Urban Plant Stress Tolerance
Researchers collaborate and work to educate consumers
By Danielle Supercinski
Drought tolerance, salinity tolerance and reduced plant water use are goals of two Rio Grande Basin Initiative (RGBI) researchers working to deliver better information to the public on attractive and stress-tolerant ornamental plants.
“Information on ornamentals that are both attractive and stress-tolerant can be used by nursery and landscape professionals to educate customers and will eventually lead to more beautified, colorful landscapes and gardens,” said Dr. Genhua Niu, Texas Agricultural Experiment Station researcher and assistant professor.
Current research by Niu, at the El Paso Agricultural Research and Extension Center, and Dr. Raul Cabrera, at the Dallas Agricultural Research and Extension Center, also focuses on educating consumers on proper plant selection and how to grow and manage plants on specific sites. They said these are the most important considerations when dealing with stressful water/soil/climatic conditions and municipal ordinances and restrictions.
Above photo: A salinity tolerance study was conducted where plants were irrigated with solutions having different salinity levels.
Niu’s current research is to identify drought-, salinity- and heat-tolerant ornamental plants for urban landscapes; determine minimum water use; and improve irrigation efficiency.
“My work is focused on urban landscape water conservation, particularly for the El Paso region,” Niu said. “El Paso has much lower rainfall than other areas in the state and drought is a constant problem. Even this year when most parts of Texas got large amounts of rainfall, far West Texas did not receive any additional (rain) to help the drought conditions.”
With the lack of natural rainfall, decreasing water supplies and poor water quality, it is sometimes necessary to find alternate sources of water. According to the El Paso Water Utilities Web site, in 2005, 21 percent of the total municipal reclaimed water was used for irrigation. The remaining 79 percent was used by industry, in-plant use, recharge to aquifer, infiltration projects, grazing and construction. Salinity of well water is rather high because the groundwater is brackish and salts accumulate in the soil. Therefore, the region needs information on salt-tolerant plants and management of soil salinity, which Niu plans to address in future projects.
At the Dallas Center, Cabrera, a doctoral student and a visiting scientist are investigating salinity tolerance and management in roses (greenhouse and garden), crape myrtles, azaleas and other woody plants, as well as studying nutrient uptake, fertilization and physiological disorders in these and other woody ornamentals. Over the last decade, Cabrera’s research has focused on water and fertilization-related issues in nursery, greenhouse and landscape plants. In particular, he has concentrated on use and management of poor water quality and recycling/reuse of effluents in commercial nurseries and greenhouses, he said.
“While we have not worked in many ornamental plant genera, our efforts have been concentrated in some of the most widely-grown and thus economically important plants,” Cabrera said. “We have identified rootstocks and cultivars that are more tolerant to salt stress and soon we will disseminate results and information on some fertilization and irrigation management strategies to cope with the use of poor/marginal irrigation water quality in landscape plants.”
Above photo: A drought tolerance study conducted where plants were irrigated with different amounts of water.
These water quality issues as well as the plants Cabrera has worked on are all relevant to the Rio Grande Basin.
“In my opinion, water quality and quantity problems are here to stay permanently, not only in the Rio Grande Basin, but throughout all urban landscapes in Texas and the southwestern United States,” Cabrera said. “Therefore, learning how to live with them and manage them effectively are the only viable solutions. Our research efforts are targeted to contribute to the identification and validation of some of these solutions.”
Aside from their individual projects, Niu and Cabrera are collaborating on research on water use of a number of ornamental shrubs.
“We are currently working on a multi-year project to determine water use and crop coefficients of selected landscape plants,” Cabrera said. “This year, we are working on woody ornamental shrubs and next year we plan to work on trees.”
In past years, Niu and Cabrera have worked on determining water use and crop coefficients of several ornamental shrubs grown in two systems: containers and lysimeters. They said preliminary results have shown that water use and crop coefficients are primarily influenced by climate and plant biomass, although growth is also influenced by the production system and the species.
“The water use of container-grown plants can be used to predict or estimate the water use of the same species that are grown in a landscape situation,” Cabrera said. “Determination (or estimation) of water uses in landscape-established plants has been a major obstacle in the development of sound irrigation management practices, whereas water use of container-grown plants is easily determined gravimetrically (by weighing).”
More research is needed to estimate plant water use and better control irrigation, Cabrera said.
Previous years’ collaborative research results are published in the Texas Nursery and Landscape Association’s Green magazine. Results have also been presented at the Southern Nursery Association’s conference, a regional nursery-landscape research conference.
Niu and Cabrera agree that collaboration is important when conducting research.
“Collaboration is synergistic, complementary and supportive,” Niu said. “The two locations have different climates; El Paso is hot and dry whereas Dallas is hot and humid. Plant water use is especially affected by climate. Therefore, we can broaden and strengthen our research results through collaboration.”
