Articles | Volume 14, issue 9
Research article
17 May 2017
Research article |  | 17 May 2017

Soil nitrogen transformation responses to seasonal precipitation changes are regulated by changes in functional microbial abundance in a subtropical forest

Jie Chen, Guoliang Xiao, Yakov Kuzyakov, G. Darrel Jenerette, Ying Ma, Wei Liu, Zhengfeng Wang, and Weijun Shen

Abstract. The frequency of dry-season droughts and wet-season storms has been predicted to increase in subtropical areas in the coming decades. Since subtropical forest soils are significant sources of N2O and NO3, it is important to understand the features and determinants of N transformation responses to the predicted precipitation changes. A precipitation manipulation field experiment was conducted in a subtropical forest to reduce dry-season precipitation and increase wet-season precipitation, with annual precipitation unchanged. Net N mineralization, net nitrification, N2O emission, nitrifying (bacterial and archaeal amoA) and denitrifying (nirK, nirS and nosZ) gene abundance, microbial biomass carbon (MBC), extractable organic carbon (EOC), NO3, NH4+ and soil water content (SWC) were monitored to characterize and explain soil N transformation responses. Dry-season precipitation reduction decreased net nitrification and N mineralization rates by 13–20 %, while wet-season precipitation addition increased both rates by 50 %. More than 20 % of the total variation of net nitrification and N mineralization could be explained by microbial abundance and SWC. Notably, archaeal amoA abundance showed the strongest correlation with net N transformation rates (r  ≥  0.35), suggesting the critical role of archaeal amoA abundance in determining N transformations. Increased net nitrification in the wet season, together with large precipitation events, caused substantial NO3 losses via leaching. However, N2O emission decreased moderately in both dry and wet seasons due to changes in nosZ gene abundance, MBC, net nitrification and SWC (decreased by 10–21 %). We conclude that reducing dry-season precipitation and increasing wet-season precipitation affect soil N transformations through altering functional microbial abundance and MBC, which are further affected by changes in EOC and NH4+ availabilities.

Short summary
We conducted a field manipulation experiment by redistributing 67 % of dry-season rainfall into the wet season while keeping the annual rainfall unchanged in a subtropical forest. Soil net nitrification and N mineralization rates were decreased by 13–20 % in the dry season and increased by 50 % with an accelerated NO3 leaching in the wet season. Functional microbial gene abundance and microbial biomass were the main factors affecting the N-process responses to the rainfall seasonality changes.
Final-revised paper