1. Long-term nitrogen (N) addition plots on an upland Cal/una vulgaris moor had been treated for more than ten years with 0,40, 80 and 120 kg N ha-1 yr- 1 • 2. Sampling of the soil solution from under the mor and the mineral gley horizons over an annual cycle revealed a high degree of retention of N, between 60 % and 80 % of ambient N inputs in the control, and rising to 90 % in response to higher inputs of the N treatments. 3. After passing through the mineral gley horizon, N was further retained, by 85 % of ambient N inputs in the control, and rising to 97 % in response to the highest N treatment. 4. There was some evidence of an inverse relation between ammonium and dissolved organic nitrogen (DON) under all N treatments. Microbial immobilisation and conversion to DON was compatible with the few significant effects on cation concentration, although calcium and calcium/aluminium ratios and pH were decreased by N treatment in the mineral gley horizon. 5. A budget revealed that the added N of the treatments had been allocated mainly to the canopy and litter at low inputs and increasingly to the mor, and to a lesser extent the gley horizon, with increasing N inputs. 6. In the system as a whole, 51 % of the entire system N was contained in the mor horizon, and with increasing inputs of added N, the whole system N accounted for 60 %, 80 % and 90 % of the added N in the low, middle and high N treatments respectively. 7. Nitrogen/phosphorus ratios in green tissue were decreased in response to increasing N inputs to levels indicative of N limitation, in spite of increases in phosphatase activity in the litter and mor layers. N uptake rates and mycorrhizal colonisation were not affected. 8. A moor management bum volatilised 90 % of the canopy N (amounting to 6 % of the total system N). Increases in the gain ofN in the gley horizon after the bum decreased with increasing N treatment, an indication of increasing N saturation in this layer and confirmed by increases in N leaching in response to higher N inputs. The same response was observed without significance in the mor layer owing to greater variance in the data. 9. Rates of net mineralisation and DON production in the litter layer increased with N inputs in both field and laboratory incubations, but net nitrification rate only showed N treatment-related increases in the laboratory incubation. Threshold values of litter % N and C/N ratios determined the onset of these processes, as well as N treatment-related increases in rates of potential denitrification. 10. Bryophyte cover under the Calluna canopy, density of the canopy, light transmission through the canopy and N inputs were all related, either negatively or positively (see chapter 5), but only in mature/degenerate plants. In "new' plots containing younger, building-phase Calluna, the addition of phosphorus raised the competitive ability of bryophytes above that of Calluna, particularly at lower inputs of N.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:273050 |
| Date | January 2003 |
| Creators | Pilkington, Michael Gerald |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0017 seconds