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PREMISE OF THE STUDY: The Million Orchid Project at Fairchild Tropical Botanic Garden is an initiative to propagate native orchids for reintroduction into Miami's urban landscapes. The aim of this study was to develop microsatellites for Encyclia tampensis and Cyrtopodium punctatum (Orchidaceae). METHODS AND RESULTS: Ten microsatellites were developed for each species. For E. tampensis sampled from the natural population, allele numbers ranged from one to four, with an average observed heterozygosity (H o) of 0.314 and average expected heterozygosity (H e) of 0.281. For the individuals from cultivation, allele numbers ranged from one to six, with an average H o of 0.35 and an average H e of 0.224. For C. punctatum, allele numbers ranged from one to three, with an average H o of 0.257 and an average H e of 0.272. CONCLUSIONS: These microsatellites will be used to assess the genetic diversity of natural and cultivated populations with the intention of guiding genetic breeding under the Million Orchid Project.
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Mineral elements stored in seed reserves meet the nutrient demands of seedlings during their initial development and growth. We experimentally examined when seed reserves become insufficient to meet demands for nitrogen (N) and phosphorus (P) of seedlings of Leucaena leucocephala (Lam.) de Wit, a tropical woody legume. Seedlings were grown from seeds with four nutrient treatments: receiving all nutrients; all nutrients except N, all nutrients except P or deionised water. Growth curves were compared to quantify the time course of the onset of N and P deficiency during 8 weeks. N deficiency became significant for leaf area and biomass growth after 11 and 16 days, respectively, whereas P deficiency became significant after 31 days for both leaf area and biomass growth. Thus, seed reserves alone could support the P demands of seedlings for more than twice as long as N demands. As nutrient deficiency developed, seedlings adjusted increased relative biomass allocation to roots, diluted organ N and P concentrations but conserved 100% of the initial nutrient pool derived from the seed.
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BACKGROUND AND AIMS: The basic set of adaptations necessary for salinity tolerance in vascular plants remains unknown. Although much has been published on salinity stress, almost all studies deal with spermatophytes. Studies of salinity tolerance in pteridophytes are relatively rare but hold promise for revealing the fundamental adaptations that all salt-tolerant vascular plants may share. The most basal pteridophytes to exhibit salinity tolerance are members of the genus Equisetum, including the giant horsetail, Equisetum giganteum, the only pteridophyte to occur in salinity-affected regions of the Atacama Desert valleys of northern Chile. Here it can constitute a significant vegetation component, forming dense stands of shoots >4 m high. METHODOLOGY: Physiological parameters (stomatal conductances; efficiency of photosystem II; sap osmotic potential) were measured in E. giganteum populations in northern Chile across a range of groundwater salinities at 11 sites. In addition, Na, K, electrical conductivity and total plant water potential were measured in the plants and groundwater from each site. PRINCIPAL RESULTS: Equisetum giganteum exhibits similar stomatal conductances and photochemical efficiencies of photosystem II across a wide range of groundwater salinities. It lowers cell sap osmotic potential with increasing salinity and produces positive root pressure, as evidenced by guttation, at the full range of salinities experienced in the Atacama Desert. Equisetum giganteum maintains low Na concentrations in its xylem fluid and cell sap when soil water Na is high. It also maintains high K/Na ratios in xylem fluid and cell sap when soil water has low K/Na ratios. CONCLUSIONS: Equisetum giganteum is well adapted to salinity stress. Efficient K uptake and Na exclusion are important adaptations and closely similar to those of the facultative halophyte fern Acrostichum aureum.
