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

• Main Authors: J. Chen, G. Xiao, Y. Kuzyakov, G. D. Jenerette, Y. Ma, W. Liu, Z. Wang, W. Shen
• Format: Article
• Language: English
• Published: Copernicus Publications 2017-05-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/14/2513/2017/bg-14-2513-2017.pdf

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 <i>amoA</i>) and denitrifying (<i>nirK</i>, <i>nirS</i> and <i>nosZ</i>) 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 <i>amoA</i> abundance showed the strongest correlation with net N transformation rates (<i>r</i>  ≥  0.35), suggesting the critical role of archaeal <i>amoA</i> 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 <i>nosZ</i> 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.