Transition of Ethiopian highland forests to agriculture-dominated landscapes shifts the soil microbial community composition

Background

Land use changes and related land management practices significantly alter soil physicochemical properties; however, their effects on the soil microbial community structure are still unclear. In this study, we used automated ribosomal intergenic spacer analysis to determine the fungal and bacterial community composition in soils from different land use areas in the Ethiopian highlands. Soil samples were collected from five areas with different land uses, natural forest, eucalyptus plantation, exclosure, grassland and cropland, which had all historically been natural forest.

Results

Our results showed a significant shift in the soil bacterial and fungal community composition in response to land use change. We also identified soil physicochemical factors corresponding to the changes in bacterial and fungal communities. Although most soil attributes, including soil organic carbon, total soil nitrogen, labile P, soil pH and soil aggregate stability, were related to the change in bacterial community composition, the total soil nitrogen and soil organic carbon had the strongest relationships. The change in fungal community composition was correlated with soil nutrients, organic carbon, soil nitrogen and particularly the labile P concentration.

Conclusions

The fungal community composition was likely affected by the alteration of vegetation cover in response to land use change, whereas the bacterial communities were mainly sensitive to changes in soil attributes. The study highlights the higher sensitivity of fungal communities than bacterial communities to land use changes.

Electronic supplementary material

The online version of this article (10.1186/s12898-018-0214-8) contains supplementary material, which is available to authorized users.

Performance of cowpea as influenced by native strain of rhizobia, lime and phosphorus in Samaru, Nigeria

The complimentary effects of a native rhizobia strain (SAMFIX 286), lime and single superphosphate (SSP) as components of ISFM were evaluated on the biomass, nodulation and N₂ fixation of cowpea (Vigna unguiculata L.). Lime was applied at the rate of 250 kg (Ca(OH)₂) ha^-1, while SSP was applied at 30 kg P ha^-1. The trial was carried out in a screen house with the treatments arranged in randomized complete block design. Results obtained show that the performance of SAMFIX 286 inoculated plants did not significantly (p < 0.05) differ from that of the un-inoculated treatment. Application of lime significantly increased root dry weight, shoot dry weight, nodule number and dry weight by 42.5%, 35.3%, 65.6% and 50%, respectively. Nodulation was significantly (p < 0.05) increased by SSP. The complimentary effect of lime with SSP significantly increased total shoot N concentration. Similarly, combined inoculation of SAMFIX 286 with lime and SSP increased N concentration by 31.9% and N derived from atmosphere (Ndfa) by 16.3% compared to the un-inoculated treatment. Inoculation of SAMFIX 286 with SSP was also effective on Ndfa by cowpea. It was concluded that lime and SSP were good combination with native rhizobia strain in improving cowpea nodulation and biological N₂ fixation.

Aberrant Meiotic Modulation Partially Contributes to the Lower Germination Rate of Pollen Grains in Maize (Zea mays L.) Under Low Nitrogen Supply

Pollen germination is an essential step towards successful pollination during maize reproduction. How low niutrogen (N) affects pollen germination remains an interesting biological question to be addressed. We found that only low N resulted in a significantly lower germination rate of pollen grains after 4 weeks of low N, phosphorus or potassium treatment in maize production. Importantly, cytological analysis showed 7-fold more micronuclei in male meiocytes under the low N treatment than in the control, indicating that the lower germination rate of pollen grains was partially due to numerous chromosome loss events resulting from preceding meiosis. The appearance of 10 bivalents in the control and low N cells at diakinesis suggested that chromosome pairing and recombination in meiosis I was not affected by low N. Further gene expression analysis revealed dramatic down-regulation of Nuclear Division Cycle 80 (Ndc80) and Regulator of Chromosome Condensation 1 (Rcc1-1) expression and up-regulation of Cell Division Cycle 20 (Cdc20-1) expression, although no significant difference in the expression level of kinetochore foundation proteins Centromeric Histone H3 (Cenh3) and Centromere Protein C (Cenpc) and cohesion regulators Recombination 8 (Rec8) and Shugoshin (Sgo1) was observed. Aberrant modulation of three key meiotic regulators presumably resulted in a high likelihood of erroneous chromosome segregation, as testified by pronounced lagging chromosomes at anaphase I or cell cycle disruption at meiosis II. Thus, we proposed a cytogenetic mechanism whereby low N affects male meiosis and causes a higher chromosome loss frequency and eventually a lower germination rate of pollen grains in a staple crop plant.

Phylogenetical coherence of Pseudomonas in unexplored soils of Himalayan region

Pseudomonas, an enormously diverse genus of the γ-Proteobacteria, is an important member of soil microbial communities. In this study, genetic heterogeneity and plant growth promotory property of Pseudomonas was compared within the group Pseudomonas sensu stricto isolated from the lesser explored niches of Himalayan region. A significant difference (P < 0.001 in total Pseudomonas count) was observed among the six types of soil samples collected from oak forest, fine forest, and agricultural soil. The highest numbers of bacteria were isolated from oak forest soil followed by pine forest soil and agricultural soil. 23.52 % of the total 238 isolates were siderophore producers and were identified as Pseudomonas on the basis of PCR amplification using 16S rDNA Pseudomonas specific primer. The molecular analysis by Jaccard's similarity coefficient resulted into eight different clusters and six outlying branches. Some of the clusters include Pseudomonas from forest as well as agricultural land. Among the 51 isolates 100 % were siderophore and IAA producers, 68.62 % were phosphate solubilizers and 62.74 % HCN producers. The results reveal that isolates from lesser explored area possess beneficial properties and show genetic heterogeneity among them.