University of Pretoria
KBotes_data_Nov21 to Apr22_Plant_stress.xlsx (161.46 kB)

Plant stress data of traditional African vegetable crops in living wall systems measured between November 2021 and April 2022

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posted on 2024-04-12, 07:02 authored by Karen BotesKaren Botes

This research analyses the performance of outdoor modular living wall systems (LWSs) with traditional African vegetables to improve household food security in South African (SA) urban environments. The JIP test, which analyses the polyphasic fluorescence transient (OJIP), is a fast and informative test widely used for analysing plant performance to indicate plant stress caused by environmental conditions. Photosynthetic parameters are efficient plant stress indicators. Therefore, measuring chlorophyll fluorescence with a portable fluorimeter has been reported as an effective measuring tool of chlorophyll fluorescence to indicate plant adaptation and stress. The plant efficiency analyser (PEA), the Handy-Pea from Hansatech Instruments Ltd., was used for the study. The Handy-Pea is a portable fluorometer that works on the principle of inducing a red LED light for 1 second on a 4mm diameter dark-adapted leaf surface area at a peak wavelength of 650 nm, which is absorbed by chlorophyll at an intensity of up to 3500 µmol photons m-2 s-1. A dark-adaptation period of a minimum of 20 minutes is required for leaves to ensure that the reaction centres of the leaf are fully oxidised and, therefore, available for photochemistry with reduced dormant chlorophyll fluorescence. Parameters measured include the quantum efficiency of the pigment-protein complex, Photosystem II (PSII) (Fv/Fm), a popular parameter measure for PSII in photosynthesis studies. The maximum quantum yield of photosystem II declines under most stress conditions and is therefore regarded as a critical plant stress indicator before any visual traces of plant stress appear. The quantum efficiency is presented as a ratio of variable fluorescence (Fv) over the maximum fluorescence value (Fm), where values of 0.83 to 0.84 in C3 plants and 0.78 in C4 plants indicate optimal conditions, with values below these indicating stress. The literature recommends different Fv/Fm values as stress indicators. An Fv/Fm value range between 0.83 to 0,88 for C3 plants and 0.87 to 0.88 for C4 plants indicates unstressed plants. If the Fv/Fm drops below these threshold values, the plant cannot cope with its environmental conditions and stresses, and its photosynthetic apparatuses start to be damaged. Values below 0.75 were accepted as an indication of photosystem damage for this study. The performance index, PItotal, was also measured as an indicator linked to plant and drought stress. The PItotal is a photosynthetic performance indicator that combines biophysical parameters and strongly correlates with plant growth, health, and survival rate. The performance index PIabsorbed quantifies the overall electron flow functionality through the pigment-protein complex, Photosystem II (PSII). The PItotal should be measured within the same species to determine trends and cannot be measured across species. Therefore, the trend in PItotal values should be assessed over a period to determine plant vitality. The researcher harvested one leaf per plant, three replicates per species per LWS typology and 3 per natural soil control area monthly for the empirical research period. Leaves were adapted to dark conditions for 2 hours, after which three readings each (9 readings per TAV species per LWS typology or natural soil) were taken with the plant efficiency analyser (PEA). The researcher removed inconsistent Fv/Fm values from the readings downloaded in Microsoft Excel before finalizing the datasets for statistical analysis based on the OJIP chart sets to address technical errors.


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