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We determined transpiration rate, survival, and rooting of unmisted, softwood cuttings of `Autumn Flame' red maple (Acer rubrum L.) and `Indian Summer' Freeman maple (Acer ×freemanii E. Murray). Effects of perlite at 24, 30, and 33 °C were assessed to determine whether responses of cuttings would be consistent with cultivar differences in resistance to root-zone heat previously shown with whole plants. During 7 d, cutting fresh mass increased by ≈20% at all temperatures for `Autumn Flame' red maple, but fresh mass of `Indian Summer' Freeman maple decreased by 17% and 21% at 30 and 33 °C, respectively. The percentage of cuttings of `Indian Summer' that were alive decreased over time and with increasing temperature. Transpiration rate decreased during the first half of the treatment period and then increased to ≈1.1 and 0.3 mmol·m-2·s-1 for `Autumn Flame' and `Indian Summer', respectively. Mean rooting percentages over temperatures for `Autumn Flame' and `Indian Summer' were 69 % and 16%, respectively. Mean rooting percentages at 24, 30, and 33 °C over both cultivars were 74%, 29%, and 25%, respectively. Over temperatures, mean root count per cutting was 41 and seven, and mean root dry mass per cutting was 4.9 and 0.4 mg, for `Autumn Flame' and `Indian Summer', respectively. Use of subirrigation without mist to root stem cuttings was more successful for `Autumn Flame' than for `Indian Summer'. Temperature × cultivar interactions for cutting fresh mass and the percentage of cuttings remaining alive during treatment were consistent with previous evidence that whole plants of `Autumn Flame' are more heat resistant than plants of `Indian Summer'. Mass and survival of stem cuttings during propagation in heated rooting medium may serve as tools for screening for whole-plant heat resistance among maple genotypes.

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Maackia amurensis Rupr. & Maxim. is a leguminous tree species possessing meritorious ornamental characteristics and is confirmed to associate with rhizobia that fix nitrogen, but few attempts to isolate symbiotically superior rhizobia have been made. Our goals were to isolate rhizobia from the root zones of indigenous trees of M. amurensis in two ecologically distinct forests in the Heilongjiang Province of China, characterize the rhizobia, and compare their effectiveness at causing nodulation of this host plant. Rhizobia were isolated and cultured from nodules that formed on seedlings grown in soils collected in May 1998, from the Maoershan (45°N, 127°E) and Liangshui (47°N, 128°E) Research Forests. Inoculants from each of the 160 isolates were applied to seedlings. A subset of 48 isolates that evoked the most nodules was partitioned by cluster analysis into 12 similarity groups based on measures of number of nodules (17.9 ± 6.5), the ratio of growth rate on two distinct media (2.26 ± 1.8), pH reaction as measured by absorption at 614 nm of bromthymol blue (0.98 ± 0.36), and tolerance to sodium chloride at 15 g/L (23 out of 48). By using single-isolate cultures of similar cellular concentration as inoculants, one isolate from each group and USDA 4349, an isolate obtained during previous research, are being compared for their capacity to infect and nodulate seedlings.

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We compared two putative Freeman maples [`Jeffersred', (Autumn Blaze ®) and `Indian Summer'] and five red maples [`Franksred' (Red Sunset ®), `Autumn Flame', `PNI 0268' (October Glory®), `Fairview Flame', and unnamed selection 59904] for effects of flooding on stomatal conductance. A method for quantifying changes in leaf color that occurred on flooded plants also was developed. Potted plants grown from rooted cuttings in a greenhouse were subjected to 75 days of root-zone inundation (flood treatment) or were irrigated frequently (control treatment). Across genotypes, stomatal conductance of flooded plants initially increased by about 20% and then fell to and was sustained below 50 mmol·s–1·m–2. Stomatal conductance of flooded plants of `Indian Summer' decreased to 20 mmo·s–1·m–2 after 8 days of inundation, and two of three flooded `Indian Summer' plants died during treatment. Other genotypes required at least twice this time to display a similar reduction in stomatal conductance, indicating `Indian Summer' may be particularly flood sensitive. Intensities of red, green, and blue color at a consistent interveinal position were analyzed with Visilog software by using scanned leaf images of the youngest fully expanded leaf of each plant in both treatments. A genotype × irrigation interaction existed for the ratio of green to red intensity. This method provided numerical data that corresponded well to differences among genotypes we observed visually. For example, while flooding did not alter the color of `Autumn Flame' leaves, the ratio of green to red was three times greater for controls of Autumn Blaze® than for the flooded plants of this cultivar.

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Morphological distinctions between sugar maples and black maples are not consistently evident, and molecular assessment of genetic diversity is lacking for these taxa. We examined restriction-site polymorphisms in the ndhA intron of the chloroplast DNA (cpDNA) in populations of sugar maples and black maples representing their zones of allopatry and sympatry in eastern North America. Restriction-site analysis of the ndhA intron after digestion with HinfI and Sau3AI yielded no polymorphisms. Restriction digestion of the ndhA intron with TaqI revealed two cpDNA haplotypes that were neither geographically localized nor taxon specific. Although testing additional accessions of sugar maples and black maples for cpDNA variation will further elucidate patterns of genetic variation, our initial results suggest that the taxa are either exchanging genes or share an ancestral cpDNA polymorphism.

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Knowing whether leguminous trees have the potential to nodulate after infection by rhizobial bacteria is important for managing nitrogen (N) applications during tree production and for culture in the landscape. Although 98% of studied species in the Papilionoideae nodulate, the nodulation status of two tree species in this subfamily is uncertain. Cladrastis kentukea (Dum.-Cours.) Rudd (American yellowwood) did not form nodules during inoculation studies in 1939 and 1992. Nodules were observed on mature Sophora japonica L. (Japanese pagodatree) in Japan and Hawaii in the 1940s, but compatible rhizobia reportedly isolated in Japan are no longer held in bacterial collections. Our objective was to verify further that American yellowwood does not nodulate and to confirm reports that Japanese pagodatree does nodulate. Rhizobia that infect many plant hosts, soil samples and rhizobial isolates from other Sophora spp., and soil samples from mature American yellowwood and Japanese pagodatree were used to inoculate 5-day-old seedlings of American yellowwood, Japanese pagodatree, and control species. Soil from indigenous and introduced trees in the continental United States, Hawaii, Japan, and China was used. Inoculated and uninoculated plants were grown for 7 weeks in sterile Leonard jars or clay pots containing perlite and irrigated with sterile, N-free Hoagland's solution. No inoculation treatment elicited nodulation of American yellowwood or Japanese pagodatree. Our results provide additional evidence that American yellowwood lacks that capacity to nodulate and cast further doubt on nodulation of Japanese pagodatree.

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Freeman maples (Acer × freemanii E. Murray) are marketed as stress-resistant alternatives to red maples (Acer rubrum L.), but few data from direct comparisons of these species are available. As a first step in comparing the stress resistance of red maple and Freeman maple, responses to drought were studied in Acer × freemanii `Autumn Fantasy', `Celebration', and `Marmo'. Plants grown from rooted cuttings were treated by withholding irrigation through four drought cycles of increasing severity that were separated by irrigation to container capacity. Drought reduced shoot dry mass, root dry mass, and height growth by 64%, 43%, and 79%, respectively, over all cultivars. Predawn leaf water potential was reduced by 1.16 MPa over all cultivars, and stomatal conductance data indicated water use was more conservative over all root-zone moisture contents after repeated cycles of drought. Specific mass of drought-stressed leaves increased by 25% for `Autumn Fantasy', and microscopy to determine leaf thickness and cellular anatomy is ongoing. `Autumn Fantasy' also had the lowest ratio of leaf surface area to xylem diameter, and `Autumn Fantasy' and `Celebration' had higher ratios of root to shoot mass than `Marmo'. Pressure-volume curve analysis revealed osmotic potential of drought-stressed plants at full turgor was 0.24 MPa more negative than controls, and droughted plants had a greater apoplastic water percentage than controls. Although osmotic adjustment during drought was similar among cultivars, differences in specific mass of leaves and in ratios of transpiring and conducting tissues suggest cultivars of Freeman maple vary in resistance to drought in the landscape.

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Can Carolina buckthorn (Rhamnuscaroliniana) persist north of its native habitat without becoming invasive? Its distribution (USDA zones 5b to 9b) suggests that genotypes vary in cold hardiness, and invasiveness of other Rhamnus sp. has been linked to unusually early budbreak each spring. Therefore, we investigated depth of cold hardiness and vernal budbreak of Carolina buckthorns from multiple provenances and made comparisons to the invasive common buckthorn (Rhamnus cathartica). Budbreak was recorded in Ames, Iowa, from 9 Apr. to 10 May 2002. Buds of common buckthorn broke earlier than those of Carolina buckthorn, and mulching plants of Carolina buckthorn hastened budbreak. Stem samples were collected in October, January, and April from a plot in Ames, Iowa (USDA zone 5a), of Carolina buckthorns from three provenances (Missouri, Ohio, and Texas) and of naturalized common buckthorns. A similar schedule was followed during the next winter, when two plot locations [Ames, Iowa, and New Franklin, Mo. (USDA zone 5b)], were compared, but Carolina buckthorns from only Missouri and Texas were sampled. Carolina buckthorn and common buckthorn survived midwinter temperatures as low as –21 °C and –24 °C, respectively. Provenance differences were minimal; Carolina buckthorns from Missouri were more hardy than those from Ohio and Texas only in April of the first winter. We conclude that its cold hardiness will permit use of Carolina buckthorn beyond where it is distributed in the southeastern United States. Delayed budbreak of Carolina buckthorn relative to that of common buckthorn may underscore the potential for Carolina buckthorn in regions with harsh winters and may lessen its potential to be as invasive as common buckthorn.

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Six red maple (Acer rubrum L.) and four Freeman maple (A. ×freemanii E. Murray) cultivars were compared for rooting of single-node stem cuttings and subsequent development of rooted cuttings. Cuttings were taken in May 1990 and 1991 and treated with either 3 or 8 g IBA/kg. Rooting after 4 weeks differed among cultivars, ranging from 22% for `Karpick' to 100% for `Schlesinger' over both years. Rooting scores, based on root counts and lengths, were highest for `Schlesinger' and lowest for `Scarlet Sentinel' and `Karpick'. IBA at 8 g·kg–1 resulted in better rooting than at 3 g·kg–1. Mean length of shoots formed on potted rooted cuttings was 22.6 cm for `Franksred', which initiated shoots on 100% of the cuttings that rooted. In contrast, <50% of `Armstrong', `Jeffersred', `Karpick', `Northwood', and `Scarlet Sentinel' rooted cuttings initiated shoots, and mean length of new shoots was <4 cm for these cultivars. The amount of leaf desiccation that occurred after removing cuttings from the propagation bench varied among cultivars, and the percentage of viable leaf surface area correlated positively with final root or shoot dry mass for all cultivars. Chemical name used: indole-3-butyric acid (IBA).

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Early nodulin genes, such as ENOD2, may be conserved and could function as molecular markers for nodulation. Many nodulating and nonnodulating legumes must be analyzed before the role of such genes in nodulation can be determined. Japanese pagodatree and American yellowwood are closely related, ornamental woody legumes. Unsubstantiated reports of nodulation in Japanese pagodatree require confirmation, and American yellowwood has not been observed to nodulate. We investigated the presence of putative ENOD2 genes in these species, and we are studying differential and temporal expression. Genomic DNA of Japanese pagodatree and primers, derived from proline-rich pentapeptide repeats of conserved ENOD2 sequences, were used to obtain a 555-bp PCR fragment. This cloned fragment was used as a probe for Southern and Northern hybridizations. Genomes of Japanese pagodatree and American yellowwood contained sequences that are similar to ENOD2 sequences in other legumes. Treatments with either cytokinin or an auxin transport inhibitor may induce expression of the putative ENOD2 genes. New data on the characteristics of nodulin genes in woody legumes will clarify the nature and evolution of nodulation in legumes and may have implications for developing sustainable nursery production protocols.

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A complete picture of legume nodulation has yet to be elucidated. Most studies of the molecular mechanisms responsible for nodule organogenesis have focused on herbaceous legumes. We investigated the presence of a putative ENOD2 gene and studied the temporal and organ-specific production of its transcripts in an ornamental woody legume, Amur maackia. Primers derived from proline-rich pentapeptide repeats of conserved ENOD2 sequences and the genomic DNA of Amur maackia were used to obtain a 543-bp PCR fragment. Southern and Northern blots were probed with this cloned fragment. The Amur maackia genome contained an ENOD2 sequence that is similar to sequences in other species. Expression of the putative ENOD2 gene was detected in roots, 4 days after rhizobial inoculation, but not in leaves or stems. New data on the characteristics of nodulin genes in woody legumes will be beneficial in clarifying the nature and evolution of nodulation in legumes and may have implications for developing sustainable nursery production protocols.

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