Background and aims Although Si is recognized as a beneficial element for crops, the determination of plant-available silicon (PAS) in soils has become challenging. A correlation between pH and PAS ...indicators has been reported in the literature due to the higher degree of weathering of acidic soil. We tested this hypothesis in the cultivated rice fields of Karnataka State, India, which exhibit gradients of pH and climate. Method Two hundred surface soil samples were collected from rice fields representing nine of the ten agroclimatic zones (ACZs) defined for Karnataka. We analyzed the Si extracted by calcium chloride (SiCC) and the Si extracted by acetate-acetic acid (SiAA) as PAS indicators. The samples were analyzed for particle size distribution, pH, electrical conductivity and cation exchange capacity. Forty subsamples were selected for mineralogical and chemical analysis. Results PCA of the 200 samples showed that PAS indicators and pH were positively correlated. SiAA was also positively correlated with electric conductivity (EC), CEC, and the silt fraction and negatively correlated with the sand fraction. A separation of the data arbitrarily made at pH 7.5 showed that below 7.5, the correlation between PAS indicators and pH was better than considering the whole 200 samples. The distribution of SiAA with pH matched the curve of adsorbed Si given in the literature. Soils characterized by low pH and high contents of sand, SiO2, Zr and Hf, showed a higher degree of weathering. They were preferentially located along the coast, where the rainfall is the most abundant. The depletion of PAS indicators was also in good agreement with the predominance of kaolinite instead of smectite, which characterizes a higher degree of desilication. Conclusion We demonstrated that the correlation between pH and PAS indicators is explained by natural Si depletion (weathering intensity) and the effect of Si adsorption. We suggest that at pH values up to 7.5, pH can be used as a proxy for PAS in similar types of pedoclimatic conditions.
Purpose
High‐dose rate (HDR) and pulsed‐dose rate (PDR) brachytherapy would benefit from an independent treatment verification system to monitor treatment delivery and to detect errors in real time. ...This paper characterizes and provides an uncertainty budget for a detector based on a fiber‐coupled high‐Z inorganic scintillator capable of performing time‐resolved in vivo dosimetry during HDR and PDR brachytherapy.
Method
The detector was composed of a detector probe and an optical reader. The detector probe consisted of either a 0.5 × 0.4 × 0.4 mm3 (HDR) or a 1.0 × 0.4 × 0.4 mm3 (PDR) cuboid ZnSe:O crystal glued onto an optical‐fiber cable. The outer diameter of the detector probes was 1 mm, and fit inside standard brachytherapy catheters. The signal from the detector probe was read out at 20 Hz by a photodiode and a data acquisition device inside the optical reader. In order to construct an uncertainty budget for the detector, six characteristics were determined: (1) temperature dependence of the detector probe, (2) energy dependence as a function of the probe‐to‐source position in 2D (determined with 2 mm resolution using a robotic arm), (3) the signal‐to‐noise ratio (SNR), (4) short‐term stability over 8 h, and (5) long‐term stability of three optical readers and four probes used for in vivo monitoring in HDR and PDR treatments over 21 months (196 treatments and 189 detector calibrations, and (6) dose‐rate dependence.
Results
The total uncertainty of the detector at a 20 mm probe‐to‐source distance was < 5.1% and < 5.8% for the HDR and PDR versions, respectively. Regarding the above characteristics, (1) the sensitivity of the detector decreased by an average of 1.4%/°C for detector probe temperatures varying from 22 to 37°C; (2) the energy dependence of the detector was nonlinear and depended on both probe‐to‐source distance and the angle between the probe and the brachytherapy source; (3) the median SNRs were 187 and 34 at a 20 mm probe‐to‐source distance for the HDR and PDR versions, respectively (corresponding median source activities of 4.8 and 0.56 Ci, respectively); (4) the detector response varied by 0.6% in 11 identical irradiations over 8 h; (5) the sensitivity of the four detector probes decreased systematically by 0–1.2%/100 Gy of dose delivered to the probes, and random fluctuations of 4.8% in the sensitivity were observed for the three probes used in PDR and 1.9% for the probe used in HDR; and (6) the detector response was linear with dose rate.
Conclusion
ZnSe:O detectors can be used effectively for in vivo dosimetry and with high accuracy for HDR and PDR brachytherapy applications.
In order to better understand the reactivity of plant phytoliths in soil solutions, we determined the solubility, surface properties (electrophoretic mobilities and surface charge) and dissolution ...kinetics of phytoliths extracted from fresh biomass of representative plant species (larch tree and elm, horsetail, fern, and four grasses) containing significant amount of biogenic silica. The solubility product of larch, horsetail, elm and fern phytoliths is close to that of amorphous silica and soil bamboo phytoliths. Electrophoretic measurements yield isoelectric point pH
IEP
=
0.9, 1.1, 2.0 and 2.2 for four grasses, elm, larch and horsetail phytoliths respectively, which is very close to that of quartz or amorphous silica. Surface acid–base titrations allowed generation of a 2-pK surface complexation model (SCM) for larch, elm and horsetail phytoliths. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 1
≤
pH
≤
8, were found to be very similar among the species, and close to those of soil bamboo phytoliths. Mechanistic treatment of all plant phytoliths dissolution rates provided three-parameters equation sufficient to describe phytoliths reactivity in aqueous solutions:
R
(
mol
/
cm
2
/
s
)
=
6
⋅
10
−
16
⋅
a
H+
+
5.0
⋅
10
−
18
+
3.5
⋅
10
−
13
⋅
a
OH
−
0.33
Alternatively, the dissolution rate dependence on pH can be modeled within the concept of surface coordination theory assuming the rate proportional to concentration of >
SiOH
2
+, >
SiOH
0 and >
SiO
− species. In the range of Al concentration from 20 to 5000 ppm in the phytoliths, we have not observed any correlation between their Al content and solubility, surface acid–base properties and dissolution kinetics.
It follows from the results of this study that phytoliths dissolution rates exhibit a minimum at pH ∼
3. Mass-normalized dissolution rates are similar among all four types of plant species studied and these rates are an order of magnitude higher than those of typical soil clay minerals. The minimal half life time of larch and horsetail phytoliths in the interstitial soil solution ranges from 10–12 years at pH
=
2–3 to <
1 year at pH above 6, comparable with mean residence time of phytoliths in soil from natural observations.
The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this ...study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why.
Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for in situ analysis of phytoliths in leaves via X-ray imaging.
PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%.
Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.
Silicon (Si) is the most abundant element on the earth’s surface after oxygen. Si can be found in minerals, electronic chips, cosmetic products, and plants for instance. Here we review the Earth's ...terrestrial Si cycle, focussing on ecosystem services. We show that silicon can participate in the inherent and manageable properties involved in all ecosystem services. As records of the past, phytoliths can be useful parameters in cultural services. Si is involved in provisioning services because Si may influence the production of food and fibers. Si is also involved in regulating services because of Si involvement in carbon sequestration. Regulating and provisioning services may be improved through Si management, e.g. by application of Si to fertilize soils and plants.
In the Lower Mekong Basin, paddy fields often appear as mosaics, with soil mounds covered by trees or other plants in a spotty distribution. These soil mounds are commonly named termite ‘lenticular ...mounds’ because termite bioturbation is considered to be at their origin. Termite mounds host a large diversity of animals and plants, increasing landscape patchiness. Because the preservation of these islands of biodiversity is threatened by modern agricultural practices, the aim of this study was to quantify their abundance and the services they provide to the local population. The abundance of mounds and their use by the population were quantified in a catchment in Cambodia. We found that mounds density reached ~2 mounds ha−1. Interviews carried out within the catchment showed that most of the interviewees used mounds for increasing the fertility of their field and for the cultivation of rice and other plants (e.g. sponge gourd and pumpkin). In addition to their potential to increase plant productivity, the survey revealed that animals (rats and snakes), mushrooms and 13 plant species found on or in mounds were consumed by the population. In addition to potentially contributing to an increase in food diversity, mounds also impacted farmers' health by allowing access to 20 medicinal plant species and indirectly via a reduction in pesticide use. In conclusion, this study is the first attempt to quantify the large number of services provided by termite mounds in Cambodia. This increase in the knowledge of the diversity of environmental and socioeconomic services provided by termite mounds is likely to contribute to their preservation and provide a basis for the sustainable management of biodiversity in paddy fields in the Lower Mekong Basin region.
Amorphous silica (ASi) pool and fluxes have become parameters of a growing interest in the understanding of the biogeochemical cycle of Si and the modeling of anthropogenic impacts. Extraction by 1% ...Na2CO3 followed by a correction for crystalline Si (DeMaster, 1981) has recently become widely used and is proposed as the standard technique for quantifying amorphous silica (ASi) pools in soil and continental aquatic environments. However, the 1% Na2CO3 method was developed to quantify diatom frustules and not phytoliths (PhSi), which constitute the most common fraction of ASi in soils. The aim of this study was to assess the 1% Na2CO3 method for fresh and aged phytoliths. We founded a significant positive correlation between Si extracted by the 1% Na2CO3 method and Si extracted by other standard procedures (Guntzer et al., 2010) for various shoot samples (elm, horsetail, fern and larch). Because the Si shoot samples are mainly composed of phytoliths, we concluded that the 1% Na2CO3 method was well adapted for the determination of PhSi of fresh phytoliths containing less than 70mg Si g−1. To assess the 1% Na2CO3 method for PhSi of aged phytoliths, we used artificial mixtures of soil phytoliths from La Réunion (Meunier et al., 1999) and quartz. Our results showed that the 1% Na2CO3 method underestimated PhSi for aged phytoliths by a factor of 3.7. Combining the 1% Na2CO3 method and a physical method of extraction using samples of various origins showed a dispersion of the data that can be explained by a combination of several factors including loss during physical extraction and the presence of resistant phytoliths. In the absence of standard technique, we recommend to check the nature of the particles using physical extraction in combination with the 1% Na2CO3 in order to provide a more careful analysis of ASi.
•The 1% Na2CO3 method is able to quantify fresh phytoliths•Aged phytoliths are only partially dissolved by the 1% Na2CO3 method.•Physical extraction is a must to identify the proportion of phytoliths while the 1% Na2CO3 method can underestimate (up to a factor of 3.7) the ASi measurements
A Perceptual Measure for Deep Single Image Camera and Lens Calibration Hold-Geoffroy, Yannick; Piche-Meunier, Dominique; Sunkavalli, Kalyan ...
IEEE transactions on pattern analysis and machine intelligence,
2023-Sept.-1, 2023-Sep, 2023-9-1, 20230901, Letnik:
45, Številka:
9
Journal Article
Recenzirano
Image editing and compositing have become ubiquitous in entertainment, from digital art to AR and VR experiences. To produce beautiful composites, the camera needs to be geometrically calibrated, ...which can be tedious and requires a physical calibration target. In place of the traditional multi-image calibration process, we propose to infer the camera calibration parameters such as pitch, roll, field of view, and lens distortion directly from a single image using a deep convolutional neural network. We train this network using automatically generated samples from a large-scale panorama dataset, yielding competitive accuracy in terms of standard <inline-formula><tex-math notation="LaTeX">\ell ^{2}</tex-math> <mml:math><mml:msup><mml:mi>ℓ</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:math><inline-graphic xlink:href="holdgeoffroy-ieq1-3269641.gif"/> </inline-formula> error. However, we argue that minimizing such standard error metrics might not be optimal for many applications. In this work, we investigate human sensitivity to inaccuracies in geometric camera calibration. To this end, we conduct a large-scale human perception study where we ask participants to judge the realism of 3D objects composited with correct and biased camera calibration parameters. Based on this study, we develop a new perceptual measure for camera calibration and demonstrate that our deep calibration network outperforms previous single-image based calibration methods both on standard metrics as well as on this novel perceptual measure. Finally, we demonstrate the use of our calibration network for several applications, including virtual object insertion, image retrieval, and compositing.
Aims Most cereals accumulate Si in their shoots. Soil bioavailability of Si may be a constraint on the beneficial role of silica in cereals but it is not yet well supported by field data. The aim of ...this study is to evaluate the long-term impact of wheat straw exports on the pool of soil phytoliths, which, it is suggested, represents the most labile and renewable pool of soil Si. Methods We measured the amorphous Si (ASi) in soils from several experiments at Rothamsted Research (UK), which provided long-term soil data back to the middle of the 19th century, using two alternative extraction techniques: Na2CO3 (referred to as ASnc) or zinc bromide extraction (referred to as ASizb). Results All samples showed a similar range of ASnc and ASizb but low values (0.1–3.4 mg g−1 DW) compared to published data on natural ecosystems. In the Broadbalk experiment, a decrease over time in ASi in the topsoil samples is in good agreement with the hypothesis that cropping and exports of straw leads to depletion of soil phytoliths. A decrease in Si concentration in straw samples was observed between 1883 and 1944. From 1944 to the present, Si concentration increased irregularly in the straw, probably as the result of liming, which enhanced the dissolution of the remaining phytoliths through increasing pH. In the reforested Geescroft field the higher phytolith concentration in the modern topsoil samples is in good agreement with a re-building of phytolith storage from litter input in an acidic environment. Conclusions Our results therefore support the hypothesis that export of wheat straw leads to a decrease in bioavailable Si.
Benefits of plant silicon for crops: a review Guntzer, Flore; Keller, Catherine; Meunier, Jean-Dominique
Agronomy for sustainable development,
2012/1, Letnik:
32, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Since the beginning of the nineteenth century, silicon (Si) has been found in significant concentrations in plants. Despite the abundant literature which demonstrates its benefits in agriculture, Si ...is generally not considered as an essential element. The integration of Si in agricultural practices is, however, effective in a few countries. Silicon fertilization by natural silicates has the potential to mitigate environmental stresses and soil nutrient depletion and as a consequence is an alternative to the extensive use of phytosanitary and NPK fertilizers for maintaining sustainable agriculture. This review focuses on recent advances on the mechanisms of Si accumulation in plants and its behavior in soil. Seven among the ten most important crops are considered to be Si accumulators, with concentration of Si above 1% dry weight. New approaches using isotopes and genetics have highlighted the mechanisms of uptake and transfer of Si
in planta
. There is a general agreement on an uptake of dissolved silica as H
4
SiO
4
and precipitation as amorphous silica particles (the so-called phytoliths), but the mechanism, either active or passive, is still a matter of debate. The benefits of Si are well demonstrated when plants are exposed to abiotic and biotic stresses. The defense mechanisms provided by Si are far from being understood, but evidences for
ex planta
and
in planta
processes are given indicating multiple combined effects rather than one single effect. Phytoliths that are located mainly in shoots of monocots return to the soil through litterfall if the plants are not harvested and contribute to the biogeochemical cycle of Si. According to recent progress made on the understanding of the biogeochemical cycle of Si and the weathering process of silicate minerals, phytoliths may significantly contribute to the resupply of Si to plants. We suggest that straw of crops, which contains large amounts of phytoliths, should be recycled in order to limit the depletion of soil bioavailable Si.
PDF
