Arbuscular mycorrhizal fungal community response to warming and nitrogen addition in a semiarid steppe ecosystem.

Understanding the response of arbuscular mycorrhizal (AM) fungi to warming and nitrogen (N) fertilization is critical to assess the impact of anthropogenic disturbance on ecosystem functioning under global climate change scenarios. In this study, AM fungal communities were examined in a full factorial design with warming and N addition in a semiarid steppe in northern China. Warming significantly increased AM fungal spore density, regardless of N addition, whilst N addition significantly decreased AM fungal extraradical hyphal density, regardless of warming. A total of 79 operational taxonomic units (OTUs) of AM fungi were recovered by 454 pyrosequencing of SSU rDNA. Warming, but not N addition, had a significant positive effect on AM fungal OTU richness, while warming and N addition significantly increased AM fungal Shannon diversity index. N addition, but not warming, significantly altered the AM fungal community composition. Furthermore, the changes in AM fungal community composition were associated with shifts in plant community composition indirectly caused by N addition. These findings highlight the different effects of warming and N addition on AM fungal communities and contribute to understanding AM fungal community responses to global environmental change scenarios in semiarid steppe ecosystems.

Interactive effects of multiple climate change factors on ammonia oxidizers and denitrifiers in a temperate steppe.

Global climate change could have profound effects on belowground microbial communities and subsequently affect soil biogeochemical processes. The interactive effects of multiple co-occurring climate change factors on microbially mediated processes are not well understood. A four-factorial field experiment with elevated CO2, watering, nitrogen (N) addition and night warming was conducted in a temperate steppe of northern China. Real-time polymerase chain reaction and terminal-restriction fragment length polymorphism, combined with clone library techniques, were applied to examine the effects of those climate change factors on N-related microbial abundance and community composition. Only the abundance of ammonia-oxidizing bacteria significantly increased by nitrogen addition and decreased by watering. The interactions of watering × warming on the bacterial amoA community and warming × nitrogen addition on the nosZ community were found. Redundancy analysis indicated that the ammonia-oxidizing archaeal community was affected by total N and total carbon, while the community of bacterial amoA and nosZ were significantly affected by soil pH. According to a structural equation modeling analysis, climate change influenced net primary production indirectly by altering microbial abundance and activities. These results indicated that microbial responses to the combination of chronic global change tend to be smaller than expected from single-factor global change manipulations.

[Responses of Soil Ammonia Oxidizers to Simulated Warming and Increased Precipitation in a Temperate Steppe of Inner Mongolia].

Soil ammonia oxidizers, as key players for the ammonia oxidation process in soil N cycling, could respond, adapt, and give feedback to global change. In this research, soil samples were collected from a long-term field experiment with increased precipitation and warming in a temperate steppe of Inner Mongolia. We analyzed the responses of the abundance, diversity, and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to warming and increased precipitation using quantitative real-time PCR, terminal restriction fragment length polymorphism (T-RFLP), and clone library. The results showed that increased precipitation significantly stimulated soil pH and warming significantly reduced soil respiration (SR). No significant difference was detected regarding the abundances of amoA genes across all treatments, whereas increased precipitation significantly affected the community structure of soil AOB. However, the interactive effect between warming and increased precipitation had no significant influence on the community structure of soil ammonia oxidizers. The result of the structural equation model indicated that the plant diversity and community structures of soil ammonia oxidizers were significantly correlated, suggesting that there were certain relationships among climate change, microbes, and plants. In conclusion, this study confirmed that soil microorganisms had the ability to adapt to climate change, which could provide important information for predicting future changes in ecosystems.

Abundance and community structure of ammonia-oxidizing Archaea and Bacteria in response to fertilization and mowing in a temperate steppe in Inner Mongolia.

Based on a 6-year field trial in a temperate steppe in Inner Mongolia, we investigated the effects of nitrogen (N) and phosphorus (P) fertilization and mowing on the abundance and community compositions of ammonia-oxidizing Bacteria (AOB) and Archaea (AOA) upon early (May) and peak (August) plant growth using quantitative PCR (qPCR), terminal-restriction fragment length polymorphism (T-RFLP), cloning and sequencing. The results showed that N fertilization changed AOB community composition and increased AOB abundance in both May and August, but significantly decreased AOA abundance in May. By contrast, P fertilization significantly influenced AOB abundance only in August. Mowing significantly decreased AOA abundance and had little effect on AOA community compositions in May, while significantly influencing AOB abundance in both May and August, Moreover, AOA and AOB community structures showed obvious seasonal variations between May and August. Phylogenetic analysis showed that all AOA sequences fell into the Nitrososphaera cluster, and the AOB community was dominated by Nitrosospira Cluster 3. The results suggest that fertilization and mowing play important roles in affecting the abundance and community compositions of AOA and AOB.