Response of soil water chemistry and fine-roots to clean rain in a spruce forest ecosystem at Solling, FRG

Throughfall in a forested area was intercepted by 300 m2 transparent polycarbonate roofs built below the canopy about 3.5 m from the ground. On 1 plot, rainfall was collected, filtered, deionized and its composition adjusted to that of clean rain. Sulphate, nitrogen and ammonium ions were reduced by 83, 80 and 100 per cent compared with natural rain. The project monitored a wide range of parameters and samples, including bulk deposition, throughfall and soil water down to a depth of 100 cm. Data had been acquired 2 years before the experiment and for 3.5 years during it. Within 1 year, the soil water composition had responded to the reduced inputs of sulphur and nitrogen. Fine root biomass of the Norway spruce in the clean rain plot increased by about 40 per cent, the improvement being greatest in the B horizon. Part of the cause might have been reduced inorganic nitrogen in the root zone, so increasing the mass of roots needed for uptake of adequate nitrogen. No effects on other variables had yet been observed. The work showed the importance of atmospheric deposition on soil water chemistry in this catchment.