Effects of environmental variables on abundance of ammonia-oxidizing communities in sediments of Luotian River, China

Effects of simulated nitrogen deposition on microbial dynamics: Altered nitrogen fixation and ammonia oxidation in biological soil crusts

Nitrogen-limited drylands are highly sensitive to environmental changes, with biological soil crusts playing a key role in biological nitrogen fixation. Ammonia oxidation, the rate-limiting step in nitrification, is essential for nitrogen retention in soils. Despite sustained high global nitrogen deposition, the impacts of varying nitrogen addition levels on nitrogen fixation, ammonia oxidation by crusts, and nitrogen cycling remain poorly understood. Crusts were sampled in April and October from plots in the Gurbantunggut Desert, where nitrogen had been applied for 13 years, to assess nitrogen fixation, ammonia oxidation rates, and the functional microbial community structure. Results indicated nitrogen addition reduced nitrogen fixation, with the highest nitrogen addition (3.0 g N m2 yr-1) causing a ∼60 % decline, suggesting a microbial shift towards reliance on added nitrogen. In contrast, low nitrogen addition (0.5 g N m-2 yr-1) enhanced ammonia oxidation by 293 %, likely due to the alleviation of substrate limitations. However, higher nitrogen addition (N1.5, N3.0) led to a reduction in ammonia oxidation, with microorganisms such as Scytonema, Nitrososphaera, and Nitrosopumilus playing key roles in both processes. Notably, nitrogen fixation rates were generally lower during the dry season, while ammonia oxidation increased under N0 treatment. Nitrogen addition influenced the nitrogen fixation and ammonia oxidation capacities of the crusts, heightening the risk of nitrogen loss but diminishing the influence of prolonged drought. These findings underscore the need to consider nitrogen levels and seasonal dynamics when managing soil nitrogen processes to maintain the stability of dryland ecosystems and the nitrogen cycle, it is essential to reduce anthropogenic nitrogen deposition and mitigate the growing impacts of drought.

Structural and functional microbial diversity of sandy soil under cropland and grassland

Background

Land use change significantly alters soil organic carbon content and the microbial community. Therefore, in the present study, the effect of changing cropland to grassland on structural and functional soil microbial diversity was evaluated. The specific aims were (i) to identify the most prominent members of the fungal communities and their relevant ecological guild groups; (ii) to assess changes in the diversity of ammonia-oxidizing archaea; (iii) to determine the relationships between microbial diversity and selected physical and chemical properties.

Methods

We investigated microbial diversity and activity indicators, bulk density and the water-holding capacity of sandy soil under both cropland and 25-year-old grassland (formerly cropland) in Trzebieszów, in the Podlasie Region, Poland. Microbial diversity was assessed by: the relative abundance of ammonia-oxidizing archaea, fungal community composition and functional diversity. Microbial activity was assessed by soil enzyme (dehydrogenase, β-glucosidase) and respiration tests.

Results

It was shown that compared to cropland, grassland has a higher soil organic carbon content, microbial biomass, basal respiration, rate of enzyme activity, richness and diversity of the microbial community, water holding capacity and the structure of the fungal and ammonia-oxidizing archaea communities was also altered. The implications of these results for soil quality and soil health are also discussed. The results suggest that grassland can have a significant phytosanitary capacity with regard to ecosystem services, due to the prominent presence of beneficial and antagonistic microbes. Moreover, the results also suggest that grassland use may improve the status of soil organic carbon and nitrogen dynamics, thereby increasing the relative abundance of fungi and ammonia-oxidizing archaea.