The addition of discrimination inhibitors stimulations discrimination potential and N2O emissions were linked to predation among microorganisms in long term nitrogen application and straw returning systems

Introduction

Ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) have been proven to be key microorganisms driving the ammonia oxidation process. However, under different fertilization practices, there is a lack of research on the impact of interaction between predators and AOA or AOB on nitrogen cycling at the multi-trophic level.

Methods

In this study, a network-oriented microscopic culture experiment was established based on four different long-term fertilization practices soils. We used the nitrification inhibitors 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxide-3-oxyl (PTIO) and 3, 4-Dimethylpyrazole phosphate (DMPP) inhibited AOA and AOB, respectively, to explore the impact of interaction between protists and AOA or AOB on nitrogen transformation.

Results

The results showed that long-term nitrogen application promoted the potential nitrification rate (PNR) and nitrous oxide (N2O) emission, and significantly increased the gene abundance of AOB, but had no obvious effect on AOA gene abundance. DMPP significantly reduced N2O emission and PNR, while PTIO had no obvious effect on them. Accordingly, in the multi-trophic microbial network, Cercozoa and Proteobacteria were identified as keystone taxa of protists and AOB, respectively, and were significantly positively correlated with N2O, PNR and nitrate nitrogen. However, Nitrososphaerota archaeon as the keystone species of AOA, had an obvious negative linkage to these indicators. The structural equation model (SEM) showed that AOA and AOB may be competitors to each other. Protists may promote AOB diversity through direct trophic interaction with AOA.

Conclusion

The interaction pattern between protists and ammonia-oxidizing microorganisms significantly affects potential nitrification rate and N2O emission, which has important implications for soil nitrogen cycle.

Effect of Long-Term Fertilization on Ammonia-Oxidizing Microorganisms and Nitrification in Brown Soil of Northeast China

The objective of this study was to find out changes in ammonia oxidation microorganisms with respect to fertilizer as investigated by real-time polymerase chain reaction and high-throughput sequencing. The treatments included control (CK); chemical fertilizer nitrogen low (N) and high (N₂); nitrogen and phosphorus (NP); nitrogen phosphorus and potassium (NPK) and organic manure fertilizer (M); MN; MN₂; MNPK. The results showed that long-term fertilization influenced soil fertility and affected the abundance and community of ammonia-oxidizing microorganisms by changing the physical and chemical properties of the soil. The abundance and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) was influenced by soil organic carbon, total nitrogen, total soil phosphorus, available phosphorus, available potassium, and soil nitrate. Soil environmental factors affected the nitrification potential by affecting the structure of ammonia-oxidizing microorganisms; specific and rare AOA and AOB rather than the whole AOA or AOB community played dominant role in nitrification.

[Influence Factors of Potential Nitrification Rates and Functional Genes Abundance in the Jinshui River and the Qihe River of the Hanjiang River Basin]

In the context of increasing nitrogen loading in river systems worldwide, it is critically important to understand nitrification to maintain river ecosystem health. This comparative study was conducted to explore the relationships among the intensity of human disturbance, environmental factors, potential nitrification rate, and functional gene abundance in the Jinshui River (slightly disturbed basin) and the Qihe River (intensely disturbed basin). The results showed that AOA-amoA gene abundance was higher than that of AOB-amoA. The potential nitrification rate in the Qihe River was higher than that in the Jinshui River. There was no significant difference in AOA-amoA gene abundance between the two rivers; however, the AOB-amoA gene abundance in the Qihe River was significantly higher than that in the Jinshui River in the low flow season. The abundance of nitrification functional genes was significantly correlated with water temperature, pH, NO₃^-, NH₄⁺, and organic carbon. The potential nitrification rate was positively correlated with water temperature, pH, and NO₃^-, and negatively correlated with AOB-amoA gene abundance. These results showed that the intensely disturbed sites had higher potential nitrification rates and nitrification functional genes abundances, and potential nitrification rates and abundances of nitrification function genes were significantly related to physical and chemical water and sediment factors. This study will be important for nitrogen pollution control in the river systems.

[Distribution and Potential Nitrification Rates of Aerobic Ammonia-Oxidizing Microorganisms in Surface Sediments of Mangrove in Sanya River]

The ammonia oxidation process is a rate-limiting step in nitrification. Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are the major drivers of ammonia oxidation. Their distribution and relative contributions to nitrification are the research highlights in the nitrogen cycle. Real-time quantitative polymerase chain reaction (qPCR) was used to study the distribution of aerobic ammonia-oxidizing microorganisms in the surface sediments of mangrove in the Sanya River, and the relative contribution rates of AOB and AOA to nitrification were calculated through the determination of the potential nitrification rates (PNR). The results showed that, in most sampling sites, the abundance of AOA amoA genes was higher than that of AOB amoA genes. The abundance of AOB was higher during the winter, whereas that of AOA was higher during the summer, and the ratio of AOA to AOB abundance was lower during the winter. The dissolved oxygen (DO) content, pH, total organic carbon (TOC) content, and nitrate concentration greatly influenced the abundance of AOB and AOA. The potential nitrification rates of AOB and AOA were both higher during the summer than during the winter, and the relative contribution rate of AOA to nitrification was higher during the winter, whereas that of AOB was higher during the summer. There were no significant correlations between the PNR and amoA genes abundance of AOB and AOA.

Response of Nitrifier and Denitrifier Abundance and Microbial Community Structure to Experimental Warming in an Agricultural Ecosystem

Soil microbial community plays an important role in terrestrial carbon and nitrogen cycling. However, the response of the soil nitrifier and denitrifier communities to climate warming is poorly understood. A long-term field warming experiment has been conducted for 8 years at Luancheng Experimental Farm Station on the North China Plain; we used this field to examine how soil microbial community structure, nitrifier, and denitrifier abundance respond to warming under regular irrigation (RI) and high irrigation (HI) at different soil depths (0-5, 5-10, and 10-20 cm). Nitrifier, denitrifier, and the total bacterial abundance were assessed by quantitative polymerase chain reaction of the functional genes and 16S rRNA gene, respectively. Bacterial community structure was studied through high throughput sequencing of the 16S rRNA gene. Under RI, warming significantly (P < 0.05) increased the potential nitrification rate and nitrate concentration and decreased the soil moisture. In most of the samples, warming increased the ammonia-oxidizing bacteria abundance but decreased the ammonia-oxidizing archaea (AOA) and denitrifier (nirK, nirS, and nosZ genes) abundance. Under HI, there was a highly increased AOA and 16S rRNA gene abundance and a slightly higher denitrifier abundance compared with RI. Warming decreased the bacterial diversity and species richness, and the microbial community structure differed greatly between the warmed and control plots. The decrease in bacterial diversity was higher in RI than HI and at the 0-5 cm depths than at the 5-10 and 10-20 cm soil depths. Warming led to an increase in the relative abundance of Actinobacteria, Bacteroidetes, and TM7 but a decrease in Acidobacteria, Alphaproteobacteria, Deltaproteobacteria, Nitrospira, and Planctomycetes. The greater shift in microbial community structure was observed only in RI at the 0-5 cm soil depth. This study provides new insight into our understanding of the nitrifier and denitrifier activity and microbial community response to climate warming in agricultural ecosystems.

Ammonia-Oxidizing Archaea Show More Distinct Biogeographic Distribution Patterns than Ammonia-Oxidizing Bacteria across the Black Soil Zone of Northeast China

Black soils (Mollisols) of northeast China are highly productive and agriculturally important for food production. Ammonia-oxidizing microbes play an important role in N cycling in the black soils. However, the information related to the composition and distribution of ammonia-oxidizing microbes in the black soils has not yet been addressed. In this study, we used the amoA gene to quantify the abundance and community composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) across the black soil zone. The amoA abundance of AOA was remarkably larger than that of AOB, with ratios of AOA/AOB in the range from 3.1 to 91.0 across all soil samples. The abundance of AOA amoA was positively correlated with total soil C content (p < 0.001) but not with soil pH (p > 0.05). In contrast, the abundance of AOB amoA positively correlated with soil pH (p = 0.009) but not with total soil C. Alpha diversity of AOA did not correlate with any soil parameter, however, alpha diversity of AOB was affected by multiple soil factors, such as soil pH, total P, N, and C, available K content, and soil water content. Canonical correspondence analysis indicated that the AOA community was mainly affected by the sampling latitude, followed by soil pH, total P and C; while the AOB community was mainly determined by soil pH, as well as total P, C and N, water content, and sampling latitude, which highlighted that the AOA community was more geographically distributed in the black soil zone of northeast China than AOB community. In addition, the pairwise analyses showed that the potential nitrification rate (PNR) was not correlated with alpha diversity but weakly positively with the abundance of the AOA community (p = 0.048), whereas PNR significantly correlated positively with the richness (p = 0.003), diversity (p = 0.001) and abundance (p < 0.001) of the AOB community, which suggested that AOB community might make a greater contribution to nitrification than AOA community in the black soils when ammonium is readily available.