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  • Author or Editor: Joseph A. Albano x
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Invasive species have disrupted thousands of acres of natural areas in Florida and appear to have a physiological competitive advantage over native species. The influence of light and temperature on germination was determined for the invasive Mexican petunia (Ruellia tweediana Griseb.) and native wild petunia (Ruellia caroliniensis Steud.). Seeds were collected and germinated in incubators with light or darkness at 15, 24, 33, and 30/20 °C. Light increased germination for each species, except at 15 °C (R. caroliniensis). For R. caroliniensis, highest germination (86% to 94%) occurred at 33 °C and 30/20 °C. Highest germination of R. tweediana (98% to 100%) occurred at 30/20 °C. Studies also were initiated to determine if R. tweediana has a competitive advantage over the native species when grown under wet and dry substrate conditions. Growth and development measurements after 8 weeks under controlled conditions revealed that R. tweediana grown in wet conditions had the greatest dry weight increase as compared to other treatments. Ruellia caroliniensis had higher specific leaf area when grown in wet or dry conditions, as compared to R. tweediana. Throughout the experiment, net CO2 assimilation of R. caroliniensis grown under dry or wet conditions was consistently lower than that of R. tweediana. Shoot nitrogen and phosphorus use efficiencies were generally greatest for R. tweediana plants grown in wet conditions. For shoot nutrient content, significant species × moisture interactions occurred for measured phosphorus (P) and calcium (Ca). When grown in wet conditions, R. tweediana had less shoot P and Ca as compared to dry conditions. For root nutrient content, species × moisture interactions were insignificant for each measured nutrient, with the exception of potassium (K). Potassium use efficiency of R. tweediana roots grown in wet conditions was higher than that of R. tweediana grown in dry conditions and R. caroliniensis grown in wet conditions.

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Floating treatment wetlands (FTWs), a modified constructed wetland technology, can be deployed in ponds for the treatment of nursery and greenhouse irrigation runoff. The pH of nursery and greenhouse operation irrigation water varies from 3.3 to 10.4 across the United States. Water flow rate, plant species selection, and variable nutrient inputs influence the remediation efficacy of FTWs and may interact with the pH of inflow water to change nutrient remediation dynamics. Therefore, an experiment was designed to quantify the effect of pH on the growth and nutrient uptake capacity of three macrophyte species using a mesocosm FTW system. ‘Rising Sun’ japanese iris (Iris ensata), bushy bluestem (Andropogon glomeratus), and maidencane (Panicum hemitomon) were grown for two 6-week periods and exposed to five pH treatment levels representing the range of nursery and greenhouse irrigation runoff, 4.5, 5.5, 6.5, 7.2, and 8.5, for a total of 15 plant and pH combinations. Water was treated with either hydrochloric acid to decrease the pH or sodium hydroxide to increase the pH. The pH-adjusted solutions were mixed with 12 mg·L−1 nitrogen (N) and 6 mg·L−1 phosphorus (P) fertilizer (64.8 g·m−3 N and 32.4 g·m−3 P). Differences in pH impacted both N and P removal from the FTW systems for two of the three species studied, maidencane and bushy bluestem. Higher pH treatments reduced nutrient removal efficacy, but plants were still capable of consistently removing nutrients across all pH treatments. Conversely, ‘Rising Sun’ japanese iris maintained similar remediation efficacies and removal rates across all pH treatments for both N and P, possibly due to the ability to acidify its rhizosphere and modify the pH of the system. Average N and P loads were reduced by 47.3 g·m−3 N (70%) and 16.6 g·m−3 P (56%). ‘Rising Sun’ japanese iris is a promising plant for use in highly variable conditions when the pH of irrigation runoff is outside the typical range (5.5–7.5). Results from model simulations poorly predict the nutrient availability of P and ammonium in effluent, most likely due to the inability to determine plant and biological contributions to the system, such as N-fixing bacteria.

Open Access