不同放牧强度下土壤氨氧化和反硝化微生物的变化特征

Abstract

Soil nitrifiers and denitrifiers play key roles in determining soil nitrogen (N) availability, nitrate leaching, and N2O emission, and thus they could be indicative to the effects of grazing intensity on grassland ecosystems as well as grassland degradation. In this study, soil samples were collected from a long-term field experiment with different grazing intensities (low-level, middle-level, and high-level grazing) in arid and semi-arid grasslands in Inner Mongolia. We analyzed the responses of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and denitrifiers, in terms of abundance, community composition, and diversity, at different grazing intensities using real-time PCR and terminal restriction fragment length polymorphism (T-RFLP) approaches. The results showed that soil pH and ammonium content ranged from 7.90-8.18 and 6.37-35.92 mg/kg, respectively. Middle-level grazing significantly increased soil pH (P = 0.03), whereas soil ammonium content was recorded as the highest in the high-level grazing treatment (P =0.02). Soil heterotrophic respiration was markedly lower owing to the effects of grazing intensity than that in the non-grazing treatment (P = 0.02). AOA-amoA and AOB-amoA gene abundances rang ed from (4.94-7.60) × 109 and (0.68-3.75) × 106 copies/g dry soil, respectively. AOA-amoA gene abundance showed no significant change in any of the treatments, whereas middle-level grazing strongly decreased AOB-amoA gene abundance (P =0.04). The abundance of nosZ gene (coding for nitrous oxide reductase) was significantly decreased in the low-level grazing treatment (P = 0. 03). The abundances of AOA and AOB were significantly influenced by ammonium content, whereas nosZ gene abundance was influenced by substrate content and soil aeration. Redundancy analysis showed that the variation in N availability induced by grazing was the major factor influencing the community composition of ammonia oxidizers and denitrifiers.