This research examined nitrogen mineralization in the top 10 cm of soils along a vegetation gradient in Hong Kong at sites where fire has been absent for 0, 1, 3, 6 and 17 years (at the time of the study), and the rel...This research examined nitrogen mineralization in the top 10 cm of soils along a vegetation gradient in Hong Kong at sites where fire has been absent for 0, 1, 3, 6 and 17 years (at the time of the study), and the relationships between N mineralization and successional development of vegetation in the absence of fire. The sites including a newly burnt area (S1), short grassland (S2), tall grassland (S3), mixed tall grassland and shrubland (S4), and woodland (S5) were selected,and the in situ core incubation method was used to estimate nitrogen mineralization. Throughout the 60-day incubation in four periods, more nitrogen was mineralized at the S3 and S4 sites, the predominantly grassland sites, which contained the highest levels of soil organic matter (SOM) and total Kjeldahl nitrogen (TKN), than the S1 site, while immobilization occurred at the S2 and S5 sites. Leaching loss decreased with successional development of the vegetation, in the order of S1 ＞ S2 ＞ S3 ＞ S4 ＞ S5. The pattern of nitrogen uptake with ecological succession was less conspicuous, being complicated by the immediate effect of fire and possibly the ability of the woodland species to extract nitrogen from the deeper ground.In the absence of fire for 3 to 6 years, the build-up of SOM and TKN was accompanied by active mineralization, thus paving the way for the invasion of shrub and tree species. A close relationship existed between nitrogen mineralization and ecological succession with this vegetation gradient. Inherent mechanisms to preserve nitrogen in a fire-prone environment including immobilization and uptake and the practical relevance of nitrogen mineralization to reforestation are discussed.展开更多
The notion of invisibility in Invisible Man is spoken out by the protagonist＇s growth as an orator. Rather than a recursive retrieving of his identity throughout the narrative, the invisible man reinvents his identit...The notion of invisibility in Invisible Man is spoken out by the protagonist＇s growth as an orator. Rather than a recursive retrieving of his identity throughout the narrative, the invisible man reinvents his identity in his pursuit of pure persuasion. Both being terms in the Burkean system of literature rhetoric, pure persuasion, and identification become one for the unconscious purpose and the other for the symbolic action respectively in the protagonist-speaker＇s growth from an ideal emulator to speaker-audience mediator. In his identification with the audience and his ardent pursuit of pure persuasion, he paradoxically finds himself distanced from both his identity-to-be and the identity of his audience, with great division in-between. Though temporary corporation is achieved and occasional identification is resolved in the last two speeches, the protagonist only finds himself in a rhetorical context which is much more varied and more manipulative than he imagined. Such a realization renders the invisible man invisible again from the public stadium, who decides to resort to the pen for a life-long identification with the broader battlefield of racial discontinuity展开更多
基金Project supported by the Commonwealth Fellowship Scheme and the United College Endowment Fund of the Chinese University of Hong Kong
文摘This research examined nitrogen mineralization in the top 10 cm of soils along a vegetation gradient in Hong Kong at sites where fire has been absent for 0, 1, 3, 6 and 17 years (at the time of the study), and the relationships between N mineralization and successional development of vegetation in the absence of fire. The sites including a newly burnt area (S1), short grassland (S2), tall grassland (S3), mixed tall grassland and shrubland (S4), and woodland (S5) were selected,and the in situ core incubation method was used to estimate nitrogen mineralization. Throughout the 60-day incubation in four periods, more nitrogen was mineralized at the S3 and S4 sites, the predominantly grassland sites, which contained the highest levels of soil organic matter (SOM) and total Kjeldahl nitrogen (TKN), than the S1 site, while immobilization occurred at the S2 and S5 sites. Leaching loss decreased with successional development of the vegetation, in the order of S1 ＞ S2 ＞ S3 ＞ S4 ＞ S5. The pattern of nitrogen uptake with ecological succession was less conspicuous, being complicated by the immediate effect of fire and possibly the ability of the woodland species to extract nitrogen from the deeper ground.In the absence of fire for 3 to 6 years, the build-up of SOM and TKN was accompanied by active mineralization, thus paving the way for the invasion of shrub and tree species. A close relationship existed between nitrogen mineralization and ecological succession with this vegetation gradient. Inherent mechanisms to preserve nitrogen in a fire-prone environment including immobilization and uptake and the practical relevance of nitrogen mineralization to reforestation are discussed.
文摘The notion of invisibility in Invisible Man is spoken out by the protagonist＇s growth as an orator. Rather than a recursive retrieving of his identity throughout the narrative, the invisible man reinvents his identity in his pursuit of pure persuasion. Both being terms in the Burkean system of literature rhetoric, pure persuasion, and identification become one for the unconscious purpose and the other for the symbolic action respectively in the protagonist-speaker＇s growth from an ideal emulator to speaker-audience mediator. In his identification with the audience and his ardent pursuit of pure persuasion, he paradoxically finds himself distanced from both his identity-to-be and the identity of his audience, with great division in-between. Though temporary corporation is achieved and occasional identification is resolved in the last two speeches, the protagonist only finds himself in a rhetorical context which is much more varied and more manipulative than he imagined. Such a realization renders the invisible man invisible again from the public stadium, who decides to resort to the pen for a life-long identification with the broader battlefield of racial discontinuity
