Effects of enhanced nitrogen deposition in a spruce forest at Klosterhede, Denmark, examined by moderate NH4NO3 addition

摘要: The fate and effects of increased N deposition were investigated by experimental manipulation in a mature Norway spruce plantation at Klosterhede, western Denmark. ambient was 15–20 kg ha−1 yr−1. Addition 35 yr−1 as ammonium nitrate to 500-m2 plot carried out handspraying monthly for 4 years. During the first year spray labeled with 15N. Tree growth depressed successive spring or summer droughts throughout treatment nitrogen concentration needles third critical low P concentrations (0.6–1 mg g−1) developed possibly combined effect drought stress on roots mycorrhizae. Reduced retranslocation indicated flux needle litterfall. Increased uptake observed all parts trees fraction input taken up from 32 43%, whereas immobilized soil decreased 40 33% N. The decomposition remained unchanged, net mineralization 85% over control. may have resulted saturation immobilization process rather than an increase gross mineralization. Soil respiration not affected, indicating that microbial activity did respond. Nitrification denitrification important either control treated soils. Soil solution chemistry responded promptly applications. Nitrate depths, leaching < 0.3 4.2 year. biological water end growing season. Ammonium down 15 cm depth, but retained system. Despite leaching, 92% total inputs retained. No changes other major ions due additions detectable. nutrient cycling caused significant interaction response addition. Continuation addition will be necessary observe full simulated this forest.