Levels Of Incident Radiation Research Articles

TRANSPIRATION AND NUTRIENT USE EFFICIENCY OF A SWEET PEPPER CROP UNDER TWO EXTERNAL SHADING SYSTEMS: MOBILE AND FIXED

High incident radiation levels during the summer cropping cycles in Mediterranean greenhouses generate microclimates of high temperature and evaporative demand so the incident radiation reduction by white-washing is usually applied. The aim of this work is to evaluate the transpiration and nutrient uptake of a sweet pepper crop (Capsicum annuum L.) in two greenhouses equipped with (i) external mobile shading (M) and (ii) external fixed shading (F). Transpiration was measured every five minutes in both greenhouses with two lysimeter balances. Leaf transpiration and intercepted radiation relationship was decreasing during the crop cycle. A multiple regression analysis, based on the simplified Penman-Monteith formula, was established between the measured transpiration and the radiative and advective components. A light extinction coefficient of 0.45 was determined and the leaf area index (LAI) was estimated in function of the days after transplanting. To get a good adjustment between observed and estimated transpiration it was necessary to change the P-M model coefficients through the crop development. Total nutrient uptake (N, K, Ca, Mg and P) was calculated weekly by the measure of supply and leached nutrient solution and its chemical analysis. It was initially similar in both treatments and finally higher in the F than the M treatment. By contrast, the nutrient uptake efficiency, in terms of fruit fresh weight (g g-1), was higher in the M treatment during the early yield period, although both treatments showed the same efficiency at the end of the crop.

How do UV radiation, temperature, and zooplankton influence the dynamics of alpine phytoplankton communities?

Plankton in mountain lakes are confronted with generally higher levels of incident ultraviolet radiation (UVR), lower temperatures, and shorter growing seasons than their lower elevation counterparts. The direct inhibitory effects of high UVR and low temperatures on montane phytoplankton are widely recognized. Yet little is known about the indirect effects of these two abiotic factors on phytoplankton, and more specifically whether they alter zooplankton grazing rates which may in turn influence phytoplankton. Here, we report the results of field microcosm experiments that examine the impact of temperature and UVR on phytoplankton growth rates and zooplankton grazing rates (by adult female calanoid copepods). We also examine consequent changes in the absolute and relative abundance of the four dominant phytoplankton species present in the source lake (Asterionella formosa, Dinobryon sp., Discostella stelligera, and Fragilaria crotonensis). All four species exhibited higher growth rates at higher temperatures and three of the four species (all except Dinobryon) exhibited lower growth rates in the presence of UVR versus when shielded from UVR. The in situ grazing rates of zooplankton had significant effects on all species except Asterionella. Lower temperatures significantly reduced grazing rates on Fragilaria and Discostella, but not Dinobryon. While UVR had no effect on zooplankton grazing on any of the four species, there was a significant interaction effect of temperature and UVR on zooplankton grazing on Dinobryon. Discostella and Dinobryon increased in abundance relative to the other species in the presence of UVR. Colder temperatures, the presence of zooplankton, and UVR all had consistently negative effects on rates of increase in overall phytoplankton biomass. These results demonstrate the importance of indirect as well as direct effects of climate forcing by UVR and temperature on phytoplankton community composition in mountain lakes, and suggest that warmer climates and higher UVR levels may favor certain species over others.

A reliable, fast and low cost maximum power point tracker for photovoltaic applications

This work presents a new maximum power point tracker system for photovoltaic applications. The developed system is an analog version of the “P&O-oriented” algorithm. It maintains its main advantages: simplicity, reliability and easy practical implementation, and avoids its main disadvantages: inaccurateness and relatively slow response. Additionally, the developed system can be implemented in a practical way at a low cost, which means an added value. The system also shows an excellent behavior for very fast variables in incident radiation levels.

Moisture Degradation of Cyanate Ester/S2 Glass Composite Insulation Systems

The fusion devices currently being developed present several challenges for magnet designers. One challenge lies within the electrical insulation, which must be able to withstand extreme temperatures, large shear and compressive stresses, high operating voltages, and high levels of incident radiation. To address the need for better performing insulation systems, Composite Technology Development (CTD), Inc. has developed CTD-403, a cyanate ester resin with increased radiation resistance, ease of processing and fabrication, low moisture absorption characteristics, and high mechanical and electrical strength at cryogenic and elevated temperatures. The moisture absorption trends of CTD-403/S2 glass composite insulation were studied. The effects of humidity exposure on interlaminar shear strength (ILSS), compressive strength, dielectric strength, and glass transition temperature were also studied. The saturation level of the insulation was seen to increase with the relative humidity of the aging environment. Fickian behavior was seen at room temperatures below 97% relative humidity exposure. Non-Fickian behavior was seen at elevated temperatures. Saturation levels after 6 months exposure were seen to be below typical epoxy-based insulation systems, averaging 0.5% weight gain. Degradation of mechanical and electrical properties was seen with increased humidity exposure and moisture absorption. ILSS showed an average retention rate of 75% after 6 months exposure. The compressive strength showed no decrease after 6 months exposure at room temperature, and show retention rates greater than 90% at 75°C/79% RH. An average dielectric strength of 98.6 kV/mm was seen for all specimens at room temperature (above 90% retention) after 6 months exposure.

Global warming and biodiversity: Evidence of climate-linked amphibian declines in Italy

Amphibians are among the most endangered animals on Earth, and climatic shifts are among the hypothesized factors in their decline. We used spatial patterns of recent amphibian declines in Italy to test hypotheses pertaining to three potential, nonexclusive factors: climate change, habitat alteration, and high levels of incident solar radiation. This study was based on patterns of presence in a geographic grid for 19 species. Grid-squares in which presence had previously been documented, but was not re-confirmed after a specific threshold year, were considered to represent declines. Using a GIS-based approach, we calculated, for each cell, the mean values – or shift in mean values – of different parameters, used as proxies for the three factors. The measures of these parameters were entered as predictors in specific autocovariate models fitted on grid-square status. Our results suggest that while multiple factors have contributed to declines, climate change has been a major cause of population disappearances. We identified a common pattern of disappearances in areas that have been especially affected by climatic shifts. Our findings also strongly suggest that habitat alteration, due mainly to urban land use, has contributed to the decline of several species and that solar irradiation, though probably not a direct cause of mortality, may have been important in association with other stressors. By identifying the most threatened species, geographical hot spots of decline, and the primary causes of decline, our work provides a basis for improving management and setting conservation priorities.

Industrialization of Radiation-Resistant Cyanate Ester Magnet Insulation

Future magnet systems require electrical insulation that can withstand high levels of incident radiation, while also providing the necessary mechanical robustness and dielectric strength to operate these devices. Moreover, the insulation must also be compatible with industrial fabrication processes to enable their efficient, large-scale manufacture. Cyanate ester-based insulations provide the necessary electro-mechanical performance and radiation resistance for these applications, but more information is needed to demonstrate application-specific issues related to magnet production. To accomplish this, a series of tests were performed to validate the long-term processing behavior of cyanate ester resins, their adhesion to Kapton, and the fabrication of small-scale coils. The results of this work demonstrated a working time of greater than 85 hours, good adhesion to Kapton, and the successful fabrication of test coils. Larger-scale industrial trials are ongoing at various sites to further demonstrate the use of cyanate ester insulation for the ITER TF coils, as well as commercial applications.

Nesting ecology of the critically endangered Fijian Crested Iguana Brachylophus vitiensis in a Pacific tropical dry forest

Tropical dry forest (TDF) ecosystems occur throughout tropical and subtropical zones and one of their primary characteristics is that they are structurally and functionally constrained by seasonal fluctuations in moisture levels. Organisms within them synchronize growth and reproduction with water availability and many exhibit adaptations to drought conditions. We examined the previously unknown nesting ecology of the Critically Endangered Fijian Crested Iguana Brachylophus vitiensis a TDF specialist, on the Fijian island of Yadua Taba over two field seasons. In Fiji, the TDF and the endemic Crested Iguanas are threatened on a national level by anthropogenic factors and Yadua Taba Island remains the only protected site. Evaluation of adult female reproductive status revealed that only 52% of adult females reproduced in a given year. We suggest that female Crested Iguanas have adopted a biennial mode of reproduction in response to resource limitation.We found no evidence for communal nesting or nest site defence by females. All nest burrows were constructed on the forest floor in shaded areas. Mean nest temperatures (24.5�C), levels of site openness (10.9%) and total incident radiation (2.57 MJ m2 day) recorded at nest sites were less than those reported for other Iguaninae. Mean egg size (17.9 g) was large relative to most Iguaninae and was independent of the small mean clutch size (2.9 eggs). Mean incubation period was extremely long (256 days) and spanned the eight-month dry season. Mean hatching success also was high (87%). We examine reproductive strategy in relation to the environmental conditions of the TDF habitat on Yadua Taba. This research provides a broader understanding of Crested Iguana nesting ecology and is a step towards the successful implementation of the Species Recovery Plan for this species.

A passive solar water heating system for vineyard frost protection

The threat of frost during spring time (after ‘bud burst’) is an ever present danger to the vineyard owner. To minimise the risk, in addition to good site selection and vineyard management, a number of active frost protection systems are available. Most active methods of frost protection are costly in monetary terms and can also have a detrimental effect on the environment. This work presents the design and performance of a passive solar water heating quilt system under real vineyard operating conditions. Two vineyard sites were selected, and the solar water heating quilt design was evaluated over a three-month period. Detailed measurements of the temperature below and above the soil surface, levels of incident solar radiation and the wind direction and speed were recorded. Field study results indicate that the quilts can improve the solar collection and heat retention of the soil, resulting in increased temperatures during frost events of up to 1 °C in air space immediately adjacent to the solar quilts when compared to conditions off the protected area. In addition, the time period during which the frost remains a danger to the vine is also reduced. When heat collection, storage and extraction rates are investigated, simplified calculations indicate that the solar quilt can improve collection by 38.5% over bare soil, resulting in the release of 32% more heat. Extrapolated to vineyard coverage, this could result in an extra 3500 MJ of heat per hectare per (typical frost event condition) day.

Arabidopsis Genotypes with Differing Levels of psbS Expression Differ in Photosystem II Quantum Yield, Xanthophyll Cycle Pool Size, and Aboveground Growth

Thermal energy dissipation protects the photosynthetic apparatus against excess light and requires de‐epoxidized xanthophyll cycle carotenoids, a low thylakoid lumen pH, and PsbS, an integral membrane subunit of photosystem II. Here, we examine photoprotection, photosynthesis, and growth in Arabidopsis thaliana genotypes whose capacities for energy dissipation have been altered via deletion or transgenic overexpression of psbS. Plants were grown in a greenhouse, where they experienced low levels of incident radiation throughout most of the day, with an ∼40‐min midmorning period of exposure to high incident radiation each day. Midday ratio of variable to maximal fluorescence and photosystem II quantum yield increased slightly with increasing levels of psbS expression, while xanthophyll cycle pool size and conversion state were negatively associated with psbS expression. Notably, transgenic overexpression of psbS led to a 12% increase in rosette diameter, while mutants with no psbS expression exhibited 16% smaller rosette diameters and 18% fewer leaves than the wild type. Thus, the protective role of thermal energy dissipation manifested in plants grown in a light environment that included a period of high incident radiation, during which the various genotypes sustained differing levels of photosystem II photoinactivation, and periods of low incident radiation, when electron transport presumably limited the rate of photosynthesis and photosystem II photoinactivation influenced the overall rate of photosynthesis and hence growth.

Helium Line Formation and Abundance during a C‐Class Flare

During a coordinated campaign which took place in May 2001, a C-class flare was observed both with SOHO instruments and with the Dunn Solar Telescope of the National Solar Observatory at Sacramento Peak. In two previous papers we have described the observations and discussed some dynamical aspects of the earlier phases of the flare, as well as the helium line formation in the active region prior to the event. Here we extend the analysis of the helium line formation to the later phases of the flare in two different locations of the flaring area. We have devised a new technique, exploiting all available information from various SOHO instruments, to determine the spectral distribution of the photoionizing EUV radiation produced by the corona overlying the two target regions. In order to find semiempirical models matching all of our observables, we analyzed the effect on the calculated helium spectrum both of A(He) (the He abundance) and of the uncertainties in the incident EUV radiation (level and spectral distribution). We found that the abundance has in most cases (but not in all) a larger effect than the coronal back-radiation. The result of our analysis is that, considering the error of the measured lines, and adopting our best estimate for the coronal EUV illumination, the value A(He)=0.075 +/- 0.010 in the chromosphere (for T>6300 K) and transition region yields reasonably good matches for all the observed lines. This value is marginally consistent with the most commonly accepted photospheric value: A(He)=0.085.

Soybean Genetic Improvement in Yield and the Effect of Late‐Season Shading and Nitrogen Source and Supply

Genetic improvement in soybean [Glycine max (L.) Merr.] yield has been associated with both assimilate and N accumulation [especially from dinitrogen (N2) fixation] during the seed‐filling period (SFP). Therefore, the physiological factors associated with genetic improvement may be dependent on abundant assimilate and N supply. The objectives of this study were to quantify genetic improvement in yield under: (i) assimilate limiting conditions, (ii) under low N fertility, and (iii) when either inorganic N fertilizer or N2 fixation is the main source of N. A randomized complete block experiment was conducted at two locations in 1998 and one in 1999. The main plot factor included no shade or a 63% shade treatment imposed after the R4/R5 developmental stage. The split plot factors were three N treatments: (i) inoculated, (ii) uninoculated with no additional fertilizer, and (iii) uninoculated plus fertilizer N. The split‐split plots were four cultivars, representing a pair of older and a pair of newer cultivars. Shading reduced dry matter (DM) accumulation, and both shading and N limitation reduced N accumulation and seed yield. However, the newer cultivars consistently maintained their yield advantage over the older cultivars under both shading and N limiting conditions as well as when the source of N was soil available N or N2 fixation. The results of the study suggest that the physiological factors that contribute to genetic improvement in yield are not dependent on the level of incident radiation during the SFP, or the source or availability of N during the SFP.

Wheat productivity in the Mediterranean Ebro Valley: Analyzing the gap between attainable and potential yield with a simulation model

Water deficit is an important constraint for wheat yield generation under Mediterranean environments. However, nitrogen (N) availability could limit yield in a more important way than poor water conditions. The aim of the work was to analyze, using the Ceres-Wheat crop simulation model, to what degree N fertilization constitutes a tool for reducing the gap between attainable and potential yield. Firstly, the model was calibrated and validated under a wide range of N and water conditions for the region of the Ebro Valley (NE Spain). Anthesis and maturity date were adequately predicted by the model. Predictions of yield tended to be quite accurate in general, though under severe water deficits precision was lower. We then assessed the gap between attainable and potential yield considering different N availabilities at sowing taking into account a weather database of 17 years for the location of Agramunt (NE Spain), representative of cereal growing conditions of the Mediterranean Catalonia. Potential yield ranged between 3.5 and 8.1 Mg ha −1. Variations in potential yield were explained by the duration of the period from sowing to anthesis and by the level of incident radiation during the period immediately previous to anthesis. Average attainable yield was 1.8 Mg ha −1 for N availability of 50 kg N ha −1; but increased to 2.8 Mg ha −1 for higher N availabilities (100–250 kg N ha −1). In the 25% of the worst years there was no effect of N availability on attainable yield. Increasing N availability beyond 100 kg N ha −1 generated a gain in yield only in 6% of the years. Variations between years in attainable yields were mainly explained by rainfall during the period from sowing to anthesis, whereas differences in attainable yield between N treatments increased with increases in rainfall. The gap between potential yield and attainable yield was higher in years with higher potential yield. On the other hand, the higher the attainable yield, the lower the gap. Thus, the proportion of the yield gap ascribed to N availability varied depending on the conditions of the growing season. In the high-yielding potential years, the main restriction for growth was water shortage, and fertilizing only slightly reduced the gap. Conversely, in rainy years characterized by low potential yields and mild water stresses, N management may constitute a simple tool for effectively reducing yield gap under rain-fed conditions.

Soybean Genetic Improvement in Yield and the Effect of Late-Season Shading and Nitrogen Source and Supply

Genetic improvement in soybean [Glycine max (L.) Merr.] yield has been associated with both assimilate and N accumulation [especially from dinitrogen (N2) fixation] during the seed-filling period (SFP). Therefore, the physiological factors associated with genetic improvement may be dependent on abundant assimilate and N supply. The objectives of this study were to quantify genetic improvement in yield under: (i) assimilate limiting conditions, (ii) under low N fertility, and (iii) when either inorganic N fertilizer or N2 fixation is the main source of N. A randomized complete block experiment was conducted at two locations in 1998 and one in 1999. The main plot factor included no shade or a 63% shade treatment imposed after the R4/R5 developmental stage. The split plot factors were three N treatments: (i) inoculated, (ii) uninoculated with no additional fertilizer, and (iii) uninoculated plus fertilizer N. The split-split plots were four cultivars, representing a pair of older and a pair of newer cultivars. Shading reduced dry matter (DM) accumulation, and both shading and N limitation reduced N accumulation and seed yield. However, the newer cultivars consistently maintained their yield advantage over the older cultivars under both shading and N limiting conditions as well as when the source of N was soil available N or N2 fixation. The results of the study suggest that the physiological factors that contribute to genetic improvement in yield are not dependent on the level of incident radiation during the SFP, or the source or availability of N during the SFP.

Melting of Snow Cover in a Tropical Mountain Environment in Bolivia: Processes and Modeling

Abstract To determine the physical processes involved in the melting and disappearance of transient snow cover in nonglacierized tropical areas, the CROCUS snow model, interactions between Soil–Biosphere–Atmosphere (ISBA) land surface model, and coupled ISBA/CROCUS model have been applied to a full set of meteorological data recorded at 4795 m MSL on a moraine area in Bolivia (16°17′S, 68°32′W) between 14 May 2002 and 15 July 2003. The models have been adapted to tropical conditions, in particular the high level of incident solar radiation throughout the year. As long as a suitable function is included to represent the mosaic partitioning of the surface between snow cover and bare ground and local fresh snow grain type (as graupel) is adapted, the ISBA and ISBA/CROCUS models can accurately simulate snow behavior over nonglacierized natural surfaces in the Tropics. Incident solar radiation is responsible for efficient melting of the snow surface (favored by fresh snow albedo values usually not exceeding 0.8) and also for the energy stored in snow-free areas (albedo = 0.18) and transferred horizontally to adjacent snow patches. These horizontal energy transfers (by conduction within the upper soil layers and by turbulent advection) explain most of the snowmelt and prevent the snow cover from lasting more than a few days during the wet season in this high-altitude tropical environment.

Effect of incident radiation integral on cauliflower growth and development after curd initiation

Two field experiments were conducted to assess the response of cauliflower cv. “Nautilus F1” to different radiation integrals after curd initiation by covering the plants with different levels (0, 38, 50 and 68%) of neutral shading materials during the autumn 1998 and summer 2000. Cauliflower growth and development declined with increasing shade levels after curd initiation. Total above ground dry matter increased linearly with accumulated incident radiation integral after curd initiation, however, under lower radiation conditions, the rate of increase per unit incident radiation integral was greater than under higher radiation conditions. Moreover, radiation conversion coefficient declined linearly with increasing incident radiation integrals up to approximately 6.1 MJ m−2 d−1 and thereafter, declined more slowly with further increase in incident radiation integrals. Therefore, dry matter accumulation was potentially more efficient under lower incident radiation than higher incident radiation levels. Radiation conversion coefficients for plants under low incident radiation levels were greater than under high incident radiation levels. Curd growth also increased linearly with increasing accumulated incident radiation integral with greater mean relative curd dry matter increase per MJ under lower incident radiation conditions than higher incident radiation levels.

Effect of Natural Sunlight on Bacterial Activity and Differential Sensitivity of Natural Bacterioplankton Groups in Northwestern Mediterranean Coastal Waters

We studied the effects of natural sunlight on heterotrophic marine bacterioplankton in short-term experiments. We used a single-cell level approach involving flow cytometry combined with physiological probes and microautoradiography to determine sunlight effects on the activity and integrity of the cells. After 4 h of sunlight exposure, most bacterial cells maintained membrane integrity and viability as assessed by the simultaneous staining with propidium iodide and SYBR green I. In contrast, a significant inhibition of heterotrophic bacterial activity was detected, measured by 5-cyano-2,3 ditolyl tetrazolium chloride reduction and leucine incorporation. We applied microautoradiography combined with catalyzed reporter deposition-fluorescence in situ hybridization to test the sensitivity of the different bacterial groups naturally occurring in the Northwestern Mediterranean to sunlight. Members of the Gammaproteobacteria and Bacteroidetes groups appeared to be highly resistant to solar radiation, with small changes in activity after exposure. On the contrary, Alphaproteobacteria bacteria were more sensitive to radiation as measured by the cell-specific incorporation of labeled amino acids, leucine, and ATP. Within Alphaproteobacteria, bacteria belonging to the Roseobacter group showed higher resistance than members of the SAR11 cluster. The activity of Roseobacter was stimulated by exposure to photosynthetic available radiation compared to the dark treatment. Our results suggest that UV radiation can significantly affect the in situ single-cell activity of bacterioplankton and that naturally dominating phylogenetic bacterial groups have different sensitivity to natural levels of incident solar radiation.

Forest encroachment into a Californian grassland: examining the simultaneous effects of facilitation and competition on tree seedling recruitment

Competition and facilitation are both considered major factors affecting the structure of plant assemblages, yet few studies have quantified positive, negative, and net effects simultaneously. In this study, we investigated the positive, negative, and net effects of tree saplings on the encroachment of two tree species, Douglas fir (Pseudotsuga menziesii) and tanoak (Lithocarpus densiflora), into a coastal California grassland. The study involved three components: sampling the spatial distributions of P. menziesii and L. densiflora in the grasslands, a field experiment examining seedling survival in different grassland environments, and a greenhouse experiment examining the effects of soil moisture on early seedling performance. The field experiment was conducted over a 2-year period, using Pseudotsuga in 2002 and both species in 2003. Seedlings were separated into four treatment groups: those planted in open grassland, in shaded grassland, under artificial (plastic) conifer saplings, and under natural Pseudotsuga saplings. Air temperature, relative humidity, soil moisture, incident radiation levels and fog water inputs were measured for each treatment group in 2003. In the greenhouse experiment, Pseudotsuga and Lithocarpus seedlings were grown for 13 weeks in watering treatments simulating the summer soil moisture conditions of the open grasslands and under Pseudotsuga saplings. Surveys of naturally established seedlings found that Lithocarpus occurred only under Pseudotsuga saplings, while most Pseudotsuga seedlings were located near but not directly under conspecific saplings. In the field experiment, positive effects of tree saplings were much larger than negative effects, resulting in strong net facilitation of seedling establishment. Survival for both species was always higher under the plastic and live trees than in the open or shade plots. The primary mechanism facilitating seedling survival appeared to be increased soil moisture caused by input of fog precipitation coupled with reduced microsite evaporation. The greenhouse experiment further showed that soil moisture strongly affected seedling performance, with both species having much higher photosynthetic rates in the higher moisture treatment. In the lower moisture treatment, Pseudotsuga seedlings had higher photosynthetic rates and stomatal conductance than Lithocarpus, suggesting they may be able to better tolerate the environmental conditions found in the open grasslands. Our combined results suggest that rate and patterning of woody plant encroachment can be strongly influenced by facilitation and that fog precipitation may play a key role in plant interactions.

SEASONAL CARBOHYDRATE AND TOTAL NITROGEN DISTRIBUTION IN ROSE PLANTS: DEVELOPMENTAL AND GROWTH IMPLICATIONS

SEASONAL CARBOHYDRATE AND TOTAL NITROGEN DISTRIBUTION IN ROSE PLANTS: DEVELOPMENTAL AND GROWTH IMPLICATIONS

Comparison and sensitivity analysis of instruments and radiometric methods for LAI estimation: assessments from a boreal forest site

Retrievals of LAI from inversion of canopy radiometric measurements, using the Li-Cor LAI-2000 Plant Canopy Analyzer and the Decagon AccuPar Ceptometer (a linear quantum probe) were analyzed and compared. Field data were collected from 34 sites in the boreal forest of interior Alaska, and sensitivity tests were conducted to estimate the effect of a variety of measurement conditions on the LAI retrievals. We also tested the response of estimated LAI to different values of the theoretical parameters in the retrieval algorithms. Uncertainty in the incident radiation level was magnified by the LAI retrieval, meaning that even small errors in this measurement significantly affected the LAI estimates. Changes in solar zenith angle over long data acquisition times also contributed to the errors. The most important quality control factors for accurate retrieval of LAI from field measurements were the incident radiation and solar zenith angle. A series of sensitivity tests showed that extreme values of leaf angle distribution could change LAI estimates, but our multi-angle measurements produced results consistent with a spherical leaf angle distribution. Alternative methods taken from the literature for post-processing of the data from the two instruments produced similar results for the LAI-2000, but widely different results for the Decagon AccuPar. Retrievals from the two instruments had an overall correlation coefficient r=0.88,( P<0.01). Agreement was considerably better in aspen stands ( r=0.85, P<0.01, N=43) than in spruce ( r=0.56, P<0.05, N=22). Some of the variability was attributed to spatial heterogeneity within stands, particularly sparse spruce canopies. Overall, our results suggest the retrievals were robust, and largely comparable between instruments over a range of measurement conditions, provided variability in measurement conditions was adequately characterized.

Características fisiológicas e de crescimento de cafeeiro sombreado com guandu e cultivado a pleno sol

O conhecimento dos efeitos do sombreamento sobre a fisiologia de cafeeiros é importante para se determinar níveis ótimos de radiação e temperatura, bem como para subsidiar estudos sobre o crescimento de plantas sombreadas, a fim de determinar a arquitetura ideal do cafeeiro que maximize a captura da radiação solar disponível em ambientes sombreados. O objetivo deste trabalho foi avaliar características fisiológicas e de crescimento de cafeeiros (Coffea arabica L.) cultivados sob sombreamento denso com guandu (Cajanus cajan (L.) Millsp.) e a pleno sol. O baixo nível de radiação incidente sobre os cafeeiros sombreados com guandu resultou em decréscimos na taxa fotossintética e na transpiração, maior altura de planta, folhas maiores e com menor quantidade de matéria seca. Esses resultados indicam que o excesso de sombra afeta drasticamente a fisiologia e morfologia de C. arabica.