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Fluorescing plants could be used to monitor crops under heat stress

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Researchers at the University of Illinois at Urbana-Champaign have reported that it is possible to detect and predict heat damage in crops using the fluorescent light signature of their leaves under heat stress. This could support monitoring of crops under the heat stress of climate change.

Higher temperatures affect the growth of plants and especially field crops, with temperatures above certain thresholds causing serious damage including stunted growth, scalding, failure to flower, and failure to produce seeds. This is a serious concern in agriculture as climate change drives extreme weather, including annual heatwaves. This study’s findings suggests that this damage could be monitored at scale using the fluorescent light signature of crops.

The study measures sun-induced chlorophyll fluorescence (SIF) to monitor a plant’s photosynthetic health. This type of fluorescence occurs when plants absorb sunlight (in the 400-700nm range) and emit a portion of photosynthetic energy in the near-infrared range (in the 650-850 range) from its leaves.

“There is a link between sun-induced chlorophyll fluorescence and photosynthetic rate in plants; however it was unclear if SIF detection could measure physiological responses in heat-stressed plants,” said lead author Hyungsuk Kimm, a graduate student. “When soybeans are exposed to high-temperature stress, for example, they do not show any distinctive changes in canopy structure and conventional remote sensing signals do not provide clear consequential spectral signatures.”

The researchers investigated the link between SIF and crop yield using a hyperspectral sensing system to measure SIF above soybean crops in Illinois. They used infrared lamps to raise temperatures gradually – up to a maximum of six degrees above ambient drop canopy temperature – while monitoring changes in chlorophyll fluorescence. This experiment, which is the first of its kind, established a correlation between heat stress, SIF, and  grain quality, clarifying how heat stress affects crop yield.

“We found that sun-induced fluorescence responds to temperature increases and corresponds with fewer and lower quality soybean leaves,” said the study director Professor Kaiyu Guan. “We also found that heat stress has a great impact on soybeans during their reproductive stages when the plants are producing grain, which ultimately affects the size and quantity of the resulting soybeans.”

Professor Lisa Ainsworth, a plant biology expert, added: “The technique may provide a tool for breeders to identify more heat-resistant crops and help farmers select the best crops to grow in the US Corn Belt as temperatures rise, as predicted by many climate models.”

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