Microbial immobilisation of added nitrogen and phosphorus in constructed wetland buffer

The dynamics of soil microbial C, N and P in response to NO3- and PO43- addition were investigated and quantified in a constructed wetland buffer zone divided into three experimental areas. The method used was fumigation-extraction method (FEM), which is commonly used to estimate total soil microbial biomass. N immobilisation in the microbial biomass during the first year after N and P additions ranged from 30.6 kg N ha in the upper experimental area (0.2 ha), which received a high N and P addition, to 2.1 kg N ha(-1) in the lower experimental area (0.3 ha) which got lower N and P additions, and 0.4 kg N ha(-1) in the control area (0.3 ha). P immobilisation ranged from 13.8 kg P ha(-1) in the upper experimental area to 2.8 kg P ha(-1) in the lower experimental area and -2.3 kg P ha(-1) in the control area. The immobilised proportions of N and P in the microbial biomass in the experimental areas were approximately 15% of the added N (90 kg N ha(-1)) and approximately 25% of the added P (30 kg P ha(-1)) during the first year after N and P addition in 1999. Microbial biomass is thus an important factor contributing to nutrient immobilisation in a constructed wetland buffer in transient conditions. (C) 2003 Elsevier B.V. All rights reserved.