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Arbutus unedo is a sclerophyllous evergreen, characteristic of Mediterranean coastal scrub vegetation. In Italy, trees of A. unedo have been found close to natural CO2 vents where the mean atmospheric carbon dioxide concentration is about 2200 μmol mol?1. Comparisons were made between trees growing in elevated and ambient CO2 concentrations to test for evidence of adaptation to long-term exposure to elevated CO2. Leaves formed at elevated CO2 have a lower stomatal density and stomatal index and higher specific leaf area than those formed at ambient CO2, but there was no change in carbon to nitrogen ratios of the leaf tissue. Stomatal conductance was lower at elevated CO2 during rapid growth in the spring. In mid-summer, under drought stress, stomatal closure of all leaves occurred and in the autumn, when stress was relieved, the conductance of leaves at both elevated and ambient CO2 increased. In the spring, the stomatal conductance of the new flush of leaves at ambient CO2 was higher than the leaves at elevated CO2, increasing instantaneous water use efficiency at elevated CO2. Chlorophyll fluorescence measurements suggested that elevated CO2 provided some protection against photoinhibition in mid-summer. Analysis of A/Ci curves showed that there was no evidence of either upward or downward regulation of photosynthesis at elevated CO2. It is therefore anticipated that A. unedo will have higher growth rates as the ambient CO2 concentrations increase. 相似文献
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ELAINE JENSEN KERRIE FARRAR SIAN THOMAS‐JONES ASTLEY HASTINGS IAIN DONNISON JOHN CLIFTON‐BROWN 《Global Change Biology Bioenergy》2011,3(5):387-400
Miscanthus sinensis, M. sacchariflorus and their hybrids have been identified as leading candidates for the provision of bioenergy production across several continents. Flowering time is an important trait affecting biomass yield as well as certain quality attributes, such as moisture content at harvest. The aim of this study was to ascertain the level of diversity available to breeders and potential for hybridisation of different accessions in a large collection of Miscanthus. We also sought to determine trends in flowering time within and between species with respect to environment and origin of collection data (where known), whether flowering order was maintained across years, and the extent of uniformity of flowering in different genotypes. Flowering time was observed weekly in 244 genotypes of two Miscanthus species (M. sinensis, M. sacchariflorus) and inter‐specific hybrids including M. x giganteus over 3 years and using 4 clonal replicates of each genotype on a trial planted near Aberystwyth (Wales, UK). Differences in flowering time across the entire collection ranged from 160 to 334 days (June to November) and photoperiods between 7.8 and 16.6 h, with associated accumulated temperatures of 161 to 865oCd. More than two thirds of the collection flowered by the end of each growing season. M. sinensis individuals were the earliest genotypes to flower and showed the greatest diversity with respect to the onset of flowering. Flowering times in genotypes of known origin in Asia could be partially explained by growing season rain fall, degree days and mean temperature. Uniform flowering was identified in some genotypes. This will be important for the development of genetically diverse seed‐based crops. Rank order of flowering was shown to be consistent across Western Europe, thereby justifying single site trials as the basis of germplasm characterisation for wider geographical deployment. 相似文献
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