Long-term N addition effects on the C mineralization and DOC production in mor humus under spruce
Publikation/Tidskrift/Serie: Soil Biology and Biochemistry
This study was based on laboratory incubations of mor humus from two N fertilized stands of Norway spruce in Sweden (Skogaby and Strasan), which had received repeated N additions (100 kg N ha(-1) yr(-1) as (NH4)(2)SO4 at Skogaby and 35, 73 and 108 kg ha(-1) yr(-1), as NH4NO3 at Strasan) during 8 and 24-29 years, respectively. The aim was to investigate long-term N effects on the mineralization of C and production of DOC. Mor humus (Oe and Oa) was incubated in columns at 20 degreesC for 49 days. Columns were leached once a week with artificial throughfall solution, which was analyzed for DOC, total N, NH4+-N and NO3--N. Prior to each leaching event, CO2 evolution from the columns was determined. C-to-N ratios in the N-treated Oe layers at Strasan (21-24) and Skogaby (24) were significantly lower than those of the controls (Strasan, 32; Skogaby, 28). The cumulative amount Of CO2-C showed a significant treatment effect in the Oe layer at Skogaby, i.e. 18 and 29 mg C g(-1) C in the N treatment and control, respectively. At Strasan, the cumulative CO2-C was significantly lower in the N3 treatment compared to the control in both layers (33 compared to 74 mg C g(-1) C in the Oe layer and 16 compared to 35 mg C g(-1) C in the Oa layer). Neither the DOC nor the DON production showed any significant treatment effects at the two sites. However, DOC was lower in the fertilized Oe layer at Skogaby throughout the incubation. The leaching of DON was highest in the Oe layers at both sites, and DON increased with time at Skogaby while there was a decreasing trend at Strasan. The DOC-to-DON ratio tended to be lower in the fertilized Oe layers at both sites. The NH4+ leaching at Skogaby decreased in the N-treated Oe and Oa layers. At Strasan, NH4+ from the Oe layer increased in N2 and control. The NO3- leaching was low and constant in both Skogaby layers. At Strasan, NO3- increased in the Oe layer of N1. Cumulative CO2 was positively correlated to C-to-N ratio (r(2) = 0.71, p < 0.01) and to cumulative DOC (r(2) = 0.63, p < 0.05) in the Oe layer at Strasan. Our conclusion was that long-term N additions caused decreased C-to-N ratios and decreased CO2 evolution rates. The correlation between CO2 and C-to-N ratio in the Oe layers at Strasan may be due to a changed quality of the fertilized forest floor material and presence of more N efficient microorganisms.
- ISSN: 0038-0717