Towards a better understanding of carbon flow in the rhizosphere: a time-dependent approach using carbon-14

 Controversies exist in interpreting rhizosphere C flow obtained by different ¹⁴CO₂ labelling methods. However, there is a need for the standardisation of methods in order to be able to compare values obtained for different plants, different stages of development and different habitats. Perennial bromegrass (Bromus erectus Huds) grown in soils of different fertility was exposed to a ¹⁴CO₂ atmosphere for different periods of time: 1 h, 298 h and 78 days. The evolution of ¹⁴CO₂ in the soil was measured during and after labelling. The ¹⁴C contents of plant and rhizosphere compartments were then estimated. The time-sequence of the rate of ¹⁴CO₂ evolution after 1 h of labelling, indicated a maximum after around 20 h, followed by an exponential decrease. When expressed as a percentage of net ¹⁴C assimilation, root-soil respiration accounted for 14% and 18% in the nutrient-poor and nutrient-rich soils, respectively. Integration of the hourly values over several days showed that the dynamics of the evolution rate were similar for the 298-h and 78-day experiments, thus indicating that rhizosphere C flow was dominated by newly assimilated C. This was confirmed by the proportions of below-ground ¹⁴C, measured for roots, respiration and soil, which were not significantly affected by the labelling regime. The differences were, however, found to be significant between the two types of soils. The conclusion was that the conditions for plant growth during labelling were more important than the length of time of labelling, and that this explained the discrepancies in the literature-cited values. A succession of short-term ¹⁴C labelling of plants at different development stages followed by an allocation period of about 1 week is proposed to give a reliable estimation of the dynamics of C flow in the rhizosphere. Received: 7 June 1999     

Landscape-level variation in temperature sensitivity of soil organic carbon decomposition

We examined landscape-level variation in temperature sensitivity of labile SOC across 71 sites at a central North American grassland. The observed range in activation energy of decomposition (E_a), an index of temperature sensitivity, was as great at the landscape scale as has been observed at the continental scale. E_a was lower for soils with more labile C, consistent with the ‘Carbon quality-temperature’ hypothesis. Soil pH explained 67% of the variation in E_a. Although there are strong environmental correlates with the E_a of SOC decomposition at landscape scales, the amount of variation within landscapes could confound regional- to global-scale predictions of the response of soil C to warming.     

滇黔桂地区土壤有机碳密度变异的影响因素研究

土壤有机碳是土壤肥力的重要指标之一,也是陆地碳库的主要部分。揭示影响土壤有机碳储量的主要因素,对合理地利用土壤资源,减少土壤温室气体的排放,增加土壤碳存储等方面都具有重要的意义。土壤有机碳储量受气候、植被、土壤属     

新疆绿洲农田不同开垦年限土壤有机碳及不同粒径土壤颗粒有机碳变化

研究不同开垦年限新疆绿洲农田土壤有机碳及不同粒径土壤颗粒有机碳的变化规律,评价长期垦殖对新疆绿洲农田土壤有机碳的影响。以相应未开垦地为对照,选取南北疆兰州湾、31团和普惠农场三个典型绿洲不同开垦年限土壤为研究对象,应用物理分组方法研究不同粒径土壤颗粒中有机碳含量及分布。结果表明:(1)开垦有利于新疆绿洲农田土壤总有机碳的积累,开垦初期(0～5a)增加迅速,年均增加0·5gkg-1,10a后增加趋于平缓。(2)垦殖增加了不同粒径土壤颗粒有机碳的含量,砂粒有机碳在垦殖10a间达到最大值后趋于相对稳定的水平;粉砂粒和黏粒有机碳随垦殖年限延长增加。(3)开垦提高了POC/MOC值,表现为开垦初期(0～5a)增加迅速,10a左右达到最大值后开始下降。研究说明,新疆绿洲区域未开垦地开垦增加了土壤总有机碳和不同粒径土壤颗粒有机碳含量,随垦殖年限延长,粉砂粒和黏粒有机碳成为绿洲农田土壤主要碳库,土壤自身生产力存在下降可能,土壤质量存在潜在退化风险。     

Roots,rhizosphere and soil: the route to a better understanding of soil science?

The centenary of Hiltner's recognition of a rhizosphere effect is a convenient point to assess the impact of such thinking on the direction of soil science. A review of the major soil journals suggests that for much of the last century, Hiltner's insight had little effect on mainstream thinking outside of soil microbiology, but this situation is changing rapidly as the consequences of spatial and temporal heterogeneity on soil functioning assumes greater importance. Studies of root growth, root distributions and of rhizosphere processes over the last 25 years demonstrate both the size and distribution of root systems and the associated inputs from roots to soils. These inputs result in a plethora of dynamic reactions at the root–soil interface whose consequences are felt at a range of temporal and spatial scales. Root growth and respiration, rhizodeposition, and uptake of water and nutrients result in biological, chemical and physical changes in soils over variable distances from the root surface so that the rhizosphere has different dimensions depending on the process considered. At the root length densities common for many crop species, much of the upper 0.1 m of soil might be influenced by root activity for mobile nutrients, water and root‐emitted volatile compounds for a substantial proportion of the growing season. This brief review concludes that roots are an essential component of soil biology and of soil science.     

北京市农田土壤有机碳密度空间变异及影响因素

探明区域农田土壤有机碳密度（soil organic carbon density, SOCD）空间分布特征及其影响因素对增加农田土壤碳汇、实现“双碳”目标具有重要意义。该研究以北京市为研究区,基于2022年采样实测的0～60 cm各层SOCD数据,采用3D概念模型、Mantel test、地理加权回归、地理探测器模型开展SOCD空间变异分析,探究不同因素对SOCD的影响程度及各因素间交互后的作用力。结果表明：1）研究区SOCD在空间上呈自表层向深层逐渐降低的趋势,其中0～15 cm土层的SOCD显著高于30～60 cm（P < 0.05）,0～60 cm土层的有机碳储量约为10.80 Tg。2）土壤含水率、土壤亚类、地形部位分别对0～15、15～60、45～60 cm土层的SOCD产生了显著影响（P < 0.05）;土壤亚类、土壤母质、土壤质地、地形部位与SOCD的空间关联性较强,关联程度自表层向下逐渐增大。3）各重要因子交互后对研究区SOCD的解释能力呈双因子增强或非线性增强的关系,土壤亚类与其他各因子交互后对SOCD的解释能力提升最为突出。今后研究区内开展土壤有机碳空间变异等相关研究时应尽可能综合考虑多因素间的交互作用,其中土壤亚类（土壤类型）可作为重点指标。研究结果可为优化农田资源空间结构,制定农田固碳增汇措施提供科学参考。     

不同有机物料对苏打盐化土有机碳和活性碳组分的影响

【目的】在大同盆地苏打盐化土上,研究不同有机物料对春玉米产量、土壤有机碳及活性碳组分的影响,明确土壤有机碳及活性碳组分与主要盐碱指标的相关关系,为苏打盐化土改良及有机物料资源化利用提供理论支撑。【方法】2016-2017年在山西省北部怀仁县开展田间定位试验,设对照(CK)、风化煤、生物炭、牛粪和秸秆5个处理,各处理有机物料施用量按照每年9000 kg/hm^2等有机碳投入量折算,收获时对春玉米进行测产。2017年春玉米收获后,采集土壤样品测定土壤有机碳总量(SOC)和水溶性有机碳(WSOC)、易氧化有机碳(EOC)、轻组有机碳(LFOC)含量,分析土壤活性碳组分占有机碳的比例、土壤有机碳及活性碳组分与盐碱指标之间的关系。【结果】与CK相比,生物炭和秸秆处理春玉米产量无明显差异,而风化煤和牛粪处理春玉米产量则分别显著提高30.2%和30.3%。添加有机物料促进了0-20 cm土层SOC累积,其中以风化煤和牛粪处理效果最佳,较CK分别提高47.6%和36.1%。在有机碳组分方面,风化煤和牛粪处理提高WSOC、EOC含量的效果显著高于生物炭、秸秆处理;风化煤、牛粪和秸秆处理的LFOC含量显著高于生物炭处理。四类有机物料处理的WSOC占总有机碳的比例差异不显著,牛粪处理的占比显著高于CK。EOC占总有机碳的比例以牛粪处理最高,风化煤次之,且二者均显著高于CK处理;LFOC占总有机碳的比例则表现为秸秆、牛粪>风化煤、生物炭> CK。此外,添加有机物料能有效降低0-20 cm土层土壤pH、电导率(EC)和碱化度(ESP),其中以风化煤和牛粪处理降幅最大。相关分析表明,土壤SOC与pH、EC和ESP呈显著负相关。【结论】通过有机物料改良效果比较,发现牛粪和风化煤处理能促进苏打盐化土有机碳累积,提高可溶性、易氧化态及轻组有机碳组分在总有机碳中的占比,降低土壤pH、EC和ESP,明显提高春玉米产量。因此,风化煤和牛粪是山西北部苏打盐化土良好的改良剂。     

Spectrophotometric determination of organic carbon in soil

Abstract

A detailed study was made of the well‐known organic carbon determination that is based on measuring the absorbance of the green chromium(III) complex generated when organic matter is oxidized by potassium dichromate in acidic medium. The green chromic colour proved to be unstable, turning slowly to a violet colour. It was also found that chromic sulphate exerts a catalytic influence on the decomposition of excess dichromate. Based on this work, a modified method was developed which is simple, rapid, and very accurate when working under carefully controlled conditions.     

Tillage effect on organic carbon in a purple paddy soil

The distribution and storage of soil organic carbon （SOC） based on a long-term experiment with various tillage systems were studied in a paddy soil derived from purple soil in Chongqing, China. Organic carbon storage in the 0-20 and 0-40 cm soil layers under different tillage systems were in an order： ridge tillage with rice-rape rotation （RT-rr） 〉 conventional tillage with rice only （CT-r） 〉 ridge tillage with rice only （RT-r） 〉 conventional tillage with rice-rape rotation （CT-rr）. The RT-rr system had significantly higher levels of soil organic carbon in the 0-40 cm topsoil, while the proportion of the total remaining organic carbon in the total soil organic carbon in the 0-10 cm layer was greatest in the RT-rr system. This was the reason why the RT-rr system enhanced soil organic carbon storage. These showed that tillage system type was crucial for carbon storage. Carbon levels in soil humus and crop-yield results showed that the RT-rr system enhanced soil fertility and crop productivity. Adoption of this tillage system would be beneficial both for environmental protection and economic development.     

Deep-burrowing earthworm additions changed the distribution of soil organic carbon in a chisel-tilled soil

We investigated the influence of earthworms on the three-dimensional distribution of soil organic carbon (SOC) in a chisel-tilled soil. By burrowing, foraging, and casting at the surface and throughout the soil, anecic earthworms such as Lumbricus terrestris L. may play a major role in regulating the spatial distribution of organic matter resources both at the surface and within the soil. In the fall of 1994, we manipulated ambient earthworm communities, which were without deep burrowing species, by adding 100 earthworm individuals m⁻² in spring and fall for 3 years. Overall, the biomass of L. terrestris was increased with earthworm additions and total earthworm biomass declined compared with ambient control treatments. To investigate the spatial variability in soil organic carbon due to this shift in earthworm community structure, we sampled soil on a 28×24 cm grid from the surface to 40 cm in four layers, 10 cm deep. Samples were analyzed for total carbon. We found that additions of anecic earthworms significantly increased average soil organic carbon content from 16.1 to 17.9 g C kg⁻¹ for the 0–10 cm soil, and from 12.4 to 14.7 g kg⁻¹ at 10–20-cm depth, and also changed the spatial distribution of soil organic carbon from uniform to patchy, compared with the ambient treatment.     

长期施肥对土壤有机碳和无机碳的影响

利用18年长期定位试验,研究了在不同施肥条件下,土壤有机碳和无机碳在0~50 cm土层分布特征。结果表明,施肥对土壤有机碳的影响随着土层深度的增加而下降,0~7.5 cm土层的土壤有机碳比7.5~15 cm、15~30 cm、30~50 cm分别增加了4.6%、22.0%、63.1%,而无机碳含量随着土层深度的增加而增加,与有机碳的变化规律正好相反。不同种类的肥料对土壤有机碳的影响也不相同,化肥、有机肥长期配合施用和长期施用有机肥可以在0~30 cm土层增加土壤有机碳含量,降低土壤中的无机碳含量,而长期单施化肥对土壤的有机碳和无机碳含量无明显差异。     

Reproducibility of a soil organic carbon fractionation method to derive RothC carbon pools

Fractionation of soil is undertaken to isolate organic carbon with distinct functional properties, such as stability and turnover times. Soil organic carbon (SOC) fractionation helps us to understand better the response of SOC to changes in land use, management or climate. However, fractionation procedures are often poorly defined and there is little information available on their reproducibility in different laboratories. In a ring trial, we assessed the reproducibility of a SOC fractionation method introduced by Zimmermann et al. (2007). The isolated fractions were linked to the model pool sizes of the Rothamsted carbon model (RothC). We found significant differences between six laboratories for all five defined fractions in three different soils with coefficients of variation ranging from 14 to 138%. During ultrasonic dispersion, the output power (energy per unit time) was identified as an important factor controlling the distribution of SOC within these five fractions, while commonly only the output energy is standardized. The amount of water used to wet‐sieve dispersed soil slurry significantly influenced the amount of extracted dissolved organic carbon (DOC). We therefore suggest using a fixed amount of power for ultrasonic dispersion (20 W) and a minimum amount of water for wet sieving (2000 ml). RothC pool sizes were predicted from the measured fractions and compared with RothC equilibrium pool size distributions. This model initialization using measured SOC fractions, however, led to an over‐estimation of stable RothC SOC pools when compared with pool size distributions derived from RothC equilibrium runs under a bare fallow soil model simulation. To improve the isolation of particulate organic matter from stable mineral‐bound organic matter, we suggest that the density should be increased from 1.8 to 2.0 g cm^?3 in the density fractionation step. We formulated a modified fractionation procedure, which aims specifically to enhance reproducibility across laboratories and to improve the match of the isolated SOC fractions with RothC's SOC pools.     

浙江省森林土壤有机碳密度空间变异特征及其影响因素

基于Moran’s I指数和GIS地统计插值方法研究浙江省森林土壤有机碳密度(SOCD)的空间自相关性及其分布特征,并采用线性回归方程分析影响因素对SOCD的作用。结果表明:浙江省森林土壤0～30 cm层次SOCD为71.2 t hm-2,较全国土壤平均碳密度低;全局Moran’s I=0.176,显示显著空间自相关性;浙江省森林SOCD呈现自西南向东北梯级递减趋势,表现为三条平行的带状分布;优势树种、坡位、龄组、海拔、灌木覆盖度、灌木平均高、平均年龄与SOCD呈极显著正相关关系,坡向与SOCD呈显著正相关关系,草本覆盖度与SOCD呈极显著负相关关系,草本平均高影响不显著;影响因素作用于SOCD14.9%的变异。     

Regional evaluation of the spatio-temporal variation in soil organic carbon dynamics for rainfed cereal farming in northern Kazakhstan

Abstract

A regional evaluation of the soil organic carbon (SOC) dynamics for the chernozem zone in northern Kazakhstan is now vitally important for agricultural and environmental policy making. The objectives of the present study were: (1) to predict spatial and temporal variability in C input as crop residues using multi-temporal MODIS satellite images, (2) to clarify spatial and temporal variability in CO₂ emission as SOC output using geostatistics and model s, (3) to clarify spatial and temporal variability in the SOC budget using the results from (1) and (2). The mean growing-season C input as plant residues in cereal fields ranged from 0.9 to 1.4 Mg C ha^?1, with higher values in wet years. Carbon input as plant residues was higher in the northern part of the area than in the other parts. The average growing-season CO₂ emission ranged from 0.9 to 1.1 Mg C ha^?1, and was also higher in wet years than in dry years. In addition, more CO₂ was emitted in the northern part of this area. Accordingly the average growing-season C budget ranged from –0.2 to 0.3 Mg C ha^?1 and showed a negative correlation with air temperature during the crop-growing season. The 5-year C budget for different crop rotation systems ranged from –1.0 (3-year cropped cereal with 2-year bare fallow) to 0.4 (5-year continuous cereal cropped) Mg C ha^?1. These results indicate that fallow-based crop rotation systems are degradative with regard to the SOC budget in the studied area.     

黑土颗粒态有机碳与矿物结合态有机碳的变化研究

确定管理措施下土壤有机碳(Soil organic car-bon,SOC),尤其是土壤团聚体稳定过程中表现活跃的有机碳组分的动态变化,对于正确评估农业管理措施对土壤结构和质量的影响作用至关重要[1]。土壤颗粒态有机质(Particulate organic matter,POM,>53μm)库是相对新形成的和对微生物有吸引力的物质,代表很大比例的“慢”分解有机碳库,其周转时间介于活性库和惰性库之间[2]。土壤POM包含有部分分解的动植物残体,是微生物活动的重要碳源[2]。增加土壤颗粒态有机碳(POM-C),有利于土壤生物活动,增加微生物生物量碳、氮,改善土壤结构及其他土壤性状[3]。土壤PO     

长期施肥对棕壤有机碳组分的影响

对起始于1979年的棕壤长期肥料定位试验田2005年的耕层土壤不同有机碳组分进行了测定与分析,以探讨长期施肥影响土壤有机碳的过程及机理。结果显示:长期单施化肥降低了土壤的游离态颗粒有机碳（FPOM-C）含量,但进一步稳定了矿物结合态有机碳(MOM-C),最终提高了土壤总有机碳(TOC)含量;长期施用有机肥和有机肥配施化肥使土壤的FPOM-C、闭蓄态颗粒有机碳(OPOC)、MOM-C以及含量均显著提高,且增加效果好于单施化肥。从各组分有机碳所占比例或相对比值来看,长期施用有机肥和有机肥配施化肥提高了POM-C/TOC比例而降低了MOM-C/TOC比例,使FPOM-C/OPOM-C比值显著增大。表明土壤有机碳结构分组的应用有助于揭示长期施肥影响土壤有机碳的机理。     

重建生态系统有机碳贮量的时空变异

In global change research, changes of soil organic carbon (SOC) reservoirs in tropical and subtropical regions are still unknown. The temporal-spatial variability of SOC stocks was determined in a basin of over 579 km² in subtropical China from 1981 to 2002. ArcGIS8.l software was utilized for spatial analysis of semivariance, ordinary kriging (OK), and probability kriging (PK). Grid and hierarchical approaches were employed for the sampling scenario in 2002 with 106 Global Position System (GPS) established spots sampled. Bulk topsoil samples (0-30 cm) were collected at three random sites on each spot. The SOC content for 1981 came from the SOC map of the Second National Soil Survey. Geostatistical results of the nugget to sill ratio (0.215-0.640) in the rehabilitating ecosystem indicated a moderate spatial dependence for SOC on this large scale. The range of SOC changed from 2.04 km in 1981 to 7.15 km in 2002. The mean topsoil SOC increased by 4.6% from 10.63 g kg^-1 (1981) to 11.12 g kg^-1 (2002). However, during this 21-year period 25.2% of the total basin area experienced a decrease in SOC. Also, the probability kriging results showed that the geometric mean probabilities of SOC ≤ 6.0 g kg^-1, ≤ 11.0 g kg^-1 and > 15.0 g kg^-1 were 0.188, 0.534 and 0.378, respectively in 2002, comparing to 0.234, 0.416 and 0.234 in that order in 1981, respectively. The SOC storage in the topsoil increased by 17.0% during this time with the main increase occurring in forests and cultivated land, which amounted to 82.5% and 17.0% of the total increase, respectively.     

土壤团聚体中有机碳研究进展

增加土壤有机碳有助于农业可持续发展, 同时对缓解温室气体增加造成的全球气候变暖等具有重要意义。土壤团聚体是土壤的重要组成部分, 影响土壤的各种物理化学性质。土壤团聚体和有机碳是不可分割的, 前者是后者存在的场所, 后者是前者存在的胶结物质。本文在综合各方面研究的基础上, 阐述了土壤团聚体和有机碳的依存关系, 影响团聚体固碳的几大因素, 团聚体对有机碳的物理保护机制以及目前应用比较广泛的团聚体内有机碳的研究方法, 为以后的研究提供理论和方法上的支持。     

不同地表覆盖栽培对旱地土壤有机碳、无机碳和轻质有机碳的影响

通过田间长期定位试验,分层采集冬小麦-休闲种植体系0—40 cm土层的土样,研究了常规、地表覆膜和覆草栽培对土壤有机碳、无机碳和轻质有机碳的影响。结果表明,覆膜或覆草可以显著增加地上部小麦生物量和子粒产量。不同地表覆盖对0—40 cm土层的无机碳含量和分布无显著影响,但与常规栽培相比,地表覆膜使0—5 cm土层的有机碳含量显著降低,0—40 cm各土层轻质有机碳表现出明显降低趋势,平均降低 C 6.1~74.5 mg/kg;地表覆草却表现出明显增加土壤轻质有机碳的趋势,0—5,5—10,10—20 cm土层的轻质有机碳含量分别增加C 235.2、190.0和144.9 mg/kg,相当于常规的38.7%,32.9%和34.5%。同时,覆草栽培还表现出降低0—10 cm土层轻质有机质含碳量的趋势,并使0—20 cm土层轻质有机碳占有机碳的比例显著高于常规栽培和地表覆膜处理。可见,地表长期覆膜不利于旱地土壤有机碳累积,覆草不仅可以增加表层土壤的轻质有机碳累积,还可改善土壤碳氮组成。