Effects of phosphorus addition on N 2 O emissions from an Acacia mangium soil in relatively aerobic condition

Abstract

Effects of phosphorus (P) addition on nitrous oxide (N 2 O) emissions from an Acacia mangium plantation soil was examined in relatively aerobic condition with carbon (C) and nitrogen (N) addition. We hypothesized that P addition reduced N 2 O emissions through stimulated microbial N immobilization and subsequent decrease in inorganic N resources for producing N 2 O. We prepared the following four experimental sets; high C (glucose 2000 µg C g soil 1) and water-filled pore space (WFPS) 40 % (H40), low C (glucose 100 µg C g soil 1) and WFPS 40 % (L40), high C and WFPS 60 % (H60), and low C and WFPS 60 % (L60). Nitrogen (NH 4 NO 3 , 20 µg N g soil 1) was also added to all soils. We prepared P-added soils (Ca(H 2 PO 4) 2 , 20 µg P g soil 1) and non-added control to test the effects of P addition on N 2 O emissions. Contrary to our hypothesis, P addition did not reduce N 2 O emissions, although soil microbial N immobilization was stimulated by P addition in soils with low C addition. Stimulated total N cycling by P addition probably offset the decrease in soil inorganic N. Meanwhile P addition reduced soil microbial biomass N (MBN) content in H60, where N 2 O emissions increased significantly by P addition. It was possible that the microbial growth reached its peak and started dying more quickly in P-added soils in H60 due to the favorable condition for microbes (higher C and water content). Thus we concluded that (i) P addition did not necessarily stimulate soil microbial N immobilization, and (ii) N 2 O emissions might not decrease even if P addition stimulated soil microbial N immobilization.