John M. Ruter

Element absorption and hydration potential of polyacrylamide gels

Abstract Element absorption and hydration potential (HP) of two polyacrylamide gels (Aa and Bb) were studied after incubation in Hoaglands nutrient solution concentrations of either 2X, 1X, 0.5X, 0.25X, 0.125X, or 0X (deionized water). Element absorption was observed and analyzed by making transects from the gel granule surface to center on a Phillips CM12S scanning transmission electron microscope (STEM) equipped with an EDAX 9800 plus EDS unit for x‐ray micro analysis. Thick sections were cut on dry glass knives using an RMC MT6000 ultramicrotome. Surface analysis of bulk specimens was also made with an AMR 1000A scanning electron microscope plus PGT1000 EDS unit. Overall, gel HP decreased curvilinearly as solution concentration increased linearly; however, HP was generally higher for gel Bb than for Aa. Surface analysis of both gels compounds (1X concentration) revealed the presence Ca, Zn, and K. Additionally, Mn, S, and P in trace amounts, and Fe were found at the surface of gel Aa. Furthermore, Fe ...

Elongation of Hibiscus acetosella Under Well-watered and Drought-stressed Conditions

Controlling the elongation of ornamental plants is commonly needed for shipping and aesthetic purposes. Drought stress can be used to limit elongation, and is an environmentally friendly alternative to plant growth regulators (PGRs). However, growers can be reluctant to expose plants to drought stress because they do not want to negatively affect overall plant quality andmarketability. Knowing how and when stem elongation is affected by water availability will help to increase our understanding of how elongation can be controlled without reducing plant quality. Rooted Hibiscus acetosella Welw. ex Hiern. cuttings were grown in a growth chamber set to a 12-hour photoperiod at 25 8C. Two plants of similar size were used for each replication of the study to compare growth under well-watered and drought-stressed conditions. Time lapse photography was used to determine the diurnal patterns of elongation over the course of the replications. Evapotranspiration was measured using load cells. Well-watered and drought-stressed plants had similar diurnal patterns of elongation and evapotranspiration, demonstrating that both follow circadian rhythms and are not just responding to environmental conditions. Stem elongation was greatest at night and coincided with evapotranspiration decreases, with greatest elongation shortly after the onset of darkness. Elongation was minimal between 800 and 1000 HR when evapotranspiration increases. During the drought-stress portion of the replications, elongation of droughtstressed plants was 44% less than well-watered plants. Final plant height and shoot dry weight for the drought-stressed plants were 21% and 30% less than well-watered plants, respectively. Total leaf area, number of leaves, and number of new visible internodes were greater for well-watered plants than drought-stressed plants. Average length of visible internodes and leaf size were similar for drought-stressed and well-watered plants. If growers want to use drought stress for elongation control, they should ensure that plants are drought stressed before the onset of and during the dark period, when most elongation occurs. Controlling plant stem elongation is common in ornamental plant production. Height control is necessary to meet industry standards for target plant height (Fisher and Heins, 1995), to increase plant aesthetics by producing more compact plants (van Iersel and Nemali, 2004) and because compact plants are less expensive to ship (Burnett and van Iersel, 2008). Plant growth regulators are commonly used (Berghage and Heins, 1991; Currey and Lopez, 2011), but are not always desirable as there is growing concern about the use of agrochemicals in production and their presence in runoff (Kaufmann et al., 2000). The selection of cultivars with shorter internodes and smaller growth habits can be used to produce smaller plants (Ecke et al., 2004), but such cultivars are not available for many taxa. Environmental conditions can also be altered to manipulate plant growth and subsequent height, including alteration of day and night temperatures (Kaufmann et al., 2000), changing the daily light integral, and adjusting plant spacing (Liu and Heins, 2002). Alteration of temperature and light conditions is not always possible depending on what other crops are growing in the greenhouse or when plants are grown outdoors. Plant spacing may not be able to be increased if there is not enough space available and can increase overall production costs. Deficit irrigation or drought stress can also limit elongation; however, many growers are reluctant to expose their plants to drought stress because they do not want it to negatively affect overall plant quality (Bailey andWhipker, 1998). Sensor-controlled irrigation has been used to precisely control the timing, severity, and duration of drought stress to control elongation of poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) (Alem et al., 2015). Alem et al. (2015) controlled the height of poinsettia with deficit irrigation by lowering substrate water content to 0.20 m·m until plant height was within the desired range to produce a target final height after which substrate water content was increased to 0.40 m·m. This effectively lowered plant height without negatively impacting plant quality. With the development of wireless sensor networks for irrigation control in commercial greenhouses and nurseries, this technology will be available soon to growers (Kohanbash et al., 2013; Lea-Cox et al., 2013). Diurnal patterns of elongation have been examined in many plant taxa. Circadian rhythms interact with environmental conditions to determine elongation rates. Stomatal conductance and transpiration are also controlled partly by the plant circadian clock (Farr e, 2012). Stem elongation has diurnal patterns (Nozue and Maloof, 2006) and leaf growth is maximal during the day or night, depending on the taxa. Environmental factors can influence the rate of growth, but not the diurnal pattern (Ruts et al., 2012). Knowing how and when stem elongation is affected by water availability will increase our understanding of how elongation can be controlled through drought stress without reducing plant quality. Our first objective was to quantify diurnal patterns of elongation of H. acetosella in response to well-watered and drought-stressed conditions. H. acetosella is a fast-growing herbaceous species with clear growth responses to irrigation volume and substrate water content (Bayer et al., 2013). Understanding the time of day when elongation occurs can be useful in using drought stress as a means of plant elongation control. Our second objective was to quantify the effect of rewatering on the elongation rate of previously droughtstressed plants. The results of this study can be used to determine the optimal time for applying drought stress for elongation control. Materials and Methods Plant material. Research was conducted in a growth chamber at the University of Georgia in Athens, GA, from 17 Feb. to 1 June 2014. Six individual replications, with one well-watered and one drought-stressed plant each, lasted 11 to 19 d. H. acetosella ‘Panama Red’ (PP20121) terminal cuttings taken from one stock plant or clones of the stock plant were rooted in a peat-perlite substrate (Fafard 1P; Fafard Inc., Agawam, MA) for 5 to 10 d after which the rooted cuttings were transplanted into 2.4-L containers filled with a peat-perlite substrate (Fafard 1P, Fafard, Inc.). Cuttings were rooted every 10 to 14 d to have similar size Received for publication 15 June 2016. Accepted for publication 9 Sept. 2016. The research was funded by USDA-NIFA-SCRI (award no. 2009-51181-05768). We thank Bob Teskey, Matthew Chappell, and SherylWells for their suggestions on thismanuscript. Corresponding author. E-mail: abayer10@umass. edu. 1384 HORTSCIENCE VOL. 51(11) NOVEMBER 2016 plants for each individual replication. Plants were grown in a growth chamber (E-15; Conviron, Winnipeg, Manitoba, Canada) set to a 12-h photoperiod (0800 to 2000 HR) and a constant temperature of 25 C, similar to the conditions during data collection. Plants were given 5–7 d for root establishment before onset of a replication. Fertilizer was supplied with a nutrient solution (Peters 15–5–15 Cal-Mag; Scotts, Marysville, OH; 15N–2.2P– 12.45K) at a rate of 100 mg·L nitrogen as needed. Treatments and data collection. Two plants similar in size were chosen for each of the six replications of the study. Axillary branches were removed so that only the central shoot remained. For the first three replications, plants were kept well watered for the first 3 to 4 d of the replication, after which one plant remained well watered while the other was allowed to become drought stressed over the remaining 6 to 11 d, only watering with 200 to 400 mL after wilting occurred. This provided enough water to keep the plants alive, but not to fully rehydrate them. For the next three replications, plants were kept well watered for the first 3 to 6 d after which one plant remained well watered and the other was allowed to become drought stressed by completely withholding water over the next 6 to 8 d after which it was again returned to well-watered conditions for an additional 2 to 7 d to determine if nodes with reduced elongation stayed short or whether nonstressed elongation resumed on rewatering. The total duration of the six replications differed because of differences in elongation rate among replications. Data collection was concluded when the plants grew out of the field of view of the camera. Well-watered plants were hand watered daily to above a weight of 1.5 kg (pot with substrate + plant), which was the weight of the well-watered plants at the start of the replication. The decrease in weight (pot with substrate + plant) of drought-stressed plants from well-watered to wilting conditions was between 0.71 and 0.96 kg, which is a decrease in volumetric water content of 0.36 to 0.48 m·m. Before the start of each replication, plant height, number of internodes, internode lengths, stem diameter, and number of leaves were measured. The weight of each plant was measured using individually calibrated load cells (LSP10; Transducer Techniques, Temecula, CA) mounted on steel platforms with an acrylic platform on top of each load cell. Plant mass was measured every minute and averages were recorded by the data logger (CR1000; Campbell Scientific, Logan, UT) every 10 min. Hourly evapotranspiration was determined as the decrease in pot weight in 1 h after correcting for irrigation when needed. Environmental conditions were measured using a temperature and relative humidity sensor (HMP50; Vaisala, San Jose, CA) and a quantum sensor (SQ-110; Apogee Instruments, Logan, UT) with measurements averaged and recorded every 10 min. Daytime temperature in the growth chamber averaged 25.5 C ± 0.021 and night temperature averaged 24.4 C ± 0.018. Relative humidity fluctuated both over the course of

Sulfuric acid scarification of Callicarpa americana L. (Lamiaceae) seeds improves germination

An experiment was conducted to determine if sulfuric acid scarification improved seed germination of Callicarpa americana L. (Lamiaceae). Treatments included a control (0 min), 15-min, and 30-min soaks in concentrated (18N) sulfuric acid followed by a 15-min rinse in tap water. The 30-min treatment had the earliest germination with seedlings appearing 18 d after treatment (DAT). The 15-min treatment had seedlings emerge at 26 DAT while seedlings in the control did not begin to emerge until 60 DAT. After 60 d, seeds from the acid treatments had approximately 50% germination while the control had less than 10%. At the conclusion of the study, the control, 15-min, and 30-min acid treatments germinated at 8.9%, 57.8%, and 48.9%, respectively. The results of this study show the benefit of sulfuric acid scarification in the germination of Callicarpa americana. Recommendations should be amended to include a 15- to 30-min soak in concentrated sulfuric acid to promote rapid and more uniform germination for this species.Contreras RN, Ruter JM. 2009. Sulfuric acid scarification of Callicarpa americana L. (Lamiaceae) seeds improves germination. Native Plants Journal 10 (3): 283–286.