We demonstrate that delta values (delta) and other relative ratio-based isotopic expressions can vary with the total amount of isotopes present in the system or subject being evaluated. Although these scaling effects are routinely overlooked, interpretive errors such as noting of spurious treatment effects or not detecting significant effects may occur. Algebraic conversions of linear or log-log equations (rare isotope predicted by common or total isotope) that suggest apparently miniscule scaling will fit the observed relationship between isotopic ratios and total or common isotopes. When the ranges of scaling induced differences in isotopic ratios are converted to the equivalent discrimination expressions (Delta) or delta values (delta), differences are within the range that is generally reported in the isotopic literature. Therefore, interpreting observed differences in isotopic ratios may require an evaluation to determine whether treatments directly affect how a rare isotope is accumulated or are associated with differences in denominator size. If effects are direct, points for different treatments fall on different linear and log-log (total isotope vs. rare isotope or common isotope vs. rare isotope) regression lines. Slope differences or derivatives may be more revealing than changes in isotopic ratios and better represent system change in a scaling system. By simply recording total common isotope or total elemental content, standard statistical procedures that evaluate changes in slopes or derivatives can be combined with an ANCOVA to better evaluate isotopic data. In many cases, scaling issues will not interfere with interpretations. In other situations it may be difficult to untangle a combination of ubiquitous scaling, treatment induced scaling and direct treatment effects.

Extensive green roofs composed of a thin layer of growing medium topped with vegetation can significantly reduce both the timing and magnitude of stormwater runoff relative to a typical impervious roof. However, regional climatic conditions such as seasonality in rainfall and potential evapotranspiration could strongly alter the stormwater performance of green roofs. In this study we evaluate the stormwater performance of green roofs in the predominately winter rainfall climate of the U.S. Pacific Northwest. We also test whether the amount of irrigation used to maintain green roof vegetation in a seasonally dry climate such as the Pacific Northwest influences stormwater performance. We monitored stormwater performance over one year for sets of experimental roofs constructed using three designs: a conventional impervious design, a medium-only design, and a typical extensive green roof design that included vegetation. During the winter rainy season vegetation had no significant influence on stormwater retention; medium-only and vegetated roofs reduced stormwater runoff nearly identically relative to the impervious roofs. In contrast, during summer vegetated roofs retained significantly more rainfall than medium-only roofs, although this effect depended strongly on the size of the rain event. In addition, total relative retention for both roof types was significantly higher during summer than during winter. Irrigation significantly reduced summer retention capacity of both medium-only and planted roofs, but only during the largest dry season rain event. These results suggest that cool wet season climates such as the Pacific Northwest are challenging ones for green roof stormwater performance. In order to optimize stormwater benefits of green roofs, designers should create explicitly regional designs that include plant selections better matched to the specific environmental and management constraints.

Extensive green roofs are a challenging environment for most plants, and this has typically limited the available plant palette. However, some functional goals for green roofs such as wildlife habitat require a broader spectrum of plant species from which to choose. In addition, pronounced seasonality in rainfall is a common climatic trait throughout much of the world; yet, few studies have evaluated green roof plant selections or the need for supplemental irrigation in a seasonally dry climate. In a field trial conducted in the Pacific northwestern United States, we evaluated the performance of eight taxa during establishment and under three different water management regimes post establishment: 1) non-irrigated; 2) irrigation based on green roof–specific water conservation guidelines for Portland, OR; or 3) the minimum irrigation required to maintain good plant condition. Plants were regionally available and represented a range of growth forms (succulents, shrubs, grasses, bulbs, and rhizomes) and potential functional attributes (habitat quality, aesthetic quality, and stormwater management proficiency). All eight species had generally high survival over the establishment year, although hardy iceplant ( Delosperma cooperi ) and common woolly sunflower ( Eriophyllum lanatum var. lanatum ) experienced some overwinter mortality. Species differed in the timing and absolute amount of growth during establishment. However, when the strong effect of initial size on growth was taken into account using analysis of covariance, there were no remaining differences between species in the relative magnitude of growth during establishment. During the summer following establishment, irrigation regime had significant effects on survival and growth, but these varied across taxa. Irrigation had no effect on survival or growth of the succulents hardy iceplant and ‘Cape Blanco’ broadleaf stonecrop ( Sedum spathulifolium ) and the bulb small camas ( Camassia quamash ). For the other taxa, plant survival and growth generally decreased with decreasing irrigation and many species did not survive at all without irrigation. Several species, particularly the grass roemer's fescue ( Festuca idahoensis var. roemeri ) and the shrub ‘Lasithi’ cretan rockrose ( Cistus creticus ssp. creticus ) suffered aesthetically under low irrigation, partly reflecting adaptive responses to drought stress. Weed pressure was high on bare substrate and was enhanced by irrigation, but weed pressure was negligible following canopy closure across all water regimes. These results suggest that succulents, bulbs, and rhizotomous forbs have potential for use on extensive green roofs in seasonally dry climates even without supplemental irrigation. Designing extensive roofs composed of more diverse growth forms will likely require some amount of supplemental irrigation. This study highlights the need to design context-specific green roofs that match appropriate plant selections with explicit functional goals and management plans. This will improve function and reduce the overall costs associated with maintenance.

Salt-tolerant landscape plants are important to ornamental growers, landscapers, and residents in coastal communities. Ornamental grasses are frequently recommended for low-maintenance landscape situations and may be candidates for coastal plantings after they are evaluated for their salt spray tolerance. 'Gracillimus' maiden grass (Miscanthus sinensis) and 'Hamelin' fountain grass (Pennisetum alopecuroides) were subjected to four treatments [100% seawater salt spray, 50% seawater salt spray, 25% seawater salt spray, or 0% seawater salt spray (100% deionized water)] applied as a foliar spray. As seawater concentration increased, root, shoot, whole-plant biomass gain, height, inflorescence number, and visual quality decreased for both cultivars; however, fountain grass appears to be slightly more tolerant of salt spray than maiden grass.

Horticulture graduates entering the landscape (design, installation, and maintenance) segment of the green industry will be faced with a myriad of complicated decision scenarios. Graduates must be able to integrate their understanding of plant science, environmental and physical site constraints, and the human impact on built and natural landscapes to make complex decisions. The objectives of this project were to develop an online case study for use in landscape management and landscape construction courses, and to determine students' perceptions of using this virtual case study to practice active problem solving in landscape horticulture. After completing a scenario from the online case study, students were asked to complete a 20-question survey instrument consisting of open- and close-ended questions evaluating the case study. Sixty-nine surveys were returned and useable, for a response rate of 76.6%. Overall student attitudes and perceptions of the online case study were positive. Participants felt comfortable using the web-based format (4.3 of 5), and felt it was an effective way to deliver information (4.1). Furthermore, participants rated their ability to summarize the scenario data as 4.2 and also felt confident in their ability (4.1) to make a landscape management recommendation to the homeowner.

It is not appropriate to compare ratio-based expressions for different cultivars or treatments if a plot of the denominator versus the numerator of a ratio-based expression has a nonzero y -intercept and the values for either the denominators or numerators differ with cultivars or treatments. Whenever nonzero y -intercepts are encountered, the value for a ratio-based expression will be dependent on both the denominator and numerator. The “ratio problem” is demonstrated with shoot N concentration in blueberries ( Vaccinium corymbosum L.) and amino acid accumulation in almonds [ Prunis dulcis (Mill.) D.A. Webb]. Data were collected from the first and second growth flush of blueberry shoots on plants that were at two in-row spacings and two rates of N fertilizer. Free amino acid:total amino acid ratios were measured in dormant almond trees fertilized at different rates with and without foliar N supplements. Functions describing the relationship between dry weight and total N content in blueberry tissues have positive y -intercepts for both N fertilizer application rates. Functions describing the relationship between total amino acids and free amino acids in almond trees have a negative y -intercept. Differences attributable to fertilization rate in blueberries probably were the result of differences in N uptake and N utilization, but the effects of spacing and growth flush are indirect and can be accounted for by differences in dry weight. Likewise, effects of fertilization rate and foliar N supplement in almonds are indirect and can be accounted for by differences in the total amino acids in dormant trees. With regression one can determine if the relationship between the denominator and numerator differs for the groups or treatments being studied. When an analysis of covariance is used to account for differences in the denominators of ratio-based expressions, results are consistent with the regression analysis. When a conclusion is based on statistical differences of a ratio-based expression, it is the researcher's responsibility to determine whether these effects are direct or indirect.

Although new and innovative measures to reduce landscape water consumption are being sought, traditional methods of water restrictions and plant selection prevail. Species native to North America are often promoted as drought tolerant with little information to support or refute such claims. Furthermore, species performance is unknown in maintained environments such as commercial and residential landscapes. Thus, 10 native and 10 exotic species, commonly used in landscapes, were evaluated independently for postestablishment growth and aesthetics under irrigated and nonirrigated landscape conditions. Growth indices were recorded monthly, with dieback and plant density evaluated at termination of the experiment. At termination of the experiment, canopy size of eight native [beautyberry ( Callicarpa americana ), fringe tree ( Chionanthus virginicus ), yaupon holly ( Ilex vomitoria ‘Nana’), virginia sweetspire ( Itea virginica ), wax myrtle ( Myrica cerifera ), chickasaw plum ( Prunus angustifolia ), saw palmetto ( Serenoa repens ), and coontie ( Zamia floridana )] and eight exotic [golden dewdrop ( Duranta erecta ), cape jasmine ( Gardenia augusta ), crape myrtle ( Lagerstroemia indica ), oleander ( Nerium oleander ), japanese pittosporum ( Pittosporum tobira ), indian hawthorn ( Rhaphiolepis indica ), sweet viburnum ( Viburnum odoratissimum ), and sandankwa viburnum ( V. suspensum )] species were similar for irrigated and nonirrigated treatments. Irrigation resulted in larger canopy sizes for two native [walter's viburnum ( V. obovatum ) and inkberry ( I. glabra )] and two nonnative [japanese privet ( Ligustrum japonicum ) and fringe flower ( Loropetalum chinensis )] species. Among the native species with larger canopy sizes under irrigated conditions, all are indigenous to swamps and streams. With the exception of virginia sweetspire, plant density and dieback were similar for irrigated and nonirrigated plants of all taxa examined. Irrigated virginia sweetspire plants had higher plant density and dieback ratings than nonirrigated plants. Results indicate that, aesthetically, irrigated and nonirrigated plants were similar. Data emphasize the importance of selecting plant material adapted to existing environmental landscape conditions.

Nonnative Miscanthus sinensis Anderss ‘Adagio’ and native Eragrostis spectabilis (Pursh) Steud. were evaluated for drought tolerance in a rain-excluded landscape setting in sandy soil in response to irrigation application volumes of 0 L, 0.25 L, 0.5 L, or 0.75 L. As irrigation rates increased, plant mass, canopy size, and shoot-to-root ratios increased for both species, being greatest at the 0.75-L rate. Shoot dry weight, root dry weight, total biomass, and shoot-to-root ratios were greater for E. spectabilis than M. sinensis . Cumulative water stress integral was also greater for E. spectabilis . Greater growth in conjunction with higher cumulative water stress indicates the native E. spectabilis is anisohydric and more drought-tolerant than the isohydric nonnative M. sinensis .

Net photosynthetic rates often are dependent on leaf size when expressed on a leaf-area basis (CO 2 assimilation as μmol·m −2 ·s −1 ). Therefore, distinguishing between leaf-size-related and other causes of differences in net photosynthetic rate cannot be determined when data are presented on a leaf-area basis. From a theoretical perspective, CO 2 assimilation expressed on a leaf-area basis (μmol·m −2 ·s −1 ) will be independent of leaf area only when total net CO 2 assimilation (leaf CO 2 assimilation as μmol·s −1 ) is linearly related to leaf area and the function describing this relationship has a nonzero y intercept. This situation was not encountered in the data sets we evaluated; therefore, ratio-based estimates of CO 2 assimilation were often misleading. When CO 2 assimilation data are expressed on a per-leaf-area basis (the standard procedure in the photosynthesis literature), it is difficult to determine how photosynthetic efficiency changes as leaves or plants mature and difficult to compare the efficiency of treatments or cultivars when leaf size or total plant leaf area varies.

Program developers and administrators in settings such as botanical gardens are increasingly in need of information on the needs and interests of various groups. A need also exists for information on how to broaden interests in garden displays (exhibits including both plants and signs centered on a theme or topic) and increase the diversity of visitors. This article reports on research that explored visitor perceptions of an ethnic garden display highlighting African-American contributions to horticulture. The research also examined overall attitudes toward a botanic garden in Florida where the display was constructed. The results suggested that race did not affect visitors' overall attitudes toward a botanic garden. Younger visitors, those who visit gardens more, and weekend visitors had a more positive attitude toward botanic gardens. Race was, however, related to visitor attitude toward the ethnic display. African-Americans liked the African-American horticulture display more than any other ethnic group. Sociodemographic characteristics, frequency of botanic garden visits, and time of year for visits all shaped visitor attitudes and opinions.

Two approaches for estimating the amount of N in plant tissues derived from labelled fertiliser were evaluated. In the first, atom percentage values obtained by mass spectrometry were converted to the percentage of total N derived from the fertiliser (%NDFF). In the second, the slope of the regression line for the relationship between labelled fertiliser N and total N was used to represent the incremental increase in fertiliser N for each unit increase in total N. These two approaches were applied to data collected for a blueberry (Vaccinium corymbosum L.) field trial, where the effects of N rate and plant spacing on fertiliser accumulation were evaluated. Since varying degrees of biological scaling can occur, and many perennial plant tissues have an initial biomass, regression equations for different tissues produced both positive and negative y-intercepts. Log(10) fertiliser N vs. log(10) total N plots produced slopes that did not equal 1.0 (from 0.40 to 1.65, depending on tissue). When either non-zero y-intercepts for linear regression lines, or slopes not equal to 1.0 for log-log plots occur, %NDFF is dependent on the size (total N) of the tissue or plant. Depending on the tissue evaluated, the %NDFF can be unrelated, or negatively or positively related to plant or tissue size. Furthermore, increased nitrogen application alters the relationship between %NDFF and plant size. For tissues in which %NDFF declines with increasing total N, the relationship weakens as more N is applied. For tissues in which %NDFF increases with increasing total N, the relationship strengthens as more N is applied. An analysis of the slopes and y-intercepts of labelled fertiliser N vs. total N relationships produces a different interpretation than evaluations of the %NDFF for treatment means. Significant %NDFF differences for spacing treatments, and significant spacing x tissue interactions were size-related rather than having other physiological causes. Increases in %NDFF associated with increasing N rate were directly related to differences in N accumulation. Difficulties associated with evaluating the ratio-based %NDFF in established perennial plants are even more problematic than the difficulties previously reported for plant systems with little initial N content. Similar scaling issues could be important when any exogenous substance is introduced into organisms or ecosystems.

Two approaches for estimating the amount of nitrogen (N) in plant tissues derived from labeled fertilizer were evaluated for two tissue types (root and shoot) in three different genera. In the first, atom percentage values obtained by mass spectrometry were converted to the portion of N derived from the fertilizer (NDFF). In the second, the slope of the regression line for the relationship between total N and labeled fertilizer N was used to represent the incremental increase in fertilizer N for each unit increase in total N. These two approaches were applied to data collected during container experiments. Unless a plot of total N versus labeled fertilizer N passes through the origin, conventional ratio-based estimates of the amount of NDFF for plants or tissues are often misleading. When nonzero intercepts occur, NDFF is dependent on the size (total N content) of the tissue or plant. Nonzero intercepts were frequently encountered. An analysis of regression lines describing the relationship between total N gain and fertilizer N produces a different interpretation than evaluations of the NDFF for treatment means. When an analysis of covariance was used to account for differences in total N between tissues and genera, results were generally consistent with the graphical observations and regression analysis. If only ratio-based approaches are used, it is difficult to determine if there are real physiological differences among treatments, genera, and tissues or if differences in NDFF are size-related. Because the data easily can be analyzed several ways, simultaneously evaluating data with ratio-based NDFF, covariates, and regression is appropriate.

Salt tolerance of landscape plants is important to ornamental growers as well as residents and landscapers in coastal communities. Damage to ornamental plants from salt spray can be prevented by evaluating and selecting plants that exhibit tolerance to aerosol salts. Ornamental grasses are frequently recommended for low-maintenance landscape situations and may be candidates for coastal plantings once they are evaluated for their salt spray tolerance. The objective of this study was to determine the salt spray tolerance of Miscanthus sinensis `Gracillimus' and Pennisetum setaceum `Hamelin'. The experiment was conducted for 90 days from 7 July to 5 Oct. 2005 in a polyethylene greenhouse in Gainesville, Fla. Plants were subjected to four treatments (100% seawater, 50% seawater, 25% seawater, or 100% deionized water) applied by spraying each plant to runoff three times per week. Plant heights, flower number, and aesthetic ratings were recorded biweekly for the duration of the experiment. Root and shoot dry weights were determined at the initiation and completion of the study. Significant growth rate differences were found between treatments. Growth rates of plants treated with 100% seawater were significantly lower than the control and other seawater concentrations. Root and shoot dry weights of the plants treated with 100% seawater were significantly lower than the other treatments. In addition, significant differences were found between the 100% seawater treatment, the 25% seawater treatment, and the control in the aesthetic ratings of plants at the end of the study.

Water use is the most important environmental issue facing the horticulture industry. As a result, many water management districts are recommending native plants for their putative low-water requirements. Numerous textbooks and trade journals claim native plants use less water than non-natives; however, previous research found no difference in water use efficiency in the field between native and non-native species. Furthermore, recommendations of ornamental grasses for use as low-maintenance and low-water-requiring landscape plants have recently escalated. This study evaluated non-native Miscanthus sinensis `Adagio' and the native Eragrostis spectabilis for irrigation requirements and drought response in a landscape setting. To simulate maximum stress, both species were planted into field plots in an open-sided, clear polyethylene covered shelter. Each species was irrigated on alternating days at 0, 0.25, 0.5, or 0.75 L for a 90-day period. Growth index and height were recorded at biweekly intervals, and final shoot and root dry masses were taken at completion of the study. Significant treatment and species effects were found for height, growth index, shoot dry weight, and biomass. Plants receiving 0.75 L of irrigation had the greatest growth, and non-irrigated plants grew significantly less. Comparisons between species found growth was greatest among Eragrostis spectabilis plants for all parameters.

Horticulture graduates entering the landscape industry will be faced with a multitude of complicated management decisions where they will need to integrate their understanding of plant science, site constraints, state and federal environmental regulations, and the human impact on the built landscape. To help students develop and refine their problem-solving skills, an interactive online case study was created. The case study was used in two different landscape horticulture courses at Iowa State University and Oregon State University. The case study centers on a residential backyard with eight landscape problem scenarios. Each scenario is identified on the clickable landscape map of the area and contains links to audio files, PDF documents, images, and Internet links. After investigating each scenario, students submit an analysis, diagnosis, and recommendation about the landscape problem via WebCT or Blackboard, depending on the institution. Student evaluation of the case study as a teaching tool was positive (3.5, where 1 = poor; 5 = excellent). Students answered additional questions using a scale where 1 = strongly disagree and 5 = strongly agree. As a result of using this teaching tool, students felt that they were able to summarize the data (3.9), diagnose the landscape problem (3.9), and make a recommendation to the homeowner (3.6). Further, they felt this teaching tool was an effective way to deliver information (3.9); the interactive format aided their learning (3.7); that they were comfortable using a web-based format (4.2); and they liked learning using case studies (4.1). Our goal is to make the case-study framework available to other teaching colleagues who can then add their own data.

The NRT1 gene family encodes transport proteins with dual or low affinity for nitrate. The objectives of this experiment were to develop a system that could be used to compare the expression of the NRT1 genes between species. This was accomplished by comparing sequences of NRT1 homologues from various species and designing degenerate primers in regions of high homology. These primers were used to amplify a region of the NRT1 gene from species of interest. A 635 bp PCR product was amplified from each species using the MD2-1 (5' ATGTTACCAAYWTGGGCMAC-3') and MD2-2 (5'-GCCAMWARCCARTAGAAAT-3') primers. The PCR products were cloned and sequenced. At the nucleotide level, Cornussericea L. `Kelseyi' and Rhododendron L. `Unique' were 79.52% identical. Species-specific primers were designed and used for RT-PCR to compare NRT1 expression in roots of hydroponically grown C. sericea, C. sericea `Kelseyi', and Rhododendron `Unique'. The relative levels of NRT1 expression, normalized using 18S rRNA as a standard, were ≈3.2 to 1.7 to 1.0 for C. sericea, C. sericea `Kelseyi', and Rhododendron `Unique', respectively. This approach may eventually be used to examine nitrate uptake potential in different taxa of plants at different times during the growing season.