Search

Abstract: This work advances the evaluation and interpretation of the Photochemical Reflectance Index (PRI) as an indicator of water stress, over a range of canopy structures and pigment content levels. Very high resolution (VHR) narrow-band multispectral (10cm) and thermal (20cm) imagery was acquired diurnally, in four airborne campaigns conducted over an experimental vineyard site undergoing three different irrigation treatments. Field measurements of leaf stomatal conductance (Gs) and leaf water potential (Ψleaf) were acquired concurrently with the airborne campaigns and compared against the Crop Water Stress Index (CWSI), a widely accepted, thermal-based indicator of water stress, and against narrow-band multispectral indices calculated from pure-vegetation pixels. The study proposes a new formulation, a normalized PRI (PRInorm), in which the standard PRI index is normalized by an index that is sensitive to canopy structure (Renormalized Difference Vegetation Index, RDVI) and by a red edge index that is sensitive to chlorophyll content (R700/R670). The hypothesis investigated is that the new index, calculated as PRInorm =PRI/[RDVI·R700/R670], not only detects xanthophyll pigment changes as a function of water stress, but also normalizes for the chlorophyll content level and canopy leaf area reduction induced by stress. Results demonstrated that when comparing PRInorm against stomatal conductance (r2 =0.79; p<0.001) and leaf water potential (r2 =0.77; p<0.001) measured at midday, the new index performed better than the standard PRI (r2 =0.52 and 0.49, respectively). Further, when using the four flights conducted during the diurnal experiment, the relationships with stomatal conductance also showed the superior performance of PRInorm (r2 =0.68) as opposed to PRI (r2 =0.4). The proposed normalized PRI was highly related (r2 =0.75; p<0.001) to the thermal indicator of water stress, CWSI, which was used here as a benchmark. In comparison, the standard PRI index was found to be significantly related to CWSI (p<0.001), although the relationship was weaker (r2 =0.58) than that obtained for PRInorm. In summary, this study demonstrates that PRInorm isolated better than PRI the physiological changes against a changing background of altered pigments and structure, tracking more precisely the diurnal dynamics of the stomatal aperture. Simulations conducted, using leaf and canopy radiative transfer models to elucidate these results, showed that PRInorm is more linearly related to canopy pigment content than the standard PRI, and was more capable of differentiating between stress levels, providing better insight into the results of this diurnal study. [Copyright &y& Elsevier]

Copyright of Journal of Politics in Latin America is the property of Sage Publications Inc. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a sorting method based on cosine weighting to improve the anti-jitter ability of histogram algorithm in radar signal sorting. This method uses variable and superposed boxes, into which the collected radar pulses repetition interval (PRI) falls, and the histogram increment of these boxes are normalized weighted by cosine window smoothly. Each peak position of the histogram that exceeds threshold is the estimated PRI of radar. The histogram obtained by this method is smooth and the peak is clear. Furthermore, the sub-harmonic is well restrained. Experimental result shows that this method has good anti - jitter ability. [ABSTRACT FROM AUTHOR]

Recently declassified Mexican spy reports that tracked and analysed revolutionary guerrilla organisations during the 1960s and 1970s collectively form an archive of counterinsurgency. The archive produced knowledge on individuals and groups deemed subversive threats to the authoritarian rule of thePartido Revolucionario Institucional (PRI). This article examines one declassified spy report produced in late August 1972 after a peasant guerrilla movement in the south–western Mexican state of Guerrero surprisingly ambushed two military convoys. In proposing a series of counterinsurgent solutions to defeat the guerrillaEl Partido de los Pobres(The Party of the Poor, PDLP), this article argues that the document reveals an anxious state's need to restore balance to a political situation unexpectedly off balance. The document's main suggestion, targeting the insurrection's base of popular support, would form the core of the counterinsurgency waged by the PRI regime in Guerrero from 1972 to 1974. [ABSTRACT FROM PUBLISHER]

Background:Forests in subarctic regions inhabit the transitional zone between the temperate region and the Arctic, where plant survival depends on the capability of individuals to adjust to changing environments. This transitional zone, generally falling between 50° N and 70° N, is becoming increasingly vulnerable under a changing climate, with treelines moving further north and also higher up slopes. Aims:The current study was carried out at 68° N, the most sensitive zone of the subarctic and northern limit of tree growth in Finnish Lapland. The physiology of trees in these conditions is still not fully understood, and an attempt is made here to contribute to a better understanding of the functionality of leaves by studying the spectral characteristics of needles ofPinus sylvestrisalong an altitudinal transect. Methods:A variety of spectral indices derived from high-resolution reflectance spectra were measured on freshly excised pine needles. The specific hypothesis is that spectral reflectance data can detect the stress that pine needles suffer at high elevations. We also wish to know which of the several possible indices is most indicative of stress. Results:All of the spectral indices, with the exception of NDVI, showed elevational as well as age-related trends consistent with the hypothesis that needles from the highest elevation suffer degradation of chlorophyll. Conclusions:We conclude that appropriate reflectance measurements provide useful information that may in future be used to detect stress effects on conifer foliage. The visual appearance of trees included in the study did also reflect in their spectral characteristics. [ABSTRACT FROM PUBLISHER]

In this article, the author provides a well-balanced analysis of the Mexican electoral processes from 1976 to 2012. After revisting the recurrent end-of-term crisis during the pri regime, the author describes the different political strategies employed by Salinas, Zedillo, and Fox, explains the troublesome and uncertain 2006 presidential election, and concludes with an evaluation of the 2012 election. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the photochemical reflectance index (PRI) for assessing plant photosynthetic performance throughout the plant life cycle. The relationships between PRI, chlorophyll fluorescence parameters, and leaf pigment indices in Solanum melongena L. (aubergine; eggplant) were studied using photosynthetic induction curves both in short-term (diurnal) and long-term (seasonal) periods under different light intensities. We found good correlations between PRI/non-photochemical quenching (NPQ) and PRI/electron transport rate (ETR) in the short term at the same site of a single leaf but these relationships did not hold throughout the life of the plant. In general, changes in PRI owing to NPQ or ETR variations in the short term were <20 % of those that occurred with leaf aging. Results also showed that PRI was highly correlated to plant pigments, especially chlorophyll indices measured by spectral reflectance. Moreover, relationships of steady-state PRI/ETR and steady-state PRI/photochemical yield of photosystem II (Φ) measured at uniform light intensity at different life stages proved that overall photosynthesis capacity and steady-state PRI were better correlated through chlorophyll content than NPQ and xanthophylls. The calibrated PRI index accommodated these pigments effects and gave better correlation with NPQ and ETR than PRI. Further studies of PRI indices based on pigments other than xanthophylls, and studies on PRI mechanisms in different species are recommended. [ABSTRACT FROM AUTHOR]

The article presents a discussion on the opinions of Mexican philosopher Emilio Uranga surrounding the Mexican Revolution, utilizing various newspaper articles written by Uranga during 1960 and 1961. Analysis of Uranga's defense of the popular view against the intellectual support of left-wing opposition is provided, and issues of political ideology, political philosophy and the intellectual participation in Mexico's political structure are also discussed. Uranga's philosophy is situated within the context of Mexican president Adolfo López Mateos and the rule of the Partido Revolucionario Institucional.

Abstract: Daily values of gross primary production (GPP) derived from an eddy-covariance flux tower have been used to analyze the information content of the MODIS Photochemical Reflectance Index (PRI) on the light-use efficiency (ε). The study has been conducted in a Mediterranean Pinus pinaster forest showing summer water stress. Advanced processing techniques have been used to analyze the effect of various external factors on ε and PRI temporal variations. The intra-annual correlation between these two variables has been found to be mostly attributable to concurrent variations in sun and view zenith angles. The PRI has been normalized from these angular effects (NPRI), and its ability to track ecosystem ε response to prolonged summer water limitations has been analyzed. The observed shift between ε and NPRI reveals that, for the study area and at MODIS spatial resolution, NPRI is informative on changes in pigments and canopy structure related to the vegetation response to prolonged water stress. [Copyright &y& Elsevier]

Background and aims: The photochemical reflectance index (PRI) is correlated to photosynthetic efficiency and has been successfully applied at multiple scales for remote estimation of physiological functioning. However, interpretation of the PRI signal can be confounded by many different variables including declines in photochemical pigments. Our study was aimed at investigating PRI in response to salinity stress, and evaluating physiological and pigment responses of two co-occurring shrubs, Baccharis halimifolia and Myrica cerifera in laboratory studies. Methods: Photosynthesis, water relations, chlorophyll fluorescence, hyperspectral reflectance and leaf pigment contents were measured following salinity treatment. Results: Physiological measurements indicated that both species exhibit adaptations which protect PSII during periods of stress. Chlorophyll fluorescence parameters were affected in both species, but indicated that other photochemical reactions (e.g. photorespiration) were important for energy dissipation in absence of chlorophyll changes. After many days of reduced photosynthesis, photochemical changes were detectable using PRI indicating chronic stress. Conclusions: Variations in PRI were not related to changes in pigments but strongly related to tissue chlorides indicating salinity effects on the PRI signal. Thus, PRI is an indicator of salinity stress in these coastal species and may be as an early signal for increasing salt exposure associated with rising sea-level and climate change. [ABSTRACT FROM AUTHOR]

In this article the author discusses the use of remote sensing to assess the health and vigour of crops and plants. The author says that when light strikes a leaf, part of the light spectrum is reflected towards the observer, and this reflected light offers information on the physical and biochemical properties of the leaf. The author says that in the visible spectrum, leaf reflectance is low because of absorption by photosynthetic pigments, such as chlorophyll and carotenoids.

Objectives We compared the accuracy of proration and linear scaling for estimating Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV), Verbal Comprehension Index (VCI), and Perceptual Reasoning Index (PRI) composites from all possible two subtest combinations. The purpose was to provide practice relevant psychometric results in a clinical sample. Design The present investigation was an archival study that used mostly within-group comparisons. We analyzed WAIS-IV data of a clinical sample comprising 104 patients with brain damage and 37 with no known neurological impairment. Results In both clinical samples, actual VCI and PRI scores were highly correlated with estimated index scores based on proration and linear scaling (all rs ≥.95). In the brain-impaired sample, significant mean score differences between the actual and estimated composites were found in two comparisons, but these differences were less than three points; no other significant differences emerged. Conclusions Overall, findings demonstrate that proration and linear scaling methods are feasible procedures when estimating actual Indexes. There was no advantage of one computational method over the other. [ABSTRACT FROM AUTHOR]

Previously, we found a significant association between photosystem II efficiency (ΦPSII) and photochemical reflectance index (PRI) measured at predawn among different species at different elevations and throughout several seasons. However, this relationship has not been evaluated under varied levels of illumination. Here, we used the Taiwan species Pinus taiwanensis (a conifer distributed at 750-3,000 m a.s.l.), Stranvaesia niitakayamensis (an evergreen tree, 1,700-3,100 m) and two Miscanthus spp. (perennial C Gramineae, coastline-3,200 m) to elucidate the ΦPSII-PRI relationship. We studied six levels of photosynthetic photon flux density (PPFD) (0, 200, 400, 800, 1,200 and 2,000 μmol m s) over several growth seasons at high (2,600 m a.s.l.) and low (800 m a.s.l.) elevation sites. In comparing the same species or genus, ΦPSII and PRI were closely correlated in darkness or under the same level of PPFD, with data obtained from different seasons and elevations pooled for regression analysis. Because both the intercept and slope of the ΦPSII-PRI equation showed a negative curvilinear correlation with PPFD, we could fit an empirical regression model, ΦPSII = c + d·ln(PPFD) + e·[ln(PPFD)] + f·PRI + g·PRI·ln(PPFD) + h·PRI·[ln(PPFD)], for multiple regression analysis. Using this model, we found a close correlation between the estimated and measured ΦPSII ( r = 0.842−0.937, P < 0.001) for all four species examined and for mango ( Mangifera indica) measured under both artificial illumination and sunlight (data from Weng et al. ). This empirical regression model could simulate both seasonal and diurnal variations of leaf-scale photosynthetic efficiency at high and low elevations. [ABSTRACT FROM AUTHOR]

Previous important studies examine the role of "risk" propensity in shaping vote choices in Mexico. However, none of these studies determine the degree to which short and long term factors influence a traditionally risk averse respondent's enthusiasm to vote for an opposition party. Using data from the 2000 election, a campaign where risk played a significant role, we evaluate whether various effects mitigate the role of risk in voting for an opposition candidate. We find that risk propensity has a deterministic impact on vote choice and no amount of campaign effects (short term) or negative image of the PRI (long term) mitigated that role. Yet, we uniquely show that this deterministic impact can vary over the campaign period and across the electoral alternatives. [ABSTRACT FROM AUTHOR]

Private participation in the management of water and sanitation has been firmly promoted and concentrated in a handful of countries and their urban centers. Latin America became one of the main recipients of investment in infrastructure projects involving private participation. However, private participation has accomplished neither the scale nor the benefits anticipated by its promoters. Not only have water and sanitation received only a tiny part of the total investment. These reforms and the theories from which they draw have failed to improve water sustainability and associated social values in urban areas of Latin America. This paper combines a theoretical framework drawing on neoliberalism with evidence from Mexico City and Buenos Aires to explore and reflect on some of the reasons why private participation has neither fulfilled its promoters' expectations nor improved the multiple dimensions of urban water system management. It finds that the main outcomes of the neoliberal water reform were economic (improvements in registered connection and billing). Yet, other dimensions of water such as overexploitation and contamination (environmental value), unequal access to water, and fragmented and weak institutional settings (political dimension) remain. The main lesson from the reform is that the multiple values of water cannot be addressed by merely passing water utilities along with their complex set of social and environmental problems over to private companies or public utilities. [ABSTRACT FROM AUTHOR]

The Mexican drug war, in full swing since December 2006, has now claimed more than 40,000 lives. Dozens of high-level cartel operatives have been captured or killed, yet the leadership of one cartel, from Sinaloa in northwestern Mexico, has remained apparently untouched. The apparent lack of a crackdown on the Sinaloa Cartel has spurred criticisms of the Calderón administration, as well as US authorities aiding in the drug fight – some critics contend that the Sinaloa Cartel has enjoyed protection from the authorities. The Sinaloa Cartel's history of protection and collusion by authorities goes back a long way – during the reign of the PRI from 1929 to 2000, Sinaloa's drug traffickers were allowed to operate with near-total impunity. But mounting evidence – captures and deaths of high-level operatives from Sinaloa as well as arrests of relatives of the leadership – suggests that the claims of collusion against the current Mexican administration are false. [ABSTRACT FROM PUBLISHER]

Aims: The aim of this study was to assess the food habits and nutritional status of free-living, non-institutionalised, elderly people of Torrevieja, a Spanish city located in the Mediterranean coast. Methods: Anthropometric and dietary survey (two 24 hour recalls) were assessed in 200 (83 men and 117 women) free-living elderly people (average age 72.3 ± 6.6 years). Results: Just married women accomplished the recommended energy intake. The contribution of macronutrients to the total energy intake was different from the Recommended Intake for the elderly, since it was too derived from proteins, fats, SFA and sugars, but in only small amounts was derived from complex carbohydrates. High percentages of elderly persons showed inadequate intake of calcium, zinc, magnesium, potassium, copper, iodine, folic acid, vitamin A, vitamin D, vitamin E, and riboflavin. Men showed lower micronutrient intake than women. Conclusions: An increase in dietary complex carbohydrate, and a decrease in protein and fats, especially SFA, is recommended. It would be desirable to increase the consumption of fruits, vegetables, whole cereals, fish and skimmed dairy products. [ABSTRACT FROM AUTHOR]

Abstract: We develop herein the theoretical foundations for a new satellite concept, utilizing multi-angle, along track spectral measurements to infer photosynthesis and gross primary production, at the landscape level over time. We validate the theory using both tower and space-borne sensors. The concept, originated in Hall et al. (2008), and Hilker et al. (2008a) and is based on two principles: (1) The first derivative of the photochemical reflectance index (PRI) with respect to shadow fraction viewed by the sensor ∂PRI/∂αs, is proportional to light-use efficiency ε. (2) This behavior can be shown both theoretically and empirically to be independent of vegetation structure and optical properties. These two principles provide the basis for a robust photosynthesis algorithm that can be applied consistently both spatially and temporally. We develop the general theoretical concept using a canopy reflectance model that incorporates a dependence of leaf reflectance on illumination strength, permitting the leaf reflectance at 531nm to depend on the intensity of photosynthetic down-regulation. Using this model we are able to show that using PRI alone to infer ε is confounded by the shadow fraction viewed by a sensor, the PRI value in a non-down-regulated physiological state, and the sunlit canopy reflectance. We are able to demonstrate that these difficulties are mitigated by using ∂PRI/∂αs—not PRI—as the primary measure of canopy level ε. We demonstrate our concept using tower and satellite data acquired over three years, in two distinct biomes and vegetation types to show that PRI/∂αs and ε are related by a single function. Building on these ideas we propose the development of a new satellite concept that can utilize a spatially and temporally robust algorithm to map photosynthesis at landscape scales and its temporal variation. [Copyright &y& Elsevier]

Copyright of Revista Mexicana de Ciencias Politicas y Sociales is the property of Revista Mexicana de Ciencias Politicas y Sociales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: This study was undertaken to investigate genotypic differences of five maize cultivars in grain yield response to two different modes of deficit irrigation, conventional deficit irrigation and partial root zone irrigation. Three irrigation treatments were implemented: (1) FULL irrigation, the control treatment where plant water requirement, 100% Class-A pan evaporation, was fully met and the furrows on both sides of the plant rows were irrigated; (2) partial root zone irrigation (PRI), 35% deficit irrigation, compared to FULL treatment, was applied in every other furrow thus irrigating only one side of the plant rows. The furrows irrigated were alternated every irrigation; (3) conventional deficit irrigation (CDI), the same amount of water as PRI was applied in furrows on both sides of the plant rows, similar to FULL irrigation treatment. Five maize cultivars (P.31.G.98, P.3394, Rx:9292, Tector and Tietar) showing extreme growth response to water stress were selected out of ten cultivars tested with earlier completed greenhouse-pot experiment. A split-plot experimental design, comprising three irrigation treatments and five maize cultivars with four replicates, was used during two years of work, in 2005 and 2006. Total of nine irrigations, with one-week irrigation interval, were annually applied using a drip-irrigation system. Soil water status was monitored using a neutron moisture gauge, in addition to measuring leaf water potential and above-ground biomass production throughout the growing season. Grain yield and other yield attributes were measured at harvest as well as assessing differences in plant root distributions. Decrease in grain yield and harvest index of the tested cultivars, compared to FULL treatment, was proportionally less under PRI than CDI. Whether or not a significant yield advantage can be obtained under PRI compared to CDI showed significant (P <0.05) genotypic variability. Tector and Tietar among the tested cultivars of maize showed significantly higher grain yield (P <0.05) under PRI than CDI. The yield advantage of the genotypes (P.3394 and Tector) under PRI compared to CDI seems related to their enhanced root biomass developed under PRI. [Copyright &y& Elsevier]

Abstract: The Photochemical Reflectance Index (PRI) is used as an indicator of leaf and plant canopy photosynthetic efficiency. However, the photosynthetic efficiency–PRI relationship has been shown to be inconsistent over time, likely due to changes in foliar pigment content. We measured reflectance spectra and biochemical properties from 24 leaves of two deciduous tree species and acquired pigment and reflectance data from the Leaf Optical Properties EXperiment database for an additional nine species. These data were used as inputs for the PROSPECT-5 leaf optical model. We found measurements of PRI to be significantly (p <0.05) correlated with chlorophyll content, carotenoid content, and the carotenoid/chlorophyll ratio. However, only the PRI–carotenoid/chlorophyll ratio relationship was consistent across all analyses. Two predictive equations were derived from PROSPECT-5 simulations: a curvilinear PRI model (PRI(clm)) predicted the carotenoid/chlorophyll ratio (r 2 =0.99), and a linear model using the chlorophyll index (CI(lm)) predicted chlorophyll content (r 2 =0.98). Multiplying PRI(clm) with CI(lm) canceled the influence of chlorophyll content on PRI(clm) and thus allowed for prediction of carotenoid content from 11 deciduous tree species (r 2 =0.83). Our results confirm that the PRI is significantly influenced by chlorophyll and carotenoid pools and demonstrate a new approach for non-destructive estimation of leaf carotenoid content using the PRI. Because variation in foliar physiological status is known to relate to leaf carotenoid content and the carotenoid/chlorophyll ratio, convolving the PRI with a chlorophyll index is likely to be useful for understanding the photosynthetic performance of deciduous vegetation across a wide range of temporal periods, ranging from daily to seasonal time scales. [ABSTRACT FROM AUTHOR]

By affecting the physiology and structure of plant canopies, increasing atmospheric CO2 and O3 influence the capacity of agroecosystems to capture light and convert that light energy into biomass, ultimately affecting productivity and yield. The objective of this study was to determine if established remote sensing indices could detect the direct and interactive effects of elevated CO2 and elevated O3 on the leaf area, chlorophyll content, and photosynthetic capacity of a soybean canopy growing under field conditions. Large plots of soybean (Glycine max) were exposed to ambient air (∼380 μmol CO2 mol−1), elevated CO2 (∼550 μmol mol−1), elevated O3 (1.2× ambient), and combined elevated CO2 plus elevated O3 at the soybean free air gas concentration enrichment (SoyFACE) experiment. Canopy reflectance was measured weekly and the following indices were calculated from reflectance data: near infrared/red (NIR/red), normalized difference vegetation index (NDVI), canopy chlorophyll content index (chl. index), and photochemical reflectance index (PRI). Leaf area index (LAI) also was measured weekly. NIR/red and LAI were linearly correlated throughout the growing season; however, NDVI and LAI were correlated only up to LAI values of ∼3. Season-wide analysis demonstrated that elevated CO2 significantly increased NIR/red, PRI, and chl. index, indicating a stimulation of LAI and photosynthetic carbon assimilation, as well as delayed senescence; however, analysis of individual dates resolved fewer statistically significant effects of elevated CO2. Exposure to elevated O3 decreased LAI throughout the growing season. Although NIR/red showed the same trend, the effect of O3 on NIR/red was not statistically significant. Season-wide analysis showed significant effects of O3 on PRI; however, analysis of individual dates revealed that this effect was only statistically significant on two dates. Elevated O3 had minimal effects on the total canopy chlorophyll index. PRI appeared to be more sensitive to decreased photosynthetic capacity of the canopy as a whole compared with previously published single leaf gas exchange measurements at SoyFACE, possibly because PRI integrates the reflectance signal of older leaves with accumulated O3 damage and healthy young, upper canopy leaves, enabling detection of significant decreases in photosynthetic carbon assimilation which have not been detected in previous studies which measured gas exchange of upper canopy leaves. When the canopy was exposed to elevated CO2 and O3 simultaneously, the deleterious effects of elevated O3 were diminished. Reflectance data, while less sensitive than direct measurements of physiological/structural parameters, corroborate direct measurements of LAI and photosynthetic gas exchange made during the same season, as well as results from previous years at SoyFACE, demonstrating that these indices accurately represent structural and physiological effects of changing tropospheric chemistry on soybean growing in a field setting. [ABSTRACT FROM PUBLISHER]

Abstract: Eddy covariance (EC) measurements have greatly advanced our knowledge of carbon exchange in terrestrial ecosystems. However, appropriate techniques are required to upscale these spatially discrete findings globally. Satellite remote sensing provides unique opportunities in this respect, but remote sensing of the photosynthetic light-use efficiency (ε), one of the key components of Gross Primary Production, is challenging. Some progress has been made in recent years using the photochemical reflectance index, a narrow waveband index centered at 531 and 570nm. The high sensitivity of this index to various extraneous effects such as canopy structure, and the view observer geometry has so far prevented its use at landscape and global scales. One critical aspect of upscaling PRI is the development of generic algorithms to account for structural differences in vegetation. Building on previous work, this study compares the differences in the PRI: ɛ relationship between a coastal Douglas-fir forest located on Vancouver Island, British Columbia, and a mature Aspen stand located in central Saskatchewan, Canada. Using continuous, tower-based observations acquired from an automated multi-angular spectro-radiometer (AMSPEC II) installed at each site, we demonstrate that PRI can be used to measure ɛ throughout the vegetation season at the DF-49 stand (r2 =0.91, p <0.00) as well as the deciduous site (r2 =0.88, p <0.00). It is further shown that this PRI signal can be also observed from space at both sites using daily observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and a multi-angular implementation of atmospheric correction (MAIAC) (r2 =0.54 DF-49; r2 =0.63 SOA; p <0.00). By implementing a simple hillshade model derived from airborne light detection and ranging (LiDAR) to approximate canopy shadow fractions (αs), it is further demonstrated that the differences observed in the relationship between PRI and ε at DF-49 and SOA can be attributed largely to differences in αs. The findings of this study suggest that algorithms used to separate physiological from extraneous effects in PRI reflectance may be more broadly applicable and portable across these two climatically and structurally different biome types, when the differences in canopy structure are known. [Copyright &y& Elsevier]

Plant photosynthesis is critical for understanding carbon cycling at landscape and global scales. While tower-based measurements of CO2 have enhanced our knowledge of ecosystem fluxes, scaling these measurements globally is difficult. Satellite observations provide full, global coverage and hold the potential of spatially continuous measurements of ecosystem fluxes, but the requirements for modeling these fluxes from satellite-derived surface parameters are not well understood. This article describes the further development of a tower-mounted, automated, multiangular spectroradiometer system (AMSPEC II) used to study the relationships between canopy-reflectance and plant-physiological processes from multiangular observations, thereby facilitating a comprehensive modeling of the bidirectional reflectance distribution of the canopy. A Webcam permits simultaneous monitoring of phenological changes over time. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the possibility of monitoring carbon fixation of a terrestrial ecosystem from high spectral resolution field spectroscopy measurements. Canopy radiance spectra were collected under clear sky conditions using high resolution spectrometers which made it possible to estimate sun-induced chlorophyll fluorescence at the oxygen absorption band O2-A located at 760nm (F 760) as well as spectral vegetation indices. Spectral observations were collected in a rice field monitored with an eddy covariance (EC) flux tower measuring the net ecosystem exchange (NEE) of the crop. Estimation of gross ecosystem productivity (GEP) from remotely sensed data was based on the widely used light-use efficiency model (LUE), which states that carbon uptake is a function of the photosynthetically active radiation absorbed by vegetation (APAR) and light-use efficiency (ɛ) which represents the conversion efficiency of energy to fixed carbon. Hyperspectral data were used to derive both the APAR and the ɛ term. Different versions of the LUE model were formalized and tested with EC fluxes during two growing seasons. We started using a LUE model in which ɛ is held constant and remote sensing data are used to estimate APAR. We then investigated the improvements in GEP modelling provided by the partitioning between photosynthetic (PV) and non-photosynthetic (NPV) components of vegetation in APAR estimation, holding ɛ constant. The use of spectral indices related to APARPV instead of APAR resulted in an improvement in midday GEP estimation of about 50% with respect to the basic LUE model, average root mean square error in cross-validation (RMSEcv) of the model class from 9.69 to 4.49μmol CO2 m−2 s−1. Afterwards, we tested the use of the apparent fluorescence yield (Fy* 760) and the scaled Photochemical Reflectance Index (sPRI) to derive ɛ. Modelling ɛ further improved the estimation of GEP up to an RMSEcv of 3.81μmol CO2 m−2 s−1 using Fy* 760 and the MERIS terrestrial chlorophyll index (MTCI) and 3.67μmol CO2 m−2 s−1 using sPRI and F 760 to estimate ɛ and APARPV, respectively. [Copyright &y& Elsevier]

Water stress in plants affects a number of physiological processes such as photosynthetic rate, stomatal conductance as well as the operating efficiency of photosystem II (PSII) and non-photochemical quenching (NPQ). Photochemical reflectance index (PRI) is reported to be sensitive to changes in xanthophyll cycle which occur during stress and could possibly be used to monitor changes in the parameters mentioned before. Therefore, the aim of this study was to evaluate the use of PRI as an early water stress indicator. Water stress treatment was imposed in a greenhouse tomato crop. CO2 assimilation, stomatal conductance, light-adapted and dark-adapted fluorescence as well as PRI and relative water content (RWCs%) of the rooting medium were repeatedly measured. The same measurements were also performed on well-irrigated plants that acted as a reference. The experiment was repeated in four consecutive weeks. Results showed a strong correlation between RWCs% and photosynthetic rate, stomatal conductance, NPQ and operating efficiency of PSII but not with PRI when the whole dataset was considered. Nevertheless, more detailed analysis revealed that PRI gave a good correlation when light levels were above 700 µmol m−2 s−1. Therefore, the use of PRI as a water stress indicator cannot be independent of the ambient light conditions. [ABSTRACT FROM AUTHOR]

In order to elucidate the effects of chlorophyll concentration and seasonal temperature on the relationship between photosystem II (PSII) efficiency and the photochemical reflectance index (PRI) of leaves under different light intensity, mango (Mangifera indica), a low-temperature-sensitive species, was used for the study. From early winter to summer, we selected several days to measure chlorophyll fluorescence and leaf spectral reflectance of mango leaves with dark green to yellow green colors, under natural sunlight from predawn to sunset and under six levels (0, 200, 400, 800, 1200 and 2000 µmol m-2s-1) of artificial illumination. When leaves were exposed to light, both PRI and PSII efficiency decreased with the increase in illumination, yet the PSII efficiency-PRI relationship varied with temperature and leaf color. Both predawn PRI and the X-intercept of the PSII efficiency-PRI regression equations were higher in dark green leaves and on the day with higher minimum air temperature, and lower on opposite conditions. These were due to the influence of chlorophyll on the reflection of wavebands for detecting PRI, and leaves retained a higher degree of epoxidation state of xanthophyll cycle pigments in cold predawn. Therefore, when data obtained at different seasons and with different leaf colors were pooled for analysis, PRI was not closely related to PSII efficiency. Yet, either in the darkness of predawn or under a given level of illumination, PSII efficiency always showed a significant positive correlation with PRI, with data from different leaf colors and seasons merged for statistics analysis. Because both the intercept and slope of the PSII efficiency-PRI equation showed a negative regression with photosynthetic photon flux (PPF), an empirical regression model, i.e., PSII efficiency=c+d⋅PPF+ e⋅(PPF)²+f⋅PRI+g⋅PPF⋅PRI, could be fitted for multiple regression analysis. Based on the close correlation between the estimated and measured PSII efficiency (r²=0.844-0.907, P< 0.001), using dynamic data obtained from leaves with yellow green to dark green colors, measurement was taken at predawn (Fv/Fm) and under any given strength of sunlight and artificial illumination (ΔF/Fm?) through different seasons. We, thus, concluded that this empirical regression model could simulate both the seasonal and diurnal variations of PSII efficiency. [ABSTRACT FROM AUTHOR]

Photosynthesis, chlorophyll fluorescence, and hyperspectral reflectance were used to evaluate diurnal changes of Elaeagnus umbellata to quantify physiological responses of the invasive species during times of stress. Field measurements showed that E. umbellata is able to maintain higher levels of photosynthesis relative to nearby Quercus alba plants, with less water loss. Plants subjected to progressive drought were able to recover photosynthesis one day following re-watering. Laboratory and field measurements revealed decreasing ΔF/F'm values in response to drought stress, with little corresponding decrease in photochemical reflectance index values. This research supports the view that xanthophyll cycle dissipation is not the photoprotective mechanism at work for Elaeagnus species under water stress. Elaeagnus umbellata maintains photosynthetic carbon assimilation even under drought conditions, in part, due to chemical dissipation of excess light, and in part because of morphological features that limit excess radiation while maximizing photosynthetic carbon gain. These characteristics may contribute to the invasive success of E. umbellata. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to evaluate the use of ground-based canopy reflectance measurements to detect changes in physiology and structure of vegetation in response to experimental warming and drought treatment at six European shrublands located along a North–South climatic gradient. We measured canopy reflectance, effective green leaf area index (green LAIe) and chlorophyll fluorescence of dominant species. The treatment effects on green LAIe varied among sites. We calculated three reflectance indices: photochemical reflectance index PRI [531nm; 570nm], normalized difference vegetation index NDVI680 [780nm; 680nm] using red spectral region, and NDVI570 [780nm; 570nm] using the same green spectral region as PRI. All three reflectance indices were significantly related to green LAIe and were able to detect changes in shrubland vegetation among treatments. In general warming treatment increased PRI and drought treatment reduced NDVI values. The significant treatment effect on photochemical efficiency of plants detected with PRI could not be detected by fluorescence measurements. However, we found canopy level measured PRI to be very sensitive to soil reflectance properties especially in vegetation areas with low green LAIe. As both soil reflectance and LAI varied between northern and southern sites it is problematic to draw universal conclusions of climate-derived changes in all vegetation types based merely on PRI measurements. We propose that canopy level PRI measurements can be more useful in areas of dense vegetation and dark soils. [Copyright &y& Elsevier]

Copyright of Evropska Volebni Studia is the property of Masaryk University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Terrestrial gross primary production (GPP) is an important parameter to explore and quantify carbon fixation by plant ecosystems at various scales. Remote sensing (RS) offers a unique possibility to investigate GPP in a spatially explicit fashion; however, budgeting of terrestrial carbon cycles based on this approach still remains uncertain. To improve calculations, spatio-temporal variability of GPP must be investigated in more detail on local and regional scales. The overarching goal of this study is to enhance our knowledge on how environmentally induced changes of photosynthetic light-use efficiency (LUE) are linked with optical RS parameters. Diurnal courses of sun-induced fluorescence yield ( FSyield) and the photochemical reflectance index of corn were derived from high-resolution spectrometric measurements and their potential as proxies for LUE was investigated. GPP was modeled using Monteith's LUE-concept and optical-based GPP and LUE values were compared with synoptically acquired eddy covariance data. It is shown that the diurnal response of complex physiological regulation of photosynthesis can be tracked reliably with the sun-induced fluorescence. Considering structural and physiological effects, this research shows for the first time that including sun-induced fluorescence into modeling approaches improves their results in predicting diurnal courses of GPP. Our results support the hypothesis that air- or spaceborne quantification of sun-induced fluorescence yield may become a powerful tool to better understand spatio-temporal variations of fluorescence yield, photosynthetic efficiency and plant stress on a global scale. [ABSTRACT FROM AUTHOR]

Abstract: Estimation of photosynthetic light use efficiency (ε) from satellite observations is an important component of climate change research. The photochemical reflectance index, a narrow waveband index based on the reflectance at 531 and 570 nm, allows sampling of the photosynthetic activity of leaves; upscaling of these measurements to landscape and global scales, however, remains challenging. Only a few studies have used spaceborne observations of PRI so far, and research has largely focused on the MODIS sensor. Its daily global coverage and the capacity to detect a narrow reflectance band at 531 nm make it the best available choice for sensing ε from space. Previous results however, have identified a number of key issues with MODIS-based observations of PRI. First, the differences between the footprint of eddy covariance (EC) measurements and the MODIS footprint, which is determined by the sensor''s observation geometry make a direct comparison between both data sources challenging and second, the PRI reflectance bands are affected by atmospheric scattering effects confounding the existing physiological signal. In this study we introduce a new approach for upscaling EC based ε measurements to MODIS. First, EC-measured ε values were “translated” into a tower-level optical PRI signal using AMSPEC, an automated multi-angular, tower-based spectroradiometer instrument. AMSPEC enabled us to adjust tower-measured PRI values to the individual viewing geometry of each MODIS overpass. Second, MODIS data were atmospherically corrected using a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which uses a time series approach and an image-based rather than pixel-based processing for simultaneous retrievals of atmospheric aerosol and surface bidirectional reflectance (BRDF). Using this approach, we found a strong relationship between tower-based and spaceborne reflectance measurements (r 2 =0.74, p <0.01) throughout the vegetation period of 2006. Swath (non-gridded) observations yielded stronger correlations than gridded data (r 2 =0.58, p <0.01) both of which included forward and backscatter observations. Spaceborne PRI values were strongly related to canopy shadow fractions and varied with different levels of ε. We conclude that MAIAC-corrected MODIS observations were able to track the site-level physiological changes from space throughout the observation period. [Copyright &y& Elsevier]

The article argues that in the 2006 Federal Chamber of Deputies election, individual candidate traits and experience affected electoral outcomes. Analyses were conducted using a unique dataset of biographical information for 171 candidates in 57 randomly drawn districts. The findings demonstrate that candidates mattered in the recent federal legislative elections. Additionally, they show that the common definition of "high quality" candidates (previous office holders) is insufficient in the Mexican case. The second part of the article analyzes how differing types of candidates were nominated by each party/pact, and examines how the types of nominated candidates can be partially predicted based on the party's nominating rules and their pool of members with previous local electoral success. [ABSTRACT FROM AUTHOR]

The disputed presidential elections of 2006 moved the PRI to third place of preferences. While there was a deep polarization between the parties of left and right, and errors in the PRI's campaign, it is also possible to find another cause in the process of choosing the candidate Roberto Madrazo. This paper reconstructs the nomination process of 2005, as well as the historical and short-term conditions that made it possible, the internal confrontations and recomposition of interests of political groups in the PRI, which allowed, for the first time in the history of this party, to make its leader a presidential candidate. [ABSTRACT FROM AUTHOR]

The Institutional Revolutionary Party (PRI) dominated Mexican politics for over 70 years, but its fortunes have been sliding in the past two decades, capped by its loss of the presidency in 2000. The results for the PRI were even worse in 2006, with a third-place finish in the presidential race and significant losses in both houses of the legislature. This paper examines whether or not the PRI risks going from being a dominant party to a third party in a Mexican two-party system. The results suggest that the PRI has fallen behind, but that it may have a limited window to regroup based upon comparative regional advantage in the northern and southern states. [ABSTRACT FROM AUTHOR]

Chlorophyll fluorescence and landscape-level reflectance imagery were used to evaluate spatial variations in stress in Myrica cerifera and Iva frutescens during a severe drought and compared to an extremely wet year. Measurements of relative water content and the water band index (WBI970) indicated that the water stress did not vary across the island. In contrast, there were significant differences in tissue chlorides across sites for both species. Using the physiological reflectance index (PRI), we were able to detect salinity stress across the landscape. For M. cerifera, PRI did not differ between wet and dry years, while for I. frutescens, there were differences in PRI during the 2 years, possibly related to flooding during the wet year. There was a positive relationship between PRI and $$ \Updelta F/F_{\text{m}}^{\prime } $$ for M. cerifera ( r2 = 0.79) and I. frutescens ( r2 = 0.72). The normalized difference vegetation index (NDVI), the chlorophyll index (CI), and WBI970 were higher during the wet summer for M. cerifera, but varied little across the island. CI and WBI970 were higher during 2004 for I. frutescens, while there were no differences in NDVI during the 2 years. PRI was not significantly related to NDVI, suggesting that the indices are spatially independent. These results suggest that PRI may be used for early identification of salt stress that may lead to changes in plant distributions at the landscape level, as a result of rising sea level. Comparsions between the two species indicate that variations in PRI and other indices may be species specific. [ABSTRACT FROM AUTHOR]

In this paper, a literature review about optical remote sensing (RS) of O3 stress is presented. Studies on O3-induced effects on vegetation reflectance have been conducted since late ‘70s based on the analysis of optical RS data. Literature review reveals that traditional RS techniques were able to detect changes in leaf and canopy reflectance related to O3-induced stress when visible symptoms already occurred. Only recently, advanced RS techniques using hyperspectral sensors, demonstrated the feasibility of detecting the stress in its early phase by monitoring excess energy dissipation pathways such as chlorophyll fluorescence and non-photochemical quenching (NPQ). Steady-state fluorescence (Fs), measured by exploiting the Fraunhofer line depth principle and NPQ related xanthophyll-cycle, estimated through the photochemical reflectance index (PRI) responded to O3 fumigation before visible symptoms occurred. This opens up new possibilities for the early detection of vegetation O3 stress by means of hyperspectral RS. [Copyright &y& Elsevier]

Abstract: A series of new mixed-ligand neutral copper(II) complexes of the general type [Cu(amine)(i-MNT)] and [Cu(tz)(i-MNT)] was prepared and characterized by elemental, spectroscopic methods, μ eff, Λ μ measurements and molecular modeling studies. The acute toxicity, the cytogenetic and the in vivo antitumor activity of the new complexes, is related to their chemical and physicochemical properties. Among the Cu(II) compounds tested the complex with 2-amino-5-methyl thiazole increases significantly the life span of leukemia P388 bearing mice in vivo. [Copyright &y& Elsevier]

This paper presents a methodology for water stress detection in crop canopies using a radiative transfer modelling approach and the Photochemical Reflectance Index (PRI). Airborne imagery was acquired with a 6-band multispectral camera yielding 15 cm spatial resolution and 10 nm FWHM over 3 crops comprising two tree-structured orchards and a corn field. The methodology is based on the PRI as a water stress indicator, and a radiative transfer modelling approach to simulate PRI baselines for non-stress conditions as a function of leaf structure, chlorophyll concentration (Cab), and canopy leaf area index (LAI). The simulation work demonstrates that canopy PRI is affected by structural parameters such as LAI, Cab, leaf structure, background effects, viewing angle and sun position. The modelling work accounts for such leaf biochemical and canopy structural inputs to simulate the PRI-based water stress thresholds for non-stress conditions. Water stress levels are quantified by comparing the image-derived PRI and the simulated non-stress PRI (sPRI) obtained through radiative transfer. PRI simulation was conducted using the coupled PROSPECT-SAILH models for the corn field, and the PROSPECT leaf model coupled with FLIGHT 3D radiative transfer model for the olive and peach orchards. Results obtained confirm that PRI is a pre-visual indicator of water stress, yielding good relationships for the three crops studied with canopy temperature, an indicator of stomatal conductance (r 2 =0.65 for olive, r 2 =0.8 for peach, and r 2 =0.72 for maize). PRI values of deficit irrigation treatments in olive and peach were consistently higher than the modelled PRI for the study sites, yielding relationships with water potential (r 2 =0.84) that enabled the identification of stressed crowns accounting for within-field LAI and Cab variability. The methodology presented here for water stress detection is based on the visible part of the spectrum, and therefore it has important implications for remote sensing applications in agriculture. This method may be a better alternative to using the thermal region, which has limitations to acquire operationally high spatial resolution thermal imagery. [Copyright &y& Elsevier]

Copyright of Foro Internacional is the property of El Colegio de Mexico AC and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When presidents do not run for reelection in democracies, the electoral connection is not straightforward. It is not obvious in this case how voters' evaluations of leaders get transformed into votes for political parties, nor how political campaigns affect such a relationship. The argument is that voters' evaluations of presidents, which can be measured by presidential approval ratings, work as an information shortcut about the future performance of the candidate; as campaigns generate information about contenders, approval of the retiring president matters relatively less in the voting decision. Based on econometric analysis and four nationwide polls conducted from October 2005 to June 2006, the article tests these hypotheses using the case of the 2006 Mexican presidential election. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of physiology, chlorophyll fluorescence and hyperspectral reflectance were used to detect salinity stress in the evergreen coastal shrub, Myrica cerifera on Hog Island, Virginia. Two experimental sites were used in our study, the oceanside of a M. cerifera thicket, which is exposed to sea spray, and the protected, leeside of the thicket. Using the physiological reflectance index (PRI), we were able to detect stress at both the canopy and landscape level. Monthly variations in stomatal conductance, photosynthesis, and relative water content indicated a strong summer drought response that was not apparent in chlorophyll fluorescence or in the water band index (WBI) derived from canopy and airborne reflectance measurements. In contrast, there were significant differences in both physiological measurements and tissue chlorides between the two sites used in the study, indicating salinity stress. This was reflected in measurements of PRI. There was a positive relationship between PRI measured at the canopy-level and light-adapted fluorescence (ΔF/F′ m; r 2 =0.69). PRI was significantly lower on the oceanside of the Myrica cerifera thicket. PRI was not significantly related to NDVI (r 2 =0.01) at the canopy-level and only weakly related (r 2 =0.04) at the landscape-level, suggesting that the indices are independent. The chlorophyll index (CI) did not show any significant changes between the two sites. Frequency histograms of pixels sampled from airborne hyperspectral imagery revealed that the distribution of PRI was shifted to the right on the backside of the thicket relative to the oceanside and there was a significant difference between sites. These results suggest that PRI may be used for early identification of salt-stress and to identify areas across the landscape where community structure may change due to sea-level rise. [Copyright &y& Elsevier]