科研之友
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摘要
Biological nitrogen fixation (BNF) is a key process in the recovery of this essential element for living organism after catastrophic disturbances, as the advance and retreat of glaciers had exhausted the soil nitrogen (N) capital. The main objective of this work was to analyze the levels of symbiotic nitrogen fixation (SNF) associated to the flora that covers the soil in a primary chronosequence developed after consecutives glacier retreats in Santa Ines Island (53 degrees 45%26apos; S), Magallanes region, occurred over the past 400 years. The flora of soil that forms carpets on the forest floor of is composed primarily by the angiosperm Gunnera magellanica Lam. and by a high diversity of bryophytes. The SNF was estimated by the acetylene reduction assay. Separate assays were performed for G. magellanica, a mixed sample of bryophytes and for individual species of bryophytes. Generalized regression models showed that the acetylene reducing activity rates (ARA) and FSN did not relate significantly with site age, probably because the availability of limiting factor such as N and phosphorus (P) with opposite effects followed the same trend along the chronosequence. The ARA was positive for seven of a total of thirteen dominant species of bryophytes analyzed. Microscopic analysis of these species showed that the colonies of cyanobacteria are localized endophitically on cavities of Nothoceros endiviaefolius (Mont.) J. Haseg. and epiphytically in hornwort species. Although the estimated FSN and ARA rates showed no clear trend, N fixation levels remained high along the chronosequence so we conclude that symbiotic associations are crucial for ecosystem development.
- 出版日期2013-9
