EFFECTS OF CLIMATE-CHANGE ON NITROGEN DYNAMICS IN UPLAND SOILS - 1 - A TRANSPLANT APPROACH

The impact of climate change on N leaching from hill land plant/soil s ystems was investigated using a transplant technique involving the mov ement of intact lysimeter cores of three contrasting soil types down a n altitudinal gradient at Great Dun Fell, Cumbria. Air and soil temper atures and precipitation were monitored at four elevations down an alt itudinal transect using automatic weather stations for a period of two years. The altitudinal sequence of air temperature followed the antic ipated pattern, providing mean annual temperatures at the four locatio ns of 3.4, 5.0, 6.3 and 8.1 degrees C. Lapse rates of both mean air an d soil temperatures over the altitudinal range 171-845 m were 6.6 (199 3) and 7.0 degrees C km(-1) (1994). Soil monthly temperature gradients for a particular soil type for each of the two years showed a seasona l range of 6.0 and 7.4 degrees C km(-1), respectively, and for air tem perature of 4.3 and 3.1 degrees C km(-1). Precipitation gradients show ed the expected general increase with altitude, but were less predicta ble. Inorganic nitrogen leaching was studied in lysimeter leachates wi th climatic amelioration resulting in dramatic reductions in leachate nitrate concentrations and associated total concentrations of inorgani c nitrogen. Decreases in leachate nitrate concentrations were observed for all three soil types studied. Soils receiving supplemented rainfa ll also showed decreased N concentrations, suggesting that temperature was the main controlling factor responsible for the observed reductio ns. Increased N uptake by the vegetation, in response to the increases in temperature, is considered to be critical in controlling soil solu tion chemistry at these sites.