Plant Microclimate Research Articles

The effects of vegetation on indoor thermal comfort: The application of a multi-scale simulation methodology on a residential neighborhood renovation case study

Despite the acknowledged positive effects of vegetation at urban, neighborhood and building scales, there are still only limited comprehensive design tools for multi-scale evaluation of the microclimate and thermal benefits of plants and building-integrated vegetation (BIV) systems.The paper describes a case study in the city of Palermo (Italy) that applied simulation methodology to quantitatively assess the microclimate effects of different neighborhood and building retrofit scenarios where vegetation plays a main role. The simulation workflow moves from a micro-urban to a building scale assessment by linking the ENVI-met software to the building energy simulation program EnergyPlus. The study takes two complementary directions. Firstly, it analyses the influence of plants on urban microclimates to enhance outdoor and indoor temperatures. Secondly, it assesses the benefits of different technical solutions applied to buildings, including BIV systems and windows substitutions, to further improve their thermal behavior.The results of the simulations show a significant reduction in outdoor and indoor temperatures, questioning traditional urban renovation practices and drawing attention to the importance of multi and inter-scale approaches for high-accuracy investigations into buildings’ thermal performances.

Role of grapevine vegetative expression on Aspergillus spp. incidence and OTA accumulation in wines produced in a temperate humid climate

ABSTRACTAspergillus spp. and Penicillium spp. are the main producers of ochratoxin A (OTA), a mycotoxin responsible for fatal human diseases. Some authorities have established a maximum of 2 μg/L of OTA in wine. Although the incidence and occurrence of OTA in grapes and wine is highly related to climate conditions, as has been extensively documented, there is no conclusive information on the effects of cultivation systems on the presence of OTA. This study focuses on determining the effect of the trellis system, planting density and cordon height on plant microclimate and thus on Aspergillus spp. contamination and OTA production in Tannat wines in Southern Uruguay. Two experiments were conducted during the 2010–2011 growing season: (1) a strip split plot design with five replicates and two cordon heights (CH) (0.5 m and 1.0 m above the soil) were compared in two planting densities (PD) (0.8 and 1.5 m between plants); (2) a randomised complete block design, vertical shoot positioning (VSP) versus Lyra trellis systems were evaluated. The results suggest that, even the macro- and micro-climate growing conditions play an important part in Aspergillus developing on grapes. Agronomical practices also have an undoubted impact on the risk and control of OTA accumulation in wine.

Метаболічний склад листків дерев залежно від умов росту

The transformation of the urban environment led to changes in the life of woody flora. These changes are not always noticeable visually, and their appearance often suggests nothing of irreversible physiological (biochemical) change body. Formation of important substances of plant organism depends on the functional processes (synthesis of protein, carbohydrates, nitrogen compounds) in which the operation is normal. Most expeditious structural and functional changes can be seen in the assimilation organs (leaves). Knowing the essence of adaptive processes at the level of metabolism tree growing in a transformed urban environment, we can understand the morphological changes and as a result find the optimal measures to improve the green spaces and maintain their livelihoods in "difficult" environment that is relevant for today urban green economy. The aim is to study the content of basic biochemical parameters in the dry mass of leaves studied groups of trees and installation possible dependence of quantitative and qualitative values of these parameters depending on growth conditions, and identifying features of life of native and exotic trees in the transformed conditions of the urban environment and their adaptive response to environmental factors. To study the biochemical parameters of life of woody plants city green zone allocated to 3 groups of tree species of oak (Quercus robur L.) and bahryanyk Japanese (Cercidiphyllum japonicum Siebold et Zucc.). Oak stands as a typical representative of the green zone. City belongs to the native flora. Cultivation bahryanyk in our area began in the last century because of our climatic zone it belongs to introduced species. Subject studied biochemical metabolic dry mass of leaves at the height of summer activities, including study of water-soluble carbohydrates, starch, protein and lipids. To evaluate the physiological response of plants to growth conditions studied makrometabolic sheet structure on the main important indicators of water soluble carbohydrates, fiber, lipids. Studies have shown that in the urban environment course of biochemical processes is worse than a close to natural environmental conditions. Environment of urban pervert the course of carbohydrate, lipid and other exchanges. A significant drop in performance microclimate, soil and air pollution sensitivity of plants to changing environmental conditions. Research of macro metabolic composition of bahryanyk and oak in the green area of Lviv allowed to find out that changes functional structures of the leaf are displayed in organic and mineral components of its dry weight. The conditions of the urban environment affect carbohydrate metabolism and "adjusting" the content of the main structural components. Transformed environment of the city causes the plant organism to accumulate a reserve stock of components - starch and lipids. Also found that rates of sugar and starch in the dry mass of leaves depends on the growth conditions and specific features. It was found difference between the metabolism of native oak and introduced bahryanyk. Last actively accumulate reserve compounds, especially in polluted outdoor environments. In turn, oak showed better adaptability to local conditions. Confirmed that the research of assimilating organs clearly shows the main changes in the plant organism on physiological and biochemical level, caused by habitat transformation and pollutants in the environment. Leaves can be considered as the primary basis of morpho-physiological adaptation of plants.

The Relatioship between Plant Density and Microclimate and Nutmeg (Myristica fragrans Houtt) Production in Nutmeg and Coconut Mixed-Planting System in Wakatobi District in Indonesia

<p>In Wakatobi district nutmeg trees are generally cultivated in mixed planting with coconut. The research employed observation method where sample plants were determined purposively based on intersection of nutmeg and coconut tree crowns; 42 plots of pairs of nearest neighboring plants. In each plot of pair of plants, plant density of nutmeg and coconut was calculated (individually and in total), then microclimate components (solar radiation, temperature and relative humidity) and nutmeg plant characteristics (vegetative and prodution components) were measured. Research results showed that plant density of nutmeg (218 plants ha<sup>-1</sup>) had exceeded its optimum number of population, plant density of coconut 144 plants ha<sup>-1</sup> with relative density ratio of 58:42% or nutmeg was more dominant than coconut. Transmitted radiation and temperature below the crown was decreasing, and in contrast, intercepted radiation and relative humidity increased in line with the increased plant density of nutmeg. This condition led to the decrease in sum of fruits, weight of mace, and weight of kernel of individual nutmeg tree. Coconut plant density had non-significant correlation and non-significantly contributed to microclimate and production components of nutmeg. This indicated that the tendency for decreased production of nutmeg is less affected by coconut trees, but more because of shading effect of nutmeg trees due to close distance among them. In other word, there occured intraspecific competition (nutmeg and nutmeg), and not interspecific (nutmeg and coconut). Therefore, coconut can be cultivated in mixed planting with nutmeg through appropriate plant spacing.</p>

English

The Sclerotinia sclerotiorum (Lib.) de Bary fungus is a necrotrophic and polyphagous pathogen with soybean crop as one of its most important hosts. However in order to occur epidemics caused by such a pathogen it is necessary that the climatic conditions, mainly air temperature and relative humidity be favorable to the occurrence and development of the disease. The current research aimed to assess the incidence and severity of S. sclerotiorum in soybean plants grown in Arapoti, PR, Brazil, as a function of different plant populations, row spacing, and microclimate. The experiment was conducted in a naturally infested area. The experimental design adopted was a randomized block in a factorial combination with 4 row spacing (0.35, 0.45, 0.60, 0.75 m) and 4 plant populations (150, 200, 250; 300 thousand plants per hectare), totaling 16 treatments and 4 replications. Throughout the current study we performed 4 assessments of incidence and severity. Local climatic conditions were favorable for the incidence and severity of the pathogen. Mean air temperature, rainfall, relative humidity and leaf wetness duration, monitored during all experimental period, favored the development of the pathogen in the experimental field. Yield and 100 seed weight did not show fluctuations as a function of variations on the incidence and severity of white mold in soybean crop fields. Nevertheless, crop yield was higher under a reduced spacing, whereas the 100 seed weight showed the highest values under the lowest plant population treatment.

English

The increased use of colored plastic mulch is a better approach to control weeds and improvement in agricultural production. Plastic mulches affect plant microclimate by modifying the soil energy balance and restricting soil water evaporation, thereby influencing plant growth and yield. A field study was conducted on 5 mulching colors (black, blue, red, silvery-grey, yellow) and wheat straw as control. The purpose of the study was to investigate the effect of different colors of plastic mulch on growth performance and yield of Cucumber (Cucumis sativus). The microclimate condition improved by the mulches have provided a suitable condition for producing superior branch characteristics, number of fruits/plant, fruit size and total yield in the plants. Marketable fruit yield significantly improved by the use of a silvery-grey colored plastic mulch (37.9t/ha) compared to the blue colored mulch (15.3t/ha) and wheat straw mulch (26.4t/ha). Also, the significant results were observed in growth parameters by mulching with silver-grey colored mulch. Fewer insect pests (thrips, aphids, cucumber moths and whiteflies) were noted on plants on Silvery grey colored mulch compared to other colored mulches. The effectiveness of the colored mulches to suppress both aphids and cucumber moth after the peak period was non-significant due to the increased vine/plant size which covered the colored mulches. In areas where thrips and cucumber moth are likely to infest cucumber, Blue colored mulch is not suggested. Where aphids and whiteflies are high, yellow colored mulches should be discouraged. This study explored the possibility of improving yield of cucumber by using the plastic mulches in which silvery-grey gave the most effective influence as compared to other color mulches.

Special features of drip-sprinkler irrigation technology

Irrigation techniques and technology based on principle of regular accumulation of moisture in active layer (surface irrigation, regular sprinkler irrigation) are most common in science and in practice. More progressive is principle of non-stop water supply of plants and soil in conformity to their water consumption. Drip irrigation and impulse sprinkling are based on this principle. The main advantage of drip irrigation is establishment of optimal water and nutritive regime directly in the plant root system. However, such irrigation is not effective enough under conditions of high air temperatures (over 25–35 °С), as growing process of several agricultural plants is known to slow down at 30–35 °С and photosynthesis, consequently, stops, which, in turn, affects plants yielding capacity. Sprinkling irrigation provides improvement of both microclimate in plant's environment and their water regime. Combination of drip and sprinkling irrigation permits the positive characteristics of each individual technology to be united, and to remove a series of disadvantages of their separate use as well as to use drip-sprinkler irrigation technology to create optimal conditions for plant development. Drip-sprinkler irrigation technology facilitates saving of irrigation water through drip irrigation in the main vegetation period and through improvement of microclimate and water regime of agricultural plants with additional sprinkling irrigation within the period of high temperatures and low air humidity that affects the growing process and increases yielding capacity of grown cultures.

Convective heat and mass exchange at surfaces of horticultural products: A microscale CFD modelling approach

Knowledge of the convective heat and mass exchange of horticultural products and other plant organs (e.g., leaves) with the environment is of interest for several pre- and postharvest technologies and for plant microclimate analysis. Although these exchange processes often occur at the microscale (e.g. at lenticels, cracks, droplets or stomata, 10−4 to 10−2m), they are still often assessed on a macroscale level. In this study, the convective passive scalar (i.e., heat) transfer from a single spherical product is investigated with computational fluid dynamics (CFD). For this purpose, the product is placed in a virtual wind-tunnel environment, thus not in its natural environment, e.g. on a tree. A sphere is used as reference system; an apple fruit is considered as model system. CFD validation is performed for a sphere, indicating a very good performance of the Reynolds-averaged Navier–Stokes shear stress transport k-ω turbulence model for the drag coefficient, Nusselt number, separation angle and recirculation length over a large Reynolds number range (10–3×104). These quantities compare well for sphere and apple. The impact of discretely distributed microscopic scalar sources on the product surface on the convective transfer is analysed by explicitly modelling them. Such sources are representative for moisture loss through lenticels and cracks in the product's cuticle and evaporation of water or pesticide droplets at the surface. As scalar transfer is assumed only to occur locally at these sources, the active surface area is reduced. In this study, it is found that even at rather low surface coverage ratios, relatively large convective flow rates are found, indicating a non-linear dependency on the active surface area. This dependency is a function of coverage ratio, the Reynolds number and the source size. The proposed computational methodology for investigating the effects of these microscopic scalar sources shows a good performance, by which it is a viable alternative for experiments, which are very challenging at such small scales.

Effect of plant life form on relationship between δD values of leaf wax n-alkanes and altitude along Mount Taibai, China

We present δD wax values from different forms of plants and soils, and δD sw values from soil water along the northern slope of Mount Taibai, China. The results show a highly negative linear correlation of the δD wax values for soils with altitude ( R 2 0.74) and we observed the same correlation for δD sw values of soil water with altitude ( R 2 0.68). The δD wax of living plants behaves like the soil, but does not exhibit a significant linear correlation with altitude ( R 2 0.11). The δD wax values of woody plants and grasses also show a similar trend with respect to altitude with significant and no linear correlation, respectively ( R 2 0.50 for woody plants and 0.17 for grass), which suggest that the “altitude effect” can not be well documented for the δD wax values of living plants, which may be due to differences in plant type and/or evapotranspiration controlled by the plant microclimate. The ε wax-sw values of woody plants, grasses and soil show minor fluctuations with altitude. However, the ε wax-sw and δD wax values of woody plants are roughly 51‰ and 50‰ more positive, respectively, than those of grasses, suggesting that an “altitude effect” could be documented in the δD wax of woody plants and grasses, with each responding independently to changes in precipitation along the altitude transect. Additionally, the ε wax-sw values of soil are relatively constant with altitude, suggesting that the altitudinal change in the proportions between woody plant and grass input to soils will likely change the relationship between the δD wax values of soil n-alkanes and altitude.

Effects of Shading Using a Retractable Liquid Foam Technology on Greenhouse and Plant Microclimates

Climate control is an important aspect of greenhouse crop management. Shading is one popular method for reducing excess solar heat radiation and high air temperatures in the greenhouse during the summer season. A new innovative technology has recently been developed and is based on the injection of liquid foam between the double layers of polyethylene of the greenhouse roof. The foam can be used as a shading method during the warm days of the summer. This is the first investigation into the effect of shading using the liquid foam technology on greenhouse and plant microclimates. Our research was conducted over 2 years in two different areas of Canada. Experimental greenhouses were retrofitted with the new technology. Tomato (Solanum lycopersicum) and sweet pepper (Capsicum annuum) were transplanted. Two shading strategies were used: 1) comparison of a conventional nonmovable shading curtain to the liquid foam shading system and application of liquid foam shading based only on outside global solar radiation; and 2) application of foam shading based on both outside global solar radiation and greenhouse air temperature. Data on the greenhouse microclimate (global solar radiation, air temperature, and relative humidity), the canopy microclimate (leaf and bottom fruit temperatures), and ventilation (opening/closing) were recorded. Our study showed that the retractable liquid foam technology improved greenhouse climate. Under some conditions (very sunny and hot days), a large difference in air temperature (up to 6 °C) was noted between the unshaded and shaded greenhouses as a result of liquid foam application (40% to 65% shading). Foam shading also increased relative humidity by 5% to 12%. Furthermore, bottom fruit temperatures stayed cooler 3 h after shading treatment was stopped. As well, a reduction in ventilation needs was observed with liquid foam shading.

Maturação de uvas Moscato Giallo sob cultivo protegido

O cultivo protegido de videiras é um sistema de cultivo recente, podendo modificar o microclima no entorno da planta e as condições de maturação da uva. Desta forma, este trabalho objetivou avaliar a influência da cobertura plástica sobre a maturação de uvas 'Moscato Giallo'. O experimento foi realizado nos ciclos de 2005/06 e 2006/07, em vinhedo com cobertura plástica impermeável (160 �m), deixando-se cinco fileiras sem cobertura (controle). Foram realizadas coletas semanais de três repetições de 100 bagas de cada área (coberta e controle). Nestas bagas, foram medidos a massa, o diâmetro e a composição do mosto: pH, sólidos solúveis, acidez total, ácidos tartárico e málico. No momento da colheita, também foram caracterizados os mostos das uvas cobertas e descobertas (ºBrix, açúcares redutores, densidade, acidez total, ácidos tartárico e málico, pH e rendimento). A despeito de uma importante interferência no microclima do dossel vegetativo e cachos, a cobertura plástica influencia na maturação das uvas. Em função da diminuição da radiação fotossinteticamente ativa, que retarda o acúmulo de açúcares, as uvas sob cobertura plástica devem ser colhidas posteriormente àquelas do cultivo convencional.

Simulation of within-canopy radiation exchange

Radiation exchange at the surface plays a critical role in the surface energy balance, plant microclimate, and plant growth. The ability to simulate the surface energy balance and the microclimate within the plant canopy is contingent upon simulation of the surface radiation exchange. A validation and modification exercise of the Simultaneous Heat and Water (SHAW) model was conducted for simulating the surface short-wave and long-wave radiation exchange over and within wheat, maize and soya bean plant canopies using data collected at Yucheng in the North China Plain and near Ames, Iowa. Whereas model testing was limited to monocultures and mixed canopies of green and senesced leaves, methodologies were developed for simulating short-wave and long-wave radiation fluxes applicable to a multi-species, multi-layer plant canopy. Although the original SHAW model slightly underpredicted reflected solar radiation with a mean bias error (MBE) of −5 to −10 W m −2, one would conclude that the simulations were quite reasonable if within-canopy measurements were not available. However, within-canopy short-wave radiation was considerably underestimated (MBE of approximately −20 W m −2) by the original SHAW model. Additionally, leaf temperatures tended to be overpredicted (MBE = +0.76 °C) near the top of the canopy and underpredicted near the bottom (MBE = −1.12 °C). Modification to the SHAW model reduced MBE of above canopy reflected radiation to −1 to −6 W m −2 and within-canopy radiation simulations to approximately −6 W m −2; bias in leaf temperature was reduced to less than 0.4 °C. Model modifications resulted in essentially no change in simulated evapotranspiration for wheat, 4.5% lower for maize and 1% higher for soya bean. Alternative approaches for simulating canopy transmissivity to diffuse radiation were tested in the modified version and had a minor influence on simulated short-wave radiation, but made almost no difference in simulated long-wave radiation or evapotranspiration. Modifications to the model should lead to more accurate plant microclimate simulation; further work is needed to evaluate their influence.

Airflow and microclimate patterns in a one-hectare Canary type greenhouse: An experimental and CFD assisted study

This study presents an analysis of air circulation and microclimate distribution during daytime in a 1-ha Canary type tomato greenhouse in the coastal area of southern Morocco. The investigation of the climate inside the greenhouse is based on a numerical simulation using a finite volumes method to solve the mass, momentum and energy conservation equations. The main novelty of this simulation lies in the realism of the 3D modelling of this very large agricultural structure with (i) a coupling of convective and radiative exchanges at the surface of the plastic roof cover, (ii) simulation of the dynamic influence of the insect screens and tomato crop on airflow movement, using the concept of porous medium, (iii) simulation, in each grid cell of the crop canopy, of the sensible and latent heat exchanges between the greenhouse air and the tomato crop, and (iv) detailed simulation of climate parameters in a 1-ha real-scale commercial greenhouse. The model simulations were first validated with respect to temperature and relative humidity fields measured inside the experimental greenhouse for fairly steady-state outside conditions marked by a prevailing sea breeze around the solar noon. A good agreement was observed between the measured and simulated values for inside air temperatures and specific humidity. It was next used for exploring the details of the inside air temperature and humidity fields and plant microclimates and transpiration fluxes throughout the greenhouse space. Simulation for a wind direction perpendicular to the side and roof openings shows that the insect screen significantly reduced inside air velocity and increased inside temperature and humidity, especially in the vicinity of the crop canopy. It revealed the details of the flow field within the greenhouse. At the windward end of the greenhouse, the flow field was marked by a strong windwise air current above the tomato canopy which was fed by the windward side vent, and a slow air stream flowing within the tomato canopy space. Then, from the first third of the greenhouse to the leeward end, the flow field was marked by the combination of wind and buoyancy forces, with warmer and more humid inside air which was evacuated through the upper roof vents, while colder and dryer air was penetrated through the upper roof vent openings. Based on these simulations, design studies of the greenhouse crop system were performed to improve inside air temperature and humidity conditions by simple modifications of orientation of the crop rows.

THE EFFECT OF COVERING MATERIAL ON THE MICROCLIMATE OF ROSE PLANTS IN A GREENHOUSE

Measurements of the radiometric properties of plastics used as covering materials of horticultural greenhouses in Zimbabwe were made, both under laboratory conditions and in an operational greenhouse. The magnitude of the changes in available solar radiation due to the use of different covering materials and their effects on leaf temperatures are presented using a dynamic greenhouse climate model. Transmittances in the whole solar and PAR bands under laboratory conditions were similar, ranging from 60 % to 85 %, while those in the thermal infrared ranged from 20 % to 60 %. Transmittance values found in the greenhouse were similar to those found for horizontal sheets under laboratory conditions. In order to generalise on the effects of different plastics on actual leaf temperatures, the Gembloux Dynamic Greenhouse Climate Model (GDGCM) was used to simulate air temperature and humidity, leaf temperature and the solar radiation at the top of the canopy using climatological observations and the radiometric properties measured under laboratory conditions as inputs. The model gave values of up to - 5 degrees C and + 1 degrees C for the extreme leaf to air temperature differences close to midday and sunrise, respectively. The model showed that the microclimate under photoselective polyethylene films was comparable to that under glass and that the range of available plastics gave little differences between daytime leaf-air temperature differences for all films, but could change the minimum temperature by up to 1 degrees C. Aging of plastic films of up to 3 years was found to have a negligible effect on the plant microclimate. The measurements made during the project, together with the use of a greenhouse climate model, provide quantitative estimates of the effect of different covering materials on the radiation available to plants within a greenhouse, and also of their influence on leaf-air temperature differences under conditions typical of horticultural operations in Zimbabwe.

Effects of deficit irrigation strategies on cluster microclimate for improving fruit composition of Moscatel field-grown grapevines

Abstract The grapevine plays a very important role in the economic, social and cultural sectors of many regions; however vineyards are often grown in regions under stressful conditions and thus they are vulnerable to climate change. The objective of this research was to investigate the effect of partial root-zone drying (PRD) irrigation on vine water relations, vegetative growth, plant microclimate, berry composition and yield components, compared to conventional deficit irrigation (DI, 50% ETc), full irrigation (FI, 100% of ETc) and non-irrigated vines (NI). The study was undertaken in mature ‘Moscatel’ grapevines ( Vitis vinifera L.) grown in Pegoes, South of Portugal. Compared to the other irrigated treatments, PRD vines showed a better microclimate at the cluster zone with higher incident photosynthetic photon flux density (PPFD). Within the more open canopies of NI and PRD treatments, berry temperatures were higher than those of denser ones (DI and FI). Compared to the conventional irrigation technique the better microclimate observed in PRD vines was a consequence of a reduction in vine growth, where lower values of leaf layer number, leaf area, canopy wideness, water shoots and shoot weight were observed. In PRD vines we observed a tendency to a development of a deeper root system, while DI and FI showed a more homogeneous root distribution throughout the different soil layers. PRD showed an improvement in berry quality with higher values of flavour precursors, and total phenols concentration without any significant yield reduction compared to DI and FI.

Leaf Area Distribution of Tomato Plants as Influenced by Polyethylene Mulch Surface Color

The influence of polyethylene (plastic) mulch surface color (white versus black) on leaf area distribution of tomato (Lycopersicon esculentum) was investigated in simulated planting beds at two sampling periods: an early sampling with relatively young plants that had been in the mulch treatment for 22 days and a late sampling with relatively mature plants that had been in the mulch treatments for 50 days. At the early sampling period, tomato plants grown with white mulch had more axillary leaves than plants in the black mulch, resulting in a greater axillary:main leaf area ratio for the plants with white mulch. Leaf area for total leaves (main + axillary) and plant biomass was unaffected by mulch surface color at the early sampling period. Tomato plants grown in black mulch at the early sampling period had significantly more area of main leaves partitioned to node 3, whereas plants grown in white mulch had more area of main leaves in nodes 8 and 9. Plants grown in the white mulch treatment had significantly more axillary leaf area at nodes 1, 2, and 3, whereas plants in black mulch had more axillary leaf area at node 6. At the later sampling period, most of the leaf area from both mulch treatments was recorded in the axillary leaves and there was no effect of mulch surface color on the amount of total leaf area partitioned to main, axillary, or total leaves; to the amount of biomass of the measured top growth; or to the nodal distribution of leaf area among main leaves or axillary leaves. Tomato plants in white mulch had significantly more fruit on plants at the later sampling period than plants in the black mulch. Mulch surface color also affected the plant light environment and soil temperatures. These results suggest that the polyethylene mulch surface color can induce changes in the plant microclimate and affect leaf area distribution of young tomato plants (as recorded at the early sampling) and fruiting of relatively more mature plants (as recorded at the later sampling).

Evaluation of SHAW Model in Simulating Energy Balance, Leaf Temperature, and Micrometeorological Variables within a Maize Canopy

Understanding and simulating plant canopy conditions can assist in better acknowledgment of plant microclimate characteristics, its effect on plant processes, and the influence of management and climate scenarios. The ability of the Simultaneous Heat and Water (SHAW) model to simulate the surface energy balance and profiles of leaf temperature and micrometeorological variables within a maize canopy and the underlying soil temperatures was tested using data collected during 1999 and 2003 at Yucheng, in the North China Plain. The SHAW model simulates the near‐surface heat and water movement driven by input meteorological variables and observed plant characteristic (leaf area index [LAI], height, and rooting depth). For 1999, the model accurately simulated air temperature and relative humidity in the upper one‐third of the canopy, but overpredicted midday temperature in the lower canopy. For 2003, although the surface energy balance was simulated quite well, radiometric canopy surface temperature and midday leaf temperature in the upper portion of the canopy were overpredicted, by approximately 5°C. Model efficiency (the fraction of variation in observed values explained by the model) for leaf temperature in the lower two‐thirds of the canopy ranged from 0.82 to 0.90, but fell to 0.38 for the uppermost canopy layer. Weaknesses in the model were identified and potentially include: the use of K‐theory to simulate turbulent transfer within the canopy; and simplifying assumptions with regard to long‐wave radiation transfer within the canopy. Model modifications are planned to address these weaknesses.

Effects of Generalist Phytoseiid Mites and Grapevine Canopy Structure on Spider Mite (Acari: Tetranychidae) Biocontrol

Specialist-feeding phytoseiid mites have a well-documented role in biological control of phytophagous spider mites. However, although there is evidence for the importance of generalist-feeding phytoseiid mites in spider mite suppression, their role is less clear than that of specialists. The effectiveness of generalists as biocontrol agents and their interactions with specialists might be directly influenced by canopy structure or indirectly affected by altering plant microclimate. We manipulated densities of generalist phytoseiid mites and canopy size (large and small) in open-field experiments in an abandoned vineyard. In the first experiment, we increased generalist densities by transferring grapevine foliage housing robust generalist populations, whereas in the second experiment, we lowered generalist densities using the broad-spectrum insecticide chlorpyrifos. In both experiments, we also altered canopy size by tying grapevine shoots. Increasing densities of generalists resulted in lower spider mite densities. Generalists initially decreased densities of specialist phytoseiid mites as well, although specialist densities rebounded as spider mite densities increased later in the experiment. Lowering generalist densities appeared to slightly increase densities of both spider and specialist mites, consistent with the first experiment. However, these effects were not statistically significant, possibly because the reduction in generalist densities through chlorpyrifos application was not as dramatic as our generalist augmentation in the first experiment. Canopy size did not significantly affect pest or predatory mite densities in either experiment. These field experiments demonstrate that generalists can slow spider mite population growth in grapes. In contrast, canopy architecture appeared to have little impact on spider mite biocontrol.

Evaluation of the SHAW Model in Simulating the Components of Net All-Wave Radiation

Radiation exchange at the surface plays a critical role in the surface energy balance, plant microclimate, and plant growth. The ability to simulate the surface energy balance and the microclimate within the plant canopy is contingent upon accurate simulation of the surface radiation exchange. A validation exercise was conducted of the Simultaneous Heat and Water (SHAW) model for simulating the surface radiation exchange (including downward long-wave and upward short- and long-wave radiation) over a maize canopy surface using data collected at Yucheng in the North China Plain. The model simulated upward short-wave and net all-wave radiation well with model efficiencies (ME) equaling 0.97 and 0.98, respectively. Downward and upward long-wave radiation were overestimated by 12.1 and 8.3 W m-2 with ME equaling 0.68 and 0.89, respectively. Two modifications to the model were implemented and tested to improve the simulated long-wave radiation exchange. In one modification, alternative schemes were tested to simulate cloudy sky long-wave radiation, and the best algorithm was employed in the model. With this modification, both downward and upward long-wave radiation were simulated better, with ME rising to 0.88 and 0.91, respectively. A second modification was implemented to use leaf temperature rather than canopy air temperature to compute emitted long-wave radiation. Although more theoretically correct, this modification did not improve simulations compared to the original model because upward long-wave radiation was already overpredicted and midday leaf temperatures at this site were typically higher than canopy air temperatures. Thus, the modification resulted in even higher overprediction of upward midday long-wave radiation. However, this modification removed some of the bias in nighttime emitted long-wave radiation. While the SHAW model simulates the radiation balance and transfer processes within the canopy reasonably well, results point to areas for model improvement.

Will photosynthesis of maize (Zea mays) in the US Corn Belt increase in future [CO2] rich atmospheres? An analysis of diurnal courses of CO2 uptake under free‐air concentration enrichment (FACE)

AbstractThe C4 grass Zea mays (maize or corn) is the third most important food crop globally in terms of production and demand is predicted to increase 45% from 1997 to 2020. However, the effects of rising [CO2] upon C4 plants, and Z. mays specifically, are not sufficiently understood to allow accurate predictions of future crop production. A rainfed, field experiment utilizing free‐air concentration enrichment (FACE) technology in the primary area of global corn production (US Corn Belt) was undertaken to determine the effects of elevated [CO2] on corn. FACE technology allows experimental treatments to be imposed upon a complete soil–plant–atmosphere continuum with none of the effects of experimental enclosures on plant microclimate. Crop performance was compared at ambient [CO2] (354 μ mol mol−1) and the elevated [CO2] (549 μmol mol−1) predicted for 2050. Previous laboratory studies suggest that under favorable growing conditions C4 photosynthesis is not typically enhanced by elevated [CO2]. However, stomatal conductance and transpiration are decreased, which can indirectly increase photosynthesis in dry climates. Given the deep soils and relatively high rainfall of the US Corn Belt, it was predicted that photosynthesis would not be enhanced by elevated [CO2]. The diurnal course of gas exchange of upper canopy leaves was measured in situ across the growing season of 2002. Contrary to the prediction, growth at elevated [CO2] significantly increased leaf photosynthetic CO2 uptake rate (A) by up to 41%, and 10% on average. Greater A was associated with greater intercellular [CO2], lower stomatal conductance and lower transpiration. Summer rainfall during 2002 was very close to the 50‐year average for this site, indicating that the year was not atypical or a drought year. The results call for a reassessment of the established view that C4 photosynthesis is insensitive to elevated [CO2] under favorable growing conditions and that the production potential of corn in the US Corn Belt will not be affected by the global rise in [CO2].