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Typically, dormant seedlings are transplanted when revegetating disturbed lands to prevent transplant shock triggered by water stress. It may be possible to transplant nondormant seedlings by inducing drought-tolerant acclimation responses such as solute accumulation. Artemisia cana and Agropyron intermedium seedlings were subjected to three different water stress preconditioning treatments. After conditioning, seedlings were dried down in their containers until leaf senescence, or were transplanted to disturbed land sites. Leaf water potential components and relative water content were measured. Following treatments, water relations parameters of preconditioned seedlings were not markedly different from controls in either species. At the end of the final dry-down, water stress preconditioning had not induced active or passive solute accumulation, prolonged leaf survival during lethal drought conditions, or differences in transplant survival under the experimental conditions of this study.
Growth of woody landscape plants is strongly affected by the underlying surface. In urban areas, plants are subjected to energy balance characteristics of a variety of surfaces. This research investigated energy balance properties of six common urban surfaces: Kentucky bluegrass, pine bark mulch, concrete, asphalt, lava rock mulch, and gravel rock mulch. Each summer over a 2-year period incoming global radiation (GW), relative humidity, and air temperature were measured over each surface, and surface reflectivity (AW), surface temperature (TS), soil temperature (TO), and soil heat flux (SF) were measured below each surface. Thermal conductivity (K) and emitted surface longwave radiation (LW) were also calculated. Surface property differences were determined by regression analysis. Incoming global radiation (independent variable) versus TS, TO, SF, LW data (dependent variable) were analyzed. Linear or quadratic curves were selected according to significance of each variable and the coefficient of determination (R2). Surface reflectivity was greatest for concrete and least for lava rock mulch, and K was greatest for asphalt and concrete and least for lava rock and pine bark mulch. Under maximum GW, regression data indicate that SF and TO would be greatest under asphalt and least under lava rock and pine bark mulch. Under similar circumstances, TS and LW would be greatest for pine bark mulch and least for Kentucky bluegrass. This research revealed that more energy was conducted into the soil below asphalt and concrete, and that a greater portion of GW was prevented from entering the soil below pine bark and lava rock mulch than below other surfaces. Due to these effects, and the lack of evaporative cooling, surface temperatures were greater, and more longwave radiation was emitted from, non-vegetative surfaces than from turf.
Gas exchange and growth of transplanted and nontransplanted, field-grown Norway maple (Acer platanoides L. `Schwedleri') and littleleaf linden (Tilia cordata Mill. `Greenspire') trees were investigated in an arid climate. In the spring of 1995, three trees of each species were moved with a tree spade to a new location within a field nursery and three nontransplanted trees were selected as controls. Predawn leaf water potential, morning-to-evening stomatal conductance and leaf temperature, leaf-to-air vapor pressure difference, midday stomatal conductance and photosynthetic rate, and growth data were collected over a 2-year period. After transplanting, weekly predawn leaf water potential indicated that transplanted trees were under greater water stress than were nontransplanted (control) trees. However, predawn leaf water potential of maple trees recovered to control levels 18 weeks after transplanting, while that of transplanted linden trees remained more negative than that of controls. In 1995, stomatal conductance and photosynthetic rates were lower throughout the day for transplanted trees. In 1996, gas exchange rates of transplanted maple trees recovered to near control levels while rates for transplanted linden trees did not. Sensitivity of stomata to leaf-to-air vapor pressure difference varied with species and with transplant treatment. Each year transplanted trees of both species had less apical growth than did control trees. Although gas exchange and apical growth of transplanted trees was reduced following transplanting, recovery of gas exchange to control rates differed with species.
We investigated water use and potential drought avoidance of Norway maple (Acer platanoides L.) and green ash (Fraxinus pennsylvanica Marsh) seedlings grown in protective plastic shelters. Gravimetric tree water use and reference evapotranspiration for fescue turf (ETo) were monitored for 1 to 3 days during the growing season. Water use of trees was 8% to 14% of ETo in shelters vs. 29% to 40% for trees not in shelters. Trunk diameter was affected more than whole-tree water relations by lack of irrigation, suggesting that the nonirrigated trees were subjected to only mild water stress. Shelters did not improve drought avoidance, as water potentials were generally more negative and trunk diameter increment was lower for nonirrigated trees in shelters. Maples in shelters were affected more adversely by lack of water than were ash. Higher temperatures in shelters also may have reduced trunk growth. Air temperatures were 13 °C warmer than ambient in nonirrigated shelters, but only 5 °C warmer in irrigated shelters. Tree shelters can reduce transpiration rates by over half, but benefits from reduced water loss may be offset by negative effects of higher air temperatures. Shelters reduced cold hardiness of both species, but maple was affected more than ash.
Bigtooth maple (Acer grandidentatum) has potential as a small, water conserving landscape tree in western landscapes. This potential has been hindered in part by the difficulty in asexually propagating superior accessions. The ability of etiolation to enhance rooting of softwood cuttings of selected wild accessions was determined by grafting six accessions onto seedling rootstocks to use as stock plants. Etiolation was applied to stock plants by placing open-ended, black, velour, drawstring bags over the end of pruned shoots at bud swell allowing new shoots to develop and grow out the end of the bag while leaving the base of the shoot covered. In 2009 and 2010, cuttings from etiolated and nonetiolated shoots were treated with 4000 ppm indole-3-butyric acid (IBA) + 2000 ppm naphthaleneacetic acid (NAA), stuck in a premoistened 3 perlite:1 peat (by volume) rooting substrate and placed under intermittent mist. After 4 weeks, 89% (2009) and 85% (2010) of the etiolated cuttings rooted and only 47% (2009) and 17% (2010) of the nonetiolated cuttings rooted. Etiolated cuttings produced on average 11.3 (2009) and 7.2 (2010) roots per cutting and nonetiolated 2.1 (2009) and 0.5 (2010) roots per cutting. Etiolation, and its application through the use of black cloth bags, can be an effective way to increase the rooting of bigtooth maple cuttings and the availability of these plants for use in water conserving landscaping.
We investigated microclimate, gas exchange, and growth of field-grown Norway maple (Acer platanoides) and green ash (Fraxinus pennsylvanica) trees in brown, white, or no treeshelters. Microclimate, tree growth, and gas exchange measurements were taken summer and winter. Treeshelter microclimate was greenhouse-like compared to ambient conditions, as short-wave radiation (S↓) was lower, and midday air temperature and relative humidity were higher. In both species, this resulted in less trunk growth and greater specific leaf area, which are growth responses characteristic of shade acclimation. Treeshelter microclimate did, however, substantially increase shoot elongation and stomatal conductance, but did not increase photosynthesis when compared to trees grown without shelters. White shelters allowed 25% more penetration of S↓ than brown shelters, but tree growth and climatic variables did not differ with treeshelter color. Stomatal conductance, however, was higher for trees in white shelters. Treeshelters also appeared to have a negative effect on plant hardiness. New shoot growth in shelters was more winter-damaged, particularly in maple, than nonsheltered trees. This may be related to winter bark (Tb) and air temperature (Ta). Winter midday Tb on trees grown in shelters was up to 15C higher than Tb on trees outside shelters, while midday Ta inside treeshelters was up to 20C higher than Ta outside treeshelters.
Gas exchange and growth of transplanted and non-transplanted Acer platanoides `Schwedleri' and Tilia cordata `Greenspire' trees were investigated. This study was conducted on trees planted in 1991 in a field nursery near Logan, Utah. In Spring 1995, three trees of each species were moved with a tree spade to a new location within the nursery and three non-transplanted trees were selected as controls. To simulate landscape conditions, all trees were watered at the time of planting and once per week during the growing season. Pre-dawn water potential, dawn-to-dusk stomatal conductance, mid-day photosynthesis, and growth data were collected over a 2-year period. Transplanted trees of each species were under more water stress (indicated by more negative pre-dawn water potential) than non-transplanted trees. However, pre-dawn water potential of transplanted A. platanoides recovered to near non-transplanted levels, while transplanted T. cordata did not. Dawn-to-dusk studies in 1995 and 1996 showed that stomatal conductance was lower throughout the day in transplanted trees. Once again, transplanted A. platanoides recovered to near non-transplanted levels, while transplanted T. cordata did not. A similar trend for mid-day photosynthesis was found for both species in 1995 and 1996. Transplanted trees of each species had less stem area increase, shoot elongation, and total leaf area than non-transplanted trees for each year. These data indicate that transplanted A. platanoides can recover to near non-transplant pre-dawn water potential and gas exchange levels earlier, and therefore establish faster, than transplanted T. cordata. However, after 2 years neither transplanted tree species were able to fully recover to non-transplanted growth rates.
Abstract
Rockwool is an inert medium for use in greenhouses. It is reported to contribute negligible nutrients to plants. However, Rosa multiflora ‘Burr’ rootstocks grown in Grodan rockwool exhibited no visible Fe chlorosis with an Fe-free nutrient solution. Leaf chlorophyll content was 2.65 mg·g-1 with Fe and 2.85 mg·g-1 without Fe. Available Fe concentrations of three commercial materials (Hortiwool, Grodan block, and Grodan loose), estimated by using diethylenetriaminepentaacetic acid (DTPA) extraction (2 DPTA : 1 rockwool, v/w), were 43.0, 0.33, and 3.95 mg Fe/liter, respectively. With long-term DTPA extractions (20:1), Fe extracted from Hortiwool and loose Grodan increased for ≈3 days before leveling off, while Fe extracted from Grodan block increased for 6 days. Measurable levels of Mn, Cu (348 mg·liter-1), and Zn were found in DTPA extracts of Hortiwool; measurable levels of Mn and Cu were extracted from loose Grodan and measurable levels only of Mn from Grodan block.
We investigated the microclimate, gas exchange, and growth of field-grown Norway maple (Acer platanoides L.) and green ash (Fraxinus pennsylvanica Marsh) trees nonsheltered, and in brown and white shelters. Shelter microclimate—air temperature (Ta), vapor pressure deficit (VPD), and radiation—and tree leaf area, growth in diameter, stomatal conductance (gs), and photosynthesis were measured during the first growing season after bare-root transplanting. Bark temperatures in midwinter were also measured. Treeshelter microclimate was greenhouse-like compared to ambient conditions, as shortwave radiation was lower, and midday Ta and relative humidity were higher. Although trees in shelters had greater shoot elongation and higher gs than trees grown without shelters, photosynthesis was not different. White shelters allowed 25% more shortwave radiation penetration and increased Ta by 2 to 4 °C and VPD by 0.5-1 kPa over brown shelters. However, tree growth and gas exchange generally were not affected by shelter color. Winter injury was increased for trees in shelters and varied with species and shelter color. Both species exhibited shoot dieback in shelters the spring following a winter where bark temperatures varied 40 to 50 °C diurnally. More new growth died on maple, particularly in white shelters where several trees were killed. These data suggest that supraoptimal summer and winter temperatures may reduce vigor and interfere with cold tolerance of some species grown in shelters.