100
S. A. El.-M. M. Abd El-Azeem
In Egypt, 93% of the cultivated soils are affected by salinization and waterlogging [20]. The distribution of water within a soil profile and its content in the soil are
changed according to rainfall cycles during the season, soil temperature and irrigation periods. In summer particularly in arid and Mediterranean climates like Egypt
ecosystems, surface soils have frequently exposed to dry long period followed by a
relatively quick wetting. These conditions created two water stresses for microbial
activity, the reducing water potential in drying soils and suddenly increase water
potential after rewetting soils. Indeed, the moist and well-aerated soils are the optimum conditions for microbial activity, whereas the dry soils led to a decrease in the
degradation of soil organic matter and respiration rates [20]. Additionally, Drying
and rewetting soils may alter the microbial populations and compositions, indicating that some microbial species or groups are more vulnerable to the drying and
rewetting stress than others. On the other hand, flooded soils may also decrease the
decomposition rate of organic matter due to restricted aeration through decreasing the
oxygen diffusion in water [14]. As there is no information available on the responses
of Egyptian soil microorganisms to climate changes. In this chapter we will discuss
the impact of climate change on belowground microbial community structure and
function.
2 Soil Microbial and Enzyme Activities
Soil microbial activity plays an important role and the main source of the biochemical
activities in the agricultural soils. The execration of root exudates in the rhizosphere
lead to change the counts and community of soil microorganisms. Therefore, the
type of cultivated plant species will affect the activity of soil microorganisms due
to their different kinds of root exudates like low or high molecular weight organic
compounds [21]. Biochemical processes or reactions affect the transformation and
biogeochemical cycles of nutrients in soils. Soil microorganisms, plant roots, and
soil animals have been mediated by biochemical processes. The mineralization of
organic matter and nutrient cycles are conducted by a huge microbial community and
involves a wide range of biological processes [22]. These processes are catalyzed
by enzymes that produced by soil microorganism, plant and animal residues. Soil
enzymes activities are classified into exoenzymes released from the living cell (free
enzyme) and endoenzymes released from disintegrating cells, and enzymes bound to
cell constituents. Soil exoenzyme is adsorbed on organic and mineral components or
complexed with humic substances, or both and accumulated in soils [23]. The exoenzymes play a vital role in the degradation of organic macromolecules such as cellulose, hemicellulose and lignin, while endoenzymes mineralized smaller molecules
like sugar and amino acids [24]. Therefore, several studies on soil enzyme activities have been conducted depending on measuring the rates of enzyme-catalyzed
reactions in soil samples. The soil enzymes of β-glucosidase, ureases, phosphatases,
and arylsulfatase are representatively being considered to trace the cycles of C, N,
P and S in agricultural soils, respectively. The measured activity of the enzyme was
S. A. El.-M. M. Abd El-Azeem
In Egypt, 93% of the cultivated soils are affected by salinization and waterlogging [20]. The distribution of water within a soil profile and its content in the soil are
changed according to rainfall cycles during the season, soil temperature and irrigation periods. In summer particularly in arid and Mediterranean climates like Egypt
ecosystems, surface soils have frequently exposed to dry long period followed by a
relatively quick wetting. These conditions created two water stresses for microbial
activity, the reducing water potential in drying soils and suddenly increase water
potential after rewetting soils. Indeed, the moist and well-aerated soils are the optimum conditions for microbial activity, whereas the dry soils led to a decrease in the
degradation of soil organic matter and respiration rates [20]. Additionally, Drying
and rewetting soils may alter the microbial populations and compositions, indicating that some microbial species or groups are more vulnerable to the drying and
rewetting stress than others. On the other hand, flooded soils may also decrease the
decomposition rate of organic matter due to restricted aeration through decreasing the
oxygen diffusion in water [14]. As there is no information available on the responses
of Egyptian soil microorganisms to climate changes. In this chapter we will discuss
the impact of climate change on belowground microbial community structure and
function.
2 Soil Microbial and Enzyme Activities
Soil microbial activity plays an important role and the main source of the biochemical
activities in the agricultural soils. The execration of root exudates in the rhizosphere
lead to change the counts and community of soil microorganisms. Therefore, the
type of cultivated plant species will affect the activity of soil microorganisms due
to their different kinds of root exudates like low or high molecular weight organic
compounds [21]. Biochemical processes or reactions affect the transformation and
biogeochemical cycles of nutrients in soils. Soil microorganisms, plant roots, and
soil animals have been mediated by biochemical processes. The mineralization of
organic matter and nutrient cycles are conducted by a huge microbial community and
involves a wide range of biological processes [22]. These processes are catalyzed
by enzymes that produced by soil microorganism, plant and animal residues. Soil
enzymes activities are classified into exoenzymes released from the living cell (free
enzyme) and endoenzymes released from disintegrating cells, and enzymes bound to
cell constituents. Soil exoenzyme is adsorbed on organic and mineral components or
complexed with humic substances, or both and accumulated in soils [23]. The exoenzymes play a vital role in the degradation of organic macromolecules such as cellulose, hemicellulose and lignin, while endoenzymes mineralized smaller molecules
like sugar and amino acids [24]. Therefore, several studies on soil enzyme activities have been conducted depending on measuring the rates of enzyme-catalyzed
reactions in soil samples. The soil enzymes of β-glucosidase, ureases, phosphatases,
and arylsulfatase are representatively being considered to trace the cycles of C, N,
P and S in agricultural soils, respectively. The measured activity of the enzyme was