Smooth Cordgrass for Large-scale Coastal Restoration

Linda Benedict, Materne, Michael D., Knott, Carrie, Utomo, Herry S., Harrison, Stephen A., Linscombe, Steven D., Wenefrida, Ida  |  9/12/2012 8:20:49 PM

Herry S. Utomo, Ida Wenefrida, Steve D. Linscombe, Michael D. Materne, Stephen A. Harrison and Carrie Knott

Preventing coastal land loss represents a major technological challenge. Between 1932 and 2000, more than 1,875 square miles of coastal Louisiana land was lost. Without intervention to stop continuing conversion of productive wetlands into open water, an additional 513 square miles will be lost by 2050. Successful efforts to reduce coastal wetland losses depend on improving the efficiency and effectiveness of vegetative restoration technology. Successful seed-based deployment can help reclaim eroding land and rejuvenate distressed habitats following destruction from natural disasters, such as hurricanes, or re-occurring dieback. In addition, planting seed is an effective way to manage the entire Louisiana ecosystem for maximum productivity.

Significant advancement in coastal engineering, such as the beneficial use of dredged materials, can help increase the speed and size of new marsh construction. Consequently, improving seed versatility, production and application is crucial in establishing efficient revegetation.

Seed-producing varieties of smooth cordgrass (Spartina alterniflora) are critical for providing not only an alternative to hand-transplanting but also the means to increase efficiency of largescale restoration. For a number of years, the LSU AgCenter has conducted extensive research to develop seed-producing varieties of smooth cordgrass.

PolyC15 is the most advanced seed-based smooth cordgrass being developed. It is produced from free pollination of 15 selected native smooth cordgrass lines. This is the first seedbased production system developed specifically for this coastal plant species for superior performance, fertility and high genetic diversity. Multi-location trials were conducted under natural marsh conditions at Rockefeller Wildlife Refuge, Bayou DuPont and Lake Pontchartrain. Control plots were established under freshwater conditions at the Rice Research Station in Crowley.

PolyC15 yielded an average of 631 pounds of seed per acre over eight environments at four trial locations. As a comparison, the variety Vermilion produced 261 pounds of seed per acre. Higher seed yield is attributed to improved seed set and increased fertility. In addition to higher seed yield, PolyC15 also has higher germination rates, averaging 74 percent compared with 35 percent for Vermilion. Seed yield and germination rates combined have more than a five-fold increase.

PolyC15 is genetically diverse as a result of random crosses of 15 genetically different parental lines. DNA markers were used to identify genetic diversity among parents. This level of diversity provided a genetic foundation that closely mimics the natural population of smooth cordgrass.

To further improve seed yield, new polycross sets containing four, five and six parental lines are being evaluated. Based on two-year preliminary yield trials, two of the most promising polycross sets have average seed yields of 1,081 and 984 pounds per acre. The overall goal is to improve seed production while maintaining high levels of genetic diversity using fewer parents to reduce the complexity in field management.

PolyC15 has been used extensively in aerial seeding using a fixed wing airplane on newly constructed marshes at Bayou DuPont and Marsh Island and distributed by airboat on bare soils along Lake Pontchartrain shorelines. The progeny of PolyC15 perform well under coastal conditions. The seed produced a robust population in a single season, providing rapid revegetation and an excellent protection for newly constructed marshes. Detailed observations on individual plants revealed a high variability for various traits, including plant stature, stem color, plant height, leaf type, leaf size, leaf color, panicle length, panicle size and heading date. The diversity displayed verified the DNA fingerprinting profiles used in the development of high seed-producing PolyC15.

Production system, weed control and mechanical harvest
Smooth cordgrass grows well across a large range of soil types from sandy to clay, with pH ranging from 3.7 to 7.9, and is adaptable to various salinity levels from freshwater to seawater. It has been successfully cultivated for more than 10 years under freshwater environments at the Rice Research Station in Crowley, La., using cultural practices similar to those for rice. Smooth cordgrass seedlings have excellent tolerance to some herbicides commonly used in rice. These provide an ample way for developing effective strategies for weed management and control under freshwater environments. Some of these herbicides have been labeled for use in aquatic environments. Currently, permits for use of three herbicides on smooth cordgrass are being filed to support the seed production system.

Plant culture, fertilization management, weed control and mechanical seed harvesting are being established to support a commercial seed production system for smooth cordgrass. Since smooth cordgrass has a great adaptation to a wide range of soil types and salinity levels, large-scale commercial seed production is probable. Because of increasing salt contamination of inland groundwater, many areas historically used for rice production have been abandoned. These could be used for the production of PolyC15 as an alternative crop with little modification to existing equipment or land.

Beyond seed production
Unlike an agricultural system where most critical growing conditions can be optimized, little intervention can be done to improve the conditions during planting and stand establishment in the coastal regions. Therefore, the capability of seed to adapt to these conditions has to be improved. Under favorable conditions, smooth cordgrass seedlings need about four weeks following germination to produce a root system to hold the soil. During this period, seeds or seedlings in a relatively calm environment – such as suspended within a thin layer of mud or biomass, trapped inside soil crevices protecting them from wave actions or landed on moist soil that experiences low-energy waves – will have a better chance to become established and produce vegetation.

Because conditions in coastal regions can change rapidly due to tides, winds, waves and rain, smooth cordgrass seed used in aerial seeding must adapt to the spikes of adverse micro temperatures, prolonged lack of moisture, prolonged inundation, high winds, wave energy and other variables. One strategy to enhance seed versatility and capability is to improve the seed properties to respond better to less-optimum growing conditions and a wide range of environmental fluctuations.

Experience has shown that applying bare seed can result in uneven stands because the seed is so light. To compensate, researchers have investigated adding a seed coating to provide weight. In addition to adding weight, various components with specific functions can be incorporated into seed pellets. For example, water-attracting materials can be added to absorb moisture and help seed survive on higher elevations that have less exposure to water during low tides. Materials can be added to the pellet to help seed stick to the soil, also.

Even though smooth cordgras seedlings can withstand more than 14 continuous days under water, oxygengenerating materials might further help seed withstand prolonged inundation. Other seed enhancement materials, such as fungicides, insecticides and micronutrients, can be placed directly in the seed pellet to decrease disease susceptibility during germination. Seed coating also is effective in controlling moldinduced diseases.

Smooth cordgrass seed applied by air has attracted a large number of local birds to feed on it, causing a tremendous seed loss. Because smooth cordgrass seed is not hard-coated, it will not pass through a bird’s digestive process. Coating or pelletizing, therefore, could include protective measures to minimize seed palatability. Otherwise, nontoxic bird repellents can be incorporated to reduce palatability.

Acknowledgment: This research is partially funded by USDA-NIFA Special Grant and Louisiana Sea Grant.

Herry S. Utomo, Associate Professor; Ida Wenefrida, Assistant Professor; Steve D. Linscombe, American Cyanamid Professor – Excellence in Plant Genetics/ Breeding/Biotechnology, Rice Research Station, Crowley, La.; Michael D. Materne, Instructor; Stephen A. Harrison, Walker T. Nolin Professor in Agronomy, and Carrie Knott, Assistant Professor, School of Plant, Environmental and Soil Sciences, Baton Rouge, La.

(This article was published in the summer 2012 issue of Louisiana Agriculture magazine.)

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