Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, rho(x), were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m(-3) for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m(-3) for an Aiouea sp. (Lauraceae) from Caxiuana, Central Para, Brazil. Analysis of variance showed significant differences in average rho(x) across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood. [References: 118
Abstract. Measurements of branch xylem density, Dx, were made for 1466 trees representing 503 species, sampled from 80 sites across the Amazon basin. Measured values ranged from 240 kg m−3 for a Brosimum parinarioides from Tapajos in West Pará, Brazil to 1130 kg m−3 for an Aiouea sp. from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average Dx across the sample plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that geographic location and plot accounted for 33% of the variation with species identity accounting for an additional 27%; the remaining "residual" 40% of the variance accounted for by tree to tree (within species) variation. Variations in plot means, were, however, hardly accountable at all by differences in species composition. Rather, it would seem that variations of xylem density at plot level must be explained by the effects of soils and/or climate. This conclusion is supported by the observation that the xylem density of the more widely distributed species varied systematically from plot to plot. Thus, as well as having a genetic component branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing and in a predictable manner. Exceptions to this general rule may be some pioneers belonging to Pourouma and Miconia and some species within the genera Brosimum, Rinorea and Trichillia which seem to be more constrained in terms of this plasticity than most species sampled as part of this study.
ABSTRACT:We tested the influence of exogenous application of brassinosteroids (BRs) on survival, growth and biomass production of Scots pine (Pinus sylvestris) seedlings. BRs are natural substances, supposedly having many positive effects on plants such as improving growth, stress tolerance, survival and biomass production. One part of the seedlings was treated with a low concentration of synthetically prepared BRs and the other part was designated as the control without any treatment. Mortality, height and root collar diameter were measured in two subsequent years, the root-to-shoot ratio of biomass volume was determined in autumn 2013. The application of BRs significantly slowed height and radial growth of pine. The height increment of the BRs-treated seedlings was lower by 11% between 2012 and 2013 compared to the control. The increment in root collar diameter (2012)(2013) in the BRs-treated seedlings was lower by 13% than in the control. The BRs-treated pines also experienced a significantly higher mortality compared to the control. No significant influence of BRs on biomass production was found.
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