الفهرس 
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Abstract
Salt-resistant or salt-tolerant plants belong to the group of halophytes which can grow in unusual extreme environments, e.g.: salt marshes, estuaries, cliffs, dunes or deserts. The unique properties of these plants enable them for many industrial and ecological applications. Another important feature of halophytes is their ability to accumulate wind- and water-borne sediments within and/or around their canopies and building phytogenic mounds (Nebkhas). Thus, it is important to study the environmental conditions and the bacteria associated with halophytes.
In the current study, the spatial and temporal variations in bacterial abundance and diversity were examined from soil samples of the two halophytes Arthrocnemum macrostachyum and Halocnemum strobilaceum communities in salt marshes of Lake Manzala. This was achieved by collecting soil samples at two depths (0-10 cm and 10-20 cm) and the estimation of the following characteristics seasonally and spatially (in nebkhas and surrounding unvegetated sites):
1- Soil physical and chemical properties.
2- Bacterial abundance by epifluorescent microscope.
3- Soil enzyme activities (amylase and CMCase).
4- Isolation and identification of halophilic bacteria.
In addition, rhizoplane sites were taken in consideration for the estimation of enzyme activities, bacterial abundance, isolation and identification of halophilic bacteria.
Results, for both species, showed that soil salinity reached its maximal values in autumn at 10 cm depth in nebkha sites while minimal values were in spring. Ion concentrations were in accordance with soil salinity except Mg++.
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Nebkhas attained higher means of organic matter contents at both depths compared to their counterparts of unvegetated sites. Soil total nitrogen exhibit the same trend of soil organic matter with the higher values in nebkhas of H. strobilaceum. No clear difference of soil total P concentrations among different microhabitats of both plants. In both species, the concentrations of the divalent ions (Ca and Mg) and monovalent ions (Na and K) were higher in shoot than their counterparts in root. In A. macrostachyum, the concentrations of total phosphorus and nitrogen were higher in roots than in shoots, while vice versa in H. strobilaceum.
For tested soil enzymes of amylase and CMCase, activities varied and cannot be predictable at any tested time. The 10 cm depth owned the highest values with the maximum activity observed for H. strobilaceum samples. For amylase enzyme of both species’ samples, amylase reached its higher activity at the rhizoplane.
Total bacterial counts at the nebkha site of both species were higher when compared with the unvegateted site and also at 10 cm depth than 20 cm depth. Generally, total bacterial counts in the nebkha of H. strobilaceum were higher than in case of A. macrostachyum. Total bacterial counts of H. strobilaceum were more related to total-N concentrations than total P and organic matter. Also results showed that the moisture content had no significant effect on total bacterial counts.
Viable halophilic bacterial counts (slight, moderate, extreme) of both species were more confined to 10 cm depth than 20 cm depth. The closer proximity to the plants, the higher counts were found. The results showed that bacterial counts increased in winter then gradually decreased in the other
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seasons for the samples of the two species. The slightly and moderately halophilic bacteria were more abundant than the extremely halophilic bacteria.
A total of 144 isolates were identified, with 70 and 74 from sites surrounding A. macrostachyum and H. strobilaceum, respectively. The microhabitats of A. macrostachyum were represented by 9 genera namely Bacillus spp., Halobacillus spp., Arthrobacter spp., Cellulomonas spp., Microbacterium spp., Listeria spp., Exiguobacterium spp., Halomonas spp., Methylophaga spp. 12 genera obtained from different microhabitats of H. strobilaceum were Bacillus spp., Lactobacillus spp., Arthrobacter spp., Cellulomonas spp., Microbacterium spp., Listeria spp., Exiguobacterium spp., Planomicrobium spp., Corynebacterium spp., Trichococcus spp., Halolactibacillus spp., Salinivibrio spp. Results demonstrated that Bacillus spp. and then Arthrobacter spp. were the dominant genera that were found at all sites in all seasons.
It can be concluded that the formation of nebkhas by halophytic vegetation can have noticeable effects on soil physio-chemical properties and bacterial composition and diversity; but with limited effects on enzyme activities. Furthermore, these effects are dependent on the identity of two species that forming the nebkha as shown by the differences between A. macrostachyum and H. strobilaceum that growing in the same site. The study suggests the importance of focusing more microbiological investigation in harsh and stressful environments to utilize their halophilic properties in reclamation of salt-affected lands and industrial applications.