Abstract: This study was conducted at the national long-term experimental site of red soil fertility and fertilizer benefit in the Qiyang Red Soil Experimental Station, Hunan Province. There were four fertilization treatments: nitrogen fertilizer (N), NK fertilizer (NK), NP fertilizer (NP), NPK fertilizer (NPK). The effects of long-term applications of chemical fertilizers on soil P forms, phosphatase activity, and bacterial phoD gene abundance and diversity in red soils were examined using real-time quantitative PCR and high-throughput sequencing. Results showed that compared with N fertilizer only, N combined with P or K could retard soil acidification, and N combined with P could significantly increase the contents of all soil P forms. Furthermore, NP and NK treatments significantly increased soil alkaline phosphatase activity and the abundance of soil total bacteria and phoD gene compared with N treatment. Similarly, NPK treatment significantly increased soil alkaline phosphatase activity and soil total bacterial abundance, but decreased soil phoD gene abundance. However, both α and β diversity of phoD gene communities was similar across all the treatments. More than 45% of phoD gene originated from Pseudomonas and Janthinobacterium in all the treatments, respectively. Furthermore, there were significantly positive correlations between the relative abundance of Streptomyces, Massilia, Brevundimonas and the contents of soil P forms. Our findings indicated that the critical factors regulating functional bacterial abundance and phosphatase activity were distinct under different nutrient input conditions. Rational fertilization of NPK could increase soil P content and phosphatase activity and change phoD gene abundance and community structure, which could improve soil P supply. However, long-term application of chemical fertilizers caused simplification of soil microbial community.

Key words: chemical fertilizer, high-throughput sequencing, phosphorus, phosphatase, phoD gene abundance and diversity