Seasonal dynamics of ammonia-oxidizing archaea and bacteria in subalpine forests of western Sichuan

Background and aimsThe composition and structure of soil ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) communities in subalpine forest ecosystems may vary depending on different forest types and seasonal variations, thus having important implications for soil nitrogen (N) cycling.MethodsUsing Abies fargesii var. faxoniana (coniferous forests, CF), Betula albosinensis (broad-leaved forests, BF), and mixed forests of A. fargesii var. faxoniana and B. albosinensis sinensis (mixed forests, MF) in western Sichuan as our objects. The amoA gene abundance and community characteristics of soil AOA and AOB were studied.ResultsAmong the three forest types, the AOB gene abundance and diversity index were generally higher than those of AOA. Forest types influenced the AOA gene abundance and the AOB community richness index. In contrast, the AOB gene abundance and AOA and AOB community diversity index were influenced by the main effect of the sampling season. Additionally, two-year average data indicated that in mixed forests, the AOA gene abundance and diversity index and the AOB community richness index were significantly higher in October than in May. Furthermore, the composition of AOA and AOB communities varies among forest types, mainly influenced by pH, ammonium nitrogen (NH4+) concentration, moisture, and soil phosphorus (P).ConclusionsIn subalpine forests, soil ammonia oxidation processes may be dominated by AOB. The AOA and AOB gene abundance and community structure differed among forest types and showed significant seasonal variations. These discoveries underscore the sensitive responsiveness of soil microorganisms in subalpine forests to changes in seasons and environmental conditions.