Location: Cereal Crops ResearchTitle: Influence of Different Nutrient Solution NH4+ to NO3-Ratios on Photosystem II Photochemistry and Thermal Energy Dissipation in Hydroponically Grown Lettuce
|Ko, Tae Seok - North Dakota State University|
|Chiwon, Lee - North Dakota State University|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/7/2018
Publication Date: 7/28/2018
Citation: Ko, T., Ohm, J., Chiwon, L. 2018. Influence of Different Nutrient Solution NH4+ to NO3-Ratios on Photosystem II Photochemistry and Thermal Energy Dissipation in Hydroponically Grown Lettuce. Meeting Abstract. p.195-196.
Technical Abstract: The objective this experiment was to compare the influence of various ammonium (NH4+) to nitrate (NO3-) ratios on growth, photosynthetic pigment composition, and photosynthetic apparatus associated with photosystem II photochemistry and thermal energy dissipation in hydroponically grown lettuce (Lactuca sativa L.). Two lettuce cultivars (Rex RZ, Black Seeded Simpson) grown with hydroponic nutrient solutions containing 5 different NH4+:NO3- ratios (100:0, 75:25, 50:50, 25:75, 0:100, adjusted to total 12 meq L-1 N) and evaluated during the first (T1) and second (T2) week of culture. Plants grown under higher NH4+/NO3- ratios exhibited significantly suppressed shoot growth with poorly developed root system, dark-green leaves, and less water and nitrate uptake. On the other hand, plants grown under higher NO3-/ NH4+ ratios exhibited vigorous shoot growth with well-developed root system and high water and nitrate uptake. There were strong correlations between growth parameters and photosynthetic pigment stoichiometry as well as ratios. Total chlorophyll content increased, but the ratios of Chl a/b and carotenoid x+c/Chl a+b decreased progressively with increasing NH4+/NO3- ratios which are associated with a greater increase in Chl b. There were significant changes in PSII efficiency under different NH4+/NO3- ratios for cultivar Rex RZ during T1 period, however these changes are likely to be temporal and cultivar-dependent. In this study, the steady-state chlorophyll fluorescence (Fs) was directly correlated with total biomass and maximum efficiency of PSII photochemistry (F'v/F'm) and inversely correlated with non-photochemical quenching (NPQ) under different NH4+/NO3- ratios, but no clear correlation with quantum yield of PSII electron transport ('PSII) and photochemical quenching coefficient (qP). Values of parameters 'PSII and qP were strongly influenced by Fs, leading these values to peak at 25% NO3- ratio and then decreasing with increasing NO3- ratios. Leaves under high NH4+/NO3- ratios exhibited increases in 'PSII (actual PSII efficiency) but maintained 'NPQ and 'NO unchanged. However, leaves under high NO3-/NH4+ ratios kept 'PSII and 'NPQ unchanged but significantly increased 'NO, enhancing thermal dissipation of the light absorbed by PSII within the antenna bed.