Response of gene abundance of ammonia-oxidizing microorganisms and denitrifying microorganisms to nitrogen and phosphorus addition in subtropical forest.

We conducted a nitrogen (N) and phosphorus (P) addition experiment in Qianjiangyuan National Park in 2015, to investigate the response of ammonia-oxidizing microorganisms and denitrifying microorganisms. There were four treatments, including N addition (N), P addition (P), NP, and control (CK). Soil samples were collected in April (wet season) and November (dry season) of 2021. The abundance of gene of ammonia-oxidizing microorganisms (., ammonia-oxidizing archaea, AOA; ammonia-oxidizing bacteria, AOB; comammox) and denitrifying microbial genes (., , and ) were determined using quantitative PCR approach. The results showed that soil pH was significantly decreased by long-term N addition, while soil ammonium and nitrate contents were significantly increased. Soil available P and total P contents were significantly increased with the long-term P addition. The addition of N (N and NP treatments) significantly increased the abundance of AOB- gene in both seasons, and reached the highest in the N treatment around 8.30×10 copies·g dry soil. The abundance of AOA- gene was significantly higher in the NP treatment than that in CK, with the highest value around 1.17×10 copies·g dry soil. There was no significant difference in N-related gene abundances between two seasons except for the abundance of comammox-. Nitrogen addition exerted significant effect on the abundance of AOB-, and genes, especially in wet season. Phosphorus addition exerted significant effect on the abundance of AOA- and AOB- genes in both seasons, but did not affect denitrifying gene abundances. Soil pH, ammonium, nitrate, available P, and soil water contents were the main factors affecting the abundance of soil N-related functional genes. In summary, the response of soil ammonia-oxidizing microorganisms and denitrifying microorganisms was more sensitive to N addition than to P addition. These findings shed new light for evaluating soil nutrient availability as well as their response mechanism to global change in subtropical forests.