Impacts of Climate Change on Microbial Activity in Agricultural …
107
fungi was observed in soil amended with sugar cane straw at 60% water content, but
the lowest was in soil mixed with broad bean straw at 100% water content.
There are several mechanisms or physical processes affecting soil microbial activity that vary with moisture content. Drought is one of the major constraints on
agricultural productivity Egyptian and worldwide and the most common environmental stress that soil microbes experience. The drought had negatively or positively
effect on mycorrhizae development and their root colonization. In general, drought
reduced the colonization by mycorrhizae. However, this kind of response is varied
based on the type of strain as reported by Davies Jr. et al. [65], who demonstrated that
drought enhanced the formation of arbuscular and hyphal development of Glomus
sp. Strain ZAC-19, while reducing the root colonization by Glomus fasciculatum. On
the contrary, the results from some studies obtained specific adaptations of certain
mycorrhizae strains to drought conditions [66]. On the other hand, drought has an
adverse effect on soil enzyme activities, which direct influence on the potential of
photosynthetic production or indirectly effect on water use efficiency and nutrient
availability in Mediterranean regions. For example, Sardans and Peñuelas [16] stated
that the activity of soil enzymes like urease, protease, β-glucosidase and acid phosphatase was decreased under drought conditions, but the activity of alkaline phosphatase not significantly affect. Moreover, Elwan and Mahmoud [67] investigated
the response of the bacterial population to the edaphic drought of the Egyptian desert
in summer. They found that spore-forming bacteria such as Bacillus subtilis, Bacillus
licheniformis and Bacillus megaterium have predominated in the soil and can survive drought conditions. Water stress was also affecting nitrification activity through
decreased the substrate availability and triggering of physiological changes (downregulation of basic metabolism and upregulation of stress-related gene expression)
to tolerate the induced osmotic changes. However, little information occurs about the
differences between ammonia oxidizing bacteria (AOB) and archaea (AOA) during
the initial stage of moisture stress. In this regard, Vasileiadis et al. [68] suggested that
the reduction of soil moisture content from 87 to 50% of the water holding capacity
leads a ~99% reduction of AOB but not of AOA amoA transcripts that did not change
significantly.
3.4 Impact of Soil Salinity
Soil salinity is one on the main environmental factors responsible for the decreasing
productivity of a wide variety of crops in an arid and semi-arid area of the world that
would challenge with their food production in the 21st century with climate change
[69]. Unfortunately, saline, saline-sodic, and sodic soils have a strong presence in
the Nile delta soils and represent an average of 37% of the total Egyptian cultivated
soils.
Numerous studies indicated that saline stress in agricultural soils due to the
irrigation practices and the application of chemical fertilizers. Therefore, several
researches have been conducted to evaluate the detrimental effect of salinity on the
107
fungi was observed in soil amended with sugar cane straw at 60% water content, but
the lowest was in soil mixed with broad bean straw at 100% water content.
There are several mechanisms or physical processes affecting soil microbial activity that vary with moisture content. Drought is one of the major constraints on
agricultural productivity Egyptian and worldwide and the most common environmental stress that soil microbes experience. The drought had negatively or positively
effect on mycorrhizae development and their root colonization. In general, drought
reduced the colonization by mycorrhizae. However, this kind of response is varied
based on the type of strain as reported by Davies Jr. et al. [65], who demonstrated that
drought enhanced the formation of arbuscular and hyphal development of Glomus
sp. Strain ZAC-19, while reducing the root colonization by Glomus fasciculatum. On
the contrary, the results from some studies obtained specific adaptations of certain
mycorrhizae strains to drought conditions [66]. On the other hand, drought has an
adverse effect on soil enzyme activities, which direct influence on the potential of
photosynthetic production or indirectly effect on water use efficiency and nutrient
availability in Mediterranean regions. For example, Sardans and Peñuelas [16] stated
that the activity of soil enzymes like urease, protease, β-glucosidase and acid phosphatase was decreased under drought conditions, but the activity of alkaline phosphatase not significantly affect. Moreover, Elwan and Mahmoud [67] investigated
the response of the bacterial population to the edaphic drought of the Egyptian desert
in summer. They found that spore-forming bacteria such as Bacillus subtilis, Bacillus
licheniformis and Bacillus megaterium have predominated in the soil and can survive drought conditions. Water stress was also affecting nitrification activity through
decreased the substrate availability and triggering of physiological changes (downregulation of basic metabolism and upregulation of stress-related gene expression)
to tolerate the induced osmotic changes. However, little information occurs about the
differences between ammonia oxidizing bacteria (AOB) and archaea (AOA) during
the initial stage of moisture stress. In this regard, Vasileiadis et al. [68] suggested that
the reduction of soil moisture content from 87 to 50% of the water holding capacity
leads a ~99% reduction of AOB but not of AOA amoA transcripts that did not change
significantly.
3.4 Impact of Soil Salinity
Soil salinity is one on the main environmental factors responsible for the decreasing
productivity of a wide variety of crops in an arid and semi-arid area of the world that
would challenge with their food production in the 21st century with climate change
[69]. Unfortunately, saline, saline-sodic, and sodic soils have a strong presence in
the Nile delta soils and represent an average of 37% of the total Egyptian cultivated
soils.
Numerous studies indicated that saline stress in agricultural soils due to the
irrigation practices and the application of chemical fertilizers. Therefore, several
researches have been conducted to evaluate the detrimental effect of salinity on the