Paclobutrazol (PBZ) was supplied in nutrient solution culture to `Nemaguard' peach rootstock [Prunus persica × P. davidiana] at concentrations of 0, 0.001, 0.01, 0.1, and 1.0 mg·liter-1. PBZ increased root: shoot ratio and decreased root length by ≈ 5-fold over the range of PBZ concentrations tested. Root tip diameter, stele diameter, and width of the root cortex were not significantly affected by PBZ. Root hydraulic conductivity decreased log-linearly with increasing PBZ concentration; however, this decrease did not affect midday leaf conductance or net photosynthetic rate. Foliar levels of N, P, K, Fe, and Mo were reduced, whereas levels of Ca, Mg, B, and Mn were increased by PBZ. The magnitude of changes in foliar nutrition were proportional to the degree of growth suppression. Chemical name used: (2RS,3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).
Mark Rieger and Giancarlo Scalabrelli
Genhua Niu, Denise S. Rodriguez and Yin-Tung Wang
The effect of drought on the growth and gas exchange of six bedding plant species—agastache [Agastache urticifolia (Benth.) O. Kuntze `Honeybee Blue'], dusty miller (Cineraria maritima L. `Silverdusty'), petunia (Petunia ×hybrida `Wave Purple'), plumbago (Plumbago auriculata Lam. `Escapade'), ornamental pepper (Capsicum annuum L. `Black Pearl'), and vinca [Catharanthus roseus (L.) G. Don `Titan']—was quantified under greenhouse conditions. Seeds were sown in January and seedlings were grown in the greenhouse until 18 Apr., when two irrigation treatments—drought (D, ≈18% volumetric moisture content at reirrigation) and control (C, ≈25% volumetric moisture content at reirrigation)—were initiated. Leaf net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) were determined in response to a range of substrate moisture content (from ≈5% to 30% by volume) and temperature (from 20 °C to 40 °C). Dry weight of agastache, ornamental pepper, and vinca was unaffected by drought, whereas that of other species was reduced. Leaf area of plumbago and height of plumbago and vinca were reduced by drought. As substrate moisture content decreased from 25% to 10%, Pn, E, and gs decreased linearly in all species except petunia and plumbago. Leaf net photosynthetic rate of all species declined as leaf temperature increased from 20 °C to 40 °C. In contrast, E of all species, except petunia, increased as temperature increased. Transpiration rate of petunia increased as temperature increased from 20 °C to 30 °C, and then decreased between 30 °C and 40 °C. Although petunia had the highest Pn among the tested species, its Pn and gs declined more rapidly compared with the other species as temperature increased from 20 °C to 40 °C or as substrate moisture content decreased, indicating that petunia was most sensitive to high temperature and drought.
C. Chun and C.A. Mitchell
For biomass production in a space-deployed Controlled Ecological Life-Support System (CELSS), efficient usage of limited resources such as light, CO2, growth area, and labor is more consequential than for biomass production on Earth. Light will be one of the most energy-consuming environmental factors to provide in CELSS. Therefore, development of an energy-efficient lighting-control strategy would make a great contribution to the sustainability of CELSS. Lettuce (Latuca sativa L.) was used as a model salad crop for the development of new control methods due to its rapid growth rate and high harvest index (≥80%). Lettuce seeds were sown and plants were cultured hydroponically in the Minitron II plant growth/canopy gas-exchange system. Canopy net photosynthetic rates (μmol CO2/m2 per s) were measured under a specific photosynthetic photon flux (PPF) and analyzed to decide the PPF of the next 1-h interval. Appropriate PPFs were provided on the initial day and during the first 1-h interval of each 20-h photoperiod. Plant-growth indices, crop yield rates (g/m2 per day), and power consumption rates were determined for different lighting strategies to identify the best compromise between energy cost and yield. Day/night temperature and CO2 concentration were maintained at 25/25C and 1100/400 μl·liter–1, respectively. This research is supported by NASA grant NAGW-2329.
B. Dansereau, Y. Zhang, S. Gagnon and H.L. Xu
We examined effects of single-layer glass and double-layer antifog polyethylene films on growth and flowering of stock (Matthiola incana L.) and snapdragon (Antirrhinum majalis L.) in a 3-year period. Stock produced more buds/spike with shorter but thicker stems under single-layer glass and under antifog 3-year polyethylene, and showed higher photosynthetic capacity (P c) under single-layer glass than under other covers regardless of light regimes. Similarly, growth and flowering of snapdragon were significantly better under single-layer glass than in polyethylene houses. A supplemental light of 60 μmol·m-2·s-1 accelerated flowering by 20 to 25 days, improved flower quality, and eliminated differences in plant growth and quality of snapdragon between covering treatments. The P c of stock was lower under all polyethylene covers than under single-layer glass. Among the three antifog polyethylene films, a slightly higher P c was measured for plants under antifog 3-year polyethylene. However, there was no difference among covering treatments in the net photosynthetic rate (P N) at low light level (canopy level). Supplemental lighting reduced P c of stock leaves, especially under single-layer glass, and diminished differences in P c among covering treatments. Dry mass was more influenced by larger leaf area caused by higher leaf temperature than by P N. Overall, antifog 3-year polyethylene was a good covering material when both plant quality and energy saving were considered.
Harmandeep Sharma, Manoj K. Shukla, Paul W. Bosland and Robert L. Steiner
Water saving, productivity, and quality of the chile pepper were evaluated under three irrigation treatments. Three drip irrigation treatments used were 1) control, where water was applied at the surface using two drip emitters; 2) partial root-zone drying vertically (PRDv), where subsurface irrigation was applied at 20 cm depth from soil surface; and 3) partial root-zone drying compartment (PRDc), where roots were divided into two compartments and irrigation was applied to one of the compartments on every alternate-day cycle for 15 days. Continuous measurements of soil water content were carried out during the growing seasons of 2013 and 2014, respectively. During both growing seasons, the stomatal conductance (g S) and net photosynthetic rates (Pn) were similar among all treatments including the control. In both PRD treatments, a higher rooting depth and root length density (RLD) than the control likely compensated for the water stress in dry soil zones by taking up more water from the water available parts of the root-soil system. In PRDc and PRDv treatments, 30% less water was applied than control without significant changes to plant stress expressed by stem water potential, plant height, capsaicinoid concentration, and yield. The increased irrigation water use efficiency (IWUE) demonstrated water saving potential of both PRD techniques for chile pepper production in water-limited arid environments.
William L. Bauerle, Joseph D. Bowden and Geoff G. Wang
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.
Letizia Tozzini, Paolo Sabbatini and G. Stanley Howell
Viticulture in Michigan is often limited by cool and humid climate conditions that impact vine growth and the achievement of adequate fruit quality at harvest. Sugars, pH, acids, and yeast available nitrogen (YAN) are indices of quality and, as such, of suitability for wine production. The aim of this study was to evaluate the efficacy of foliar nitrogen (N) fertilization applied as a 1% w/v urea solution at veraison as a method to increase canopy N availability during the fruit ripening stage. To test the effect on different source sink conditions, we imposed three levels of defoliation (0%, 33%, and 66% of leaves removed per vine) and measured net photosynthetic rate (Pn), leaf efficiency parameters, yield components, and fruit quality parameters. Apical leaf Pn was increased by the 33% defoliation (+12% from the undefoliated control) and by the urea application (+6%) 2 weeks after veraison. In basal leaves we observed a reduction in chlorophyll content (SPAD) and maximum photochemical efficiency of PSII (Fv/Fm) as a result of the defoliation treatment and secondarily by the N application, which resulted in a reduction in Pn. Therefore, mean shoot Pn was unaffected by the treatments. Although neither main nor lateral shoot growth was increased by any defoliation treatment, both percent soluble solids (%SS) and berry weight were significantly reduced by the 66% defoliation treatment. Application of urea increased yeast available amino acids by 20% but did not impact %SS or other chemical parameters indicating a different accumulation pathway for sugars and amino acids in the berry.
K. Stanciel, D.G. Mortley, D.R. Hileman, P.A. Loretan, C.K. Bonsi and W.A. Hill
The effects of elevated CO2 on growth, pod, and seed yield, and gas exchange of `Georgia Red' peanut (Arachis hypogaea L.) were evaluated under controlled environmental conditions. Plants were exposed to concentrations of 400 (ambient), 800, and 1200 μmol·mol–1 CO2 in reach-in growth chambers. Foliage fresh and dry weights increased with increased CO2 up to 800 μmol·mol–1, but declined at 1200 μmol·mol–1. The number and the fresh and dry weights of pods also increased with increasing CO2 concentration. However, the yield of immature pods was not significantly influenced by increased CO2. Total seed yield increased 33% from ambient to 800 μmol·mol–1 CO2, and 4% from 800 to 1200 μmol·mol–1 CO2. Harvest index increased with increasing CO2. Branch length increased while specific leaf area decreased linearly as CO2 increased from ambient to 1200 μmol·mol–1. Net photosynthetic rate was highest among plants grown at 800 μmol·mol–1. Stomatal conductance decreased with increased CO2. Carboxylation efficiency was similar among plants grown at 400 and 800 μmol·mol–1 and decreased at 1200 μmol·mol–1CO2. These results suggest that CO2 enrichment from 400 to 800 μmol·mol–1 had positive effects on peanut growth and yield, but above 800 μmol·mol–1 enrichment seed yield increased only marginally.
Rita Giuliani and James A. Flore
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.
Xuan Huang and Liangjun Zhao*
As well as investigating physiological characteristics of the new yellow cultivar of Celtis julianae—`Golden Phoenix' (Julian hackberry, which originally distributed in south of China, is important environmental plant, because there are numerous hairs on surfaces of the leaf, which can absorb dust and clean the air. Julian hackberry is deciduous big tree, more than 25 meters in high, with deep green leaf, red flower and orange fruit, blossoming in April.), differences in leaf color between the new cultivar and the normal Celtis julianae were evaluated. The new cultivar is a natural seed mutant from some cultivated seedlings of Celtis julianae found in 2001. It has golden yellow leaf, average color is Yellow-Green150A mensurating by English Color Card, is significantly more different than those of the normal. It can normally growing but slowly, with smaller plant-size and shorter internode than common plant. The new cultivar's leaf contains less chlorophyll than the normal, but same carotenoid. Its net photosynthetic rate is lower than that of Julian hackberry common cultivates in full sunlight. Shading of leaf to 50% sunlight decreases chlorophyll content and photosynthetic rate compared with full sunlight and sharper in photosynthetic, resulting in deepen green color. Leaves of the new cultivar show higher values of lightness and yellow-green as compared with other normal. Shoot multiplication frequency was highest on woody plant medium containing 1.5 mg 6-BA(benzyladenine)/ml, producing 6 shoots from a single explant, but these are some troubles to root.