Experimental nitrogen, phosphorus, and potassium deposition decreases summer soil temperatures, water contents, and soil COsub2/sub concentrations in a northern bog

摘要

Ombrotrophic peatlands depend on airborne nitrogen (N), whose deposition hasincreased in the past and lead to disappearance of mosses and increasedshrub biomass in fertilization experiments. The response of soil watercontent, temperature, and carbon gas concentrations to increased nutrientloading is poorly known and we thus determined these data at the long-term Nfertilization site Mer Bleue bog, Ontario, during a two month period insummer. Soil temperatures decreased with NPK addition in shallow peat soilprimarily during the daytime (t-test, p < 0.05) owing to increased shading,whereas they increased in deeper peat soil (t-test, p < 0.05), probably byenhanced thermal conductivity. These effects were confirmed by _RMANOVA,which also suggested an influence of volumetric water contents asco-variable on soil temperature and vice versa (p < 0.05). Averaged over allfertilized treatments, the mean soil temperatures at 5 cm depth decreased by1.3 °C and by 4.7 °C (standard deviation 0.9 °C) at noon.Water content was most strongly affected by within-plot spatial heterogeneity butalso responded to both N and PK load according to _RMANOVA (p < 0.05).Overall, water content and CO₂ concentrations in the near-surface peat(t-test, p < 0.05) were lower with increasing N load, suggesting more rapidsoil gas exchange. The results thus suggest that changes in bog ecosystemstructure with N deposition have significant ramifications for physicalparameters that in turn control biogeochemical processes.