Nitrogen loading levels affect abundance and composition of soil ammonia oxidizing prokaryotes in semiarid temperate grassland

Purpose  

Global nitrogen deposition has profound impact on the terrestrial ecosystem including the semiarid temperate grassland, causing vegetation community shifts and soil acidification. Little is known regarding the effect of nitrogen (N) deposition on the belowground microbial communities. This study aimed to examine the response of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to added N in semiarid temperate grassland.     

Effect of different fertilization treatments on indole-3-acetic acid producing bacteria in soil

Purpose  

Soil microorganisms directly affect the growth of plants. Especially, plant growth-promoting rhizobacteria (PGPR) play an important role in plant growth. There are many studies about the effects of different fertilization treatments on soil microbial community structure; however, the effects on PGPR, including indole-3-acetic acid (IAA)-producing bacteria have not been previously reported. The objective of this study is to determine the effects of different types of fertilizers on IAA-producing bacteria.     

Distributions and environmental drivers of archaea and bacteria in paddy soils

Purpose

The aim of this study is to investigate the abundance, diversity, and distribution of archaea and bacteria as affected by environment parameters in paddy soils, with focus on putative functional microbial groups related to redox processes. Because there is generally a high iron content in the soil, we also want to test a hypothesis that soil iron concentration significantly affects microbial diversity and distribution.

Materials and methods

Quantitative PCR and barcoded pyrosequencing of 16S ribosomal RNA genes were employed to investigate the abundance and community composition of archaeal and bacterial communities in 27 surface paddy soil samples. Pearson’s correlation, analysis of variance, partial least squares regression, principal coordinates analysis, and structural equation models were performed for the analyses of gene copy numbers, α-diversity, β-diversity, and relative abundances of archaea and bacteria and their relationships with environmental factors.

Results and discussion

Archaeal abundance was correlated greatest with temperature, but bacterial abundance was affected mainly by soil organic matter and total nitrogen content. Soil pH and concentrations of different ions were associated with archaeal and bacterial β-diversity. The relative abundances of Euryarchaeota and Thaumarchaeota were 61.3 and 13.1% of archaea and correlated with soil pH, which may affect the availability of substrates to methanogens and ammonia oxidizers. Dominant bacterial phyla were Proteobacteria (32.4%), Acidobacteria (17.8%), Bacteroidetes (9.3%), and Verrucomicrobia (6.0%). The relative abundances of putative bacterial reducers of nitrate, Fe(III), sulfate, and sulfur, and oxidizers of ammonia, nitrite, reduced sulfur, and C1 compounds had positive, negative, or non-significant correlations with the concentrations of their substrates. Soil iron concentration was correlated only with the distributions of some putative iron-reducing bacteria.

Conclusions

In paddy soils characterized by dynamic redox processes, archaea and bacteria differ in relationships of abundance, diversity, and distribution with environmental factors. Especially, the concentrations of electron donors or acceptors can explain the distributions of some but not all the putative functional microbial groups related to redox processes. Depending on pH range, soil pH has a strong impact on microbial ecology in paddy soils.