Ecological traits such as an extensive range of natural distribution and tolerance to varying soil conditions, suggest that bigtooth maples (Acer grandidentatum Nutt.) could be popular landscape trees. But information on the tolerance of bigtooth maples to environmental stresses, such as drought, is virtually nonexistent. We studied physiological, growth and developmental traits of bigtooth maple plants from 15 trees native to Arizona, New Mexico, Texas, and Utah. Plants were grown in pots in a greenhouse and maintained as well-irrigated controls or exposed to drought and irrigated in cycles based on evapotranspiration. The ratio of variable to maximal fluorescence (Fv/Fm) was not different between drought-stressed and control plants, but the low Fv/Fm in plants designated as LM2 from the Lost Maples State Natural Area in Vanderpool, Tex., suggests these plants were relatively inefficient in capturing energy at PSII. Plants from another tree (LM5) originating from Lost Maples State Natural Area maintained similar predawn water potentials between drought-stressed and control plants after five cycles of drought. Plants from Dripping Springs State Park in Las Cruces, N.M., and those from LM2 had a strong, significant linear relationship between transpiration and stomatal conductance. Drought-stressed plants from Dripping Springs State Park, two plant sources from the Guadalupe Mountains in Salt Flat, Tex., designated as GM3 and GM4, and plants from trees designated as LM1 and LM2, had high relative growth rates and net assimilation rates. Drought-stressed plants from three of the four Guadalupe Mountain sources (GM1, GM3, GM4) had among the longest and thickest stems. Drought reduced shoot and root dry weight (DW). Although bigtooth maples showed several provenance differences in drought adaptation mechanisms, the lack of an irrigation effect on biomass allocation parameters such as root to shoot DW ratio and leaf area ratio implies that altered biomass allocation patterns may not be a common drought adaptation mechanism in bigtooth maples. Plants from selected provenances from the Guadalupe Mountains and Lost Maples State Natural Area in Texas, and to a lesser extent, provenances from Dripping Springs State Park in New Mexico might hold promise for selecting bigtooth maples for arid environments.
Emad Bsoul, Rolston St. Hilaire, and Dawn M. VanLeeuwen
Hans-Peter Kläring and Angela Schmidt
rates were present during the entire fruit growth period ( Figs. 2A and B ). Increasing the DIF resulted even in enhanced relative growth rates for all fruit sizes in both experiments ( Figs. 3A and B ). Fig. 2. Growth of cucumber fruits depending on the
D. Brault, K.A. Stewart, and S. Jenni
Lettuce plants (Lactuca sativa L. cv. Ithaca) were transplanted into organic soil and onto beige paper, black paper, and coextruded white/black polyethylene mulches in 1997 and 1998. A weeded bare ground plot was also tested. Transplanting in 1997 occurred in July under warm and dry conditions. Plants grown on mulch established better when the mean air temperature during the week after transplanting was 22.5 °C. The mortality rates of the bare ground control were 30%. All mulches significantly reduced plant mortality in 1997. In 1998, air temperature during the week after transplanting (June) was 14.6 °C. Plant mortality in 1998 was 1.3% for the control and 1.5% for the mulched plots. For both years, plants grown on mulched plots had higher relative growth rates than the control at the start of the season. Head fresh weight was 3.6 times (1997) and 1.2 times (1998) greater for lettuce grown on mulch compared with lettuce grown in a weeded control. Soil bulk density was lower under mulch than in the control plots in 1997.
Thomas G. Ranney, Nina L. Bassuk, and Thomas H. Whitlow
Growth and physiological characteristics were evaluated in autografted and reciprocally grafted plants of Prunus avium L. ×pseudocerasus Lindl. `Colt' and Prunus cerasus L. `Meteor'. Containerized plants were grown for 150 days in a greenhouse under either well-watered or water-stressed conditions. Both the scion and rootstock influenced growth (relative growth rate, R̄), morphological [leaf area : root surface area (LARSA) and specific leaf area (SLA)], and physiological (mean net assimilation rate, Ē) characteristics of grafted plants. Regardless of the watering regime, plants with `Meteor' scions and `Colt' rootstocks maintained higher R̄ than plants with `Colt' scions and `Meteor' rootstocks. This enhanced growth occurred as a result of higher Ē. Measurements on water-stressed plants also showed that the graft combination of `Meteor' on `Colt' had the lowest LARSA, while the reciprocal combination of `Colt' on `Meteor' had the highest. Differences in LARSA among water-stressed plants primarily reflected changes in SLA, as influenced by both rootstock and scion, and not in partitioning of dry weight between these organs.
Fahrurrozi Aziz, Katrine A. Stewart, and Sylvie Jenni
Field experiments were conducted during 1997, 1998, and 1999 to determine effects of 10 combinations of mulched minitunnel and thermal water tube on air, soil, and water-tube temperatures and on vegetative growth of `Earligold' netted muskmelon (Cucumis melo L. Reticulatus Group) within the tunnels. Use of mulched minitunnels significantly increased air, soil and water temperatures during the preanthesis phase in all years compared with control treatments. Inclusion of water tubes and venting the tunnels decreased air temperature fluctuations in the tunnels. During the first 10 to 15 days after transplanting, plants grown in nonperforated tunnels had higher relative growth rates (RGRs), net assimilation rates (NARs), and dry weights (DWs) than those grown under perforated tunnels and control plots. Plants in tunnels containing thermal water tubes generally had higher RGRs, NARs, and DWs than those without tubes. During the later part of the experiment, from 11 to 16 days after transplanting until anthesis, however, there were no consistent effects of mulched minitunnels on RGR, NAR, and plant DW. Tunneled muskmelons had significantly higher RGRs, but generally lower NARs than those grown without tunnel. Use of mulched minitunnels significantly increased plant DW at anthesis in 1997, but not in 1998 and 1999. Plants grown in the minitunnels containing a thermal water tube generally had higher RGRs, NARs, and DWs than those without water tubes. Ventilating nonperforated tunnels generally increased RGR, NAR, and plant DW. Plants grown in the tunnels reached anthesis 10 days earlier than those without tunnels.
C.M. Grieve, M.R. Guzy, J.A. Poss, and M.C. Shannon
Agroforestry plantations offer environmentally acceptable strategies for the reuse of saline drainage waters. Tree species suitable for use in such systems must be selected for survival and sustained growth under highly saline conditions. In this screening trial, four clones of Eucalyptus camaldulensis Dehn. (4543, 4544, 4573, and 4590) and one clone of E. rudis Endl. (4501) were grown in greenhouse sand cultures irrigated with sodium sulfate–dominated waters. Solution compositions were prepared to simulate saline drainage waters typically found in the San Joaquin Valley of California. Electrical conductivities of the solutions ranged from 2 to 28 dS·m–1. Treatments were replicated three times. All plants survived and were harvested after 7 weeks under saline treatment. Plant height was measured weekly and shoot biomass was determined at final harvest. The salinity levels that resulted in a 50% reduction in biomass production (C50) were 16.4 (4573), 17.1 (4543), 17.7 (4544), 29.0 (4590), and 30.0 dS·m–1 (4501). Over the range of salinities from 4 to 20 dS·m–1, clones 4501, 4590, and 4573 generally maintained higher relative growth rates (RGR) than did clones 4544 and 4543. However, at the highest salinity, RGRs of clones 4501, 4544, and 4573 were significantly greater than those of clones 4543 and 4590. Assessed on the basis of biomass production, clones 4501 (E. rudis) and 4590 (E. camaldulensis) showed exceptional potential for use in agroforestry systems where the saline drainage waters are sodium sulfate–dominated.
Marc W. van Iersel
Bedding plants are exposed to a wide range of environmental conditions, both during production and in the landscape. This research compared the effect of short-term temperature changes on the CO2 exchange rates of four popular bedding plants species. Net photosynthesis (Pnet) and dark respiration (Rdark) of geranium (Pelargonium ×hortorum L.H. Bail.), marigold (Tagetes patula L.), pansy (Viola ×wittrockiana Gams.), and petunia (Petunia ×hybrida Hort. Vilm.-Andr.) were measured at temperatures ranging from 8 to 38 °C (for Pnet) and 6 to 36 °C (for Rdark). Net photosynthesis of all species was maximal at 14 to 15 °C, while Rdark of all four species increased exponentially with increasing temperature. Gross photosynthesis (Pgross) was estimated as the sum of Pnet and Rdark, and was greater for petunia than for the other three species. Gross photosynthesis was less sensitive to temperature than either Pnet or Rdark, suggesting that temperature effects on Pnet were caused mainly by increased respiration at higher temperatures. Gas exchange-temperature response curves were not useful in determining the heat tolerance of these species. There were significant differences among species in the estimated Rdark at 0 °C and the Q10 for Rdark. Differences in the Q10 for Rdark were related to growth rate and plant size. Large plants had a greater Q10 for Rdark, apparently because these plants had a higher ratio of maintenance to growth respiration than small plants. The Q10 of the maintenance respiration coefficient was estimated from the correlation between the Q10 and relative growth rate, and was found to be 2.5 to 2.6.
Dongsheng Zhang, James R. Brandle, Kenneth G. Hubbard, Laurie Hodges, and Entin Daningsih
The relationships between shelterbelt (tree windbreak)-induced microclimate and muskmelon (Cucumis melo L.) growth and development were investigated at the Univ. of Nebraska-Lincoln Agricultural Research and Development Center near Mead, Nebr., during the 1992 and 1993 growing seasons. Wind speed, wind direction, air and soil temperatures, relative humidity, and soil moisture were monitored in both sheltered and nonsheltered areas. Plant growth parameters (plant height, vine length, plant dry weight, and leaf area) were measured at various stages of development. Shelterbelts provided improved growing conditions for muskmelon transplants. Direct wind damage and duration of higher wind speeds were reduced 47% to 56% in sheltered areas. Air temperatures in sheltered areas were slightly higher during daytime and slightly lower at night, and significantly so early in the growing season. Relative humidity was increased significantly in sheltered areas in 1992 and, while higher in 1993, the difference was nonsignificant. Soil moisture content was not affected significantly by wind protection. Sheltered plants exhibited earlier development and faster growth. The first female flower appeared 2 days earlier in sheltered areas in both years. The first fruit set, as indicated by fruit swelling and retention on the vine, occurred 6 days earlier and matured 5 and 6 days earlier in sheltered areas in 1992 and 1993, respectively. Leaf areas and dry-matter accumulation of sheltered plants were greater than those of exposed plants. The shoot relative growth rate of sheltered plants increased earlier in the growing season, but decreased slightly later in the growing season. The earlier development and faster growth of sheltered plants were related mainly to the reduction of wind speed, higher total accumulated air temperatures during the daylight hours (sum of daily average daytime air temperatures based on hourly averages), and higher soil temperature in sheltered areas. Total yields were not affected significantly in either year; however, early yields were significantly greater in sheltered areas in 1993. If earlier maturity and increased yield are possible in large sheltered fields, this practice would provide an economic benefit to producers.
D.H. Willits, P.V. Nelson, M.M. Peet, M.A. Depa, and J.S. Kuehny
Abbreviations: RAR, relative accumulation rate; RGT, relative growth rate. 1 Professor, Dept. of Biological and Agricultural Engineering. 2 Professor, Dept. of Horticultural Science. 3 Associate Professor, Dept. of Horticultural Science. 4 Former
Donita L. Bryan, Michael A. Arnold, Astrid Volder, W. Todd Watson, Leonardo Lombardini, John J. Sloan, Luis A. Valdez-Aguilar, and Andrew D. Cartmill
were determined at initial transplant and at harvest (365 d), as described previously, and relative growth rate (RGR) was calculated: ( Hoffman and Poorter, 2002 ), where W 1 = initial height or initial diameter, W 2 = final height or final