By Susan Varlamoff
University of Georgia

By measuring the nighttime respiration rate of plants, University of Georgia scientists hope to develop a way farmers can detect environmental stresses in their fields.

Stresses like low soil moisture, high or low air temperatures, weeds, insects and diseases can reduce plants' growth, yields and quality. They can hurt a plant before it shows any signs of problems.

During the recent drought, the lack of rain greatly damaged plants. Finding a way to know when soil moisture levels become low before the damage occurs is an important reason for this research.

Looking for a connection

"We're essentially looking for a correlation between environmental stress and high nighttime carbon dioxide respiration rates," said Anandakumar Karipot, an assistant research scientist with the UGA College of Agricultural and Environmental Sciences.

Karipot, professor Monique Leclerc and postdoctoral associate Gengsheng Zhang are analyzing the data for this project in the UGA Laboratory for Environmental Physics in Griffin, Ga. CAES agronomist John Beasley and U.S. Department of Agriculture physiologist Diane Rowland are also members of the research team.

Environmental stresses typically reduce the transpiration rate and the amount of water vapor given off by plants. Lower transpiration rates increase plant temperatures. They also increase nighttime respiration rates that produce carbon dioxide.

Reduced growth, yield and quality

When the plant expends energy to respire faster, it can't produce as much food for itself (photosynthesis). This reduces its growth, yield and quality.

"It's similar to a human being: if you can't prespire, your body overheats and your respiration rate increases," Beasley said. "When a peanut plant is stressed, it can't produce the pod or fruit."

The scientists are measuring carbon dioxide fluxes above a peanut field at the UGA Southwest Georgia Research and Education Center in Plains, Ga.

The sensors, known as an Eddy covariance system, include a fast- response, sonic gauge that measures the wind speed in three directions and an infrared gas analyzer that determines carbon dioxide concentration fluctuations.

Together, these sensors provide information on plants' uptake of carbon dioxide emissions.

They also record supporting measurements of soil temperature, soil water content and solar and earth radiation. The scientists collect data from planting until harvest. That helps them study variations in carbon dioxide fluxes and their relation to water stress at different stages of plant growth.

Uniform fields work best

There is no photosynthesis at night. That's when plants respire and release carbon dioxide. So the variations in nighttime carbon dioxide levels will indicate environmental stress.

"It's important that the peanut field we chose for this study is fairly large, flat and uniform with similar soil properties," Karipot said. "This ensures that similar conditions exist throughout the field and the carbon dioxide variations are representative of the peanut crop."

A weather-monitoring station also measures wind speed and direction, rainfall, air temperature and humidity and solar radiation in the field. This information will help the scientists understand the microclimatic influence on the plants' growth and yield. It will help them better interpret the carbon dioxide respiration data.

"We would like to extend our research next year to two fields," Karipot said, "one with irrigation and one without irrigation, and see the difference in respiration rates of the crops with and without water stress."

This research could be developed into a tool to warn farmers of water stress in their fields and help them manage irrigation better.