Effects of Environmental Factors on Leaf Tipburn and Photosynthesis in Eustoma
Date Issued
2015
Date
2015
Author(s)
Wang, Hsin-Wen
Abstract
Abstract Leaf tipburn of Eustoma grandiflorum (Raf.) Shinn. is a calcium-deficient disorder. The published reports of environmental factors on incidence of tipburn are often inconsistent. Low transpiration rate and unbalanced Ca distribution are reported as the main causes of tipburn on unfolding leaves, while differentiating flower competes with the young leaves for Ca also induce tipburn. Eustoma ‘King of Orchid’ was treated with various irradiance, temperature, and relative humidity (RH) conditions to have a better understanding of leaf tipburn. We measured stomatal density, vein density of unfolding leaves, and developmental stages of shoot tips, to elucidate the main cause of leaf tipburn. Leaf gas exchange under various irradiance, temperature, leaf to air vapor pressure deficit (VPD), and CO2 concentration conditions was measured to elaborate the tipburn incidence and severity. Effects of foliar spray of calcium chloride on tipburn occurrence were also investigated. Eustoma ‘King of Orchid’ plants with five fully expanded leaf pairs were placed in a growth room at 36/23℃. Twelve treatments were conducted as follows: moderate humidity condition (MRH; 76% RH, 206 μmol·m-2·s-1 PPF) for 1, 3, 5, 7, 9 days then moved to low humidity condition (LRH; 53% RH, 356 μmol·m-2·s-1 photosynthetic photon flux, PPF), and LRH conditions for 1, 3, 5, 7, 9 days then moved to MRH, and continuous MRH or LRH treatments. Plants under continuous MRH exhibited tipburn occurrence, while those under LRH did not. Plants expressed tipburn symptoms after 5 days under MRH conditions. In contrast, plants did not express any tipburn under LRH conditions until they were placed to MRH conditions. Plants at 4th, 6th, and 8th leaf pairs stages were placed under 76% RH (0.99 kPa VPD) and received 206 μmol·m-2·s-1 PPF. Results showed that plants with four or six leaf pairs onset tipburn 18 to 6.5 days after treatment, while plants with eight fully expanded leaf pairs showed tipburn symptoms 5 days after treatment. Vegetative plants with five fully expanded leaf pairs were placed in growth rooms at 36/23℃ or 25/18℃, and each with 74% RH (0.73 - 1.11 kPa VPD) and 90% RH (0.23 - 0.37 kPa VPD) treatments under 167 to 422 μmol·m-2·s-1 PPF. Results showed that leaf tipburn occurred only in plants at sepal and petal primordia formation under 90% RH conditions, and symptoms appeared 8 days earlier under 36/23℃ than 25/18℃. Plants had a higher incidence and whole-plant severity level were observed at 36/23℃ than at 25/18℃. Consistently lower transpiration and reduced leaf vein density was measured in the third young leaf pairs in plants under 90% RH that may limit the uptake and transport of calcium to the leaf tips. Vegetative plants with five fully expanded leaf pairs were grown under 28 - 35℃/23℃, and 167 to 422 μmol·m-2·s-1 PPF conditions with six treatments. When humidity was elevated from 71% RH (0.32 kPa VPD) to 91% RH (1.19 kPa VPD), tipburn incidence increased from 50% to 100%. Plants with 91% RH showed the earliest and the most severe tipburn symptoms. It took 8 days for plants with 91% RH and 14 days for those with 71% RH from onset to peak of tipburn incidence. Characteristics of gas exchange were measured under controlled environments. At 25℃, the dark respiration of mature leaves was 2.6 μmol·m-2·s-1, light compensation point was 18.2 μmol·m-2·s-1 PPF, and quantum yield was calculated as 0.04 μmol CO2/μmol PPF. Maximum net photosynthesis rate (Pn) was 15 to 18.5 μmol·m-2·s-1 at 800 μmol·m-2·s-1 PPF, leaf temperature (TL) between 24 and 28℃, and VPD below 1.08 kPa. CO2 saturation point was estimated as 686 μL·L-1, with maximum Pn was recorded as 22.5 μmol·m-2·s-1. At 1.07 ± 0.08 kPa VPD with irradiance increasing from 0 to 1000 μmol·m-2·s-1 PPF, transpiration rate (E) remained constant at 2.18 to 3.28 mmol·m-2·s-1, indicating that E was not affected by different irradiances when VPD was constant. At 1.2 ± 0.1 kPa VPD, E decreased from 3.09 to 2.06 mmol·m-2·s-1 with increasing TL from 16℃ to 30℃.However, E increased linearly from 1.60 to 5.25 mmol·m-2·s-1 with increasing TL and VPD from 0.51 kPa to 4.06 kPa, indicating that VPD might play a major role in Eustoma transpiration. Exposure to CO2 concentration up to 1000 μL·L-1 reduced stomatal conductance and thus decreased transpiration to 1.84 mmol·m-2·s-1. Effects of calcium chloride on mitigation of tipburn was studied in plants under 31/23℃ with 77% RH (0.82 kPa VPD) and received 221 μmol·m-2·s-1 PPF. Results showed that spraying 25 mM calcium chloride twice per week reduced the incidence of tipburn, while spraying 25 mM daily, and spraying 50 mM and 100mM daily or twice a week calcium chloride could fully prevent tipburn occurrence. However, leaf bleaching was observed in 100 mM treatments.
Subjects
physiologicl disorder
transpiration rate
Type
thesis
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