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Impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology to support an energy conscious greenhouse heating

Bruno Pollet UGent (2010)
abstract
Since the first energy crisis in early 1970’s improving the energy efficiency of the Phalaenopsis greenhouse industry started gaining importance. Today, in the context of global change and the commitment of Europe to become the most climate friendly region of the world, efficient energy use has never been more crucial. Taking into account that nighttime greenhouse heating is about 80% of the total heating budget, the main objective of this work was to explore the impact of cool night temperatures on the photosynthetic activity and physiology of Phalaenopsis. To this end, experiments were conducted in growth chambers under controlled environmental conditions as well as in greenhouses in which duration and interaction with external environmental conditions (e.g. light) came close to common cultivation practices. In a first explorative study of this research, the application of chlorophyll fluorescence to assess temperature stress in Phalaenopsis was investigated. Upon exposure to a warm day/cool night temperature of 37/18°C, chlorophyll fluorescence was measured continuously over 48 h and the results revealed a crucial role of the internal malic acid pool in the diel course of PSII operating efficiency (Fq′/Fm′) and non-photochemical quenching (NPQ). Moreover, temperature and PAR evolution closely correlated with the daytime course of Fq′/Fm′ and maximum quantum efficiency of PSII photochemistry (Fv/Fm). Taking these finding into account as well as the impact of temperature and light on the amount of nocturnally accumulated malate and diel photosynthetic activity, it was therefore recommended to carry out chlorophyll fluorescence measurements after the onset of the photoperiod (i.e. far before the potential malic acid depletion), within a reasonable time span (i.e. 40 – 60 min) and at least in combination with CO2 flux measurements to generate meaningful fluorescence data. In a second part of this doctoral research, a more in depth assessment was made of the impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology. First, the energy saving night temperature was determined for the key CAM processes in Phalaenopsis: leaf net CO2 exchange, malate and citrate accumulation, PSII photochemistry and soluble sugar synthesis. Phalaenopsis was subjected to night temperatures of 12°C to 27°C. A new approach was suggested to determine the upper and lower energy saving night temperature limits in a precise and objective manner, thereby relying on the temperature response curve of a particular physiological process and its 5th and 95th percentile line. The energy saving night temperature range differed with the physiological process, but for the whole of the afore-mentioned physiological processes the temperature range from 17.1°C to 19.9°C could be defined as being energy saving. To validate our newly developed method, 8 Phalaenopsis hybrids were grown during a complete vegetative cultivation period at a warm day/cool night temperature regime of either 29/17°C or 29/23°C and potential differences in response with plants grown at a constant warm temperature regime (i.e. 28/28°C) were investigated. This survey revealed that a day/night temperature of 29/17°C resulted in a significantly lower biomass growth and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28°C and 29/23°C. More importantly, it was shown that undesired premature flowering could only be sufficiently suppressed in 3 hybrids (i.e. ‘Boston’, ‘Bristol’ and ‘Lennestadt’). As such, the implementation of warm day/cool night temperature regimes for commercial cultivation of Phalaenopsis is acceptable for hybrids like ‘Boston’, ‘Bristol’ and ‘Lennestadt’ but not for hybrids similar to the other 5 (i.e. ‘Chalk Dust’, ‘Fire Fly’, ‘Liverpool’, ‘Precious’ and ‘Vivaldi’). After determination of the energy saving night temperature range, the next step was to investigate the mechanistic background and to which extent the photosynthetic capacity and metabolic activity of Phalaenopsis is able to acclimate to a suboptimal night temperature. During this survey, the night temperature was gradually reduced from 28°C to 16°C over 4 consecutive days and compared to responses of plants subjected to an abrupt night temperature drop. The reduction in leaf net CO2 uptake, while nocturnal malate content increased, suggested an enhanced refixation of respiratory CO2. Indeed, the contribution of respiratory CO2 recycling to nocturnal malate accumulation increased from 23.5% to 47.0%. The subsequent evolution of CAM photosynthesis towards CAM idling was accompanied by a transition from a malate dominated organic acid metabolism to an organic acid metabolism with comparable levels of malate and citrate. This organic acid modulation suggested a strategy to avoid over-excitation of PSII photochemistry as well as an important carbon recycling mechanism and therefore the diversion of the organic acid metabolism to citrate accumulation could be considered as an essential step in the low night temperature acclimation of Phalaenopsis. In contrast to starch, glucose and fructose, which were shown to act as major carbohydrate sources for PEP generation at high night temperatures (i.e. > 24°C), sucrose appeared to play a distinct role in the recovery of the membrane stability after a cool night temperature event. After a gradual decrease in night temperature from 28°C to 16°C, membrane stability showed a depression at the start of the photoperiod. Consistent with the relatively high PSII electron transport rates and the view that malate decarboxylation was not yet started at that time, these findings indicated the involvement of oxidative stress. Membrane stability recovered however relatively quickly and it was striking to find that this recovery was preceded by a temporarily up-regulation of mainly sucrose and to a lesser extent also glucose and fructose. In this respect, the observed metabolic flexibility in Phalaenopsis could be regarded as an important factor in alleviating the oxidative burden at suboptimal night temperatures. Finally, the photosynthetic performance of Phalaenopsis subjected to a distinctive warm day/cool night temperature regime was evaluated during one month in autumn and spring. A first major outcome of this survey was the characterization of the efficiency of carbon fixation in Phalaenopsis. To the best of our knowledge, efficiency of carbon fixation was quantified for the first time in Phalaenopsis and revealed a considerable seasonality with a carbon fixation efficiency of 1.06-1.27% during spring and as half as high in autumn. A second important finding of this study was the involvement of photorespiration in CAM photosynthesis. Photorespiration was evidenced by the decline in the Phase II and Phase IV contribution to the total daily net CO2 assimilation from 15% to maximally 7%. Consistently a slightly lower carbon fixation efficiency upon exposure to the distinctive warm day/cool night temperature was found. In addition, cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative.
Please use this url to cite or link to this publication:
author
promoter
Kathy Steppe and UGent
organization
alternative title
Impact van lage nachttemperaturen op de fotosynthetische activiteit en fysiologie van Phalaenopsis ter ondersteuning van een energiebewuste temperatuursturing
year
type
dissertation (monograph)
subject
keyword
photosynthetic efficiency, temperature acclimation, energy saving night temperature, Chilling, Phalaenopsis, orchid, temperature response curve, chlorophyll fluorescence, carbon fixation efficiency, Crassulacean Acid Metabolism (CAM)
pages
VII, 173 pages
publisher
Ghent University. Faculty of Bioscience Engineering
place of publication
Ghent, Belgium
defense location
Gent : Faculteit Bio-ingenieurswetenschappen (A0.030)
defense date
2010-12-14 16:00
ISBN
9789059894105
language
English
UGent publication?
yes
classification
D1
additional info
dissertation consists of copyrighted materials
copyright statement
I have transferred the copyright for this publication to the publisher
id
1085053
handle
http://hdl.handle.net/1854/LU-1085053
date created
2010-12-08 15:18:42
date last changed
2010-12-08 17:06:26
@phdthesis{1085053,
  abstract     = {Since the first energy crisis in early 1970{\textquoteright}s improving the energy efficiency of the Phalaenopsis greenhouse industry started gaining importance. Today, in the context of global change and the commitment of Europe to become the most climate friendly region of the world, efficient energy use has never been more crucial. Taking into account that nighttime greenhouse heating is about 80\% of the total heating budget, the main objective of this work was to explore the impact of cool night temperatures on the photosynthetic activity and physiology of Phalaenopsis. To this end, experiments were conducted in growth chambers under controlled environmental conditions as well as in greenhouses in which duration and interaction with external environmental conditions (e.g. light) came close to common cultivation practices.
In a first explorative study of this research, the application of chlorophyll fluorescence to assess temperature stress in Phalaenopsis was investigated. Upon exposure to a warm day/cool night temperature of 37/18{\textdegree}C, chlorophyll fluorescence was measured continuously over 48 h and the results revealed a crucial role of the internal malic acid pool in the diel course of PSII operating efficiency (Fq{\textquotesingle}/Fm{\textquotesingle}) and non-photochemical quenching (NPQ). Moreover, temperature and PAR evolution closely correlated with the daytime course of Fq{\textquotesingle}/Fm{\textquotesingle} and maximum quantum efficiency of PSII photochemistry (Fv/Fm). Taking these finding into account as well as the impact of temperature and light on the amount of nocturnally accumulated malate and diel photosynthetic activity, it was therefore recommended to carry out chlorophyll fluorescence measurements after the onset of the photoperiod (i.e. far before the potential malic acid depletion), within a reasonable time span (i.e. 40 -- 60 min) and at least in combination with CO2 flux measurements to generate meaningful fluorescence data.
In a second part of this doctoral research, a more in depth assessment was made of the impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology.
First, the energy saving night temperature was determined for the key CAM processes in Phalaenopsis: leaf net CO2 exchange, malate and citrate accumulation, PSII photochemistry and soluble sugar synthesis. Phalaenopsis was subjected to night temperatures of 12{\textdegree}C to 27{\textdegree}C. A new approach was suggested to determine the upper and lower energy saving night temperature limits in a precise and objective manner, thereby relying on the temperature response curve of a particular physiological process and its 5th and 95th percentile line. The energy saving night temperature range differed with the physiological process, but for the whole of the afore-mentioned physiological processes the temperature range from 17.1{\textdegree}C to 19.9{\textdegree}C could be defined as being energy saving. 
To validate our newly developed method, 8 Phalaenopsis hybrids were grown during a complete vegetative cultivation period at a warm day/cool night temperature regime of either 29/17{\textdegree}C or 29/23{\textdegree}C and potential differences in response with plants grown at a constant warm temperature regime (i.e. 28/28{\textdegree}C) were investigated. This survey revealed that a day/night temperature of 29/17{\textdegree}C resulted in a significantly lower biomass growth and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28{\textdegree}C and 29/23{\textdegree}C. More importantly, it was shown that undesired premature flowering could only be sufficiently suppressed in 3 hybrids (i.e. {\textquoteleft}Boston{\textquoteright}, {\textquoteleft}Bristol{\textquoteright} and {\textquoteleft}Lennestadt{\textquoteright}). As such, the implementation of warm day/cool night temperature regimes for commercial cultivation of Phalaenopsis is acceptable for hybrids like {\textquoteleft}Boston{\textquoteright}, {\textquoteleft}Bristol{\textquoteright} and {\textquoteleft}Lennestadt{\textquoteright} but not for hybrids similar to the other 5 (i.e. {\textquoteleft}Chalk Dust{\textquoteright}, {\textquoteleft}Fire Fly{\textquoteright}, {\textquoteleft}Liverpool{\textquoteright}, {\textquoteleft}Precious{\textquoteright} and {\textquoteleft}Vivaldi{\textquoteright}).
After determination of the energy saving night temperature range, the next step was to investigate the mechanistic background and to which extent the photosynthetic capacity and metabolic activity of Phalaenopsis is able to acclimate to a suboptimal night temperature. During this survey, the night temperature was gradually reduced from 28{\textdegree}C to 16{\textdegree}C over 4 consecutive days and compared to responses of plants subjected to an abrupt night temperature drop. The reduction in leaf net CO2 uptake, while nocturnal malate content increased, suggested an enhanced refixation of respiratory CO2. Indeed, the contribution of respiratory CO2 recycling to nocturnal malate accumulation increased from 23.5\% to 47.0\%. The subsequent evolution of CAM photosynthesis towards CAM idling was accompanied by a transition from a malate dominated organic acid metabolism to an organic acid metabolism with comparable levels of malate and citrate. This organic acid modulation suggested a strategy to avoid over-excitation of PSII photochemistry as well as an important carbon recycling mechanism and therefore the diversion of the organic acid metabolism to citrate accumulation could be considered as an essential step in the low night temperature acclimation of Phalaenopsis.
In contrast to starch, glucose and fructose, which were shown to act as major carbohydrate sources for PEP generation at high night temperatures (i.e. {\textrangle} 24{\textdegree}C), sucrose appeared to play a distinct role in the recovery of the membrane stability after a cool night temperature event. After a gradual decrease in night temperature from 28{\textdegree}C to 16{\textdegree}C, membrane stability showed a depression at the start of the photoperiod. Consistent with the relatively high PSII electron transport rates and the view that malate decarboxylation was not yet started at that time, these findings indicated the involvement of oxidative stress. Membrane stability recovered however relatively quickly and it was striking to find that this recovery was preceded by a temporarily up-regulation of mainly sucrose and to a lesser extent also glucose and fructose. In this respect, the observed metabolic flexibility in Phalaenopsis could be regarded as an important factor in alleviating the oxidative burden at suboptimal night temperatures.
Finally, the photosynthetic performance of Phalaenopsis subjected to a distinctive warm day/cool night temperature regime was evaluated during one month in autumn and spring. A first major outcome of this survey was the characterization of the efficiency of carbon fixation in Phalaenopsis. To the best of our knowledge, efficiency of carbon fixation was quantified for the first time in Phalaenopsis and revealed a considerable seasonality with a carbon fixation efficiency of 1.06-1.27\% during spring and as half as high in autumn. A second important finding of this study was the involvement of photorespiration in CAM photosynthesis. Photorespiration was evidenced by the decline in the Phase II and Phase IV contribution to the total daily net CO2 assimilation from 15\% to maximally 7\%. Consistently a slightly lower carbon fixation efficiency upon exposure to the distinctive warm day/cool night temperature was found. In addition, cumulated leaf net CO2 uptake of the distinctive warm day/cool night temperature regimes declined with 10-16\% as compared to the more constant temperature regimes, while the efficiency of carbon fixation revealed no substantial differences in both seasons. As a result, only in the case where a net energy reduction between the temperature regimes compensates for the reduction in net CO2 uptake, warm day/cool night temperature regimes may be recommended as a practical sustainable alternative.},
  author       = {Pollet, Bruno},
  isbn         = {9789059894105},
  keyword      = {photosynthetic efficiency,temperature acclimation,energy saving night temperature,Chilling,Phalaenopsis,orchid,temperature response curve,chlorophyll fluorescence,carbon fixation efficiency,Crassulacean Acid Metabolism (CAM)},
  language     = {eng},
  pages        = {VII, 173},
  publisher    = {Ghent University. Faculty of Bioscience Engineering},
  school       = {Ghent University},
  title        = {Impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology to support an energy conscious greenhouse heating},
  year         = {2010},
}

Chicago
Pollet, Bruno. 2010. “Impact of Cool Night Temperatures on Phalaenopsis Photosynthetic Activity and Physiology to Support an Energy Conscious Greenhouse Heating”. Ghent, Belgium: Ghent University. Faculty of Bioscience Engineering.
APA
Pollet, B. (2010). Impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology to support an energy conscious greenhouse heating. Ghent University. Faculty of Bioscience Engineering, Ghent, Belgium.
Vancouver
1.
Pollet B. Impact of cool night temperatures on Phalaenopsis photosynthetic activity and physiology to support an energy conscious greenhouse heating. [Ghent, Belgium]: Ghent University. Faculty of Bioscience Engineering; 2010.
MLA
Pollet, Bruno. “Impact of Cool Night Temperatures on Phalaenopsis Photosynthetic Activity and Physiology to Support an Energy Conscious Greenhouse Heating.” 2010 : n. pag. Print.