作业帮英文翻译求助呀3急111
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英文翻译求助呀3急111
Under optimal conditions,
the rates at which white rot fungi
mineralize lignin rival their rates of polysaccharide
degradation. Basidiomycetes
and xylariaceous Ascomycetes that cause
white rot are the organisms principally
responsible for wood decay in hardwood
forests and in tropical forest ecosystems,
and also play a prominent role in temperate
coniferous forests (Eriksson et al.,
1990; Blanchette, 1991; Dix and Webster,
1995). Several hundred species in numerous
taxa have been described. Communities
of white rot fungi and associated
organisms in forest ecosystems have been
described in extensive studies by British
researchers (Rayner and Boddy, 1988;
Boddy, 1992; Dix and Webster, 1995).
The brown rot fungi comprise a relatively
small group of Basidiomycetes that
decay the cellulose in wood preferentially.
They do not degrade the lignin extensively,
although they modify it by demethylating
it. Brown rot fungi thus stand out as an
exception to the usually valid observation
that lignocellulose must be delignified first
if organisms are to gain access to plant cell
wall polysaccharides. The biochemical system
that enables brown rot fungi to
circumvent the lignin while degrading the
cellulose and hemicelluloses in wood has
not been characterized. Although these
fungi secrete cellulases and hemicellulases,
the enzymes are too large to penetrate the
cell wall matrix in wood, and it is evident
that other degradative systems must participate
as well. Brown rot fungi make a
large contribution to wood decay, especially
in coniferous forests (Dix and Webster,
1995), and the residual modified lignin
they leave behind is an important humus
precursor (Hudson, 1986). They deserve
much more research attention, but have
been difficult to study because they do not
exhibit full degradative activity on defined
media in vitro (Eriksson et al., 1990). 第三部分
Under optimal conditions,
the rates at which white rot fungi
mineralize lignin rival their rates of polysaccharide
degradation. Basidiomycetes
and xylariaceous Ascomycetes that cause
white rot are the organisms principally
responsible for wood decay in hardwood
forests and in tropical forest ecosystems,
and also play a prominent role in temperate
coniferous forests (Eriksson et al.,
1990; Blanchette, 1991; Dix and Webster,
1995). Several hundred species in numerous
taxa have been described. Communities
of white rot fungi and associated
organisms in forest ecosystems have been
described in extensive studies by British
researchers (Rayner and Boddy, 1988;
Boddy, 1992; Dix and Webster, 1995).
The brown rot fungi comprise a relatively
small group of Basidiomycetes that
decay the cellulose in wood preferentially.
They do not degrade the lignin extensively,
although they modify it by demethylating
it. Brown rot fungi thus stand out as an
exception to the usually valid observation
that lignocellulose must be delignified first
if organisms are to gain access to plant cell
wall polysaccharides. The biochemical system
that enables brown rot fungi to
circumvent the lignin while degrading the
cellulose and hemicelluloses in wood has
not been characterized. Although these
fungi secrete cellulases and hemicellulases,
the enzymes are too large to penetrate the
cell wall matrix in wood, and it is evident
that other degradative systems must participate
as well. Brown rot fungi make a
large contribution to wood decay, especially
in coniferous forests (Dix and Webster,
1995), and the residual modified lignin
they leave behind is an important humus
precursor (Hudson, 1986). They deserve
much more research attention, but have
been difficult to study because they do not
exhibit full degradative activity on defined
media in vitro (Eriksson et al., 1990). 第三部分
在理想的条件下,白腐真菌矿化木质素的速率与降解多糖的速率相当.担子菌类和繁殖白腐真菌的xylariaceous子囊菌类是腐化热带森林生态系统中的硬木森林的主要生物,在温带针叶林中也占有举足轻重的地位（埃里克森等人,1990年；布兰切特,1991年；迪克斯和韦伯斯特,1995年）.针对大量类群中的上百个物种已经有相关研究.英国学者们对森林生态系统中的白腐真菌和其它相关生物做了广泛研究（雷纳和伯迪,1988年；伯迪,1992年；迪克斯和韦伯斯特,1995年）.一小部分有选择性腐化木材纤维素的担子菌构成了棕腐真菌.它们并不完全降解木质素,但却通过脱甲基反应改变木质素的结构.以往如果生物要进入植物细胞壁的多糖组织,必先使木质纤维素发生脱木素反应,因此在这点上,棕腐真菌是个特例.使棕腐真菌在降解木材中的纤维素和半纤维素时得以规避木质素的生化系统尚未得到研究.尽管这种真菌能否分泌纤维素和半纤维素,但酶的体积太大,无法进入木材的细胞壁基质,而且其它降解系统肯定也参与了反应过程.棕腐真菌对木材的腐烂作出了重要贡献,尤其是在降解温带针叶林的方面（迪克斯和韦伯斯特,1995年）.而被改变了结构的木质素成为了重要的腐殖质前体（哈德森,1986年）.应该对棕腐真菌进行更多的研究,但研究的困难非常大,因为一旦脱离本体,在实验环境中他们不会进行完整的降解过程.