Drought Tolerance Responses of Purple Lovegrass and 'Adagio
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HORTSCIENCE 42(7):1695–1699. 2007. Florida Mid-Florida Research and Education Center in Apopka, FL (lat. 28°41#N, long. 81°31#W). Thirty-two plants of each species Drought Tolerance Responses of Purple for a total of 64 plants were planted to original container depth in six rows oriented Lovegrass and ‘Adagio’ Maiden Grass north–south on 0.6-m centers in 1.5-m wide 1 2,4 3 strips. Planting rows were covered with Erin Alvarez , S.M. Scheiber , and Richard C. Beeson, Jr. 7.5- to 10-cm screened pine bark nuggets to University of Florida, IFAS, Environmental Horticulture Department, a depth of 7.6 cm (Sunrise Landscape Supply, MREC, 2725 Binion Road, Apopka, FL 32703 Orlando, FL.). Areas between strips were covered with 0.9-m wide strips of polypro- 2 David R. Sandrock pylene ground cloth (BWI Companies, Oregon State University, Department of Horticulture, 4151 Ag and Life Apopka, FL) to inhibit weed growth. Before Sciences Building, Corvallis, OR 97331 transplant, soil under the shelter was satu- rated to a depth of 0.9 m. Additional index words. ornamental grasses, Eragrostis spectabilis, Miscanthus sinensis The experiment was conducted as a ran- ‘Adagio’, landscape establishment, landscape irrigation, irrigation application rates, landscape domized complete block design with two water management, microirrigation, roots, isohydric, anisohydric species and four treatments with four repli- cations per treatment · species combination. Abstract. Nonnative Miscanthus sinensis Anderss ‘Adagio’ and native Eragrostis specta- There were 32 experimental units (i.e., each bilis (Pursh) Steud. were evaluated for drought tolerance in a rain-excluded landscape species · treatment combination replicated setting in sandy soil in response to irrigation application volumes of 0 L, 0.25 L, 0.5 L, or four times) with each unit containing two 0.75 L. As irrigation rates increased, plant mass, canopy size, and shoot-to-root ratios plants of the same species for a total of increased for both species, being greatest at the 0.75-L rate. Shoot dry weight, root dry 64 plants. One plant of each species was used weight, total biomass, and shoot-to-root ratios were greater for E. spectabilis than for water potential measurements and the M. sinensis. Cumulative water stress integral was also greater for E. spectabilis. Greater other plant of each species was used for growth in conjunction with higher cumulative water stress indicates the native growth measurements. Blocks were spatially E. spectabilis is anisohydric and more drought-tolerant than the isohydric nonnative L-shaped across rows to account for varia- M. sinensis. tions in the environment of the rainout shelter. One of four irrigation volumes was applied to each plant within an experimental Drought and corresponding water restric- between adaptation mechanisms of native unit: 0 L, 0.25 L, 0.50 L, and 0.75 L. Irriga- tions are forcing landscapers and consumers and exotic species. Glenn et al. (1998) found tion volumes were applied as one event on to seek alternative irrigation practices and no difference in water use efficiency between alternate days for a 90-d period beginning at plants that require minimal irrigation for two native and two invasive riparian species transplant through 25-mm polyethylene pipe survival (Knox, 1990). Ornamental grasses from the Colorado River delta. However, and 90° gray spray stakes (Roberts Irrigation are generally regarded as problem-free, Blicker et al. (2003) found that native Pseu- Products, San Marcos, CA). Pressure com- low-maintenance plants (Dana, 2002) and doroegneria spicata (Scribn. and Smith) and pensators (Bowsmith Super-Drip N.D., Exe- recommended for their putative low-water Pascopyrum smithii (Rybd.) produced more ter, CA) were placed inline for each emitter requirements. Relationships between orna- biomass under drought conditions than inva- to regulate water flow at 1.9 LÁh. Two spray mental grasses and water use have been sive Centaurea maculosa (Lam). A study in stakes were placed 0.46 m apart in the north- reported (Blicker et al., 2003; Bolger et al., Australia of seven native and three intro- west and southeast directions to cover a 2005; Greco and Cavagnaro, 2002; Guenni duced perennial grass species subjected 0.21-m2 area around each plant. The Chris- et al., 2002; Mohsenzadeh et al., 2006), yet grasses to continuous drought and found tiansen Coefficient of Uniformity was a mini- research quantifying water requirements of mixed results among performance of native mum of 0.77 before planting (Haman et al., ornamental grasses for establishment or main- and exotic species (Bolger et al., 2005). 2005). Irrigation of each experimental unit tenance in a residential landscape is limited Drought resistance may be less a function was controlled as a separate zone using an (Zollinger et al., 2006). Many Florida water of a plant’s status as native or nonnative, and automated irrigation time clock (model Ster- management districts have recommended more that of its individual physiology and ling 12; Superior Controls Co., Valencia, native plants to their consumers (Southwest natural range (Chapman and Auge, 1994). CA). Irrigations began at 0500 HR and were Florida Water Management District (SFWMD), In addition, ecology of cultivated land- completed by 0600 HR each day. Flow meters 2001, 2003) under the premise that Florida scapes is not the same as natural environ- (model C700TP, ABS, Ocala, FL) were native plants use less water than nonnative ments. Plant selection should take into installed for each zone to record irrigation plants (Haehle, 2004; Hostetler et al., 2003; account individual site criteria and plants’ volumes Monday through Friday. SFWMD, 2001). cultural requirements in addition to their Weather data. Weather data were Limited research has been done to sub- native or nonnative status (Anella, 2000; obtained from a weather station site at the stantiate the assumption that native plants use Knox, 1990). The objective of this study research site. Reference evapotranspiration less water than nonnative plants. Kissel et al. was to quantify water stress and growth of (ET0) was calculated daily by a CR10X data (1987) examined water relations of four nonnative Miscanthus sinensis ‘Adagio’, a logger (Campbell Scientific, Logan, UT) exotic and three native New Zealand species 1.5-m tall fine-textured C4 grass native to using a program supplied in Campbell’s and found no overall difference existed Asia, and the Florida native Eragrostis spec- Application Note 4D. This program calcu- tabilis, a 0.5-m medium-textured C4 grass, in lates ET0 on an hourly basis using the ASCE response to different irrigation volumes. Penman-Monteith equation with resistances Received for publication 25 Mar. 2007. Accepted (Allen et al., 1989). Input for ET0 calcula- for publication 24 June 2007. Materials and Methods tions was measured with a pyranometer This work supported by the Florida Agricultural (Li-190; LI-COR, Lincoln, NE), anemometer Experiment Station. 1Graduate Research Assistant. On 25 April 2005, 0.72-L containers of (014; Met-One Instruments, Meford, OR), 2Assistant Professor. E. spectabilis and M. sinensis ‘Adagio’ were and temperature/humidity sensor (HMP45C- 3Associate Professor. planted in native soil (Apopka fine sand L; Campbell Scientific). Rainfall was 4To whom reprint requests should be addressed; series) in an open-sided clear polyethylene recorded with a tipping bucket rain gauge e-mail scheiber@ufl.edu. covered shelter 4 m tall at the University of (TE525; Texas Instruments, Dallas, TX). HORTSCIENCE VOL. 42(7) DECEMBER 2007 1695 Each midnight, the data logger calculated were analyzed as a two · four factorial with separately by species. Analysis was by split daily ET0. two species and four irrigation volumes. plot with irrigation volume as the main plot Growth indices and biomass. At planting, Comparisons were made between species to and month after transplanting as the subplot. six additional plants of each species were determine effects of both species and irriga- Cumulative water stress integral values, pre- partitioned into roots and shoots, washed to tion volume on dry weight gain. Regression dawn YT, midday YT, and dusk YT, were remove substrate, then dried at 70 °C until a equations were also calculated for growth analyzed as repeated measures using a split constant mass was obtained for initial shoot indices over time at each irrigation volume. plot design with irrigation volume as the and root dry weight values. Plant height, Growth indices were analyzed separately by main plot, species as a subplot, and stress widest canopy width (width 1), and width species. Comparisons were only made within day as a subsubplot (Snedecor and Cochran, perpendicular to the widest width (width 2) a species to determine effects of irrigation 1980). Each sampling date was analyzed sepa- were recorded to calculate growth indices volume on growth rate. Where at least one of rately. Where significant differences were (growth index = height · width 1 · width 2) the regression lines was quadratic, data were indicated, mean separation was by Fisher’s at transplant and every 14 d after planting. additionally analyzed as repeated measures protected least significant differences On 27 July 2005, the southernmost plant of each species in each experimental unit, the plant not used for water potential readings, was destructively harvested. Shoots were removed to the crown. To obtain root bio- mass gain, one-fourth segments of the soil volume outside of the original root ball and extending beyond the longest root to the depth of the deepest root in each quadrant were removed from the northeast and south- west sides of each plant. Soil was removed from roots, and shoots and roots were pro- cessed as described previously. Dry weights of northeast and southeast segments were summed and multiplied by two to obtain total root biomass gain. Average initial root dry weight in the root ball and total root biomass gain were summed to obtain an estimated total root dry weight for calculation of shoot- to-root ratios.