Plant Canopy Surface Research Articles

A CFD analysis on improving lettuce canopy airflow distribution in a plant factory considering the crop resistance and LEDs heat dissipation

In a plant factory, improper design of the indoor ventilation system may cause tip burn on lettuce plants due to the existence of stagnant air in the leaf boundary layer and low transpiration rates. In this study, three types of air ducts with different pore numbers and diameters were designed to generate a constant horizontal airflow on the surface of plant canopy. A three-dimensional computational fluid dynamics (CFD) model was established to analyse the airflow pattern on the crop canopy under different ventilation modes in a single cultivation bed. For this simulation model, the lettuce leaves were treated as a porous medium, and the drag coefficient (CD) was assumed to be 0.02, which resulted in a permeability (Kp) and nonlinear momentum loss coefficient (CF) of 0.02 and 0.134, respectively. The LED lamps were set as the energy source, and the heat released was calculated to be 297.5 kW m−3. All the data above were validated. Three Designs with different pore numbers and diameters were simulated to predict the distribution of airflow. The design with 12 pores and 15 mm diameter was predicted to give the highest percentage of mean air velocity between 0.28 m s−1 and 1.04 m s−1 on the lettuce canopy surface, at 70.3%. This duct design is recommended as the best of the three Designs in this study.

Analysis of canopy temperature depression between tropical rainforest and rubber plantation in Southwest China

Temperature change is an important environmental variable for global change sciences since it largely affects the physiology of plants in forest ecosystems. Canopy temperature depression (CTD) - the result of the deviation of the air temperature (Ta) from the plant canopy surface temperature (Tc) - varies depending on the meteorological and environmental conditions of the forests. Here, we evaluated the differences in CTD between a rubber plantation (RP) and a tropical rainforest (TR) in Xishuangbanna, southwestern China across the various time series of the period of 2011 to 2015. The mean maximum CTD values at the TR site and the RP site were 2.4°C and 0.6°C at diurnal level, 1.3°C and -0.5°C at monthly level, 0.6°C and -0.8°C at seasonal level and 5.6°C and 0.2°C at yearly time series level, respectively, while they were only significant (p < 0.01) in the diurnal time series. There was a significant (p < 0.01) negative linear relationship between CTD and global radiation (Q) in both sites at diurnal level and a significant (p < 0.05) negative linear relationship in the RP site at monthly time series level. A significant (p < 0.05) positive linear relationship between CTD and precipitation (P) at the RP site was found at diurnal level, as well as a significant (p < 0.01) positive linear relationship in the TR site at monthly time series level. The variation of CTD was critical for these two sites and largely depended on the amount of global radiation and the precipitation, while it will mainly affect the physiological variables. This study may prove useful for assessing the physiological response in terms of high temperature and drought conditions to regional and global change.

Development of an Android-tablet-based system for analyzing light intensity distribution on a plant canopy surface

An Android application system for the simple and real-time estimation of light intensity distribution on a plant canopy surface was developed, and its usefulness was tested under artificial lighting. The application system was designed to semi-automatically analyze the photosynthetic photon flux density (PPFD) distribution on the canopy from a reflection image acquired by the tablet. A single manual measurement by a quantum sensor at a point on the canopy was performed to build a regression model that estimated the PPFD on leaves from the pixel values of the image. Measured and estimated PPFD histograms, as well as parameters derived from histograms, were compared at three different growth stages of a plant canopy in a closed plant factory with artificial lighting. The measured and estimated histograms exhibited a similar pattern at each growth stage with close values of the parameters. The results suggested that the reflection-image-based estimation system developed in this study was a useful method for analyzing the light conditions under artificial lighting. Although the developed system will require additional improvements in automation and performance before it can be applied to actual cultivation-management procedures, this simple method for estimating the light intensity distribution is expected to help improve the efficiency and reproducibility of light control methods used for plant production.

Fine-Scale Patterns of Soil and Plant Surface Temperatures in an Alpine Fellfield Habitat, White Mountains, California

Within alpine environments the interactions of air temperature, solar irradiance, wind, surface albedo, microtopography, and biotic traits all influence patterns of soil and plant canopy temperatures. The resulting mosaic of surface temperatures has a profound impact on ecosystem processes, plant survival, and ecophysiological performance. Previous studies have documented large and persistent variations in microhabitat temperatures over mesoscale alpine terrains. We have used a novel mobile system to examine changes in soil and plant canopy surface temperatures at spatial scales of centimeters and temporal scales of minutes in an alpine fellfield habitat in the White Mountains of California. In the middle of a summer day, the mean surface temperature differences between points 2, 5, and 10 cm apart were 2.9, 5.4, and 9.0 °C, respectively, and extreme differences of 18 °C or more were found over distances of a few centimeters. These thermal patterns are due not only to substrate material but also to biotic conditions of plant canopy architecture and ecophysiological traits of individual species. The magnitude of temperature variation at these fine scales is greater than the range of warming scenarios in Intergovernmental Panel on Climate Change (IPCC) projections, suggesting that these habitats offer the capacity of significant thermal heterogeneity for plant survival.

A Portable Rainfall Simulator for Evaluating the Wet Deposition of Plant Pathogens

A portable, single nozzle rainfall simulator was designed for evaluating the wet deposition of plant pathogens within field crop canopies. The simulator consisted of a black iron and galvanized pipe frame with a single nozzle (24WSQ or 50WSQ) centered at least 3 m above the upper plant canopy surface and had an attachment that allowed for fungal spores to be injected into the simulated rainfall. At the operating nozzle pressure of 34.5 kPa, the water volume distribution was relatively uniform (coefficients of uniformities of 85% and 86%) within the 2- 2-m sample area. Drops ranged in size from 0.2 to 3.3 mm with median drop diameters of 1.0 mm for the 24WSQ nozzle and 1.6 mm for the 50WSQ nozzle. The measured rainfall intensities were 45 and 85 mm h-1, however the calculated kinetic energy and cumulative drop volume distribution values indicate that the rainfall produced by the 24 and 50WSQ nozzles was equivalent to long periods (>20 min) of natural rainfall at the intensities of 20 and 75 mm h-1, respectively. The rainfall simulator is easily transported, set up, and operated within a field environment by two individuals and is an effective tool for examining plant pathogen wet deposition processes.

Bowen‐Ratio Comparisons with Lysimeter Evapotranspiration

AbstractWater use in agriculture by different cropping systems is of interest in determining crop water use efficiency of different tillage practices that will lead to reduced crop production risk. Lysimeters are considered the standard for evapotranspiration (ET) measurements; however, these units are often not replicated and are few in number at any given location. Our objective was to determine if a simple Bowenratio system with nonexchanging psychrometers could provide accurate measurements of ET from lentil (Lens culinaris Medikus) in a semiarid climate. The study was conducted in 1993 and 1994 on two adjacent 180‐ by 180‐m fields with weighing lysimeters (1.68 by 1.68 by 1.83 m) located in the center of each field, on a Williams loam (fine‐loamy, mixed Typic Argiboroll) soil near Sidney, MT. A Bowen‐ratio system comprised of two nonexchanging psychrometers and anemometers at 0.25 and 1.25 m above the plant canopy surface was placed in the lentil field along with a net radiometer and soil heat flux plate. Precipitation during the growing season from planting to swathing was 367 mm in 1993 and 227 mm in 1994. In 1993, soil water content of the lysimeter was greater than the field after large precipitation events around Day of Year (DOY) 210, even though the lysimeter was drained. After this time, the lysimeter ET exceeded that measured by the Bowen‐ratio system. Agreement was closer in 1994, when precipitation was near normal and there was no excess soil water in the lysimeter. Cumulative ET totals from the lysimeter were reflective of the seasonal precipitation patterns. Differences between the lysimeter and Bowen‐ratio occurred when there was excess precipitation and inadequate drainage from the lysimeter. Halfhourly ET fluxes from lysimeter and Bowen‐ratio values agreed to within 10% throughout the season. Bowen‐ratio systems with nonexchanging psychrometers can provide satisfactory estimates of daily and seasonal ET and can be used to estimate ET in semiarid climates.

An Improvement of Semiempirical Method of Evaluating the Total Photosynthesis of a Plant Community

In this paper a semiempirical method in evaluating the total photosynthesis of a plant community was improved as a preliminary to further experimental studies, by taking into consideration the influence of the concentration of carbon dioxide and of the leaf age within the community on photosynthesis of leaves.The following assumptions were used to derive the equation for evaluating the total photosynthesis:1. p/p∞=I/K+I′ (1)where p and p∞ are the photosynthesis and the maximum value of it, I the radiation intensity at leaves surface, and K a constant (the value of I at which p/p∞=0.5).2. p∞=DcC, (2)where Dc is the total integral exchange coefficient between surrounding airs and the chroloplast, C the carbon-dioxide concentration in the air.3. Dc=DcH+βF, C=CH+γF, (3)where DcH and CH are the values of Dc and C at the top surface of plant canopy, β and γ the vertical gradients in Dc and C within the canopy, respectively.4. I=IH/(1+αF), (4)where IH is the radiation intensity at the top surface, α a canstant depending upon the canopy structure, and F the downward cummulative leaf area index.Substituting Eqs. (2), (3) and (4) into Eq. (1) and integrating it with respect to the leaf area depth (subject to the conditions Pt=0, Ft=0) givePt=IH/B[lnA+BFt/A{a-bA/B+cA2/B2}+(b-cA/B)Ft+c/2Ft2], where Pt is the total photosynthesis of the plant community with leaf area index of Ft, A=K+IH, B=Kαa, a=DcH⋅CH, b=(DcHγ+CHβ), and c=βγ.Fig. 3 represents, for a canopy with Ft=5, the variation of the maximum of photosynthesis (p∞) and the photosynthesis (p) camputed from the reciprocal law and exponential law for the light attenuation. With increasing the vertical gradient in CO2 concentration and integral CO2 exchange coefficient within the conopy, p and p∞ appreciably decreased with increase of the leaf area depth. It can be concluded from this result that an assumption concerning the constancy of the maximum value (p∞) of photosynthesis over the canopy, as has been adopted by many researchers, may not be valid in practical plant canopies.Fig. 4 suggests that the variation of integral CO2 exchange coefficient (Dc) with the leaf area depth is a conspicously most important factor controlling the total photosynthesis (Pt) of the plant community. Thus, much attention must be paid into the vertical change of photosynthetic activity of plant leaves in relation to the foliage structure. Fig. 4 revealed that though the CO2 concentration at the top of the canopy gives much influence on the total photosynthesis (Pt), the variation in the concentration within the conopy is not very influential on it. The optimum leaf area index was computed from Eq. (17). Results obtained are shown in Fig. 5 as a function of radiation intensity and the vertical gradient of integral exchange coefficient. The following relation was obtained to define the dependence of the total photosynthesis on both the conentration in carbon dioxide and the radiation intensity:dPt/dCH=IH/0.75+2.75IH.A similar relation was also obtained from the data of gross photosynthesis of cotton leaves.

Studies on the Micro-Climate within the Plant Communities

It is well known that the values and the distributions of net radiation and turbulent transport number within plant canopy are most important physical parameters much controlling the micro-climate within plant canopy. The knowledge on transport number within plant canopy has been insufficient for understanding the energy and material exchanges between plant leaves and air layer, whereas the informations about the net radiation within plant canopy are being gathered by means of observation and semi-empirical theory.The author intends in this paper to present a preliminary method for evaluating the transport number within the plant canopy and to present the some features about the build-up of heat, water vapour and momentum fluxes within the plant canopy.In general, the vertical transport of heat within the plant canopy is approximated by∂/∂z{S0e-k∫z0A(z)dz-cpρaKH(z)∂T/∂z-0.622/PlρaKw(z)∂e/∂z}=0Integrating the above equation with respectto Z, the following equation is obtainedS0e-k∫z0A(z)dz-cpρKH(z)∂T/∂z-0.622/P lρaKw(z)∂e/∂z=CBy assuming the equality of turbulent conductivity and turbulent diffusivity, and the equality of integral constant and storage heat, the transport number within the plant canopy can be determined byK(z)=S(z)-B/cpρa(∂T/∂z|z+2∂e/∂z|z)In order to take some clue in investigation of micro-climate within the plant canopy, above equation was applied on the micro-meteorological observational data at the paddy plant field and the young forest published by FRANCESCHINI (1959) and BAUMGARTNER (1956), respectively.These results are set out in Figures, 1, 2, 3, 4, 5. It appeared that the vertical distribution of transport number within the plant canopy(paddy rice)had the different sort of shape between the daytime and the nighttime. The main reason for such discrepancy in vertical distributions seems to be thermal stratification observed in the lower plant layer. In day-time, the transport number decreased in proportion to decrease of height in the upper plant layer ranged from plant canopy surface to 50cm. height(corresponding to the zero-plane displacement at this paddy field). In the lower plant layer, the transport number shows the contrary diurnal course with maximum in night-time and minimum in daytime. As shown in Fig. 3, this characteristic diurnal course in transport number may result from diurnal course of thermal stratification (Δθ0-50) in lower plant layer. The values of transport number in the lower plant layer is well supported with that in wheat field obtained by PENMAN. LONG (1960).Comparing the build-up of each flux and the productive structure of plant canopy, it is shown that the vertical distribution of source or sink intensities for such flux, viz, contribution of each plant layer to the streams of various physical quanties within plant canopy, depends considerably upon the productive structure.During the night-time, water amount equivalent to one-third of daily evaporation from underlying water surface has condensed in plant layer, implying that the heat transport from water surface to upper plant layer is accelerated by such a movement of water vapour.ξ5 introduces the heat balance characteristics at paddy field (in stage of booting). As shown in Tablel 1 and Fig. 6, the daily latent heat consumed to evapotranspiration from paddy field is equivalent to about 90 per cent of daily net radiation, and agrees well with results obtained by other researchers. But the ratio of evaporation to transpiration obtained in this paper is about 0.37 and is slightly more than that reported by the present author (1961).