Topography Modulates Effects of Nitrogen Deposition on Asymbiotic N₂ Fixation in Soil but not Litter or Moss in a Secondary Karst Forest

This is the authors' abstract. We don't add key points for this paper.

Evidence shows that nitrogen (N) addition may suppress or have no significant effect on asymbiotic N 2 fixation (ANF) in soil, litter, or moss. However, the mechanisms underlying the differential responses of ANF to N addition are not well understood. The main objectives of the current study were to assess how ANF in soil, litter, and moss responds to N addition and whether topography modulates the responses of ANF in soil, litter, or moss to N addition. We conducted an N addition experiment at two topographic positions, that is, valley and slope of a secondary karst forest in southwest China. Three N addition treatments, that is, control (0 kg N·ha −1 ·year −1 ), moderate N addition (N 50 , 50 kg N·ha −1 ·year −1 ), and high N addition (N 100 , 100 kg N·ha −1 ·year −1 ) were included. Nitrogen addition had no significant effect on moss ANF at both topographic positions. Soil ANF was lower by 17.1% in the N 100 plots relative to the control in the valley but was not significantly altered by N addition on the slope. In contrast, litter ANF was suppressed by N addition at both topographic positions by 77.9% to 87.4%. Our findings suggest that topography may modulate the responses of ANF to N addition, but the modulation effects likely differ among different ecosystem compartments.