Soil oxygen flux measured polarographically in an Alaskan tussock tundra

Soil oxygen flux was measured polarographically in undisturbed tussock tundra and in an old vehicle track at Eagle Creek, Alaska. Because some polarograms did not show effective voltage plateaus, the polarographic method was tested for use in the tundra by experimental manipulation of soil water content and microbial oxygen demand. The response of soil oxygen flux was as predicted for artificially waterlogged systems, and the response to increased microbial demand indicated relatively high oxygen availability. Soil oxygen flux ranged from 25.9 ng O₂ cm⁻² min⁻¹ in Sphagnum mats to 3.9 ng O₂ cm⁻² min⁻¹ in unvegetated ruts of the vehicle track. Most sites in unvegetated ruts did not have measurable soil oxygen flux. In contrast, oxygen flux beneath Eriophorum vaginatum tussocks growing in the vehicle track averaged 10.7 ng O₂ cm⁻² min⁻¹.     

Refining and unifying the upper limits of the least limiting water range using soil and plant properties

The least limiting water range (LLWR) was introduced as an integrated soil water content indicator, measuring the impact of mechanical impedance, oxygen and water availability on water uptake and crop growth. However, a rigorous definition of the upper limit of the LLWR using plant physiological and soil physical concepts was not given. We introduce in this study an upper limit of the LLWR, based on soil physical and plant physiological properties. We further evaluate the sensitivity of this boundary to different soil and crop variables, and compare the sensitivity of the upper limit of the LLWR to previous definitions of soil water content at field capacity. The current study confirms that the upper limit of the LLWR can be predicted from knowledge of the soil moisture characteristic curve, plant root depth and oxygen consumption rate. The sensitivity analysis shows further that the upper limit of the LLWR approaches the volumetric soil water content at saturation when the oxygen consumption rate by plants becomes less than 2 µmol m^?3 s^?1. When plants are susceptible to aeration (e.g. potato and avocado), there is a big difference between the upper limit of the LLWR and the soil water content at field capacity, in particular for sandy soils. Results also show that the soil water content at aeration porosity corresponding to 10% cannot be considered as an appropriate upper limit of LLWR because it does not appropriately reflect the crop water requirements. Similar poor results are obtained when considering the soil water content at matric potential ?0.033 MPa or when defining the soil water content at field capacity based on drainage flux rate. It is observed that the upper limit of the LLWR is higher than either soil water content at ?0.033 MPa matric potential or soil water content at field capacity as based on drainage flux rate, especially in sandy soils.     

旱改水型农田整治对土壤碳排放的短期影响

灌溉农业可提升粮食生产潜力,已成为全球农业重要的发展方向,但此类土地利用转换势必影响旱作农田土壤的稳定性,尤其是碳循环。然而,旱改水整治过程中土壤碳通量变化及其与环境因子间的互馈机制尚不清楚。为此,采用大田模拟实验,连续7 d监测土壤碳通量变化,评估旱改水整治对土壤碳库组成及环境驱动的短期效应。结果表明：①旱地、水田的土壤碳通量和温度均呈昼高夜低的单峰型曲线,且碳通量与温度峰值出现于每日13：00前后,但水田土壤碳通量稍高于旱地。②旱改水后短期内土壤可溶性有机碳（DOC）、微生物量碳（MBC）、易氧化有机碳（EOC）、惰性有机碳（ROC）、总有机碳（TOC）和土壤碳库管理指数均呈减少趋势,其中土壤微生物量碳、易氧化有机碳降幅分别达28.55%、29.09%。③土壤含水量、微生物OTU数、碳库含量是影响碳通量速率变化的关键因子（P<0.05）,土壤温度、理化性状是制约土壤碳库的主控因子（P<0.05）。农业活动是重要的碳源之一,深入研究大范围旱改水诱发的碳排放问题可为低碳农业、气候减缓及其应对策略制定提供科学依据。     

The use of stable isotopes to study ecosystem gas exchange

Stable isotopes are a powerful research tool in environmental sciences and their use in ecosystem research is increasing. In this review we introduce and discuss the relevant details underlying the use of carbon and oxygen isotopic compositions in ecosystem gas exchange research. The current use and potential developments of stable isotope measurements together with concentration and flux measurements of CO₂ and water vapor are emphasized. For these applications it is critical to know the isotopic identity of specific ecosystem components such as the isotopic composition of CO₂, organic matter, liquid water, and water vapor, as well as the associated isotopic fractionations, in the soil-plant- atmosphere system. Combining stable isotopes and concentration measurements is very effective through the use of ”Keeling plots.” This approach allows the identification of the isotopic composition and the contribution of ecosystem, or ecosystem components, to the exchange fluxes with the atmosphere. It also allows the estimation of net ecosystem discrimination and soil disequilibrium effects. Recent modifications of the Keeling plot approach permit examination of CO₂ recycling in ecosystems. Combining stable isotopes with dynamic flux measurements requires precision in isotopic sampling and analysis, which is currently at the limit of detection. Combined with the micrometeorological gradient approach (applicable mostly in grasslands and crop fields), stable isotope measurements allow separation of net CO₂ exchange into photosynthetic and soil respiration components, and the evapotranspiration flux into soil evaporation and leaf transpiration. Similar applications in conjunction with eddy correlation techniques (applicable to forests, in addition to grasslands and crop fields) are more demanding, but can potentially be applied in combination with the Keeling plot relationship. The advance and potential in using stable isotope measurements should make their use a standard component in the limited arsenal of ecosystem-scale research tools. Received: 8 July 1999 / Accepted: 10 January 2000     

Radial Oxygen Loss from Roots: The Theoretical Basis for the Manipulation of Flux Data Obtained by the Cylindrical Platinum Electrode Technique

A résumé is given of the cylindrical platinum electrode technique for measuring the rate of oxygen release from the submerged roots of intact plants. Methods are then described for manipulating the oxygen flux data to quantify the following root characteristics: total effective internal diffusional resistance, non-metabolic (pore-space) resistance, internal apical oxygen concentration, effective diffusion coefficient of internal transport and fractional porosity, and the respiratory contribution to internal transport. The diffusional resistance of the root wall is discussed and the method formerly suggested for converting low temperature flux data to the appropriate room temperature values (Armstrong 1971) is revised. Finally, suggestions are made for overcoming the difficulties encountered in using flux data for comparative work if the roots differ in their apical radii.     

模拟氮沉降增加对寒温带针叶林土壤 CO2排放的初期影响

研究大气氮沉降增加情景下北方森林土壤CO2排放通量及其相关控制因子至关重要。在大兴安岭寒温带针叶林区建立了大气氮沉降模拟控制试验,利用静态箱-气相色谱法测定土壤CO2排放通量,同时测定土壤温度、水分、无机氮和可溶性碳含量等相关变量,分析寒温带针叶林土壤CO2排放特征及其主要驱动因子。结果表明:氮素输入没有显著改变森林土壤含水量,但降低了有机层土壤溶解性无机碳(DIC)含量,并增加有机层和矿质层土壤溶解性有机碳(DOC)含量。增氮短期内不影响土壤NH+4-N含量,但促进了土壤NO-3-N的累积。增氮倾向于增加北方森林土壤CO2排放。土壤CO2通量主要受土壤温度驱动,其次为土壤水分和DIC含量。虽然土壤温度整体上控制着土壤CO2通量的季节变化格局,但在生长旺季土壤含水量对其影响更为明显。在分析增氮对土壤CO2通量的净效应时,除了土壤温度和水分外,还要考虑土壤有效碳、氮动态的影响。     

Oxygen demand and supply in Zizania latifolia and Phragmites australis

The oxygen demand of underground organs in tall emergent plants was assumed to be supplied with the oxygen flux through aerial shoots. Measurements were made of the respiratory activity of underground organs and oxygen flux through aerial shoots in Zizania latifolia (Griseb.) Stapf and Phragmites australis (Cav.) Trin. ex Steud.Oxygen uptake rates of Z. latifolia roots and rhizomes decreased as the supply of oxygen decreased. Phragmites australis, however, did not respond to decreases in the supply of oxygen until the oxygen supply was relatively low. The values for old rhizomes of P. australis were very low. Most of the oxygen flux for P. australis was derived from standing dead shoots. The important role of dead shoots of P. australis in plant aeration is suggested. The degree of sufficiency of oxygen supply for Z. latifolia was 179% in May and 92% in August. The values for P. australis were 45% both in May and August. Furthermore, estimation of mean oxygen concentration of inner underground organs for P. australis showed very low values, 1.6% both in May and August, even in shallow water.     

The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation

The most commonly observed change in soil following slash-and-burn clearing of tropical forest is a short-term increase in nutrient availability. Studies of shifting cultivation commonly cite the incorporation of nutrient-rich ash from consumed aboveground biomass into soil as the reason for this change. The effects of soil heating on nutrient availability have been examined only rarely in field studies of slash-and-burn, and soil heating as a mechanism of nutrient release is most often assumed to be of minor importance in the field. Few budgets for above and belowground nutrient flux have been developed in the tropics, and a survey of results from field and laboratory studies indicates that soils are sufficiently heated during most slash-and-burn events, particularly in dry and monsoonal climates, to cause significant, even substantial release of nutrients from non-plant-available into plant-available forms in soil. Conversely, large aboveground losses of nutrients during and after burning often result in low quantities of nutrients that are released to soil. Assessing the biophysical sustainability of an agricultural practice requires detailed information about nutrient flux and loss incurred during management. To this end, current conceptual models of shifting cultivation should be revised to more accurately describe these fluxes and losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

面向区域土壤碳通量估算的多向插值空间采样策略

区域土壤碳通量的准确测量对陆地生态系统碳循环过程分析具有十分重要的作用。由于土壤碳通量空间异质性强,采用随机抽样的方法无法对区域土壤碳通量进行准确估算,而大范围的多点采样则需要大量的人力及设备成本。基于一种自制的仪器,提出了一种递增式采样的多向插值采样策略(MDI Multiple Directional Interpolation):在设定初始采样点的基础上,通过对已有采样点的测量,通过径向插值的方法计算采样点连线交点,将不同径向计算值差异最大的点作为新增采样点,以此逐步增加。通过对20幅的50×50网格区域仿真,结果表明(1)MDI布局策略能够针对土壤碳通量的变化情况而反馈采样点的疏密。(2)误差分析得出采样点数量(n=10)较少,MDI布局策略对碳通量的估算误差比随机布局策略低,比平均布局策略稍高;随采样点增多,3种布局策略误差均降低;采样点数量n=40,MDI布局策略对碳通量的估算误差(0.028)比平均布局策略的误差(0.32)降低了12.5%,比随机布局策略的误差(0.04)降低了30.0%。MDI布局策略根据土壤碳通量的变化梯度合理分配采样点,降低区域土壤碳通量监测误差。     

Submersion respiration in small diving beetles (Dytiscidae)

Some small diving beetles can survive submerged through weeks and months, because they can extract oxygen, dissolved in the water, through respiratory pores in their integument. An air flux from the outside to the inside through the respiratory pores has been demonstrated. All diving beetles capable of such pore respiration are small, but not all small diving beetles have pore respiration. With increasing size, more and more of the surface must be covered by respiratory pores to meet the increasing demand of oxygen. In running water species the pore-respiration mode is regarded as an adaptation to life in current exposed substrates, thus they avoid the risk of being swept away during frequent surface visits. In stagnant water species the pore respiration mode reduces the risk of falling victim to pelagic predators. The submersion tolerant species can switch to surface respiration, e.g. during low oxygen content. The pore respiratory mechanism is believed to be a specialised plastron. The oxygen flux through the scattered, small respiratory pore area may be enhanced by a functional thinning of the boundary layer.     

植物对有机氮源的利用及其在自然生态系统中的意义

近来大量实验研究表明,许多植物能够在不经矿化的情况下直接吸收、利用环境介质中的生物有机氮,尤其氨基酸类。而且,有些植物利用氨基酸的效率可以与矿质氮源(NH4 、NO3)相当或更高。自然界植物赖以生存的土壤生境中同时存在多种有机氮和矿质氮养分,这是导致植物(至少部分植物)进化产生利用各种不同氮源能力的环境驱动力。土壤中的游离氨基酸尽管含量不高,但其周转快、通量大,理论上可远大于植物的氮需求。尽管植物在与土壤微生物的有机氮源竞争中处于根本性劣势,但土壤中氨基酸的巨大潜在通量和植物相对于微生物的生命周期仍可使植物在长期竞争中获取数量可观的氮。基于植物根对氨基酸的吸收能力、土壤中游离氨基酸库的大小和通量、植物与土壤微生物对氨基酸氮源的竞争以及有关的原位实验结果,近来许多研究者都认为植物有机氮营养在多种生态系统中是重要或潜在重要的。尤其是在一些极地、高山、亚高山、北方针叶林或泰加林生态系统中,由于低温等因素限制有机氮矿化,土壤氨基酸浓度常超过矿质氮(NH4 、NO3-)浓度,氨基酸可能代表着植物的一个主要氮源。认识到现实生态系统中植物对有机氮源利用的重要性意味着传统的矿质营养观念的更新,这将在很大程度上改变人们对某些重要生态过程的理解,并导致对若干生态学中心问题的再认识。研究以森林生态系统为例,阐述了我国开展该领域研究的科学意义和基本框架。     

Production process monitoring by serial mapping of microbial carbon flux distributions using a novel sensor reactor approach: I--Sensor reactor system

A novel Sensor Reactor technology is presented which permits 13C labeling experiments for metabolic flux analysis during large-scale, semi-industrial, (fed-) batch fermentation processes deriving a series of flux maps that document fermentation courses in detail. The small-scale Sensor Reactor can be inoculated within 1.50-1.20s via a special inoculation unit with an inoculation volume accuracy of 1.025+/-0.021 L. The large-scale production reactor (here: 300 L) and the Sensor Reactor were run in parallel master/slave modes to control the current pH, temperature, pressure and dissolved oxygen values as changing set points for the Sensor Reactor. Using an automated pulsing technology, glucose pulses of 5 g/L could be realized within 0.51 s. The similarity of fermentations in the Sensor Reactor with the production process was demonstrated by studying L-lysine production with C. glutamicum during multiple, 'simulated' labeling experiments each lasting 2.5h. 'Real' labeling experiments are presented in Part II.     

Self-referencing optrodes for measuring spatially resolved, real-time metabolic oxygen flux in plant systems

The ability to non-invasively measure metabolic oxygen flux is a very important tool for physiologists interested in a variety of questions ranging from basic metabolism, growth/development, and stress adaptation. Technologies for measuring oxygen concentration near the surface of cells/tissues include electrochemical and optical techniques. A wealth of knowledge was gained using these tools for quantifying real-time physiology. Fiber-optic microprobes (optrodes) have recently been developed for measuring oxygen in a variety of biomedical and environmental applications. We have adopted the use of these optical microsensors for plant physiology applications, and used the microsensors in an advanced sensing modality known as self-referencing. Self-referencing is a non-invasive microsensor technique used for measuring real-time flux of analytes. This paper demonstrates the use of optical microsensors for non-invasively measuring rhizosphere oxygen flux associated with respiration in plant roots, as well as boundary layer oxygen flux in phytoplankton mats. Highly sensitive/selective optrodes had little to no hysteresis/calibration drift during experimentation, and an extremely high signal-to-noise ratio. We have used this new tool to compare various aspects of rhizosphere oxygen flux for roots of Glycine max, Zea mays, and Phaseolus vulgaris, and also mapped developmentally relevant profiles and distinct temporal patterns. We also characterized real-time respiratory patterns during inhibition of cytochrome and alternative oxidase pathways via pharmacology. Boundary layer oxygen flux was also measured for a phytoplankton mat during dark:light cycling and exposure to pharamacological inhibitors. This highly sensitive technology enables non-invasive study of oxygen transport in plant systems under physiologically relevant conditions.     

Interpreting diel hysteresis between soil respiration and temperature

Increasing use of automated soil respiration chambers in recent years has demonstrated complex diel relationships between soil respiration and temperature that are not apparent from less frequent measurements. Soil surface flux is often lagged from soil temperature by several hours, which results in semielliptical hysteresis loops when surface flux is plotted as a function of soil temperature. Both biological and physical explanations have been suggested for hysteresis patterns, and there is currently no consensus on their causes or how such data should be analyzed to interpret the sensitivity of respiration to temperature. We used a one‐dimensional soil CO₂ and heat transport model based on physical first principles to demonstrate a theoretical basis for lags between surface flux and soil temperatures. Using numerical simulations, we demonstrated that diel phase lags between surface flux and soil temperature can result from heat and CO₂ transport processes alone. While factors other than temperature that vary on a diel basis, such as carbon substrate supply and atmospheric CO₂ concentration, can additionally alter lag times and hysteresis patterns to varying degrees, physical transport processes alone are sufficient to create hysteresis. Therefore, the existence of hysteresis does not necessarily indicate soil respiration is influenced by photosynthetic carbon supply. We also demonstrated how lags can cause errors in Q₁₀ values calculated from regressions of surface flux and soil temperature measured at a single depth. Furthermore, synchronizing surface flux and soil temperature to account for transport‐related lags generally does not improve Q₁₀ estimation. In order to calculate the sensitivity of soil respiration to temperature, we suggest using approaches that account for the gradients in temperature and production existing within the soil. We conclude that consideration of heat and CO₂ transport processes is a requirement to correctly interpret diel soil respiration patterns.     

基于区域剖分算法的土壤碳通量空间采样策略

由于土壤碳通量在空间分布上具有很强的异质性,传统的采样方法难以对区域土壤碳通量进行精确估算,因此确定适当的采样策略对区域土壤碳通量的估算具有重要意义.本文提出一种逐点递增式采样的区域剖分部署策略(RDPG):设定初始采样点,使用改进的凸包插值算法构造Delaunay三角网,根据邻近已知采样点插值计算三角形各边垂直平分线的交点的离散度,选择离散度最大的点作为新增采样点.采用该方法对变异系数为0.42～0.59的仿真试验区域进行多次试验,结果表明:在相同试验条件下,RDPG布局策略能够获得比随机采样和均匀采样策略更高的区域土壤碳通量估算准确度.RDPG方法考虑了区域土壤碳通量的空间异质性,提高了区域土壤碳通量拟合精度.     

Effect of non-Newtonian and pulsatile blood flow on mass transport in the human aorta

To investigate the effects of both non-Newtonian behavior and the pulsation of blood flow on the distributions of luminal surface LDL concentration and oxygen flux along the wall of the human aorta, we numerically compared a non-Newtonian model with the Newtonian one under both steady flow and in vivo pulsatile flow conditions using a human aorta model constructed from MRI images. The results showed that under steady flow conditions, although the shear thinning non-Newtonian nature of blood could elevate wall shear stress (WSS) in most regions of the aorta, especially areas with low WSS, it had little effect on luminal surface LDL concentration (c(w)) in most regions of the aorta. Nevertheless, it could significantly enhance c(w) in areas with high luminal surface LDL concentration through the shear dependent diffusivity of LDLs. For oxygen transport, the shear thinning non-Newtonian nature of blood could slightly reduce oxygen flux in most regions of the aorta, but this effect became much more apparent in areas with already low oxygen flux. The pulsation of blood flow could significantly reduce c(w) and enhance oxygen flux in these disturbed places. In most other regions of the aorta, the oxygen flux was also significantly higher than that for the steady flow simulation. In conclusion, the shear shining non-Newtonian nature of blood has little effect on LDL and oxygen transport in most regions of the aorta, but in the atherogenic-prone areas where luminal surface LDL concentration is high and oxygen flux is low, its effect is apparent. Similar is for the effect of pulsatile flow on the transport of LDLs. But, the pulsation of blood flow can apparently affect oxygen flux in the aorta, especially in areas with low oxygen flux.     

Enhancing the Potential for in situ Bioremediation of RDX Contaminated Soil from a Former Military Demolition Range

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a toxic, mobile groundwater contaminant common to military sites. Biodegradation of RDX is an alternative, cost effective and environmentally friendly remediation approach. The effects of carbon amendments (waste glycerol and cheese whey) used alone or with a potential electron shuttle (ammonium lignosulfonate) on RDX biodegradation were assessed. These substrates are readily available waste materials that can be used as nutrients to promote oxygen consumption, creating a more reducing environment. Nutrient amended batch assays were conducted using RDX spiked contaminated demolition range soil under anaerobic conditions. The amendments that improved RDX mineralization the most were subsequently tested in a scaled up repacked soil column study to verify if this strategy could be effectively implemented on-site. Microcosm results indicated that RDX mineralization by indigenous anaerobic microorganisms was enhanced the most by the low carbon amendment concentration. The use of ammonium lignosulfonate was not effective, exhibiting an inhibitory effect on RDX biodegradation that was stronger at higher concentrations. The soil column study showed that the low concentration of waste was the most promising treatment scenario. These results offer good prospects for the use of waste glycerol for in situ treatment of soils contaminated with energetic-materials, such as RDX.     

基于湿度分布特征的小尺度土壤碳通量空间采样策略

由于土壤碳通量的空间异质性很强,传统的随机抽样方法无法对区域土壤碳通量进行准确估算,而多点采样需耗费大量的人力及设备成本,因此确定适当的采样点数量及分布策略对于区域土壤碳通量的测算非常重要。提出一种基于湿度空间分布特征的小尺度土壤碳通量空间采样策略:首先利用无线传感网密集测量区域的土壤湿度,根据湿度数据的空间分布特征划分监测区域,通过Hammond Mc Cullagh方程计算各子区域内的最优采样点数量,最终确定整个监测区域的空间采样点部署策略。提出的方法考虑了各子区域间土壤碳通量空间分布的差异,使得采样点的部署位置与土壤碳通量的分布具有较好的相关性。研究结果证明:土壤碳通量部署策略能够获得比均匀部署策略、随机部署策略更高的区域土壤碳通量估算准确度。     

Regional analysis of soil–atmosphere nitrous oxide emissions in the Northern Atlantic Zone of Costa Rica

Regional analysis of greenhouse gas emissions is becoming increasingly important in answering questions related to environmental change, and typically employs a Geographic Information System (GIS) linked with a process‐based simulation model. For the Northern Atlantic Zone (NAZ) in Costa Rica (281 649 ha), a regional analysis of soil–atmosphere nitrous oxide fluxes from the dominant land‐use types forest, cattle pastures, and banana plantations was performed with both deterministic and stochastic variable representations. The stochastic representation accounted for soil and land management variability across nongeoreferenced fields within 1572 georeferenced land units in 13 relevant classes. Per class, frequency distributions of field‐scale fluxes were simulated with a process‐based model and Monte Carlo methods. Stochastic incorporation of both soil and land use variability resulted in areal (i.e. land unit‐scale) fluxes that were 14–22% lower than estimates based on averaged inputs. Soil heterogeneity was dominant. In addition, spatial flux patterns for current (1992) land use and two alternative land‐use scenarios were evaluated using stochastic inputs. With current management, the regional nitrous oxide‐N flux (standard deviation in parentheses) from agricultural land was 0.43 (0.13) Gg y^?1. Replacing natural grasses with mixtures of grasses and N‐fixing species on relevant soil types and introducing different forms of banana plantation management (alternative I) increased the regional flux by 51% to 0.65 (0.22) Gg y^?1. When all natural grasses were replaced by fertilized improved species and allowing different forms of banana plantation management (alternative II), the regional flux increased by 126% to 0.97 (0.68) Gg y^?1. Using the revised IPCC methodology, the 1992 nitrous oxide emission from agriculture in the NAZ was estimated to be 0.32 Gg y^?1. Due to formidable data requirements, regional analysis may not easily be used to produce country‐level estimates. However, regional analysis does provide a valuable benchmark against which the more straightforward IPCC methodology can be evaluated.     

Performance of an anaerobic membrane bioreactor in which granular sludge and dynamic filtration are integrated

To alleviate the fouling of a filter, simple substrates, dynamic filtration, and granular sludge were applied in an anaerobic membrane bioreactor (AnMBR). The results showed that under a transmembrane pressure < 20 kPa, the filter flux ranged between 15 and 20 l (m^?2 h)^?1 for a period of 30 days. The flux was higher than the typical flux of AnMBRs with conventional membranes and most current dynamic filters. In addition, the low cost of the filter avoided the need for a higher flux. Moreover, a stable granular sludge bed, which consumed all volatile fatty acids, was maintained. A compact fouling/filtration layer formed on the filter, which contributed to low effluent chemical oxygen demand concentrations and turbidity. In addition, substrate scarcity in the filtration zone resulted in the evolution of diverse bacteria on the filter.