plant surface microbiology.pdf

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Ramesh Chander Kuhad et al.
cellular lignocellulolytic enzyme activity in the assessment of soil quality is
established by the essential role of soil microbes in nutrient cycling within
agricultural ecosystems (Christensen and Johnston 1997). During the microbial
degradation and humification of plant residues, about 80 % of the residual
carbon is released to the atmosphere as CO 2 (Omar 1994). The amendment
of infertile or saline soils with plant residues and their subsequent
degradation by cellulolytic soil microflora with a concomitant increase in CO 2
could increase soil aeration, improve its structure and also increase soil fertility.
The activities of cellulolytic microbes affect the availability of energy and
specific nutrients to a group of organisms deficient in hydrolytic enzyme
activities (Jensen and Nybroe 1999).
Soils managed with organic inputs generally have larger and more active
microbial populations than those managed with mineral fertilizers (Badr El-
Din et al. 2000). Reincorporation of organic matter into the soil improves soil
fertility, enhances microbial growth and buffers the soil environment from
sudden changes. There are many types of agroindustrial organic refuse which
can be transformed and applied to soil as crop amendments, such as compost,
thus reducing the need for chemical fertilizers. During the composting
process, the organic substrate present in the agricultural wastes is mainly
transformed oxidatively into a stabilized organic matter. The slow transformation
of lignocellulosic material results in the formation of humic substances.
Several researchers have established a positive correlation between
the amount of humic substances and promotion of plant growth. Application
of different combinations of coir with peat and vermiculate significantly
increased the growth of tomato transplants with respect to root dry weight,
stem diameter and leaf area (Arenas et al. 2002).
Straw incorporation could also be beneficial in enhancing symbiotic nitrogen
fixation and crop growth (Abd-Alla and Omar 1998). In nonsymbiotic
nitrogen fixation studies in the laboratory and in the field, a significant
increase in nitrogenase activity associated with the breakdown of straw after
inoculation with various combinations of cellulolytic fungi and bacteria has
been reported (Halsall and Gibson 1991; Chapman et al. 1992). Application of
wheat straw with cellulolytic fungi, Trichoderma harzianum significantly
enhanced growth, nodulation, nodule efficiency and increased the concentration
of Ca, Mg and K in the shoots and roots of fenugreek plants grown in
saline soil (Abd-Alla and Omar 1998). The increase in dry matter production
and nitrogen content was due to improved N 2 fixation reflected by enhanced
formation and growth of nodules as well as nitrogenase activity.
Inoculation of straw with lignocellulolytic organisms offers potential for
manipulating and improving the composting of cellulosic waste (Verstraete
and Top 1999; Hart et al. 2002). Composts produced using this method provide
a more sustainable approach to agriculture, enabling subsistence farmers
to utilize their agricultural waste products as a means to improve soil quality.
Saprophytic lignin-decomposing basidiomycetes isolated from plant litter