Genetic and Physiological Diversities of Bacteria from the Rhizosphere of Woody Plants Grown on Soil from Girar Jarso District and their Effect on the Growth and Establishment of Tree Seedlings in North Shewa Zone Ethiopia

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Addis Ababa University


Land degradation (LD) is one of the major problems the planet earth has been facing. It has severely affected 1.9 billion hectares and decreased ecosystem services by 60%. In Eastern Africa, particularly in the northern highlands of Ethiopia, 1 billion tons of topsoil are lost annually. Thus, the land becomes bare, nutrient-depleted, water-stressed and abandoned by the community. Hence, it needs urgent rehabilitation with the application of eco-friendly microbes and organic amendments (OAs) through the exploitation of different types of trees/shrubs. Therefore, the overall objective of the study was to rehabilitate degraded habitat through the application of OAs and phytobeneficial bacteria for the establishment of multipurpose trees. Soil samples were collected from nine random corners at depth of 30 cm for soil physicochemical analysis before and after OAs. Six different treatments (biochar, compost, manure, mixed, bacterial inoculation (BI), and control) were considered at a 1:1 ratio of OAs per pot. Application BI was done for field trials during transplanting and quarterly for a year. Six plots measuring 41 m x 4 m were established in completely randomized block design and assigned at the random block for the field trial. Following OAs, microbial counts were done for one year every month. Bacteria were isolated from the rhizosphere of Acacia and Juniperus. The primary selection of isolates was based on drought stress (DS) tolerance and phosphate solubilization, other stress, and plant growth-promoting traits. The potential isolates were subjected to carbohydrate and amino acid utilization tests, BOX PCR, and 16S rRNA profiling. DS tolerant, phosphate solubilizer strains with multiple plant growth-promoting traits were chosen for Acacia seeds germination and field application alone and in combination with OAs. Plant growth parameters and their survival rate at each amended plot were assessed. There is a significant increase in soil pH (5.69-8.13), CEC (43.78-49.98 cmolc/kg), OM (2.43-3.91%), total nitrogen (0.13-0.76%), and available P (18.9-26.31 ppm) following OAs compared the control. Combined treatment had the largest effect on cover crops biomass with 3.43 g, 4.54 g, 0.7 g, 2.07g in alfalfa, grass pea, and control respectively p ≤ 0.05. The C and N utilization revealed metabolic versatility of the strains (14.29 to 100%). Ochrobactrum, Pseudomonas, and Klebsiella spp expressed remarkable metabolic versatilities. BOX-PCR showed greater genetic diversity and confirmed by Simpson’s Index of Diversity (0.883) took the leading position with Bacillus species. The 16S rRNA genes sequence showed 21.92% Firmicutes and 78.08% Proteobacteria with Pseudomonas 23% and Ochrobactrum 21% dominant species. Out of 73 isolates, 10 (14%) were highly tolerant of 40% polyethylene glycol. All the isolates can grow in wider ranges of pH (5-9), temperature (15-45°C). The inoculated bacterial strains significantly p ≤ 0.05 increased root, shoot length, and dry biomass of acacia. According to solubilization index (SI) 45% isolates were classified as high and medium phosphate solubilizers with 195 to 373 μg/mL. The maximum P and IAA were produced by Pseudomonas FB-49 (373 and 659.07μg/mL), respectively. The highest (100%) seed germination caused by Pseudomonas BS-26 and Pseudomonas FB-49. There is a significant difference in microbial counts following OAs compared to the control. The greatest counts in bacteria, actinomycetes, and fungal (21.66, 2.29, 0.82 x 105 CFU g-1) of soil, respectively in the combined amended plot. There was a significant increase in stem height, girths, and branch numbers in amended plots relative to the control. The survival rate was observed in apple (80%) followed by acacia (66%) and prunus (51%). The survival is in the order of BI x OAs > BI > biochar > compost > manure > control amended soil. This study concluded that degraded land could be rehabilitated with cheap OAs, potential bacterial strains, and bring multipurpose tree establishment with greater survival rate and best performance.



Acacia, Ds, Ethiopia, Multipurpose Trees, Oas, Plant Growth Promoting Rhizobacteria, Rehabilitation, Survival Rate, Tree Establishments