Plant Leaf Temperature Research Articles

Determination of Salt Stress by Plant Leaf Temperature and Thermal Imaging in Black Cumin Grown Under Different Salt Sources

ABSTRACT Thermal imaging has been used in recent years to determine salinity stress in certain crops. However, no information is available on this regarding black cumin (Nigella sativa L.). The main purpose of this study was to investigate the determinability of the salt stress on black cumin by thermal imaging. The leaf temperature values were obtained by acquiring the thermal images for black cumin grown under different irrigation water salinity levels (0.6 as control, 1.5, 2.5, and 5.0 dS/m) prepared for different salt sources (CaCl2, MgCl2, NaCl, Ca(NO3)2, MgSO,4 and Na2SO4). Plant leaf temperatures averaged over all irrigation water salinity levels did not show a significant difference among salt sources. On the other hand, plant leaf temperatures independent of the salt sources significantly increased with increasing salinity levels. The order for salinity levels in terms of their effect on the leaf temperature of black cumin was determined as 5.0 dS/m > 2.5 dS/m > 1.5 dS/m ≥ 0.6 dS/m. The highest leaf temperature was obtained under 5.0 dS/m salinity level with CaCl2, MgCl2, Ca(NO3)2, MgSO4, and Na2SO4 salt sources, but the values for MgSO4 and Na2SO4 salt sources were not significantly different from those under 2.5 dS/m salinity. In addition, a strong-negative relationship between plant water consumption and leaf temperature under CaCl2 and MgSO4 and a moderate-negative relationship under MgCl2 and NaCl salt sources were determined. The results of this study showed that the plant leaf temperature values obtained by thermal imaging reflected salt stress conditions, especially under high salinity levels.

EVALUAREA COMPORTARII TERMICE A PLANTELOR IN MICROSERA CU SENZORI DE IMAGINE MICROBOLOMETRICI

In this research, the data from temperature measurements obtained with the InfiRay T2S+ device, an infrared thermal imaging camera have been checked to monitor plant thermal behaviour. Plant leaf temperature is a parameter frequently used as representative for stomatal conductance, as stomatal confinement results in attenuated transpiration, and consequently leads to increased plant temperature. Also, to identify the stress of the plant, indices of thermal and modified stress have been calculated. The results obtained show that the Kalanchoe blossfeldiana species chosen for this study, when exposed to extreme values of temperature or water requirements, presented significant changes in the infrared electromagnetic wave spectra.

Development of an IoT-Based SCADA System for Monitoring of Plant Leaf Temperature and Air and Soil Parameters

Plant leaf temperature and its environmental parameters provide valuable information on plant growth. This paper presents the development of a plant monitoring system using an IoT-based SCADA (Supervisory Control and Data Acquisition). The developed SCADA system monitors the leaf temperature and the air parameters of temperature and humidity, as well as the soil parameters of temperature, moisture, pH, electrical conductivity, nitrogen, phosphorous, and potassium. A novel method is proposed for measuring the leaf temperature using a low-cost 8 × 8 array thermal camera. The sensor systems in the field are developed to wirelessly communicate with the Hawell IoT Cloud HMI via a Modbus TCP protocol. To visualize the thermal image on the HMI dashboard, a novel approach is proposed wherein the data are transferred using the Modbus TCP protocol. The HMI is connected to a cloud server and can be accessed by the users using the web browser or mobile application on a smartphone. The experimental results show that the proposed hardware, software, and communication protocol are reliable for real-time and continuous plant monitoring. Further, the evaluation of sensor data shows that the data from the thermal camera and air parameters sensor can be independently interpreted. However, the data from the soil sensor should be interpreted in consideration of the other parameters.

Determination of Water Stress in Wheat Crops by Thermal Images Under Mediterranean Conditions

ABSTRACT Canopy temperature is used as an indicator of plant water stress. In recent years, technological advances have allowed improved applications in agriculture from temperature sensors clamped on leaves to short-range remote-sensing, such as infrared thermometry and thermal imaging. There are many scientific studies on the use of thermal imaging to determine crop water stress; however, no study on wheat crops has been found in the literature. Therefore, this study aimed to determine the detectability of water stress in wheat by using thermal images. In the experiment, drainage-type, weighable lysimeters were used to make precise irrigations and obtain components of the water budget for calculating the plant water consumption. Wheat crops were grown under four different irrigation levels including no water stress as control (I100), mild water stress (I75), moderate water stress (I50), and severe water stress (I25). When the thermal images were examined, it can be seen that pre-irrigation images reflect water stress conditions better than post-irrigation. The warm color distribution was more evident under severe water stress, whereas cold colors were dominant under no water stress. During the experimental period, the plant leaf temperatures varied from 17.5 to 34.2°C, while the spike temperatures ranged from 26.6°C to 36.3°C. The lowest plant leaf and spike temperature values were observed under control, whereas the highest values were obtained under severe water stress. It can be said that thermal cameras that provide fast and contactless data acquisition have the potential to be used in detecting water stress in wheat crops.

The Potential of a Low-Cost Thermal Camera for Early Detection of Temperature Changes in Virus-Infected Chili Plants

One effect of viral infection on plant physiology is increased stomata closure so that the transpiration rate is low, which in turn causes an increase in leaf temperature. Changes in plant leaf temperature can be measured by thermography using high-resolution thermal cameras. The results can be used as an indicator of virus infection, even before the appearance of visible symptoms. However, the higher the sensor resolution of the thermal camera, the more expensive it is, which is an obstacle in developing the method more widely. This article describes the potential of thermography in detecting Tobacco mosaic virus infection in chili-pepper plants using a low-cost camera. A FLIR C2 camera was used to record images of plants in two treatment groups, non-inoculated (V0) and virus-inoculated plants (V1). Significantly, V1 had a lower temperature at 8 and 12 days after inoculation (dai) than those of V0, but their temperature was higher than V0 before symptoms were visible, i.e., at 17 dai. Thermography using low-cost thermal cameras has potency to detect early viral infection at 8 dai with accuracy levels (AUC) of 80.0% and 86.5% based on k-Nearest Neighbors and Naïve Bayes classifiers, respectively.

IRimage: open source software for processing images from infrared thermal cameras.

IRimage aims at increasing throughput, accuracy and reproducibility of results obtained from thermal images, especially those produced with affordable, consumer-oriented cameras. IRimage processes thermal images, extracting raw data and calculating temperature values with an open and fully documented algorithm, making this data available for further processing using image analysis software. It also allows the making of reproducible measurements of the temperature of objects in a series of images, and produce visual outputs (images and videos) suitable for scientific reporting. IRimage is implemented in a scripting language of the scientific image analysis software ImageJ, allowing its use through a graphical user interface and also allowing for an easy modification or expansion of its functionality. IRimage’s results were consistent with those of standard software for 15 camera models of the most widely used brand. An example use case is also presented, in which IRimage was used to efficiently process hundreds of thermal images to reveal subtle differences in the daily pattern of leaf temperature of plants subjected to different soil water contents. IRimage’s functionalities make it better suited for research purposes than many currently available alternatives, and could contribute to making affordable consumer-grade thermal cameras useful for reproducible research.

Design and implementation of a low-cost sensor network to monitor environmental and agronomic variables in a plant factory

Monitoring equipment for plant-factory automation requires big capital investments. Low-cost open-source microcontroller platforms have been employed in agriculture to monitor and control different variables of importance for crop production. A low-cost plant-factory monitoring system for measuring air temperature, relative humidity, plant-leaf temperature, pH, electrical conductivity, dissolved oxygen and temperature of the nutrient solution is presented here. All the information is recorded in a micro SD memory and can be accessed by Bluetooth in real-time. The developed system was tested during a cycle of a lettuce crop in a research plant-factory facility. The quality of the collected data was evaluated and compared with a well-known research-grade monitoring system. The low-cost sensors showed an easy to correct bias when were compared to those of research-grade, with a correlation coefficient over 0.96. The results showed that low-cost systems, like the one implemented here, are a good alternative for monitoring environmental and physiological variables in controlled environmental agriculture facilities.

Root ABA Accumulation Enhances Rice Seedling Drought Tolerance under Ammonium Supply: Interaction with Aquaporins.

In previous studies, we demonstrated that ammonium nutrition enhances the drought tolerance of rice seedlings compared to nitrate nutrition and contributes to a higher root water uptake ability. It remains unclear why rice seedlings maintain a higher water uptake ability when supplied with ammonium under drought stress. Here, we focused on the effects of nitrogen form and drought stress on root abscisic acid (ABA) concentration and aquaporin expression using hydroponics experiments and stimulating drought stress with 10% PEG6000. Drought stress decreased the leaf photosynthetic rate and stomatal conductivity and increased the leaf temperature of plants supplied with either ammonium or nitrate, but especially under nitrate supply. After 4 h of PEG treatment, the root protoplast water permeability and the expression of root PIP and TIP genes decreased in plants supplied with ammonium or nitrate. After 24 h of PEG treatment, the root hydraulic conductivity, the protoplast water permeability, and the expression of some aquaporin genes increased in plants supplied with ammonium compared to those under non-PEG treatment. Root ABA accumulation was induced by 24 h of PEG treatment, especially in plants supplied with ammonium. The addition of exogenous ABA decreased the expression of PIP and TIP genes under non-PEG treatment but increased the expression of some of them under PEG treatment. We concluded that drought stress induced a down-regulation of aquaporin expression, which appeared earlier than did root ABA accumulation. With continued drought stress, aquaporin expression and activity increased due to root ABA accumulation in plants supplied with ammonium.

ALGUNOS ASPECTOS SOBRE LA TEMPERATURA DE HOJAS PERTENECIENTES A PLANTAS DE LA REGIÓN XEROFÍTICA DE SANTA MARTA (COLOMBIA)

Leaf temperatures of several plant species of the xerophytic vegetation near Santa Marta (Colombia) were studied during the dry and the wet season. The leaves of species growing in a cactus thorn scrub reached very high temperatures, especially in the dry season, while leaf temperatures of plants in the area of a disappeared semi-deciduous seasonal forest were lower because of more favorable conditions of water supply and microclimate.

Thermal sensitivity of grapevine leaves affected by Plasmopara viticola and water stress

Introduction: There has been an increasing interest in using non-destructive thermal imagery to determine leaf temperature of plants. Leaf temperature has been proven as an indicator of plant responses to various stressors (CHAERLE and VAN DER STRAETEN 2000), in particular for plant water availability (JONES 1999). The theory is that a reduced stomatal aperture restricts transpiration and consequently heat dissipation, resulting in an increase in leaf temperature (GATES 1964). The recognition of variations in leaf temperature led to the combined efforts to use infrared thermography and visible imagery to identify plant stress and non-destructively monitoring of plant’s physiological status, particularly for plant water availability in grapevines (JONES et al. 2002, STOLL and JONES 2007) or in response to various pathogen attacks (CHAERLE et al. 2004, OERKE 2006). The research objective was to test whether infrared thermography could be used to distinguish between confined and infected versus non-infected areas upon attack by Plasmopara viticola in grapevine leaves under varying water status conditions.

Parametric and Performance Analysis of a Naturally Ventilated Floriculture Greenhouse Using a Thermal Model

Greenhouse technology is a method of cultivation of flowers, vegetables and medicinal plants under a controlled environment. The main objective of the greenhouses located in the plains of India is to protect the plants from excessive sensible heat from the solar radiation and ambient temperature. The structure also protects the plants from the storm and pest. Natural ventilation (along with shading screens) can be employed to regulate the required greenhouse microclimate in a cost effective manner. In the present paper the authors analyze the performance of a greenhouse from the view point of cultivation of varieties of Gerbera flower using a thermal model developed and presented earlier. Parametric analysis has been done to understand the effect of various crop, design and climatic parameters on the performance of the system. From the performance analysis of the greenhouse, it is revealed that the plant leaf temperature could be maintained within the permissible limit for the cultivation of the target flowers for various seasons of a climatic cycle. The study reveals that the natural ventilation along with shading in a greenhouse can lead to the sustainable cultivation of target flowers in the region under consideration.

Ecophysiological function of leaf ‘windows’ in Lithops species – ‘Living Stones’ that grow underground

Leaf temperatures were lower when light entry at the leaf tip window was prevented through covering the window with reflective tape, relative to leaf temperatures of plants with leaf tip windows covered with transparent tape. This was true when leaf temperatures were measured with an infrared thermometer, but not with a fine-wire thermocouple. Leaf tip windows of Lithops growing in high-rainfall regions of southern Africa were larger than the windows of plants (numerous individuals of 17 species) growing in areas with less rainfall and, thus, more annual insolation. The results of this study indicate that leaf tip windows of desert plants with an underground growth habit can allow entry of supra-optimal levels of radiant energy, thus most likely inhibiting photosynthetic activity. Consequently, the size of the leaf tip windows correlates inversely with habitat solar irradiance, minimising the probability of photoinhibition, while maximising the absorption of irradiance in cloudy, high-rainfall regions.

THEORETICAL MODELING OF TEMPERATURE PULSATIONS IN PLANT LEAF WHICH ARE CAUSED BY LEAF SWING WITH RESPECT TO THE SUN / LOKALIŲ AUGALO TEMPERATŪROS PULSACIJŲ, KURIAS SUKELIA LAPO SVYRAVIMAI SAULĖS ATŽVILGIU, TEORINIS MODELIAVIMAS / ТЕОРЕТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ЛОКАЛЬНЫХ ПУЛЬСАЦИЙ ТЕМПЕРАТУРЫ,ВЫЗЫВАЕМЫХ КОЛЕБАНИЕМ ЛИСТ AРАСТЕНИЯО ТНОСИТЕЛЬНО CОЛНЦА

The plant leaf temperature is a result of biological processes occurring in an organ of the plant and its energy exchange with the environment. The plant leaf temperature always differs from the ambient temperature except for the moments of transition from a positive to a negative (or vice versa) temperature gradient. It is determined that the plant leaf temperature continuously changes during the sunny time of the day. Temperature pulsations emerge in plant tissues when the leaf naturally changes its position with respect to the Sun (e.g. impacted by the wind) during the sunny period of the day. When a leaf position changes with respect to the source of radiation, a temperature change in the plant leaf also depends on local plant leaf thickness δ, leaf position angle β, leaf oscillation frequency ƒ and a temperature difference between the leaf surface and the atmosphere. When changing its position with respect to the Sun during the sunny period of the day the plant leaf plate becomes a temperature mosaic. Changing the leaf tillt angle from 30° to 60° depending on leaf thickness δ, it is estimated by mathematical modeling that during 6 s the temperature change in the plant leaf reaches 0,03-0,29° C (when β=30°) and 0,11-1,04°C (when β=60°) respectively. Temperature pulsations in the plant leaf entail local temperature gradients in the leaf plate as well as changes in the local balance of plant leaf energies. The anatomic framework of the plant leaf predetermines different local impulses of temperature changes in the plant leaf. The emerged temperature gradient generates heat fluxes in the plant leaf plate. Santrauka Augalo organo temperatūra yra augalo organe vykstančių biologinių procesų ir jo energinės apykaitos su aplinka rezultatas. Augalo lapo temperatūra, išskyrus perėjimo momentus iš teigiamo į neigiamą (arba atvirkščiai) temperatūros gradientą, visuomet skiriasi nuo aplinkos temperatūros. Nustatyta, kad saulėtu paros metu augalo lapo temperatūra nuolat kinta. Saulėtu paros metu natūraliai keičiantis augalo lapo padėčiai Saulės atžvilgiu (pvz., dėl vėjo poveikio) lapo audiniuose kyla temperatūros pulsacijos. Temperatūros pokytis augalo lape, kintant lapo padėčiai spinduliavimo Šaltinio atžvilgiu, priklauso ir nuo lokalaus augalo lapo storio δ, lapo padėties kampo β, lapo svyravimo dažnio ƒ ir temperatūrų skirtumo tarp lapo paviršiaus ir aplinkos. Augalo lapo plokštelė, saulėtu paros metu keisdama padėtį Saulės atžvilgiu, tampa temperatūrine mozaika. Kintant lapo posvyrio kampui nuo 30° iki 60°, matematiškai modeliuojant nustatyta, per 6 s temperatūros pokytis augalo lape priklausomai nuo lapo storio δ (0,11 mm) atitinkamai siekia 0,03-0,29° C (kai β=30°) ir 0,11-1,04° C (kai β=60°). Dėl temperatūros pulsacijų augalo lape susidaro lokalieji temperatūros gradientai lapo plokštelėje, atsiranda pokyčių lokaliame augalo lapo energijų balanse. Dėl augalo lapo anatominės sandaros augalo lape susidaro lokalūs temperatuūros pokyčio impulsai. temperatūros gradientas augalo lapo plokštelėje sukuria šilumos srautus. Резюме Температура органа растения является результатом биологических процессов в нем и его энергетического обменас окружающей средой. Температура листа растения, за исключением моментов перехода от положительного котрицательному (или наоборот) градиенту температуры, всегда отличается от температуры окружающей среды.Установлено, что в солнечные часы дня при натуральном изменении положения листа по отношению к Солнцутемпература листа постоянно меняется. В солнечные часы дня при натуральном изменении положения листаотносительно Солнца (например, под влиянием ветра) в тканях листа возникают температурные пульсации.Температурные изменения в листе растения зависят от локальной толщины листа δ, угла положения листа β,частоты колебаний листа f и разницы между температурой листа и окружающей среды. В солнечные часы дняпластинка листа растения под влиянием ветра меняет положение относительно Солнца и становитсяпульсирующей температурной мозаикой. Математическим моделированием установлено, что изменение угла положения листа β от 30° до 60° в зависимости от толщины листа δ (0,1–1 мм) в течение 6 с вызывает температурные изменения соответственно 0,03–0,29 °C (при β = 30°) и 0,11–1,04°C (при β = 60°). Пульсации температуры влисте растения вызывают локальные градиенты температуры, а также изменения в локальном энергетическомбалансе листа растения. Анатомическая структура листа растения является причиной, вызывающей локальныеизменения температуры, что создает тепловые потоки в пластинке листа растения под влиянием температурногоградиента.

Energy Saving Achieved by Retractable Liquid Foam between Double Polyethylene Films Covering Greenhouses

Heating is a major cost component in greenhouse crop production. A retractable liquid foam insulation technology was developed recently in Canada to reduce energy use for greenhouse heating. The system dynamically generates and injects liquid foam into the cavity between two polyethylene films in the greenhouse roof. Several experiments were conducted in southwestern Ontario, Canada, from December 2007 through May 2008 to evaluate the energy saving potential of this technology. The liquid foam system was installed in two independent greenhouses; in one of them, the system was shut off to serve as control. The foam was used only during the night for greenhouse insulation. In December 2007, no crop was grown inside the greenhouses. During the first five months of 2008, tomato (Lycopersicon esculentum) and sweet pepper (Capsicum annuum) plants were grown inside both greenhouses. Natural gas consumption for heating, and inside microclimate and outside climatic conditions (air and leaf temperature, humidity, solar radiation, and wind speed) were recorded. Heat loss from the roof with or without liquid foam was calculated. During December 2007, the liquid foam reduced the heat loss through the roof by 31%. During 2008, the heat loss was reduced by 29%, 36%, and 42% for January, February, and March, respectively. A larger reduction in roof heat loss (higher energy saving) was recorded during spring nights: 62% and 58% in April and May 2008, respectively. Therefore, the liquid foam showed a good energy saving potential (29% to 62%), but its energy saving decreased with low outside temperature. Further improvement in liquid foam formulation may be needed to increase its energy saving potential during the winter under low outside temperature conditions. Finally, liquid foam insulation resulted in higher greenhouse air temperature and plant leaf temperature; this should benefit plant growth and development and promote early yield.

EFFECTS OF POLYETHYLENE POT REMOVAL AND IRRIGATION METHOD ON GROWTH AND FLOWERING OF GARDEN-TYPE CYCLAMEN

As garden-type cyclamens are intolerant to high temperature or strong irradiation, their growth is stunted under such conditions during the summer season in southwest Japan. Evaporative cooling from the surface of compacted medium without polyethylene pot is expected to enhance the growth of garden-type cyclamens. The effects of polyethylene pot removal and irrigation method on growth and flowering of garden-type cyclamen during the summer season were investigated. Water was supplied by wick irrigation, ebb and flow irrigation (once a day) and overhead irrigation from 25 July to 4 September. From half of the plants in each treatment, polyethylene pots were removed from compacted media. Maximum, minimum and average temperatures of compacted medium without polyethylene pot decreased significantly compared to that of compacted medium with polyethylene pot. The medium temperature of the wick irrigation with polyethylene pot was highest. However, the temperature differences among irrigation methods without polyethylene pot were slight. The leaf temperature of plants grown in compacted medium without polyethylene decreased significantly compared to that with polyethylene pot. At planting, total fresh weight, leaf number and bud number of plants grown on compacted medium without polyethylene pot were significantly higher than those with polyethylene pot. However, there was no difference with regard to tuber weight and size among treatments. Subsequent growth after planting showed the same tendency as the size at planting. These results suggest that in garden-type cyclamen production during summer season, evaporative cooling by compacted medium without polyethylene pot may decrease medium and plant temperature, thus, plant growth may be enhanced.

Automated canopy temperature estimation via infrared thermography: A first step towards automated plant water stress monitoring

Canopy temperature estimation is an important process for plant water status monitoring. In this paper the problem for measurement data of the scene acquired via an infrared (IR) thermography system is considered. An optical image taken from the plant canopy is aligned with the underlying IR image, so that plant leaf area can be extracted via simple colour identification techniques and then the temperature distribution of the leaf area is obtained. The success of this procedure relies on the assumption that both optical–IR image alignment and leaf area extraction are perfect. In practice, such assumptions are rarely justifiable and the computed result can often be found undesirable. Particularly, the simple colour identification technique fails when temperatures of reference leaves, which are embedded in the canopy and provide known conductance to water vapour, are required to be estimated. In this paper, we address this issue and propose a novel algorithm to solve the problem. The underlying plant leaf temperature distribution is considered to be the fusion of two temperature densities separable via a combination of colour identification and Gaussian mixture distribution extraction techniques. A N-average method is tested with moderate success to estimate reference leaf temperatures from the estimated leaf temperature distribution. Our experimental results demonstrate the effectiveness and consistency of the proposed algorithm.

SEWAGE SLUDGE AS NUTRIENT SOURCE FOR BIOENERGY CROPS

Sewage sludge is rich in organic matter, and plant nutrients such as nitrogen, phosphorus andpotassium. Nevertheless, using sludge as fertilizer for crops to produce food or feed is limited due to thepresence of trace contaminants such as heavy metals. Therefore, the aim of this study was to investigatethe use of sewage sludge as a nutrient source for bioenergy crops such as fibre hemp, oilseed rape andwhite lupin. Specific attention is paid to the biomass accumulation and the quality of the plant material aswell as the ability of the crops to take up the heavy metals from soils in order to ensure that the amount ofpollutant does not cumulate.Fibre hemp (Cannabis sativa L.) cv. Uso, oilseed rape (Brassica napus L.) cv. Wildcat and whitelupin (Lupinus albus L.) cv. Amiga were sown in 5-L pots in a greenhouse. Three potting mixes wereused: a standard peat-based potting compost with 50% sludge, sludge with peat (50%:50% by weight), or100% sludge, and a constant mass of 666 g potting mix per pot. Dry weight of plants and leaf area weremeasured four times during the growth of fibre hemp and oilseed rape and at maturity of white lupin. Netphotosynthesis and leaf temperature of plants were measured three times. Ash content and elementalanalysis was made from samples collected at harvest.Sewage sludge application significantly affected most parameters measured. In fibre hemp,maximum dry weight, leaf area and photosynthesis values were obtained from the sludge – peat treatment.In oilseed rape, the maximum values of dry weight of plant, leaf area, photosynthesis, number of siliquesper plant and number of seeds per plant were obtained from the 100% sludge treatment. However, thehighest number of branches per plant, weight of siliques per plant, seed weight per plant and whole plantweight were obtained from the sludge – peat treatment. In white lupin, the sludge – peat treatment resultedin highest net photosynthesis, number of pods per plant, number of seeds per plant and whole weight plantat harvest. Highest sludge application resulted in highest heavy metal concentration in plant material offibre hemp and white lupin. However, high heavy metal concentration in oilseed rape were obtained whensludge was mixed with peat.It is concluded that sewage sludge is suitable for use as a nutrient source for bioenergy cropsstudied. In future experiments we will estimate the optimum level of sewage sludge for each one of thesecrops and determine its potential for use in field conditions.

Light microhabitats, growth and photosynthesis of an epiphytic bromeliad in a tropical dry forest

In the tropical dry forest of Dzibilchaltun, Yucatan, Mexico, light microhabitats, tissue acidity changes, chlorophyll fluorescence and growth were investigated for the epiphytic bromeliad Tillandsia brachycaulos Schltdl. Most individuals occurred in sites between 20 and 60% of the height of the tree, and directly on the main trunk or branches closed to the main trunk. During the dry season, individuals received about nine times more photon flux density (PFD) than during the rainy season. Individuals that occurred under 30-59% of the daily ambient PFD showed greater leaf length increase and monthly leaf production, and produced more flowers than individuals in the brighter ( > 60% of ambient PFD) and the darker (11-29% of ambient PFD) light microhabitats. Well-watered plants acclimated to deep shade (6% of ambient PFD) showed values of tissue acidity similar to plants under higher light treatments. Well-watered plants under 60% of daily ambient PFD showed low values of maximum quantum efficiency at midday during most of the year but showed similar values of tissue acidity than plants under 6 and 30% of ambient PFD. Leaf temperatures of plants in low sites within the canopy and on the forest floor were significantly higher than the air during about 1 h, indicating that those plants could not dissipate the excess of heat. Individuals located in the most shaded microhabitats could also receive less amount of water from rainfall and dew. Therefore, it would be less damaging for this epiphytic bromeliad to occur in the most exposed micro habitats than in the most shaded microhabitats in this tropical dry forest.

Permanent Magnetic Field and Plant Leaf Temperature

We investigated the effect of a permanent magnetic field as an environmental factor on fluorescence spectra and temperature of intact plant leaves. It has been shown that magnetic fields can induce significant changes in fluorescence spectra and leaf temperature. The fluorescence intensity ratio (FIR) and change of leaf temperature ΔT increase with the increase of magnetic field intensity. The increase of ΔT due to magnetic fields is explained with a simple model. Reasonable agreement between calculated ΔT, based on the model, and measured ΔT was obtained.

Infrared Radiometry for Measuring Plant Leaf Temperature during Thermal Weed Control Treatment

One side of a plant leaf was exposed to liquefied petroleum gas flames, while the temperature of the other side was measured continuously with an imaging infrared radiometer. Temperature histories of leaves and the performance of the measuring system were studied by flaming over 200 leaves and recording the measurements for off-line analysis. Flaming raised the temperature of the leaves very rapidly. The peak heating rate was typically around 180°C s −1. The imaging speed of the radiometer, 50 fields s −1, was sufficient to evaluate the temperature histories. Flaming induced marked temperature differences in the flamed leaves, with veins heated to lower temperatures than the thin areas between them. Thermograms with good spatial resolution were essential to characterise the temperature distribution with gradients as steep as 50°C over a 1 mm interval. With a factory calibrated radiometer an accuracy of ±2·1°C in absolute temperature values for a temperature range of 20–90°C was achieved by determining the target emissivity with the radiometer. By calibrating the radiometer for the actual conditions under measurements the error could be reduced to ±1·0°C. In conclusion, an imaging infrared radiometer is a superior instrument for measuring fast, spatially distributed temperature changes in plant leaves during thermal weed control treatment.