Maintenance of high levels of genetic diversity and significant fine-scale genetic structure among age classes in single-tree populations of the endangered epiphytic orchid Laelia speciosa (Orchidaceae) in central Mexico

<p><strong>Background: </strong>Epiphytic plants exist within the complex three-dimensional habitat of the tree canopy. This can have a profound effect on patterns of both genetic diversity and structure and may be important for conservation of epiphytic species.<strong> </strong></p><p><strong>Objective:</strong> To evaluate how the epiphytic habit affects fine-scale three-dimensional genetic structure in single canopy tree populations. </p><p><strong>Studied species:</strong><em> Laelia speciosa</em>, a threatened endemic Mexican epiphytic orchid.<em> </em></p><p><strong>Study site and dates:</strong> Field sampling occurred during Spring 2006 in the municipality of Caurio de Guadalupe, Michoacán.</p><p><strong>Methods: </strong>All individuals occurring in two trees of <em>Q. deserticola</em> (178 in Tree 1 and 276 in Tree 2) were mapped, assigned to four discrete age classes, and genotyped at six microsatellite loci to understand patterns of genetic diversity and structure. </p><p><strong>Results:</strong> High levels of genetic diversity (polymorphic loci = 100 %, <em>Ho</em> = 0.398 – 0.506) occurred across size classes and trees but were not significantly different between the two trees. Significant fine-scale genetic structure was found in the Juvenile (plants 2-10 years old) and Adults I (11-20 years old) age classes in distances up to 15 cm. This significant structure was larger (up to 25 cm) when all individuals were treated as a single age class.<strong></strong></p><strong>Conclusion: </strong>The distribution and structure of genetic diversity is attributable to the epiphytic habit, particularly localized seed dispersal, limited selfing, and selection of adaptive traits. Conservation implications related to the sampling for <em>in vitro</em> propagation are given in light of the metapopulation genetic variability maintained within single-tree populations.

Effects of simulated nitrogen deposition and a stable isotopic assessment for the neotropical epiphytic orchid Laelia speciosa

The accelerated increase of nitrogen deposition is the third cause of biodiversity loss, as a result of saturation of ecosystems worldwide. The effects of nitrogen deposition on the endemic and endangered neotropical epiphytic orchid, Laelia speciosa, were evaluated via a dose-response experiment and a stable isotopic field assessment for individuals from a city and from an oak forest, in order to evaluate the potential risk facing this orchid, and record the history of the nitrogen deposition of series of consecutive annually produced pseudobulbs. Lower doses of nitrogen of up to 20 kg N ha yr–1 the dose that led to optimal performance of plants, acted as fertilizer. For instance, chlorophyll content and chlorophyll fluorescence (Fv/Fm) peaked at 0.66 ± 0.03 g m-2 and 0.85 ± 0.01, respectively. In contrast, toxic effects were observed at the higher doses of 40 and 80 kg N ha yr–1, leading a decrease of 38% of the chlorophyll content and 23% of the chlorophyll fluorescence. For the field assessment, a tissue nitrogen content of 1.2 ± 0.1% (dry mass basis) for the orchids suggested non-toxic deposition rates both at the city and the oak forest. However, their respective isotopic signatures revealed different sources of N at each site. Indeed, in the oak forest δ15N amounted –3.1 ± 0.3‰, typical of places with low industrial activities, while in the city the δ15N reached 5.6 ± 0.2‰, typical of sites with some degree of industrial and automobile activity. Laelia speciosa would be an adequate bioindicator of nitrogen deposition because its ability to take up nitrogen from the atmosphere while preserving its isotopic signature and showing a clear physiological response to increasing inputs of nitrogen. However, its limited geographical distribution precludes the orchid as an ideal candidate for biomonitoring. Thus other vascular epiphytes should be considered for this purpose.

Effects of simulated nitrogen deposition and a stable isotopic assessment for the neotropical epiphytic orchid Laelia speciosa

The accelerated increase of nitrogen deposition is the third cause of biodiversity loss, as a result of saturation of ecosystems worldwide. The effects of nitrogen deposition on the endemic and endangered neotropical epiphytic orchid, Laelia speciosa, were evaluated via a dose-response experiment and a stable isotopic field assessment for individuals from a city and from an oak forest, in order to evaluate the potential risk facing this orchid, and record the history of the nitrogen deposition of series of consecutive annually produced pseudobulbs. Lower doses of nitrogen of up to 20 kg N ha yr–1 the dose that led to optimal performance of plants, acted as fertilizer. For instance, chlorophyll content and chlorophyll fluorescence (Fv/Fm) peaked at 0.66 ± 0.03 g m-2 and 0.85 ± 0.01, respectively. In contrast, toxic effects were observed at the higher doses of 40 and 80 kg N ha yr–1, leading a decrease of 38% of the chlorophyll content and 23% of the chlorophyll fluorescence. For the field assessment, a tissue nitrogen content of 1.2 ± 0.1% (dry mass basis) for the orchids suggested non-toxic deposition rates both at the city and the oak forest. However, their respective isotopic signatures revealed different sources of N at each site. Indeed, in the oak forest δ15N amounted –3.1 ± 0.3‰, typical of places with low industrial activities, while in the city the δ15N reached 5.6 ± 0.2‰, typical of sites with some degree of industrial and automobile activity. Laelia speciosa would be an adequate bioindicator of nitrogen deposition because its ability to take up nitrogen from the atmosphere while preserving its isotopic signature and showing a clear physiological response to increasing inputs of nitrogen. However, its limited geographical distribution precludes the orchid as an ideal candidate for biomonitoring. Thus other vascular epiphytes should be considered for this purpose.

Evidencia molecular revela hongos asociados dentro de la orquídea epifita Laelia speciosa (HBK) Schltr.

Las relaciones de orquídeas-hongos han sido estudiadas principalmente en orquídeas terrestres. El trabajo aquí presentado trata sobre la diversidad y signifi cado biológico de los hongos asociados a la orquídea epifi ta endémica Laelia speciosa. Se registró la presencia fungal en semillas, protocormos y plántulas durante la germinación y primeros estadíos de desarrollo in vitro de L. speciosa mediante evidencia molecular. Las secuencias de ITS confi rmaron la presencia de hongos en raíces, cápsulas, semillas y también en plántulas cultivadas in vitro. Ninguno de los hongos encontrados formó pelotones característicos por lo que no se asume que sean hongos micorrízicos. Se identifi caron 18 taxa de hongos pertenecientes a ocho géneros (Alternaria, Curvularia, Cylindrocarpon, Fusarium, Myrmecridium, Neonectria, Penicillium y Tetracladium) y especies desconocidas de Atractiellales, Helotiales, Hypocreales, Lasiosphaeriaceae, Nectriaceae, Sordariomycetes y Tricholomataceae. De éstos, se infi rió la biología de nueve parásitos, cuatro saprobios y dos endófi tos. Uno de los hongos, perteneciente a una especie de Helotiales coloniza todos los tejidos de la orquídea, incluyendo semillas y plántulas cultivadas in vitro; por tanto, aun si todas las precauciones son tomadas, es difícil obtener “cultivos axénicos”de L. speciosa. Existe una considerable diversidad de hongos endófi tos dentro de los órganos de L. speciosa a través de todo su ciclo de vida.