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Abstract
Dew is one of the important water resources on the earth and is beneficial to the survival, growth and development of the plants based on the arid and semiarid environment. The disputed effects of dew on plants, beneficial and harmful, were reviewed in this study. The beneficial effects mainly consist of five aspects: (1) Supplying important water resource. In the arid and semiarid regions or in the dry season, dew is the main or the only water resource because of its higher frequency and sustaining time comparing with the precipitation, which keeps the organic synthesis and metabolism, accelerates the increase of biomass in plants. (2) Regulating inner water of plants. The function of dew on regulating inner water of plants includes the following several aspects based on related studies: helping plant to rapidly activate photosynthetic activity during desiccation and rehydration; supplying a moisture environment in repairing embryo DNA of seeds, maintaining seed viability under harsh desert conditions; regulating the transpiration pressure and helping the wilting plant arrive a higher steady restoration state; etc. (3) Improving water balance of soil. There is an indirect effect of dew on plant through improving water balance of soil. On one hand, dew forms on the soil surface or drops into the soil from the nearby plants, becoming an importing water resource. On the other hand, the soil evaporation decreases along with dew event appears, leading a mitigation of soil water tension to some extent. (4) Regulating growing environment of forest plants. The regulation effect appears on canopy firstly, and then into the forest. Dew deposition increases the water resource of forest, improves its water cycle. Along with the dew deposition and evaporation, the forest micro-climate changes, especially the wind speed, moisture and heat. Dew, as a medium, is concerned with the water-heat exchange process of the forest. (5) Dew was used widely in the performing process of foliage dressing, defoliant and pesticide for its characteristics including small dew amount, long time sustaining on objects, leading an accreting of long time, extending the time of sterilization. The harmful effects mainly consist of two aspects: (1) Inducing plant disease. The pathogen of fungus and bacteria releases spores and infects the host plant under a moisture condition, and induces plant disease easily, thus dew supplies opportunities for pathogen. The infection intensity differs from the differences of dew quantity and sustaining time. (2) Reducing output and quality of crops. The influence on the output and quality of crops is related to the quantity, sustaining time, acidification level of dew. The plant stomata movement was inhibited and the route of pollen diffusing was discouraged when the quantity and sustaining time of dew arrive at a higher level. Acid dew could lead to a degradation of vegetation for the decreasing of CO2 assimilation efficiency. Furthermore, the black spot disease of fruit could be induced by dew. The main problems in related researches were also pointed out in present paper. For example, the information of dew action effect on plants was absent; few documents referred to the changing environment, such as urban heat island and the polluted atmosphere etc; researches of dew on plant diversity and the use on biological control were lack. Future studies were recommended to (1) researches of the action effect and mechanisms of dew on plants; (2) researches on the interactions of dew and plants based on the interferential factors including acid dew and the urban heat island effect; (3) researches of the influence of dew on the plant diversity; (4) applied researches on controlling harmful plants using dew.
... It was also reported that the majority of microwave emission models for the determination of soil moisture content do not account for the presence of dew on leaves which may represent a significant source of error for the models (Hornbuckle et al., 2006). Consequently, the evaporation of moisture from the soil decreases with the presence of dew (Ye & Peng, 2011). Inclusion of dew events or indeed the presence of leaf wetness would facilitate more accurate measurements of evapotranspiration and soil moisture content. ...
... The main use of leaf wetness measurements is as an input into disease prediction models (Bregaglio et al., 2011;Chungu et al., 2001;Montone et al., 2016;Morales et al., 2018;Rowlandson et al., 2015). The pathogens of fungi and bacteria release spores and infect the host plants under the presence of moisture, inducing plant disease easily, thus dew supplies opportunities for growth of pathogens (Ye & Peng, 2011). Accurate measurements of this phenomenon would allow for timely interventions on the part of farmers reducing the risk of yield loss and the need for increased levels of pesticides to deal with more major epidemics of specific diseases. ...
Leaf wetness is an important input parameter into disease prediction models. The use of machine learning algorithms for the classification of leaf wetness measurements from 30 meteorological stations in North Western Europe during the period of January 2014 to October 2018 was assessed in this study. The accuracy of the empirical models utilised within in this study was enhanced by increasing the relative humidity threshold from 90% to 92%. Increasing the relative humidity threshold led to an average increase in the classification accuracy of 1.12%. The use of machine learning classification algorithms consistently provided more accurate results for the prediction of leaf wetness when compared to the empirical models that were studied with an average increase in the classification accuracy of 4.85%. The sub-division of the data into regional subsets had a greater effect on the accuracy of the models than the temporal sub-division of the data. Machine learning classification techniques performed well compared with previously established empirical models for the prediction of leaf wetness. Further improvements in the algorithms are possible, making the techniques studied here a viable research tool.
... Pollinators visit flowers frequently in the morning with only a few visits after 1700 h. As a result, uplifting the second batch of stamens the next morning after flowering not only efficiently replaces the first batch of pollen, but also avoids reduction in pollen viability due to low night temperatures (Shaked et al. 2004) and the adverse effect of dew in the early morning (Ye and Peng 2011). ...
Approximately 80 % of angiosperm species produce hermaphroditic flowers, which face the problem of male–male sexual interference (one or more anthers gets in the way of disseminating pollen from other anthers) or male–female sexual interference (the pistil interferes with disseminating pollen from the anthers by preventing the anther from touching a pollinator, or the anther prevents pollinator from depositing outcross pollen on the stigma). Slow stamen movement in hermaphrodite flowers has been interpreted as an adaptation for reducing male–male sexual interference. Using slow stamen movement in Lychnis cognata (Caryophyllaceae), this study presents new evidence that this phenomenon can reduce both male–male and male–female sexual interference. Ten stamens in L. cognata flowers vertically elongated their filaments in two batches and displayed similar patterns in pollen dispensing. More importantly, 10 stamens bend out of the floral centre by curving the filament also in 2 batches and pollen grains located at the flower centre displayed the highest viability. Thus, three stages of stamen movement can be identified, comprising two male stages (M1 and M2) and one female stage (F). We found that the main pollinator for L. cognata, Bhutanitis yulongensis (Papilionodae) generally preferred M1 flowers. Manipulation experiments show that vertical stamen movement enabled the anthers to dehisce at different times to prolong the presentation of pollen grains. Horizontal movement of the stamen decreased both male–male and male–female interference. However, vertical stamen movement had a minor role in increasing amount of pollen received by the stigma. This study provides the first direct experimental evidence of concurrent male–male and male–female interference in a flower. We suggest that the selection pressure to reduce such interference might be a strong force in floral evolution. We also propose that other selective pressure, including pollen dispensing mechanisms, pollen longevity, pollinator behaviour and weather, might contribute to floral evolution.
... Many of the microorganisms involved in biological control, as well as many of the microorganism targets, are moisturelimited, i.e. they require free water on surfaces for growth, movement and infection. Changes in dew frequency and abundance and the availability of free water will have signifi cant impacts on the incidence of plant disease and on the effi cacy of biological controls employing microorganisms (Chakraborty and Newton, 2011;Garrett et al., 2011;Ye and Peng, 2011). Extreme drought will likely impair microbial biological control organisms, but will also likely impair some of the microbial plant pathogens. ...
This volume (71 chapters), the fifth in a series documenting biological control programmes in Canada, presents new information on specific insect, weed or plant diseases, some of which are updates of on-going studies on historical biological control projects while other chapters report on biological control efforts for new emerging invasive alien species. In each case, information is presented in a consistent and logical manner, starting with the pest status in Canada, followed by a comprehensive background on previous studies, review of the use of biological control in these programmes, and an evaluation of the biological control efforts and future needs in research or implementation activities. A total of 64 chapters is dedicated to biological control case studies over the past 11 years - 36 on insect pests of agricultural importance and forestry or ornamental pests; 18 on the control of weeds for crops, rangeland, pastures or aquatic areas; and 10 on the biological control of plant disease causal agents. This book is intended for researchers and students in biological control, pest management, ecology and risk assessment.
This paper considered relationship between soil weed seed bank seedlings and soil physicochemical parameters in arable farmlands was sampled in rainy and dry seasons at 3 different depths of 0-5, 5-10 and 10-15cm. Arable farmlands were 22 and 3 controls. Soils were collected at four points randomly with a soil auger, prepared for laboratory analyses and 100g each placed into 225 small bowls replicated 3 times, which were perforated and having tissue papers at base for soils to prevent soil and weed seeds wash off at watering. Emerged weed seedlings were counted, identified weekly for 12 weeks. Soils were allowed to dry and turned over at 4 and 8 weeks, respectively. Unidentified weeds seedlings were transferred into bigger bowls with humus soils, labeled to grow further and then identified. The parameters considered included soil weed seed bank seedlings and soil physicochemical properties. Weed seedlings data and result from physicochemical analysis were subjected to correlation analysis. Result at 5cm depth for rainy season revealed abundance of weed species significant (p<0.05) correlated with parameters K and Cu with a correlation coefficient (p-value) of 0.507 (0.016) and 0.611(0.003), respectively. But at 10cm depth it was only correlated with pH with a correlation coefficient (p-value of 0.501 (0.018). However, at 15cm weed species abundance was significant (p<0.05) correlated with parameters pH, P, Mg, K and Cu with correlation coefficient (p-value) of 0.488 (0.021), 0.459 (0.032) 0.458 (0.032), 0.445(0.038) and 0.525 (0.012), respectively. The correlation result in dry season revealed that at various depths weed species abundance was not significant (p<0.05). Conclusively, soil, water and cultural practices adopted by farmers might have impacted on the macro and micro nutrients availability with pH as master catalyst, while the non mobility of nutrients in dry season also affected non correlation. It can be determined from this study that the relationship between soil seed weed bank and soil properties in arable fields shows differences at the three depths.
As an important source of non‐rainfall input of land–surface liquid water, dew has considerable ecological and hydrological significance in desert ecosystems. Dew moisture regime is commonly used for characterizing available dew. It discloses not only the contributions of dew to plants, small animals, and biological crusts but also the mechanism by which desert organisms adapt to extreme climates. By reviewing the existing researches on dew moisture regimes in desert ecosystems, this study reveals the variations in the amount and duration of dew, as well as its influencing factors at site‐, catchment‐, and regional scales, based on the radiation cooling theory and the physical mechanisms of dew formation. Furthermore, it compares the differences in dew moisture between various sites and catchments, illustrates the trends in daily and annual dew moisture in various deserts, and identifies the existing problems of researches on dew moisture regimes amid climate change. The findings of this study enhance preliminary knowledge on the reasonable utilization of dew water, worldwide.
This article is categorized under:
• Science of Water > Hydrological Processes
• Water and Life > Nature of Freshwater Ecosystems
Dew is an important water source for plants in arid and semi-arid regions. However, information on dew is scarce in such regions. In this study, we explored dew formation, amount and duration of rain-fed jujube (Zizyphus jujube Mill) trees in a semi-arid loess hilly region of China (i.e., Mizhi County). The data included dew intensity and duration, relative humidity, temperature and wind speed measured from 26 July to 23 October of 2012 and from 24 June to 17 October of 2013 using a micro-climate system (including dielectric leaf wetness sensors, VP-3 Relative Humidity/Temperature Sensor, High Resolution Rain Gauge and Davis Cup Anemometer). The results show that atmospheric conditions of relative humidity of >78% and dew point temperature of 1°C–3°C are significantly favourable to dew formation. Compared with the rainfall, dew was characterized by high frequency, strong stability, and long duration. Furthermore, heavy dew accounted for a large proportion of the total amount. The empirical models (i.e., relative humidity model (RH model) and dew point depression model (DPD model)) for daily dew duration estimation performed well at 15-min intervals, with low errors ranging between 1.29 and 1.60 h, respectively. But it should be noted that the models should be calibrated firstly by determining the optimal thresholds of relatively humidity for RH model and dew point depression for DPD model. For rain-fed jujube trees in the semi-arid loess hilly regions of China, the optimal threshold of relative humidity was 78%, and the optimal upper and lower thresholds of dew point depression were 1°C and 5°C, respectively. The study further demonstrates that dew is an important water resource that cannot be ignored for rain-fed jujube trees and may affect water balance at regional scales.
Dew forming on plant leaves through water condensation plays a significant ecological role in arid and semi-arid areas as an ignorable fraction of water resources. In this study, an artificial intelligent climate chamber and an automatic temperature-control system for leaves were implemented to regulate the ambient temperature, the leaf surface temperature and the leaf inclination for dew formation. The impact of leaf inclination, ambient temperature and dew point-leaf temperature depression on the rate and quantity of dew accumulation on leaf surface were analyzed. The results indicated that the accumulation rate and the maximum volume of dew on leaves decreased with increasing the leaf inclination while increased with the increment of dew point-leaf temperature depression, ambient temperature and relative humidity. Under the horizontal configuration, dew accumulated linearly on leaf surface over time until the maximum volume (0.80 mm) was reached. However, dew would fall down after reaching the maximum volume when the leaf inclination existed (45 degrees or 90 degrees), significantly slowing down the accumulative rate, and the zigzag pattern for the dynamic of dew accumulation appeared.
Dewwater was collected from January 1993 to December 2000 in Yokohama, Japan, and analyzed for weak acid anions with other major chemical components. The volume-weighted average and medium pH of the dewwater were 4.88 and 6.08, respectively, at our sampling site. Weak acids (carbonate, nitrite, sulfite, formate, and acetate ions) were the major species in the dewwater and were several times higher than those in the rain- and fogwater. The concentrations of these species and ammonium ion can be estimated by the resistance model. The estimated values of N(III) correlate relatively well with the measured values, which shows the origin of N(III) in dewwater is nitrous acid in the ambient air. On the other hand, ammonium ion in the dewwater originated from not only gaseous ammonia but also aerosol ammonium ions. Hydrogensulfite ions in the dewwater which originated from sulfur dioxide are an important species as the precursor of the sulfate and they were stabilized by forming hydroxyalkanesulfonate (HASA). Formic acid and acetic acid in the dewwater originated mainly from gas, while the oxalic acid is from aerosol.
Above-ground parts of Phaseolus vulgaris L. plants were treated with artificial misty rain (‘rain’) in a growth chamber to investigate the effects of leaf wetness on photosynthetic performance. The following results were obtained. (1) Stomata closed completely within 2 min of the onset of continuous ‘rain’ application and gradually opened to half the original aperture by 60 min. The rate of CO2 exchange measured on such wet leaves changed in parallel with the changes in stomatal aperture and attained 60 to 70% of the control level by 1h. (2) The dependence of the rate of leaf photosynthesis, A, on the intercellular CO2 concentration, ci [A(ci) relationship], examined in thoroughly dried leaves which had been treated with ‘rain’ did not change until after 4 h of treatment. However, leaves treated for 6h showed discernible decreases in A at high ci (ci>500μmolmol −1). The photosynthetic rate of leaves treated with ‘rain’ for 24 h was reduced at all ci, and A at the ambient CO2 concentration of 350μmolmol−1 was 60 to 70% of that of the control level. The rate of photosynthesis did not recover even after 3 d of treatment of the plants in a dry environment. These results clearly indicate that leaf wetness causes not only instantaneous suppression of photosynthesis but also chronic damage to the photosynthetic apparatus. Potential effects of leaf wetness on photosynthetic performance in nature are also discussed.
Repair of damage to DNA of seed embryos sustained during long periods of quiescence under dry desert conditions is important for subsequent germination. The possibility that repair of embryo DNA can be facilitated by small amounts of water derived from dew temporarily captured at night by pectinaceous surface pellicles was tested. These pellicles are secreted during early seed development and form mucilage when hydrated.
Seeds of Artemisia sphaerocephala and Artemisia ordosica were collected from a sandy desert. Their embryos were damaged by gamma radiation to induce a standard level of DNA damage. The treated seeds were then exposed to nocturnal dew deposition on the surface of soil in the Negev desert highlands. The pellicles were removed from some seeds and left intact on others to test the ability of mucilage to support repair of the damaged DNA when night-time humidity and temperature favoured dew formation. Repair was assessed from fragmentation patterns of extracted DNA on agarose gels.
For A. sphaerocephala, which has thick seed pellicles, DNA repair occurred in seeds with intact pellicles after 50 min of cumulative night dew formation, but not in seeds from which the pellicles had been removed. For A. ordosica, which has thin seed pellicles, DNA repair took at least 510 min of cumulative night dewing to achieve partial recovery of DNA integrity. The mucilage has the ability to rehydrate after daytime dehydration.
The ability of seeds to develop a mucilaginous layer when wetted by night-time dew, and to repair their DNA under these conditions, appear to be mechanisms that help maintain seed viability under harsh desert conditions.
Duration and amount of dew under a variety of topographic and vegetative-cover conditions were studied on the Priest River Experimental Forest in northern Idaho during the summer of 1958. Dew was measured by a continuous-recording device that registered the change in weight of an expanded polystyrene (Styrofoam) block. Dew deposits ranged from zero on cloudy, windy nights to a maximum of 0.014 inch during a clear night following a day with rain. Monthly amounts of dew ranged from 7 to 29 per cent of the monthly rainfall. Dew was deposited only on the flat of the Priest River Valley and along the Benton Creek valley bottom. Dew was not deposited under the forest canopy or on the slopes.
A method is described to produce inoculum of Alternaria cassiae Jurair and Khan for biocontrol studies. Approximately 8 g of a conidial preparation containing 1 × 10 ⁸ conidia/g were produced per liter of growth medium. In greenhouse studies the effectiveness of A. cassiae as a biocontrol agent for sicklepod ( Cassia obtusifolia L.) was affected by dew-period temperature, dew-period duration, inoculum concentration, and the stage of growth of sicklepod seedlings at the time of inoculation. Optimum environmental conditions included at least 8 h of free moisture at 20 to 30C. Spray mixtures containing approximately 5 × 10 ⁴ or more conidia/ml gave maximum control when sicklepod seedlings were sprayed to runoff. Sicklepod seedlings in the cotyledon to first-leaf stage were most susceptible to the pathogen.
In a previous field study in coastal California, infection of lettuce by downy mildew (Bremia lactucae) occurred primarily on days when leaves dried late in the morning (at 1000 h or later), suggesting that fungicide sprays against the disease could be scheduled according to a morning leaf wetness threshold. Seven field trials were carried out in 1993 to 1994 to test whether sprays of maneb or fosetyl Al, applied when measured or forecast morning leaf wetness ended at 1000 h or later, would lead to a reduction in the number of fungicide applications and/or improved downy mildew control compared with a calendar-based schedule with three sprays. Based on measurements of morning leaf wetness, the total number of sprays in the seven trials was reduced by 67% relative to the calendarbased schedule, with no difference in disease intensity. Based on forecasts of morning leaf wetness, which were generated using a physical dew simulation model with numerical weather forecasts from the National Meteorological Center as input, about 90% of the days were correctly classified as days with or without prolonged morning wet period. However, the occurrence of important wet periods due to fog drizzle was not predicted and the forecasts for the exact time of onset and end of leaf wetness were inaccurate. It is concluded that the number of fungicide applications against lettuce downy mildew can be reduced substantially with sprays scheduled according to a morning leaf wetness threshold of 1000 h and that fog drizzle should be included in leaf wetness forecasts for coastal California.
Endolithic and epilithic lichens proliferate on calcareous cobbles and rock outcrops in the Negev Highlands, Israel. Whereas epilithic lichens predominate in shaded mesohabitats, extensively covering rock outcrops, endolithic lichens proliferate on loose cobbles. Endolithic lichens were thought to predominate in habitats having a poor dew regime. Dew measurements were carried out at habitats of endolithic and epilithic lichens. The measurements took place on loose and partially embedded cobbles with 90-100% of endolithic lichen cover, and on rock outcrops inhabited by epilithic lichens (75-90% cover). In addition, independent dew measurements were carried out with the Plate Cloth Method (CPM). A total of 60 days of measurements was performed. Average daily dew amount as obtained by the CPM was 0.20 mm, as compared to 0.18 mm obtained on the loose cobbles, 0.09 mm obtained by the partially embedded cobbles and 0.04-0.08 mm obtained on the bedrock surfaces. The dew amounts obtained on the cobbles were significantly higher than those obtained on the bedrock surfaces (paired t-test, p < 0.001). Thus, although exposed to the first sun beams during the early morning hours, cobbles, due to their excessive heat loss and subsequent higher cooling rates, form a mesic microhabitat (as far as dew amount is concerned) within an unshaded and hence xeric (as far as dew duration is concerned) mesohabitat. The results point out that endolithic lichens are not necessarily adapted to a poor dew regime. The advantage of the endolithic habitat in light of the present findings is discussed.
Dew-water was collected from January 1999 to February 2000 in Yokohama, Japan and analyzed for not only soluble major components but also insoluble or trace components. The pH of dew-water ranged from 5.36 to 6.71 and volume-weighted average pH was 5.81. In dew-water, Si, Al, Fe, Cl, and Na were abundant and they were confirmed to be transported from natural sources, sea and soil dust. The concentrations of Si, Al, Fe, and Ti contained in coarse mode aerosol were several times higher in dew-water than those in rain-water, while the concentrations of V and Pb contained in fine mode aerosol were about the same level to each other. Besides these elements derived from aerosol, the elements derived from gaseous species are also major components in dew-water. The high concentration of weak acid is one of the significant characteristics of dew-water. Bisulfite ion in dew-water is the important species as the precursor of the sulfate ion but it is stable by forming hydroxyalkanesulfonate (HASA). The HASA concentrations were evaluated by using concentrations of total S(IV) and aldehydes and hydroxymethanesulfonate (HMSA) was shown to be the dominant species in S(IV).
The hydrologic balance of a 28-meter Douglas fir tree in a weighing
lysimeter was determined for 2 clear days in May 1972. The results
indicated dew accumulations of 6.4 and 10.9 liters, which represent 15
and 20% of 42.5 and 55.2 liters of evaporation from the tree. Since the
dew was recorded as a weight increase, its source has to be the
atmosphere. In the Pacific Northwest, conditions are favorable for dew
formation during most of the summer and fall. Thus dew formation could
represent a large part of the hydrologic balance of fir forests.
Peroxides and hydrogen peroxide were determined by a fluorometric method in dew and rain collected in the atmosphere of Santiago of Chile city. The measured peroxides comprise hydrogen peroxide (the main component) and peroxides not decomposed by catalase. The collected natural peroxides readily decompose in the natural matrix, rendering difficult an estimation of the values present in real-time. In order to establish the kinetics of the process and the factors that condition their decomposition, the kinetics of the decay at several pHs and/or the presence of metal chelators were followed. The kinetics of hydrogen peroxide decomposition in the water matrix was evaluated employing the natural peroxides or hydrogen peroxide externally added. First-order kinetics was followed, with half decay times ranging from 80 to 2300min. The addition of Fe(II) in the micromolar range increases the decomposition rate, while lowering the pH (
Germination of Cercospora kikuchii conidia, at 25 C, with relative humidities of 100% wet, 100% dry, and 99%, was influenced by light-period regime. Germination was significantly lower at 24 h of light (35.6%) compared to 24 h of dark, to, sequentially, 12 h of light/12 h of dark, and to, sequentially, 12 h of dark/12 h of light. Identical light treatments (25 C and 24 h of leaf wetness) had a similar, significant effect (P=0.05) on disease severity, based on pairwise comparisons []
We study experimentally and theoretically new aspects of condensation, growth and coalescence of droplets on a substrate. We address in particular the dynamics of a ‘marked’ droplet which undergoes coalescences with neighbouring droplets. We find that the number of coalescences of the droplet grows as log t (t is time) and that the traveled distance increases as 〈R(t)〉, the average radius of the droplets at time t. The fraction of the surface which was never covered by any droplet (an important quantity for applications, such as drug spreading or surface decontamination), decays as t−θ, showing that completion occurs only slowly. Heuristic arguments, accurate numerical simulations on simplified models (which neglect polydispersity) and an exact solution reported elsewhere [A. Bray, B. Derrida and C. Godréche, Europhys. Lett. 27 (1994) 175] strongly support these findings, and show that this power law decay is a generic feature, common to many different situations. Finally, the contour of the ensemble of ‘dry’ sites appears fractal with dimension dƒ ⋍ 1.22, an experimental result not reproduced by the simplified models.
Hydroxyl radical (OH) is one of the most highly reactive of all active oxygen species. Aqueous-phase OH is photochemically generated in polluted dew droplets on needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc., an evergreen coniferous tree) in declining pine forests. In former studies, we examined the effects of OH-generating mist solutions, which simulate polluted dew droplets, on needle ecophysiological traits of pine seedlings. Two types of solution with different OH-generating sources, i.e. the photo-Fenton reaction (H2O2-Fe-oxalate) and photolysis of HONO and NO2− [N(III)], had contrasting functional effects on needle gas exchange characteristics even though they had similar OH photoformation rates. In the present study, we investigated the effects of OH-generating mist solutions containing mixed-sources of OH (photo-Fenton and N(III)) on needle gas exchange and the biomass production of potted Japanese red pine seedlings. The N(III) and H2O2 concentrations of the OH-generating mist solutions were regulated to the same concentration (0, 25, 50, 75 or 100μM, pH 5.2–5.3). Treated needles with the lowest photoformation rate and scavenging rate constant of OH had the smallest CO2 assimilation rate (Amax) and needle conductance (gn) of all treated pine seedlings. This suggests that the photoformation rate and scavenging rate constant do not always explain the ecophysiological disorders of pine needles subjected to OH-generating wet deposition. On the other hand, the calculated steady-state concentration of OH in the mist solutions was significantly negatively correlated with Amax. In addition, pine seedlings with reduced Amax showed suppressed biomass (dry weight) production. These results suggest that the OH concentration in the mist solutions is the decisive factor in explaining the negative effects of pseudo dew droplets not only on needle but also plant productivity. We propose that the deposition of polluted dew with chemical components and systems that result in a high OH concentration is one of the causes of growth decline of Japanese red pine.
A model to estimate the duration of condensed water on the surface of cocoa pods after sunrise is modified to use readily available meteorological data. Changes in wind speed, air temperature and humidity with height and time in a cocoa plantation are presented. Pod temperature and the amount of condensation calculated from the maximum and minimum temperatures and humidity at 0900h agree well with measured values. The effects on pod wetness of changing pod size, short-wave radiation and wind speed are investigated.
With the occurrence of soybean rust (Phakopsora pachyrhizi) now a seasonal problem in the United States, increased research is needed to ascertain the potential transmission of this disease among soybean (Glycine max L.) in major growing regions throughout the nation. The fungal disease spores are deposited on leaves in the lower region of the canopy through rain events or wind transport from nearby plants during the growing season and must then have moist conditions on the lower trifoliolates for several hours in order to infect the plant. These moist conditions can be achieved through any form of wetness. This wetness was measured in a soybean canopy at West Lafayette, IN, during the summer of 2007 using resistance-grid wetness sensors located at three heights representative of the top, mid-level, and lowest trifoliate of the canopy. Temperature, relative humidity, wind speed, and precipitation measurements were used to determine the cause of wetness. Over the course of the experiment, wetness events were classified as dew, rain, or neither. The dew events were then compared to rain events with an emphasis on differences in vertical and horizontal duration of wetness. Dew events were found to be the dominant wetness source in the upper canopy. Rain events were the most dominant cause of wetness in the lower canopy. Upper canopy wetness events had the longest duration. Horizontal variation in wetness and wetness duration was large.
Dry deposition and dew components on pine foliage were measured from 1998 to 2000 on the urban- and mountain-facing sides of Mt. Gokurakuji in order to estimate the effect of anthropogenic activities to dry deposition and dew concentration on the surfaces of pine foliage. A leaf wash experiment was employed to determine the dry deposition rates on the pine foliage. The NO3− and SO42− dry deposition rates per unit surface area of pine foliage were 1.47 and 0.28 μmol m−2 h−1 respectively on the urban-facing side and 0.32 and 0.09 μmol m−2 h−1 on the mountain-facing side. Dry deposition fluxes of N (NO3−+NH4+) and S (SO42−) to the forest floors were 8.4 kg N ha−1 yr−1 and 2.8 kg S ha−1 yr−1 on the urban-facing, and 3.3 kg N ha−1 yr−1 and 1.8 kg S ha−1 yr−1 on the mountain-facing side, respectively. The higher dry deposition fluxes of N and S on the urban-facing side could be attributed to its proximity to traffic roads and the urban area. The concentrations of most ions in the dew were higher on the urban-facing side (U130) than on the mountain-facing side (M430). NO3− and SO42− concentrations in dew at U130 were 802 and 428 μeq l−1, respectively, while at M430 they were 199 and 222 μeq l−1, respectively, suggesting that higher dry deposition rates on the urban-facing side enhanced their concentrations in the dew on this side. The role of dry deposits and subsequently dissolved ones in dew on the needle surfaces is discussed in terms of pine tree damage by atmospheric depositions.
Cations (pH, potassium, sodium, calcium, magnesium, and ammonium) and anions (sulfate, nitrate, nitrite, and chloride) concentrations were measured in Santiago city rain and dew waters collected during the 1995 to 1999. Concentrations measured in dews are considerably higher than those measured in rains. The high ionic concentration present in dew waters could contribute to their corrosion potential. Natural dust makes an important contribution to the ions present in dews, but the presence of rather high sulfate concentrations (up to 900 μeq/l) indicate a significant contribution of anthropogenic sources.A peculiar characteristic of dew waters is the relatively high nitrite concentrations (up to 180 μeq/l). This nitrite can be resuspended into the boundary layer after dew water evaporation, possibly due to the relatively high volatily of ammonium nitrite. This upward flux could constitute an important source of hydroxyl radicals in the early morning, contributing so to the initial steps of the observed photochemical smog.
Dew is an important water source for desert organisms in semiarid and arid regions. Both field and laboratory experiments were conducted to investigate the possible roles of dew in growth of biomass and photosynthetic activity within cyanobacterial crust. The cyanobacteria, Microcoleus vaginatus Gom. and Scytonema javanicum (Kütz.) Born et Flah., were begun with stock cultures and sequential mass cultivations, and then the field experiment was performed by inoculating the inocula onto shifting sand for forming cyanobacterial crust during late summer and autumn of 2007 in Hopq Desert, northwest China. Measurements of dew amount and Chlorophyll a content were carried out in order to evaluate the changes in crust biomass following dew. Also, we determined the activity of photosystem II(PSII) within the crust in the laboratory by simulating the desiccation/rehydration process due to dew. Results showed that the average daily dew amount as measured by the cloth-plate method (CPM) was 0.154 mm during fifty-three days and that the crust biomass fluctuated from initial inoculation of 4.3 μg Chlorophyll a cm−2 sand to 5.8–7.3 μg Chlorophyll a cm−2 crust when dew acted as the sole water source, and reached a peak value of approximately 8.2 μg Chlorophyll a cm−2 crust owing to rainfalls. It indicated that there was a highly significant correlation between dew amounts and crust moistures (r = 0.897 or r = 0.882, all P < 0.0001), but not a significant correlation between dew and the biomass (r = 0.246 or r = 0.257, all P > 0.05), and thus concluded that dew might only play a relatively limited role in regulating the crust biomass. Correspondingly, we found that rains significantly facilitated biomass increase of the cyanobacterial crust. Results from the simulative experiment upon rehydration showed that approximately 80% of PSII activity could be achieved within about 50 min after rehydration in the dark and at 5 °C, and only about 20% of the activity was light-temperature dependent. This might mean that dew was crucial for cyanobacterial crust to rapidly activate photosynthetic activity during desiccation and rehydration despite low temperatures and weak light before dawn. It also showed in this study that the cyanobacterial crusts could receive and retain more dew than sand, which depended on microclimatic characteristics and soil properties of the crusts. It may be necessary for us to fully understanding the influence of dew on regulating the growth and activity of cyanobacterial crust, and to soundly evaluate the crust's potential application in fighting desertification because of the available water due to dew.
Black Sigatoka is an important fungal disease of bananas and plantains. Dew duration on the upper leaves of these plants (Leaves 0 and 1) is an important factor in the development of the disease. A general dew estimation scheme, based on an energy budget approach, was adapted to the particular case of banana and plantain upper leaves in order to provide a tool for Black Sigatoka management. This scheme allows the estimation of dew duration from standard weather station measurements of air temperature and humidity, wind velocity, solar radiation and cloud cover. Values of dew duration estimated by this scheme were compared with observed values on plantain during 18 nights. On average, the differences between observed and estimated values were less than 1 h.