2013 Annual Report
1a.Objectives (from AD-416):
Water stress is a common occurance in greenhouse production due to failures of automatic irrigation systems, lack of labor to hand water, and unexpected changes in weather conditions. Certain crops such as garden chrysanthemums require copious water during production, while others like zinnia and New Guinea impatiens do not tolerate even mild drought conditions, resulting in dessication or loss of leaves. The element silicon (Si) is reported to mitigate water stress in many field crops, but the extent of its beneficial effects are not known for floricultural crops. We plan to test the effects of supplemental silicon nutrition of the aforementioned crops' ability to withstand drought stress. Furthermore, we will compare reagent-grade silicon, from potassium silicate, to a less expensive source of silicon from slag. Finally, we will test the plant material tissue for amounts of Si as well as other essential elements and heavy metals to determine if any metal is leaching from the slag and being taken up by the plants.
1b.Approach (from AD-416):
ARS will grow three crops (garden chrysanthemums, zinnia, and New Guinea impatiens) in soilless media and hydroponics with and without supplemental Si in two forms (reagent grade potassium silicate and slag), induce water stress either by withholding water in soilless media or adding salt in hydroponics, and monitor how quickly plants succumb to water stress. Plants will then be rewatered or switched to salt-free nutrient solutions to monitor their recovery. At harvest, plant tissue will be separated into roots, stems, and leaves, dried, and analyzed for Si, essential elements, and heavy metals using our in-house nutrient analysis equipment. In parallel with this research, a colleague at Utah State University will be doing similar work investigating drought effects on corn, soybean, rice, and wheat, and evaluating the potential benefit of silicon in mitigating that stress.
A series of silicon extraction procedures, utilizing the Molybdenium Blue Colorimetric method, were evaluated to quantify the amount of “available” silicon that is present in various slag-like materials including steel slag. These studies were used to determine the release rate and effect of steel slag on the elemental composition of several crops. A study utilizing potato and analyzing tuber tissue showed no significant increase in the presence of heavy metal elements above acceptable concentrations. No effect could be demonstrated, under our growth conditions (greenhouse, growth chamber), on drought stress in Zinnia and New Guinea Impatiens suggesting that drought stress alone does not involve the Silicon defense pathway. Under field conditions, plants are simultaneously affected by numerous stressors and it may be that two or more environmental cues are essential for the observed differences between silicon-treated and non-treated plants. We have been able to observe that there is a Si recognition and uptake mechanism present in a diverse sampling of plants independent of their accumulation potential. Preliminary research suggests that there are some factors, such as proteins, interacting with silicic acid to keep the compound from polymerizing prior to its transport to appropriate tissues. A silicon-binding assay is being developed to identify proteins that may interact directly with silicon. Studies are being planned to determine the effect of Si on the “shelf-life” of the floricultural crops Poinsettia, New Guinea Impatiens and Petunia.
This project pertains to sub-objective 1b of the parent project: Determine the uptake, accumulation, and potential benefit of silicon in ornamental crops and explore the potential for its use as a buffer to Cu toxicity and an alternative approach to pathogen control.