Imaging plant responses to water deficit using electrical resistivity tomography

Background and aims

Monitoring root water uptake dynamics under water deficit (WD) conditions in fields are crucial to assess plant drought tolerance. In this study, we investigate the ability of Electrical Resistivity Tomography (ERT) to capture specific soil water depletion induced by root water uptake.

Methods

A combination of surface and depth electrodes with a high spatial resolution (10 cm) was used to map 2-D changes of bulk soil electrical conductivity (EC) in an agronomic trial with different herbaceous species. A synthetic experiment was performed with a mechanistic model to assess the ability of the electrode configuration to discriminate abstraction patterns due to roots. The impact of root segments was incorporated in the forward electrical model using the power-law mixing model.

Results

The time-lapse analysis of the synthetic ERT experiment shows that different root water uptake patterns can be delineated for measurements collected under WD conditions but not under wet conditions. Three indices were found (depletion amount, maximum depth, and spread), which allow capturing plant-specific water signatures based moisture profile changes derived from EC profiles. When root electrical properties were incorporated in the synthetic experiments, it led to the wrong estimation of the amount of water depletion, but a correct ranking of plants depletion depth. When applied to the filed data, our indices showed that Cocksfoot and Ryegrass had shallower soil water depletion zones than white clover and white clover combined with Ryegrass. However, in terms of water depletion amount, Cocksfoot consumed the largest amount of water, followed by White Clover, Ryegrass+White Clover mixture, and Ryegrass.

Conclusion

ERT is a well-suited method for phenotyping root water uptake ability in field trials under WD conditions.

     

Correction to: Imaging plant responses to water deficit using electrical resistivity tomography

Plant and Soil - Soil microorganisms play an important role in biogeochemical cycles in terrestrial ecosystems. Increasing nitrogen (N) and phosphorus (P) deposition are likely to regulate...     

Correction to: Imaging plant responses to water deficit using electrical resistivity tomography

Plant and Soil - The original version of this article unfortunately contained a mistake. The authors would like to add Andreas Kemna as the fifth author of this paper. The updated list of authors...     

Assessing land cover change in Kenya's Mau Forest region using remotely sensed data

Kenya's Rift Valley has been undergoing rapid land cover change for the past two decades, which has resulted in ecological and hydrological changes. An effort is under way to quantify the timing and rate of these changes in and around the River Njoro watershed located near the towns of Njoro and Nakuru using remote sensing and geographic information system (GIS) methods. Three Landsat TM images, representing a 17‐year period from 1986 to 2003 in which the area underwent a significant land cover transition, were classified and compared with one another. Vegetation diversity and temporal variability, common to tropical and sub‐tropical areas, posed several challenges in disaggregating classified data into sub‐classes. An iterative approach for the resolving challenges is presented that incorporates unsupervised and supervised classification routines in coordination with knowledge‐based spatial analyses. Changes are analysed at three spatial scales ranging from the highly impacted and deforested uplands to the watershed and landscape scales. Land cover transitions primarily occurred after 1995, and included large forest losses coupled with increases in mixed small‐scale agriculture and managed pastures and degraded areas. These changes in cover type are highly spatially variable and are theorized to have significant impacts on ecological and hydrologic systems with implications for environmental sustainability.     

Assessing and improving the green performance using a compound approach

This study presents a compound approach with a five-phase process to assess and improve the green performance. Based on the Six Sigma approach, the five-phase process consists of definition, measurement, analysis, improvement and control (DMAIC) phases. During the first three phases, an evaluation the assessment model is developed based on the analytical hierarchy process. Particle swarm optimization is also performed to search for the sequence of actions in order to improve the green performance based on the output of the assessment model. Managers can monitor the progress of the improvement plan during the control phase. A case study involving two global footwear manufacturers demonstrate the effectiveness of the proposed approach.     

电阻率成像法在树干水分吸收过程研究中的应用

将地球物理学中广泛运用的电阻率成像法成功地运用于树干内部截面电阻率分布特性的监测,利用电阻率平面分布图来分析树干内水分的空间分布和动态变化特征。结果表明：截面内树干水分的含量具有从核心部沿径向向外逐渐递增的趋势;位置较高的截面比较低的截面具有更多的水分含量,但充足的水分补给能打破这种水分分布的规律性,靠近补给源的截面含水率上升幅度最高;即使是在水分补给充足的情况下,树干内水分的吸收并不是面状饱和推进的过程,而是存在着优先纵向流动的生理机制;利用电阻率的变化,可以实现水分在截面上的优势流的定位。     

Quantitative evaluation of the performance of different electrical tomography devices.

Two widely used electrical tomography systems, the Sheffield Mark I and the DAS-01P, were quantitatively evaluated and compared to the newly developed Goe-MF system. The performance was quantified using a hardware phantom which closely matches the real input and transfer impedances of the human thorax and allows measurements equivalent to different states of lung inflation. Our results demonstrate that adequate averaging is necessary for noise reduction for the Mark I and especially for the DAS-01P system to get meaningful results even in visualizing maximal respiratory manoeuvres. The Goe-MF system showed a notably improved signal-to-noise ratio which allows also dynamic measurements at low levels of lung volume changes, e.g., in intensive care lung injury patients.     

Assessing simulated land use/cover maps using similarity and fragmentation indices

Land use/cover changes (LUCC) are significant to a range of issues central to the study of global environmental change. Over the last decades, a variety of models of LUCC have been developed to predict the location and patterns of land use/cover dynamics. The simulation procedures of most computational LUCC models can be sub-divided into three basic steps: (1) a non-spatial procedure which calculates the quantity of each transition; (2) a spatial procedure that allocates changes to the more likely locations and eventually replicates the patterns of the landscape and; (3) an evaluation procedure to compare a simulated land use/cover map with the true map for the same date. Most of the evaluation techniques are focused on assessing the location of the simulated changes in comparison to the true locations and do not assess the ability of the model to simulate the overall landscape pattern (e.g. size, shape and distribution of patches). This study aims at evaluating simulated land use/cover map patterns obtained using two models (DINAMICA and Land Change Modeler). Simulated maps were evaluated using a fuzzy similarity index which takes into account the fuzziness of locations within a cell neighborhood with fragmentation indices. Results show that more realistic simulated landscapes are often obtained at the expense of the location coincidence. When aggregate patterns of a landscape are important (e.g. when considering fragmentation impacts on biodiversity), it is important to incorporate indices that take into account not merely location, but also the spatial patterns during the model assessment procedure.     

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

Saving water for crop production is an old, but ongoing, challenge which requires a better understanding of the in situ functioning of root systems. In particular, this requires a better quantification and understanding of the spatial and temporal variability of the root water uptake at the field scale. Electrical Resistivity Tomography (ERT) is a non-destructive soil imaging technique, related to water content, which could help in spatializing active zones of water uptake. In this article, we evaluate ERT as an alternative method for quantifying and spatializing root water uptake at the field scale. To this aim, an experimental field study with maize and sorghum submitted to different water supply levels (Fully, Moderately or Poorly Irrigated treatments—FI, MI, PI zones) was conducted for 3 months with concomitant conventional, local, water balance measurements and 2D ERT imaging. ERT images showed an heterogeneous depletion of soil water by the crops, particularly, in the MI and PI zones with patches of high/low electrical resistivity (and thus water content) variations. This heterogeneity was greatest in the MI zone and points to spatial variations in rooting pattern and/or root efficiency. The 5-days difference in electrical resistivity could be quantitatively related to root uptake in the surface layer (down to 60 cm) but the relationship depends on the mean soil water content. At greater soil depth, in the water stressed zones, the water extraction front progressing downwards could not be assessed with the ERT surface setting used in this study. As a conclusion, ERT can be a useful, unique, technique for monitoring and estimating field water uptake by plant roots and its variability if combined water content measurements are available for in situ calibration and if the sensitivity/resolution of the technique is improved for estimation over the whole root zone.     

Diversity and activity of methanotrophs in landfill cover soils with and without landfill gas recovery systems

Aerobic CH₄ oxidation plays an important role in mitigating CH₄ release from landfills to the atmosphere. Therefore, in this study, oxidation activity and community of methanotrophs were investigated in a subtropical landfill. Among the three sites investigated, the highest CH₄ concentration was detected in the landfill cover soil of the site (A) without a landfill gas (LFG) recovery system, although the refuse in the site had been deposited for a longer time (∼14–15 years) compared to the other two sites (∼6–11 years) where a LFG recovery system was applied. In April and September, the higher CH₄ flux was detected in site A with 72.4 and 51.7 g m⁻² d⁻¹, respectively, compared to the other sites. The abundance of methanotrophs assessed by quantification of pmoA varied with location and season. A linear relationship was observed between the abundance of methanotrophs and CH₄ concentrations in the landfill cover soils (R = 0.827, P < 0.001). The key factors influencing the methanotrophic diversity in the landfill cover soils were pH, the water content and the CH₄ concentration in the soil, of which pH was the most important factor. Type I methanotrophs, including Methylococcus, Methylosarcina, Methylomicrobium and Methylobacter, and type II methanotrophs (Methylocystis) were all detected in the landfill cover soils, with Methylocystis and Methylosarcina being the dominant genera. Methylocystis was abundant in the slightly acidic landfill cover soil, especially in September, and represented more than 89% of the total terminal-restriction fragment abundance. These findings indicated that the LFG recovery system, as well as physical and chemical parameters, affected the diversity and activity of methanotrophs in landfill cover soils.     

An influence of methane concentration on the methanotrophic activity of a model landfill cover

Evaluation of kinetic parameters of methane oxidation under various conditions, on the basis of an analysis of the literature and the authors’ own laboratory research, is presented. Variation in methanotrophic activity in the profile of a simulated landfill cover was observed. The greatest activity was found at a depth of 60 cm. A low affinity (1/K_M) and high potential activity (V_max) were observed. V_max values ranged from 0.11 × 10⁻³ to 0.86 × 10⁻³ units. The values of K_M ranged from 0.6 to 2.9% of CH₄ (v/v).     

An assessment of the performance of a resistivity fish counter

Closed-circuit television was used to provide a visual record of the events associated with the counts recorded by a resistivity fish counter. The fish seen were classified as' large'fish > 50 cm length and' small'fish of < 50 cm. Some of the' large' fish escaped detection by the counter, some' small'fish were counted and some counts were registered when nothing was seen. The sensitivity of the counter varied inversely with water conductivity which varied inversely with discharge.
Evidence was obtained suggesting that fish ascending a weir tend to swim closer to the bottom than do those descending. It was found that fish tended to move upstream just after sunset and downstream just before sunrise except when the water was turbid and when the fish were very close to spawning. The numbers of fish movements recorded increased during those periods when discharge was decreasing after a spate but when spawning activity was at its peak, increased activity occurred in the complete absence of any change in discharge. Instances of the same fish re-crossing the counting zone several times were recorded and the simultaneous passage of more than one fish through the counting zone was observed.     

Assessing the performance of DNA barcoding using posterior predictive simulations

Accurate estimates of biodiversity are required for research in a broad array of biological subdisciplines including ecology, evolution, systematics, conservation and biodiversity science. The use of statistical models and genetic data, particularly DNA barcoding, has been suggested as an important tool for remedying the large gaps in our current understanding of biodiversity. However, the reliability of biodiversity estimates obtained using these approaches depends on how well the statistical models that are used describe the evolutionary process underlying the genetic data. In this study, we utilize data from the Barcode of Life Database and posterior predictive simulations to assess the performance of DNA barcoding under commonly used substitution models. We demonstrate that the success of DNA barcoding varies widely across DNA substitution models and that model choice has a substantial impact on the number of operational taxonomic units identified (changing results by ~4–31%). Additionally, we demonstrate that the widely followed practice of a priori assuming the Kimura 2‐parameter model for DNA barcoding is statistically unjustified and should be avoided. Using both data‐based and inference‐based test statistics, we detect variation in model performance across taxonomic groups, clustering algorithms, genetic divergence thresholds and substitution models. Taken together, these results illustrate the importance of considering both model selection and model adequacy in studies quantifying biodiversity.     

Assessing river ecological quality using benthic macroinvertebrates in the Hindu Kush-Himalayan region

We developed a system for the assessment of ecological condition for rivers in the lower mountains and lowlands of the Hindu Kush-Himalayan region (Pakistan, India, Nepal, Bhutan, and Bangladesh). We used benthic invertebrates collected from 198 rivers, located in five different ecoregions and covering degradation gradients; samples were taken twice (pre-monsoon and post-monsoon) applying a multi-habitat sampling procedure. Out of 38 environmental parameters, we constructed complex principal component analysis (PCA) gradients, separately for the stressors organic pollution, eutrophication, floodplain land use, and hydromorphological degradation. Correlation analysis between invertebrate metrics and environmental parameters revealed those biological metrics that are most responsive to river deterioration. Redundant metrics were deleted, and the most robust metrics were selected. The range of the index values under reference conditions was defined, and a five-class river quality system was generated.     

典型功能层带-填埋场覆盖层中四氯化碳代谢机制及功能微生态响应

垃圾填埋场是四氯化碳(carbon tetrachloride, CT)污染的重要来源,明晰覆盖层功能层带中CT的转化机制对其污染控制尤为重要。本研究通过构建模拟覆盖层系统,开展了CT沿程生物降解及微生态研究。覆盖层理化特性分析表明,长期生物氧化使覆盖层形成了稳定存在的厌氧层(>45 cm)、缺氧层(15–45 cm)和好氧层(0–15 cm)功能层带,各特征层带氧化还原电位、微生物群落结构差异显著,为CT降解提供了生物资源和有利条件。降解结果显示,CT在厌氧层和缺氧层脱氯产生氯仿(chloroform,CF)和二氯甲烷(dichloromethane,DCM)及氯离子(Cl–),副产物在30 cm处浓度最大,好氧层中CF和DCM迅速发生好氧降解;CT降解速率为13.2–103.6μg/(m2·d),随填埋气通量增大而增大。多样性测序结果表明,不同层带功能菌属差异显著,中慢生根瘤菌(Mesorhizobium)为好氧层CT潜在降解菌属,硫杆菌(Thiobacillus)和间孢囊菌(Intrasporangium)为厌氧层和缺氧层潜在功能菌属;覆盖土中6种脱氯菌属和18种甲烷氧化菌...     

Feasibility of ley-farming system performance in a semi-arid region using spatial analysis

In order to assess feasibility of ley farming system performance in the Aq-Qala township, a semi-arid region in north of Iran, Multi-Criteria Analysis (MCA) method and Geographic Information System (GIS) techniques were integrated to evaluate the suitability of wheat, barley and annual alfalfa cultivation. The agronomic and ecological requirements of three crops were identified from available scientific literatures. In this study, environmental variables were included: 1) average, minimum and maximum temperatures, 2) precipitation, 3) slope, 4) slope aspects, 5) elevation and 6) soil characteristics such as organic matter, pH, electrical conductivity (EC), texture, nitrogen, phosphorus, potassium, calcium, iron, and zinc. Weights of these variables were extracted from analysis of Analytical Hierarchy Process (AHP) questionnaires. The suitability analysis was based on matching between land qualities/characteristics and crop requirements. It was done by the weighted overlay technique (WOT) in GIS. In order to assess the land suitability of ley farming system performance, the digital suitability layers of three crops were overlaid and integrated in GIS media by raster calculator functions, then zoning of region was done in 4 classes, including: Highly suitable, moderately suitable, marginally suitable and non-suitable. Our results indicated that 35.1% (35495.20 ha) of total areas of studied region is suitable for ley farming system. According to the generated agricultural suitability map, it was determinate that 15.2% (20681.77 ha) of the region is non-suitable for ley-farming performance, 19.5% (23245.74 ha) is marginally suitable and, 30.2% (33725.60 ha) is moderately suitable. Highly suitable, moderately suitable and marginally suitable lands were expected to have a crop yield of 80–100%, 60–80% and 40–60% of the yield under optimal conditions with practicable and economic inputs, respectively. It was found that the most areas of the southern and central parts of Aq-Qala are the highly and moderately suitable regions. The results demonstrated that the high EC, low OM and low rainfall are the key limiting factors in non-suitable areas.     

Characterization of methane oxidation by a methanotroph isolated from a landfill cover soil, South Korea

A methane-oxidizing bacterium was isolated from the enriched culture of a landfill cover soil. The closest relative of the isolate, designated M6, is Methylocystis sp. Based on a kinetic analysis, the maximum specific methane oxidation rate and saturation constant were 4.93 mmol·g--dry cell weight--1·h?1 and 23 microM, respectively. This was the first time a kinetic analysis was performed using pure methanotrophic culture. The methane oxidation by M6 was investigated in the presence of aromatic (m- and p-xylene and ethylbenzene) or sulfur (hydrogen sulfide, dimethyl sulfide, methanthiol) compounds. The methane oxidation was inhibited by the presence of aromatic or sulfur compounds.     

基于像元三分模型的锡林郭勒草原光合植被和非光合植被覆盖度估算

定量的估算草原光合植被覆盖度(f_(PV))和非光合植被覆盖度(f_(NPV))对草原畜牧业和土地荒漠化具有重要的意义。以锡林郭勒盟西乌珠穆沁旗为研究区,以MODIS 500 m分辨率地表反射率产品MOD09GHK为数据源,采用干枯燃料指数(DFI)指数构建NDVI-DFI像元三分模型估算了锡林郭勒草原的fPV和f_(NPV),并分析了锡林郭勒草原fPV和f_(NPV)的动态变化。研究结果表明:锡林郭勒草原NDVI-DFI特征空间表现为三角形,与理论上的概念模型基本一致,符合像元三分模型的基本假设;NDVI-DFI像元三分模型适用于对草原黄枯期_(NPV)的监测,对草原生长期_(NPV)监测并不十分敏感;利用NDVI-DFI像元三分模型估算的fPV和f_(NPV)动态变化与牧草物候发育特征相吻合,可以有效的估算典型草原地区fPV和f_(NPV)值,进一步将其应用于长时间序列的典型草原fPV和f_(NPV)动态变化分析。     

Assessing the benefits of focal pair cryo-electron tomography

Cryo electron tomography provides nanometer-scale information on biological matter preserved in a close-to native state. The resolution of tomograms and structures resolved by sub-tomogram averaging is typically limited by the contrast transfer function of the electron microscope, which is especially critical for thick samples. Here, we report a method to increase the attainable resolution by recording tomographic 'focal pairs', which are pairs of tilt series of the same object acquired in complementary defocus conditions. Low defocus imaging provides high resolution at low contrast, while high defocus imaging yields high contrast at the price of limited resolution. Quantitative assessment of the quality of lipid bilayer reconstructions in the resulting tomograms demonstrates stable resolution preservation beyond 3 nm for cells thicker than 500 nm. Further, in computational simulations on synthetic datasets we show the applicability of the method to sub-tomogram averaging, demonstrating its potential for achieving higher resolution.