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111.
Elevated atmospheric CO2 stimulates aboveground biomass in a fire-regenerated scrub-oak ecosystem 总被引:2,自引:0,他引:2
Paul Dijkstra Graham Hymus Debra Colavito David A. Vieglais† Christina M. Cundari‡ David P. Johnson Bruce A. Hungate§ C. ROSS Hinkle‡ Bert G. Drake 《Global Change Biology》2002,8(1):90-103
The effect of elevated atmospheric CO2 concentration (Ca) on the aboveground biomass of three oak species, Quercus myrtifolia, Q. geminata, and Q. chapmanii, was estimated nondestructively using allometric relationships between stem diameter and aboveground biomass after four years of experimental treatment in a naturally fire‐regenerated scrub‐oak ecosystem. After burning a stand of scrub‐oak vegetation, re‐growing plants were exposed to either current ambient (379 µL L?1 CO2) or elevated (704 µL L?1 CO2) Ca in 16 open‐top chambers over a four‐year period, and measurements of stem diameter were carried out annually on all oak shoots within each chamber. Elevated Ca significantly increased aboveground biomass, expressed either per unit ground area or per shoot; elevated Ca had no effect on shoot density. The relative effect of elevated Ca on aboveground biomass increased each year of the study from 44% (May 96–Jan 97), to 55% (Jan 97–Jan 98), 66% (Jan 98–Jan 99), and 75% (Jan 99–Jan 00). The effect of elevated Ca was species specific: elevated Ca significantly increased aboveground biomass of the dominant species, Q. myrtifolia, and tended to increase aboveground biomass of Q. chapmanii, but had no effect on aboveground biomass of the subdominant, Q. geminata. These results show that rising atmospheric CO2 has the potential to stimulate aboveground biomass production in ecosystems dominated by woody species, and that species‐specific growth responses could, in the long term, alter the composition of the scrub‐oak community. 相似文献
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SAVEL R. DANIELS MIKE D. PICKER ROSS M. COWLIN MICHELLE L. HAMER 《Biological journal of the Linnean Society. Linnean Society of London》2009,97(1):200-216
The endemic South African velvet worm genus Peripatopsis currently contains eight recognized species described from variable morphological characters and the current taxonomy is unsatisfactory. In an attempt to investigate evolutionary relationships within Peripatopsis, we collected 137 individuals from 34 sample localities for six of the eight species. Sequence data derived from two partial mitochondrial (mt)DNA gene loci (COI and 12S rRNA), as well as partial sequence data from the ribosomal nuclear 18S rDNA locus in combination with gross morphological characters and scanning electron microscopy (SEM), was used to examine evolutionary relationships. Phylogenetic relationships were investigated using minimum evolution (ME) and Bayesian inferences (BI). Additionally, we also undertook a maximum likelihood (ML) analyses on the combined DNA sequence data set. The combined DNA evidence topologies derived from the ME, BI, and ML was highly congruent and was characterized by the presence of multiple lineages within recognized taxa. Peripatopsis clavigera, Peripatopsis moseleyi, and Peripatopsis sedgwicki each comprised two evolutionary lineages; Peripatopsis capensis comprised three; and Peripatopsis balfouri comprised six operational taxonomic units respectively. Genealogical exclusivity at both mtDNA and nuclear DNA among the geographically coherent groups coupled with pronounced sequence divergence suggested a two‐fold increase in the number of species within Peripatopsis. Previously used gross morphological characters (such as the number of leg pairs and colour) were either highly variable within operational taxonomic units, or were invariant, suggesting that alternative morphological characters are necessary for species discrimination. SEM results revealed potentially useful diagnostic characters that can discriminate between at least discriminate some of the newly‐identified lineages. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society 2009, 97 , 200–216. 相似文献
113.
TROY J. SEILER DANIEL P. RASSE† JIAHONG LI PAUL DIJKSTRA‡ HANS P. ANDERSON DAVID P. JOHNSON THOMAS L. POWELL BRUCE A. HUNGATE‡ C. ROSS HINKLE§ BERT G. DRAKE 《Global Change Biology》2009,15(2):356-367
This study reports the aboveground biomass response of a fire-regenerated Florida scrub-oak ecosystem exposed to elevated CO2 (1996–2007), from emergence after fire through canopy closure. Eleven years exposure to elevated CO2 caused a 67% increase in aboveground shoot biomass. Growth stimulation was sustained throughout the experiment; although there was significant variability between years. The absolute stimulation of aboveground biomass generally declined over time, reflecting increasing environmental limitations to long-term growth response. Extensive defoliation caused by hurricanes in September 2004 was followed by a strong increase in shoot density in 2005 that may have resulted from reopening the canopy and relocating nitrogen from leaves to the nutrient-poor soil. Biomass response to elevated CO2 was driven primarily by stimulation of growth of the dominant species, Quercus myrtifolia , while Quercus geminata , the other co-dominant oak, displayed no significant CO2 response. Aboveground growth also displayed interannual variation, which was correlated with total annual rainfall. The rainfall × CO2 interaction was partially masked at the community level by species-specific responses: elevated CO2 had an ameliorating effect on Q. myrtifolia growth under water stress. The results of this long-term study not only show that atmospheric CO2 concentration had a consistent stimulating effect on aboveground biomass production, but also showed that available water is the primary driver of interannual variation in shoot growth and that the long-term response to elevated CO2 may have been caused by other factors such as nutrient limitation and disturbance. 相似文献
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