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- Author or Editor: William L. Bauerle x
Recent work has shown that stomatal conductance (gs) and net photosynthesis (Anet) are responsive to the hydraulic conductance of the soil to leaf pathway (Xp). Two tree species with differing xylem structures were used to study the effect of systematic manipulations in Xp that elevated xylem hydraulic resistance. Simultaneous measures of gs, Anet, bulk leaf abscisic acid concentration (ABAL), leaf water potential (L), and whole plant transpiration (Ew) were taken under controlled environment conditions. Quercus shumardii Buckl. (shumard oak), a ring porous species and Acer rubrum L. `Summer Red' (red maple), a diffuse porous species, were studied to investigate the short-term hydraulic and chemical messenger response to drought. Both species decreased Anet, gs, L, and Ew in response to an immediate substrate moisture alteration. Relative to initial well-watered values, red maple Anet, gs, and Ew declined more than shumard oak. However, gs and Anet vs. whole-plant leaf specific hydraulic resistance was greater in shumard oak. In addition, the larger hydraulic resistance in shumard oak was attributed to higher shoot, as opposed to root, system resistance. The results indicate hydraulic resistance differences that may be attributed to the disparate xylem anatomy between the two species. This study also provides evidence to support the short-term hydraulic signal negative feedback link hypothesis between gs and the cavitation threshold, as opposed to chemical signaling via rapid accumulation from root-synthesized ABA.
A process-based whole-tree simulation model was used to simulate crown transpiration in several species and cultivars of nursery crops. To validate estimates, we measured transpiration in cultivars of red maple (Acer rubrum L.) to determine if there were differences in intraspecific variation that could affect estimates of whole tree water use. We used a combination of field and published data to parameterize additional species and cultivar differences in response to environment and/or management. The different water use estimates of the species and cultivars were related to their genetic variability in leaf biochemical limitations, where the relationship between stomatal conductance and photosynthetic rate may be so closely matched that stomatal conductance appears to adjust itself to the photosynthetic capacity of the species or cultivar. Model predictions indicated that species and cultivars that had higher biochemical limitation regulated transpiration by down regulation of the rate of carboxylation (Vcmax) and coupled photosynthetic electron transport (Jmax), whereas the reverse occurred as Vcmax and Jmax increased. Our model simulations show significant variation in transpiration due to both inter and intraspecific variation in biochemical limitations. These results suggest that models that do not account for inter and intraspecific variation, to reflect genetic variation in physiology, may over or under estimate transpiration. Therefore, physiology-based species and cultivar variation should be part of process-based simulations that assess nursery water use. Results also suggest that effects of leaf dark respiration adaptation interactions can concurrently reduce variation in water use estimates.
This report describes a system for integrating photosynthetically active radiation (PAR) using fiberoptics. Many photoelectric sensors or 1-m-long line sensors that integrate individual interception points for spatial averaging were replaced with fiberoptics, which integrate interception points. Depending on the positioning of optical fibers and the amount of fibers terminated at a PAR sensor, whole-plant, canopy layer, and individual leaf light interception can be determined. The use of fiberoptics has the added advantage of being very small in comparison to the bulk of a typical quantum sensor. The fiberoptic-based system potentially is a more accurate, less expensive method to integrate PAR throughout plant canopies than PAR sensors.
A multiplicative model of stomatal conductance was developed and tested in two functionally distinct ecotypes of Acer rubrum L. (red maple). The model overcomes the main limitation of the commonly used Ball-Berry model by accounting for stomatal behavior under soil drying conditions. It combined the Ball-Berry model with an integrated expression of abscisic acid-based control mechanisms (gfac). The factor gfac = exp(-β[ABA]L) incorporated the stomatal response to abscisic acid (ABA) concentration in the bulk leaf tissue [ABA]L into the Ball-Berry model by down-regulating the slope and coupled physiological changes at the leaf level with those of the root. The stomatal conductance (gs) down regulation is pertinent in situations where soil drying may modify the delivery of chemical signals to leaf stomates. Model testing results indicated that the multiplicative model was capable of predicting stomatal conductance under wide ranges of soil and atmospheric conditions in a woody perennial. Concordance correlation coefficients (rc) were high (between 0.59 and 0.94) for the tested ecotypes under three different environmental conditions (aerial, distal, and minimal stress). The study supported the use of the gfac factor as a gas exchange function that controlled water stress effects on gs and aided in the prediction of gs responses.
Leaves are key factors in the global water exchange cycle. As the primary control interface involved in regulating water loss, understanding the relative influence of leaf morphological and physiological transpiration factors is critical to accurate evapotranspiration predictions. We parameterized a three-dimensional array model, MAESTRA, to establish a link from the leaf to canopy scale and attempted to isolate and understand the interplay among variation in morphological and physiological variables affecting transpiration. When physiological differences were accounted for, differences in leaf width (L w) among Acer rubrum L. genotypes significantly affected leaf temperature and transpiration under slow to moderate wind velocities. In instances, L w variation among genotypes resulted in a 25% difference in transpiration. This study demonstrates how simple morphological traits like L w can provide useful selection criteria for plant breeders to consider in a changing climate.
The influence of 3 watering frequencies and 5 volumes of medium on a spring crop of greenhouse tomatoes (Lycopersicon esculentum Mill.) was evaluated. Watering frequencies of 1, 4, or 8 times/day had no effect on leaf area, total flower and fruit numbers per plant, percentage of fruit set, leaf number between clusters, or percentage of water in leaves, shoots, or fruit. Plants watered once per day had higher shoot fresh and dry weights than those watered 4 or 8 times per day. Plants grown in 14 liter/plant bags had greater leaf relative water content when measured at noon or midmorning, than plants grown in 7 or 35 liter/plant treatments. Percentage of water and percentage of roots in the medium increased from the upper to lower portion of the bags. Plants grown in the 7 liter/plant bag produced lower yield, smaller fruit, and poorer quality fruit (due mostly to blossom-end rot) than plants from the 14, 21, and 35 liter/plant medium volume treatments.
Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red maple (Acer rubrum L.) and one freeman maple (Acer ×freemanii E. Murray) cultivar were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response of five different maple genotypes, including four red maple cultivars [`Summer Red', `October Glory', `Autumn Flame', and `Franksred' ('Red Sunset')] and one hybridized freeman maple cultivar ['Jeffersred' ('Autumn Blaze')]. Two-year-old cloned genotypes of red maple and freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and wholetree sap flow measurements were conducted under well-watered and drought stress conditions. Over the course of the drought stress and recovery phase, net photosynthesis (Anet), stomatal conductance (gs), and transpiration (E) declined as ABAL and instantaneous water use efficiency (A/gs) increased. Until severe water stress conditions were prominent, water use was higher in `Summer Red' as compared to `October Glory'. This study found that ABAL tracked gs and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf level physiological response to substrate volumetric water content that appears to depend on ABAL concentration. In addition, the evidence in this study indicates that ABAL may be used as a potential surrogate for the gs response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red maple and freeman maple.
Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red (Acer rubrum L.) and one Freeman maple (Acer × freemanii E. Murray) were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response of five different maple cultivars, including four red maple genotypes, `Summer Red', `October Glory', `Autumn Flame', and `Franksred' (Red Sunset), as well as one hybridized Freeman maple genotype, `Jeffersred' (Autumn Blaze). Cloned genotypes of red and Freeman maple were subjected to two treatments: 1) irrigated daily to container capacity or 2) irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and whole-tree sap flow measurements were conducted under both conditions. Over the course of the drought stress and recovery phase, net photosynthesis (Anet), stomatal conductance (gs), and transpiration (E) declined as ABAL and instantaneous water use efficiency (A/gs) increased. This study found that ABAL tracked gs and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf-level physiological response to substrate volumetric water content that appears to depend on ABAL concentration. In addition, the evidence in this study indicates that ABAL may be used as a potential surrogate for the gs response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red and Freeman maple.
Substrate moisture sensors offer an affordable monitoring system for containerized tree production. However, root system distribution can vary greatly among species within ornamental container production systems, resulting in variation within substrate readings among sensors within a container. The aim of this study was to examine the relationship of substrate moisture sensor readings in six ornamental trees to their root distribution patterns within a container. Following root anatomical analysis, tree root systems were dissected by root order as a means to separate fine (uptake) roots and coarse (transport) roots. Substrate moisture variability was measured through the deployment of 12 substrate moisture sensors per container. Of the tree species studied, we found the following two patterns of root distribution: a shallow, “conical-shaped,” root system, with the broadest portion of the root system in the shallow soil layer, and a more evenly distributed “cylindrical-shaped” root system. Root system distribution type influenced substrate moisture reading variability. Conical root systems had lower substrate moisture variability and high fine root variability, whereas the opposite was true for cylindrical root systems—most likely due to the larger, coarse woody mass of roots. We were unable to find any correlations between fine root morphological features including root diameter, length, or surface area and substrate moisture variability. However, higher specific root length was associated with higher substrate moisture variability. Classifying a tree’s root system by its growth and distribution within a container can account for variation in substrate moisture readings and help inform future decisions on sensor placement within containerized systems.
This study set out to test the hypothesis that the development in the capacity for the maximal rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (VCmax) and the maximum regeneration rate of ribulose-1,5-bisphosphate (Jmax) per unit mass is proportional to the growth temperature under which the leaf develops and to investigate whether the capacity for photosynthetic acclimation to temperature varies genetically within a species by testing genotypes that originated from diverse thermal environments. Acer rubrum L. (red maple) genotypes were subjected to short-term and long-term temperature alteration to investigate the photosynthetic response. We minimized the variation of within-crown light gradients by growing trees in open grown field conditions and controlled temperature on a crown section basis. Thus, we singled out the temperature acclimation affects on the photosynthetic temperature optimum. In response to temperature acclimation, the genotype from the northern United States downregulated both VCmax and Jmax and had a 5 and 3 °C lower temperature optimum than the genotype native to the southern United States. The activation energy increased and was higher for Jmax than for VCmax in both genotypes. With respect to respiration, both genotypes downregulated about 0.5 μmol·m-2·s-1. Although respiration was lower, the increased energy of activation in response to growth temperature resulted in a decrease in maximum net photosynthetic rate (Amax) under saturating light and CO2. The results illustrate that the photosynthetic capacity adjusted in response to growth temperature but the temperature optimum was different among genotypes.