were not related to PON; (5) The correlations between labile organic matter varied with soil depth. The labile organic matter fractions were spatially correlated with each other at all depths, except POC and PON on the surface. Our results suggest that the spatial heterogeneity and dependency of SOM fractions are different at small scales in a Broad-Leaved Korean Pine forest in Changbai Mountain, providing an important theoretical basis to understand the ecological function of soil nutrient cycling in forest ecosystems. 参考文献 相似文献 引证文献

Characteristics and distributions of humic acids in two soil profiles of the southwest China Karst area

Characteristics and distributions of humic acid (HA) and soil organic matter (SOM) in a yellow soil profile and a limestone soil profile of the southwest China Karst area were systematically investigated to reveal their evolutions in different soils of the study area. The results showed that characteristics and distribution of SOM along the two soil profiles were notably different. Total organic carbon (TOC) contents of soil samples decreased just slightly along the limestone soil profile but sharply along the yellow soil profile. TOCs of the limestone soils were significantly higher than those of the corresponding yellow soils, and C/N ratios of SOMs showed a similar variation trend to that of TOCs, indicating that SOM can be better conserved in the limestone soil than in the yellow soil. The soil humic acids were exhaustively extracted and further fractionated according to their apparent molecular weights using ultrafiltration techniques to explore underlying conservation mechanisms. The result showed that C/N ratios of HAs from different limestone soil layers were relatively stable and that large molecular HA fractions predominated the bulk HA of the top soil, indicating that HA in the limestone profile was protected while bio and chemical degradations were retarded. Combined with organic elements contents and mineral contents of two soils, we concluded that high calcium contents in limestone soils may play a key role in SOM conservation by forming complexation compounds with HAs or/and enclosing SOMs with hypergene CaCO3 precipitation.

Comparison of sampling schemes for the spatial prediction of soil organic matter in a typical black soil region in China

Data on the spatial distribution of soil organic matter (SOM) are important for the spatio-temporal modeling of soil organic carbon dynamics and soil carbon sequestration potential estimates. A total of 175 topsoil samples (0–20 cm) were collected from a typical black soil area in central Hailun County in northeastern China. Seven sampling design schemes, ordinary kriging (OK), and regression kriging (RK) were applied to the re-sampled SOM data for predicting the spatial distribution of SOM. The results showed that single sampling designs, such as simple random, stratified random (STR), and conditional Latin hypercube (CLH), produced poor estimates of SOM, while hybrid sampling designs, such as uniform distribution of point pairs for variogram estimation combined with spatial coverage, STR combined with spatial coverage (STRC), and CLH combined with spatial coverage (CLHC), had a higher predicting accuracy when the sample size was relatively small (≤262). For square grid sampling, a higher predicting accuracy could be achieved only when the sample size was sufficiently large (i.e., ≥402). The inclusion of prior knowledge or SOM-related secondary data in the sampling design and the trade-off between the even and uneven distribution of sampling points are especially important for designing a small-size sampling scheme. Moreover, although the SOM-predicting accuracy of RK was not as good as OK in this study, increasing the sample size may improve the predicting accuracy of SOM. Therefore, the optimal sampling design and spatial predicting method are both important for the predictive mapping of SOM spatial distribution in this area.

Effect of conservation farming practices on soil organic matter and stratification in a mono-cropping system of Northern China

An arid environment under long-term traditional agriculture has resulted in serious environmental and agricultural problems on a number of fragile soils with distinguishing physical and chemical properties in Northern China. Conservation agriculture is an alternative sustainable agriculture management system, which contributes to conserving soil, water and fertility, while changing vertical distribution of soil organic matter (SOM). No-tillage with straw cover (NTSC) and traditional tillage with straw removal (TTSR) in four regions of northern China (Tailai, Wuchuan, Nailin, Yaodu) were investigated to determine how tillage and soil type affected SOM stratification. SOM content, total N (TN), soil water content (SWC) and soil bulk density (ρd) in the 0–5, 5–15, 15–30 and 30–40cm layers and the time since implementation of tillage treatments were evaluated. The top layer (0–5cm) and total SOM content were markedly improved by NTSC. The influence dramatically decreased with depth in all sites. SOM content increased during the first 10 years following NTSC implementation, but the rate of increase was reduced in subsequent years. There was high positive correlation between SOM and SWC, high positive correlation between SOM and TN, and high negative correlation between SOM and bulk density. Effects of conservation measures on SOM content were expressed by a stratification ratio. The stratification ratio of SOM, in most sites, under long-term NTSC were >2. These results from northern China, suggest that long-term no-tillage with straw cover significantly improved topsoil conditions and whole of soil profile SOM and this improvement was obvious in different layers.

Tillage, seasonal and depths effects on soil microbial properties in black soil of Northeast China

Tillage practice can alter the content and distribution of soil organic matter by burying crop residue and soil disturbance, which would impact soil microbial properties. The objective of the present study was to evaluate the effects of tillage practices (no tillage, NT; ridge tillage, RT; mouldboard plow, MP) and sampling date (April, June, September) on soil microbial properties at different soil depths. Soil core samples were taken at 0–5, 5–10 and 10–20cm depths from a long-term tillage experiment site (initiated in 2001) in black soils in northeast China. Microbial biomass and extractable organic C were determined using by chloroform-fumigation-extraction method. Microbial abundance and community structure were determined using the phospholipid fatty acid (PLFA) method. Principal response curve (PRC) analysis revealed the magnitude of the effect of sampling date on the PLFA relative abundance decreased with depth within the tilled layer, whereas increased with depth for tillage practice. Microbial biomass carbon, abundance and the F/B ratio varied with the variation in available substrates at the 0–5cm depths. NT and RT improved microbial abundance (total, fungal and bacterial abundance) in the 0–5cm depth soil, but they did not contribute to a higher F/B ratio in the 0–5cm depth soil, and had a lower F/B ratio than MP in the deeper soils below 5cm depth. These results demonstrated that long-term conservation tillage practice has potential for improving microbial properties in surface soil, but may not cause a shift of microbial community structure in Northeast China.

C–N–P interactions control climate driven changes in regional patterns of C storage on the North Slope of Alaska

As climate warms, changes in the carbon (C) balance of arctic tundra will play an important role in the global C balance. The C balance of tundra is tightly coupled to the nitrogen (N) and phosphorus (P) cycles because soil organic matter is the principal source of plant-available nutrients and determines the spatial variation of vegetation biomass across the North Slope of Alaska. Warming will accelerate these nutrient cycles, which should stimulate plant growth. We applied the multiple element limitation model to investigate the spatial distribution of soil organic matter and vegetation on the North Slope of Alaska and examine the effects of changes in N and P cycles on tundra C budgets under climate warming. The spatial variation of vegetation biomass on the North Slope is mainly determined by nutrient mineralization, rather than air temperature. Our simulations show substantial increases in N and P mineralization with climate warming and consequent increases in nutrient availability to plants. There are distinctly different changes in N versus P cycles in response to warming. N is lost from the region because the warming-induced increase in N mineralization is in excess of plant uptake. However, P is more tightly cycled than N and the small loss of P under warming can be compensated by entrainment of recently weathered P into the ecosystem cycle. The increase in nutrient availability results in larger C gains in vegetation than C losses from soils and hence a net accumulation of C in the ecosystems. The ongoing climate warming in Arctic enhances mineralization and leads to a net transfer of nutrient from soil organic matter to vegetation, thereby stimulating tundra plant growth and increased C sequestration in the tundra ecosystems. The C balance of the region is predominantly controlled by the internal nutrient cycles, and the external nutrient supply only exerts a minor effect on C budget.

Targeted management of organic resources for sustainably increasing soil organic carbon: Observations and perspectives for resource use and climate adaptations in northern Ghana

ABSTRACTSince soil organic matter (SOM) buffers against impacts of climatic variability, the objective of this study was to assess on-farm distribution of SOM and propose realistic options for increasing SOM and thus the adaptation of smallholder farmers to climate change and variability in the interior northern savannah of Ghana. Data and information on spatial distribution of soil organic carbon (SOC), current practices that could enhance climate adaptation including management of organic resources were collected through biophysical assessments and snap community surveys. Even though homestead fields were more frequently cultivated, higher amounts of SOC (15 ± 2 g kg−1) were observed in homesteads when compared to the periphery cropped sections in bushes (SOC = 9 ± 1 g kg−1). Possibly, a combination of household wastes, droppings of domestic animals that are mostly reared in a free-range system, manures applied to crops and cultural norms of chieftaincy, which cause short-term fallowing of homestead fields could account for the differences in SOC. Use of organic resources for soil amendment among farmers was low (31% of interviewed farmers) due largely to ignorance of fertilizer values of manures and residues, traditions for bush-burning and competing use of organic resources for fuels. Our findings suggest a need for effective management practices, training and awareness aimed at improving management of organic resources and, consequently, increasing SOC and resilience to climate-change-induced risks.

Landscape heterogeneity drives contrasting concentration–discharge relationships in shale headwater catchments

Abstract. Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of three shale-underlain headwater catchments located in Pennsylvania, USA (the forested Shale Hills Critical Zone Observatory), and Wales, UK (the peatland-dominated Upper Hafren and forest-dominated Upper Hore catchments in the Plynlimon forest), dissimilar concentration–discharge (C–Q) behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation and soil organic matter (SOM). Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Furthermore, concentration–discharge relationships of non-chemostatic solutes changed following tree harvest in the Upper Hore catchment in Plynlimon, while no changes were observed for chemostatic solutes, underscoring the role of vegetation in regulating the concentrations of certain elements in the stream. These results indicate that differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where SOM is dominantly in lowlands (e.g., Shale Hills), we infer that non-chemostatic elements associated with organic matter are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), these non-chemostatic elements are released later during rainfall events. The distribution of SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.

Geogenic CO2 affects stabilization of soil organic matter

SummaryThe soil on mofette sites is affected by ascending geogenic carbon dioxide (CO2), which partially fills the soil atmosphere. We hypothesized that geogenic CO2 affects the stabilization of soil organic matter (SOM) at lower partial pressures than had been discussed previously for mofette sites. We studied loamy Ah horizons (n = 22; pH 3.4–4) of the soil along a transect on a grassland mofette site in the northwest Czech Republic with CO2 partial pressures (p(CO2)) of up to 0.52. The samples were fractionated by particle size, density and solubility (water‐soluble organic matter (WSOM)), and analysed quantitatively for organic carbon (C) and total nitrogen (N) and qualitatively (13C‐NMR spectroscopy). Soil OM with a narrower C:N ratio accumulated in the clay fraction, but at p(CO2) less than approximately 0.1 the proportion of SOM in the clay fraction relative to total SOM tended to decrease with increasing p(CO2), whereas that of particulate organic matter (POM) fractions increased with increasing p(CO2). We attribute the distribution of SOM among the mineral soil and POM to decreased interactions with minerals of the clay fraction. The formation of iron (Fe) hydroxides, which potentially sorb SOM, was not affected negatively by CO2. The potential reactivity of Fe hydroxides was even positively affected by increased p(CO2). Export of dissolved SOM into the subsoil might increase at mofette sites because of the large amounts of WSOM and decreasing interactions with minerals of the clay fraction. Therefore, our results show negative effects of CO2 on SOM stabilization even at moderate p(CO2).

Spatial distribution of soil organic matter in two fields on tidal flat sediments (Zhejiang Province, China) differing in duration of paddy management

AbstractDespite of its ecological and economic importance, only limited information is available on spatial variability of soil organic C (OC) in paddy fields during soil development. To obtain deeper insights into the accumulation and spatial distribution of OC with ongoing paddy management, the present study investigates spatial heterogeneities in puddled topsoil layers, in the plough pan, as well as in the underlying subsoil of a 50‐ and 300‐y old paddy site at the area of Cixi (Hangzhou Bay, E China). Sampling of the plots was done on the basis of a regular, orthogonal grid. The grid combined a large‐scale design with distances of 5 m with a small‐scale nested sampling ranging within 0.5 to 1 m. Samples have been taken with an auger in three sampling depths: (1) puddled topsoil layer, (2) dense plough layer, (3) mixed subsoil horizon. All samples were analyzed for their OC and total N concentrations as well as for their soil color (lightness value) to assess relationships between soil lightness and OC amount and distribution. The spatial behavior of all analyzed parameters in the different soil layers was investigated by calculating variograms; the degree of spatial dependence was determined by nugget‐to‐sill ratios. The results show that for each analyzed soil layer, OC and N concentrations were significantly higher in the field with 300 y of paddy management than in the field with 50 y of paddy management. Topsoil OC concentrations changed from 13.8 to 23.6 mg g−1, OC in the plough layer changed from 3.3 to 9.6 mg g−1, and also the subsoil showed a slight increase from 2.9 to 3.3 mg g−1.Although only two points in time were compared, we assume that paddy soil formation is the most likely reason for differences in the spatial distribution of OC between the two sites. Comparing the spatial depth distribution of the 50‐ and 300‐y old paddy sites suggests that the development of a spatial pattern of OC proceeded with time from topsoil to the underlying soil horizons. Measuring soil lightness was insufficient to predict amount and distribution of soil OC in paddy soils, especially in soils with interfering dark‐colored burnt straw residues. The degree of spatial homogeneity was equal in the two sites, suggesting that cultivation practices (puddling, levelling, burning and incorporation of straw residues) most likely maintained a rather high random spatial variability of approx. 45%. The spatial pattern of OC in the topsoil was dissimilar to the plough layer, revealing that transport of OC in the plough pan occurred mainly in preferential flow paths along localized cracks and biopores.