summer, from June to August or September, using rainout shelters, we can control the water the plants receive. We can dry them down to see the stress and keep them there, adding smaller amounts of water to keep them just above the stress level, documenting when these plants are at what degree of water deficiency. We’re trying to determine how little water they need to maintain quality and how that compares to older, commonly-used cultivars. We’re detailing how much water they are using during drought periods and when they are using it.”
Test grasses grown in lysimeters under a rainout shelter in Raleigh, NC, for determining daily water use. Photo courtesy of Dr. Grady Miller
within the plant, trying to identify how they change and ‘why’ they perform as they do in drought situations.”
Planting materials to work on this grant started in the fall
of 2019, but with the Covid protocols that kicked in soon afterward, it was a little slow to get started. Miller says, “Initially, we did some preliminary studies concentrating specifically on Bermudagrasses. We were able to identify those drought tolerant cultivars that had some percent greater ability to regulate water use while developing our research methods. We were excited about being able to refine those techniques with just one species. After all our plant material was grown-in we began looking at multiple species and at cultivars within a species to determine if they could regulate the water loss. Like someone who just sweats to the point of severe dehydration, some of the plants couldn’t regulate.”
Jespersen adds, “Now that the field plots are established and healthy and the greenhouse trials are going, we’re at the phase where the researchers are replicating some initial experiments as well as going broader to quantify how much better some cultivars perform and how much less water they use. We’re working with the details they provide to dig deeper into understanding the mechanisms that facilitate less water use.”
Miller reports, “During the field research trials, we’re monitoring the plants during the ambient conditions of the summer, focusing on how they handle water when it is freely available. We can measure the canopy temperatures of the individual plots. We know the potential evapotranspiration (ET) rate and using lysimeters placed within the soil, we get daily weights to see how much water the plants have lost. By monitoring their water use when water is readily available, we can calculate how they transpire to develop crop coefficients.
“Ten we’re studying how the different plant materials handle water during the drought stress cycle. Over the
82 TPI Turf News July/August 2022
How do they osmo-regulate but still maintain plant quality? Jespersen says, “Just like a well-trained athlete does not use water in the same way as the average person, these plants function differently. Our research is digging into the why of that. I’d say we know approximately one-third of the performance factors, so we’re researching the other aspects of why a plant is better—what mechanisms they use, how they use them, if those mechanisms do or don’t interrelate, and if so, why.”
Within the controlled environments, as water becomes limited, Jespersen’s team is studying how the plants react. He says, “Some shut down. Others adapt prior to cells being severely damaged by drought, maintaining quality, and keeping their metabolism going when exposed to the water deficit. Tere are a lot of factors to consider, many of which are interrelated. Do they have a finer root system? Do the stomates stay open or close sooner? Do they produce sugars more efficiently? Do they accumulate different compounds? We discovered some surprising things while looking at seashore paspalum during one of the controlled environment studies, including a high level of plasticity within the plant that reacts to drought, giving the plant improved performance.”
Test grasses are shown in this growth chamber, which Dr. Jespersen defines as “a very controlled, extremely uniform environment.” Photo courtesy of Dr. David Jespersen
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