Abstract
Loss of beneficial microbes and lack of native inoculum have hindered reforestation efforts in the severely-degraded lands worldwide. This is a particularly pressing problem for Ethiopia owing to centuries-old unsustainable agricultural practices. This study aimed to evaluate the inoculum potential of soils from church forest in the northwest highlands of Ethiopia and its effect on seedling growth of two selected native tree species (Olea europaea and Albizia gummifera) under a glasshouse environment. Seedlings germinated in a seed chamber were transplanted into pots containing sterilized and/or non-sterilized soils collected from under the canopy of three dominant church forest trees: Albizia gummifera (AG), Croton macrostachyus (CM), and Juniperus procera (JP) as well as from adjacent degraded land (DL). A total of 128 pots (2 plant species × 4 soil origins × 2 soil treatments × 8 replicates) were arranged in a factorial design. Overall, seedlings grown in AG, CM, and JP soils showed a higher plant performance and survival rate, as a result of higher soil microbial abundance and diversity, than those grown in DL soils. The results showed significantly higher plant height, root collar diameter, shoot, and total mass for seedlings grown in non-sterilized forest soils than those grown in sterilized soils. Furthermore, the bacterial relative abundance of Acidobacteria, Actinobacteria, and Nitrospirae was significantly higher in the non-sterilized forest soils AG, CM, and JP (r2 = 0.6–0.8, p < 0.001). Soil pH had a strong effect on abundance of the bacterial community in the church forest soils. More specifically, this study further demonstrated that the effect of soil microbiome was noticeable on the performance of Olea seedlings grown in the soil from CM. This suggests that the soils from remnant church forests, particularly from the canopy under CM, can serve as a good soil origin, which possibly would promote the native tree seedling growth and survival in degraded lands.
Highlights
Land degradation is a major global problem affecting all terrestrial biomes in arid and humid regions [1,2]
The relative abundance of Proteobacteria was higher in sterilized soils (47% and 53%, respectively) than in non-sterilized ones (28% and 29%, respectively); in contrast, the relative abundance of Actinobacteria was higher in non-sterilized soils (Figure 3b,c)
In non-sterilized soils, the abundance of Acidobacteria was higher in degraded land (DL), Croton macrostachyus (CM), and Juniperus procera (JP) for Olea seedlings (Figure 3b) and in all soil origins for Albizia seedlings (Figure 3c)
Summary
Land degradation is a major global problem affecting all terrestrial biomes in arid and humid regions [1,2]. Symbiotic relationships between the roots of higher plants and microbes (fungi and bacteria) strongly influence plant survival, growth, and ecosystem properties [11] These beneficial microbes can enhance soil nutrient supply, drought tolerance, and pathogen resistance [12] of the host plant. The interaction of soil microbes with plant roots and organic matter can improve soil aeration and resistance to slaking and erosion by enhancing soil aggregation and structural stability; the microorganisms influence soil aggregation via chemical stabilization, and the organic matter contributes a cementing effect [13] These functional roles of soil microbes are limited in degraded ecosystems because of a low level of microbial diversity, poor vegetation cover, high soil disturbance, and severe erosion rates [10,14,15]. In the case of the Ethiopian highlands, very little information exists about the source of native inoculum for the successful restoration of lost microbial community functions in degraded landscapes
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