RESUMO
Amazonian savannas are isolated patches of open habitats found within the extensive matrix of Amazonian tropical forests. There remains limited evidence on how Amazonian plants from savannas differ in the traits related to drought resistance and water loss control. Previous studies have reported several xeromorphic characteristics of Amazonian savanna plants at the leaf and branch levels that are linked to soil, solar radiation, rainfall and seasonality. How anatomical features relate to plant hydraulic functioning in this ecosystem is less known and instrumental if we want to accurately model transitions in trait states between alternative vegetation in Amazonia. In this context, we combined studies of anatomical and hydraulic traits to understand the structure-function relationships of leaf and wood xylem in plants of Amazonian savannas. We measured 22 leaf, wood and hydraulic traits, including embolism resistance (as P50), Hydraulic Safety Margin (HSM) and isotope-based water use efficiency (WUE), for the seven woody species that account for 75% of the biomass of a typical Amazonian savanna on rocky outcrops in the state of Mato Grosso, Brazil. Few anatomical traits are related to hydraulic traits. Our findings showed wide variation exists among the seven species studied here in resistance to embolism, water use efficiency and structural anatomy, suggesting no unique dominant functional plant strategy to occupy an Amazonian savanna. We found wide variation in resistance to embolism (-1.6 ± 0.1 MPa and -5.0 ± 0.5 MPa) with species that are less efficient in water use (e.g. Kielmeyera rubriflora, Macairea radula, Simarouba versicolor, Parkia cachimboensis and Maprounea guianensis) showing higher stomatal conductance potential, supporting xylem functioning with leaf succulence and/or safer wood anatomical structures and that species that are more efficient in water use (e.g. Norantea guianensis and Alchornea discolor) can exhibit riskier hydraulic strategies. Our results provide a deeper understanding of how branch and leaf structural traits combine to allow for different hydraulic strategies among coexisting plants. In Amazonian savannas, this may mean investing in buffering water loss (e.g. succulence) at leaf level or safer structures (e.g. thicker pit membranes) and architectures (e.g. vessel grouping) in their branch xylem.
RESUMO
Abstract:The quantification of genetic diversity and intrapopulation spatial genetic structure (SGS) of tree species are important aspects for in and ex situ conservation practices. In this study we seek to understand the importance of conservation areas by quantifying the genetic diversity and the spatial genetic structure of a natural population of Theobroma speciosum. Within this population, 49 adults and 51 subadults were genotyped for five microsatellite loci. The results showed that adults and subadults have similar levels of genetic diversity and inbreeding (adults: A= 10.4, Ae = 10.3, F= 0.68, subadults: A= 10.6, Ae= 10.6, F= 0.57). Genetic diversity was spatially structured within the population, and the results suggest that near-neighbor trees up to a distance of 70 m are likely related. SGS is likely the result of short-distance seed dispersal, the short-distance range of pollinators, and infrequent breaches of the self-incompatible mating system. Considering the high demographic density of the species and size of the study area, as well as the high average number of alleles per locus and the presence of rare alleles, we believe that the study population is an excellent resource for in situ genetic conservation of T. speciosum. The study area is also a useful resource for collecting germplasm for ex situ conservation and seed collection, either for breeding programs used in the restoration of degraded areas or forest improvement. Rev. Biol. Trop. 64 (3): 1091-1099. Epub 2016 September 01.
ResumenLa cuantificación de la estructura de la diversidad genética e genética intrapoblacional espacial (SGS) de especies de árboles son importantes en las prácticas de conservación ex situ. En este estudio se busca determinar la importancia de las unidades de conservación mediante la cuantificación de la diversidad genética y la estructura espacial de una población natural de Theobroma speciosum. Dentro de esta población, a 49 adultos y 51 subadultos se les analizó el genotipo para cinco microsatélites loci. Los resultados mostraron que los adultos y subadultos tienen niveles similares de diversidad genética y endogamia (adultos: A= 10.4, Ae = 10.3, F= 0.68; subadultos: A= 10.6, Ae = 10.6, F= 0.57). La diversidad genética detectada fue estructurada espacialmente dentro de la población y los árboles vecinos hasta una distancia de 70 m estaban probablemente relacionados. Esta SGS es probablemente el resultado de la dispersión de semillas de corta distancia. El establecimiento de unidades de conservación permanentes como el Parque Nacional Juruena mostró que las áreas de conservación son herramientas valiosas en la preservación de la diversidad genética en las poblaciones naturales. Debido a la alta densidad demográfica de la especie y el tamaño del área de estudio, así como el elevado número promedio de alelos por locus y la presencia de alelos raros, creemos que la población de estudio es un excelente recurso para la conservación genética in situ de T. speciosum y también es un recurso útil de germoplasma para la recolección de conservación ex situ y la semilla, ya sea para programas de mejoramiento utilizados en la restauración de áreas degradadas o mejora de los bosques.
