Infrared thermometry was applied to estimate the canopy temperature of apple trees with the aim to detect a water stress condition early by remote sensing. The measurements were taken in Michigan during Summer 1998 in a 4-year-old apple orchard. Digital thermo-images of the canopy were taken using a IR imaging radiometer on well-watered trees and trees in a water shortage condition. The images were taken considering the geometrical relationship among camera position, canopy, and sun position. During the measurements, environmental (air and soil) conditions were also monitored. A software program was developed to analyze the thermal data, to show the thermal frequency distribution and to estimate the statistical parameters, which are able to represent the physiological condition of the trees. An increase of the canopy surface temperature (connected to the partial stomatal closure that is affecting the leaf energy balance) was detected early in the non-irrigated plants, compared to the well-irrigated trees, already when physiological responses as photosynthetic activity and fruit growth were not yet negatively affected by water deficit. The study confirms that there are the theoretical basis to use infrared thermometry and digital image processing to early detect the water stress on fruit trees.
Ground-based infrared thermal imagery was applied for early detection of plant water deficit, i.e., before photosynthetic activity is depressed and before growth processes are negatively affected by water shortage. Remote and real-time sensing of radiative canopy surface temperature was performed in Michigan in Summer 1999 on peach and apple orchards, using a digital IR imaging radiometer. Still images and videos were acquired on single canopies of well-watered plants and plants subjected to water depletion. Atmospheric parameters were monitored simultaneously. On apple trees, the apparent canopy temperature showed a wider thermal dispersion [10 °C], compared to peach tree canopies [2–5 °C]. Central tendency and shape parameters describing the canopy thermal distribution could identify, even for apple canopies, the thermal signal [1–2 °C] of plant water deficit, before changes in leaf net photosynthetic rate and fruit diameter were observed. The results of this study support the application of digital infrared thermal imagery and image processing for early recognition of plant water deficit. The decrease of the cost of available thermographic cameras makes their use feasible.
This study demonstrates that thermal image analysis can be used to localize stomatal opening and closing on leaves of apple, and cherry. An attached leaf was placed in an environmental chamber used for gas exchange and leaf temperature was monitored with cromel-constantan thermocouples, (0.08 mm) pressed against the underside of the leaf, or with an Inframetrics 600 thermal image analyzer that was focused on the upper side of the leaf. Radiation was monitored in the 8–12 μm range and the image was recorded on video tape. A two-degree temperature difference due to stomatal opening was detected. Stomatal opening as monitored by gas exchange was correlated significantly with leaf temperature. Under steady state conditions, stomata from cherry oscillated at 20-minute intervals. Stomata opened and closed uniformly. Factors investigated were light, carbon dioxide, ABA, and water stress. In all cases changes in temperature correlated with stomatal opening and closing. Response time to a change in environment was less than 10 minutes. The practical implications of this study are discussed.
Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.
The naturally occurring carbon isotope composition (or 13C: 12C ratio, expressed with the notation d13C) of plant tissue may be used as an indicator of water use efficiency during plant growth. d13C has been shown to be an effective tool to study physiological response of plant to environmental conditions, especially water stress. The objective of this work was to test if d13C could be an indicator of carbon limitations or a low source: sink ratio. Trees of `Imperial Gala'/Bud 9 (n = 12), 6-years-old, field grown at the Clarksville Horticultural Research Station (Clarksville, Miss.), were assessed with different crop load (LCL = Low Crop Load, 0.76 ± 0.44 fruit per trunk sectional area (TCA); NCL = Normal Crop Load, 7.25 ± 1.83 fruit/TCA; HCL = High Crop Load, 15.83 ± 1.76 fruit/TCA) and leaf: fruit ratio (LCL: 52.78 ± 8.55, NCL: 13.33 ± 3.06, HCL; 4.31 ± 0.68) immediately following June drop. Net photosynthetic rate of leaves were monitored during the season and elevated rates were observed in NCL and HCL and correlated with the fruiting process. Photosynthesis was inhibited in LCL more in the afternoon (from 20% to 42% in relation to NCL) than in the morning (from 5% to 20%) and this was positively correlated with crop sink strength. Variations of the stable carbon isotope composition of roots (fine and coarse), fruit, leaves, and current-year stems were examined. The d13C varied by tissue (fruit > shoot and leaf > root) and in relation to the level of crop load (d13C‰ in fruit: LCL –23.513 ± 0.248, NCL –24.891 ± 0.594; and HCL –24.935 ± 0.375). These results may have implications for analysis of isotopic signals in carbohydrate stress and fractionation steps will be discussed.
The influence of phyllotaxy and stage of leaf and fruit development on the initiation and direction of carbohydrate (CH2O) export from sour cherry (Prunus cerasus L.) leaves was investigated during two different seasons. One-year-old ‘Montmorency’ sour cherry trees on ‘Mahaleb’ rootstock were pruned to a single shoot, the seventh and 10th leaf (from the base) were pulsed with 14CO2, and labeled carbon products were located after 24 hr using autoradiography. In 1983, gross export (EG) from the seventh and 10th leaf was initiated when the area of the seventh leaf reached 8.5 cm2 (27% expansion) and when that of the 10th leaf reached 14 to 21 cm2 (48% to 72% expansion), respectively. EG was generally initiated later in 1985 than in 1983, for the seventh leaf later than 26 cm2 (47% expansion) and for the 10th leaf at 36 cm2 (78% expansion). Leaf size was greater at full expansion in 1985 than in 1983. On defoliated shoots, the 10th leaf (54 ± 16 cm2 full expansion) started export between 24 and 28 cm2 (44% to 52% expansion), whereas control leaves on nondefoliated shoots started export at 36 cm2 (78% expansion). We suggest that, after a leaf has developed the potential for phloem loading, the onset of CH2O export is a function of the CH2O availability in the plant at the time of leaf expansion. Translocation paths followed closely the orthostichy of the exporting leaf. Fruit effects on the direction of translocation were studied in 2-year-old trees. During stages I and III of fruit development, leaves closest to the base showed basipetal translocation only. All leaves during stage II and leaves distal to the midpoint of the shoot during stages I and III showed bidirectional translocation to the shoot apex and the fruits.
Highbush (Vaccinium corymbosum L. ‘Bluecrop’) and rabbiteye (V. ashei Reade ‘Woodard’) blueberry plants were flooded in the greenhouse to determine how transpiration, stomatal conductance to water and CO2, residual conductance, and C assimilation are affected during flooding and recovery. Carbon assimilation was measured using a portable CO2 analyzer and stomatal conductance using a steady-state porometer. Stomatal conductance and transpiration decreased significantly after 4 to 5 days of flooding, and responses were similar for highbush and rabbiteye blueberries. Carbon assimilation decreased for both species within 9 days and became negative in 11 to 19 days due to decreased photosynthesis, stomatal conductance to CO2, and high leaf temperatures, which increased respiration. Recovery after 24 days of flooding to preflood stomatal conductance values required 18 days for ‘Woodard’ and more than 18 days for ‘Bluecrop’. In laboratory experiments flooded plants were less responsive to changes in ambient CO2 and vapor pressure deficits than unflooded plants, and flooding durations of greater than 9 days significantly decreased residual conductance of the leaves.
Instrumentation to measure soil respiration is currently readily available. However, the relationship between soil respiration and root activity or root mass is not known. Herein we report on preliminary result using a 13CO2 pulse to the foliage to determine if 13C respiration can be related to either root activity or root mass. An experiment was performed in the field on a 5-year-old apple tree (cv. Jonagold on M7). The tree canopy was enclosed in a Mylar® balloon and 2.1 g 13CO2 were pulsed in the balloon for 1 hr. After the pulse, air emitted by the soil and selected roots was collected every 6 hr for 8 days, by bubbling it in 2 M NaOH. 13C/12C ratios were measured with the mass spectrometer. The emission of 13CO2 from the roots gradually increased after the pulse reaching a peak after 100 hr. The emission trend was not linear, but it seemed related to soil temperature. Leaves and fruit were also collected daily. 13C content in leaves was 1.15% right after the pulse, but it progressively decreased to 1.09% at the end of the experiment. The experiment was then repeated on 12 potted apple trees (cv. Redcort on M7) in greenhouse conditions. Six of them were maintained well-watered, whereas six plants were subjected to a mild water stress, by watering them with half of the volume of water used for well-watered plants. After the two soil moisture levels were achieved, the tree canopies of all the 12 trees were pulsed. Leaves, stems, and roots were ground and run in the mass spectrometer. The results of root emission rate were found to be similar to the field experiment. Results also indicated that, in our experiment, stress did not affect root respiration rate. Specific details of the physiology data will be presented.
Low root-zone temperature is one of the potential causes of low rate of plant nutrient uptake in spring. In this period, fruit trees are frequently supplied with nitrogen and a delay in root absorption could lead to an increase of nitrate leaching. In this study we assessed the effect of low root temperature on kinetic of nitrogen absorption of apple trees. One-year-old rooted cuttings of `Mark' apple rootstocks were subjected to two root temperature: 8 ± 1°C (LT) and 23 ± 1°C (HT). Four days after treatment imposition, the potted plants were supplied with 20 mg of N as NH4N03, enriched with 10 atom% of 15N. One, 2, 4, and 8 days after fertilization, tree root system was inserted into a Sholander bomb where a 0.325-Mpa pressure was applied to collect the xylem sap from the stem cross section. The sap exudation rate was always depressed by low root temperature. Nitrogen flow through the xylem vessel was highest in HT plants the day after fertilization (10-fold higher than LT), then decreased constantly. In LT plants, N flow was low the first and the second day after fertilization then reached the maximum 4 days after fertilization, when it was significantly higher than in HT plants. The amount of fertilizer-N found in leaves reflected the different movement rate of N observed in the two treatments. In HT trees fertilizer-N reached a plateau 2 days after fertilization, while in LT it linearly increased over time. This results suggest that root zone temperature of 8°C, although causes a delay (2–4 days) in nitrogen uptake, does not represent a serious limiting factor for N nutrition of tested apple trees.
This study was conducted to determine whether standard and dwarfing sweet cherry rootstocks under water deficit conditions respond differently relative to plant growth and gas exchange parameters, water-use efficiency, and leaf carbon isotope composition. One-year-old potted sweet cherry cv. `Rainier' grafted on the standard rootstock `Mazzard' and on the dwarfing rootstock `Gisela 5' were compared under two different water treatments: 1) well-watered, which received daily 100% of the amount of water lost by ET, and 2) a water deficit treatment, which received 50% of the water applied to the control. Relative shoot growth rate, leaf emergence rate and cumulative leaf area were recorded every three to seven days during the experiment. Leaf net carbon dioxide assimilation rate, stomatal conductance, transpiration rate, internal CO2 concentration, and WUE were measured daily for the duration of the experiment. At the end of the experiment, leaf samples were collected to determine leaf carbon isotope composition. The growth parameters measured were affected similarly in the two rootstocks indicating a similar degree of sensitivity to water deficit in the genotypes tested. Cumulative leaf area was affected earlier by water deficit than relative shoot growth, and leaf emergence rate. Gas exchange parameters were affected earlier than growth parameters. Overall, WUE was not significantly different between dwarfing and standard rootstocks, and did not appear to increase under water deficit condition, indicating that irrigation should be considered as an important practice in sweet cherry orchards, especially when dwarfing rootstocks are selected.