Limiting Nutrients in Acid-Mire Vegetation: Peat and Plant Analyses and Experiments on Plant Responses to Added Nutrients

Abstract

(1) In pot experiments on a wet-heath peat from east Devon, Cirsium dissectum showed a strong positive response to lime but not to CaCl2, and to added P but not to N. Carex echinata responded strongly to lime, N and P. Neither species responded significantly to added K. (2) Peat samples were analysed from six sites in Devon: two lowland wet heaths (Ericion tetralicis), an upland blanket bog (Calluno-Sphagnion papillosilOxycoccoEricion), and three upland poor-fens (Caricion nigrae). (3) Extractable amounts of the major cations were similar at the six sites, with somewhat higher levels of K in the wet heaths, Mg and Na in the blanket bog, and Ca in the poor-fens. The wet-heath sites were lowest in extractable NH4-N and P; the highest NH4-N values were in the poor-fens. (4) Total P was highest in the poor-fens; total Mn and Al were lowest in the blanket peat. C-N and C-P ratios were highest in the wet heath and blanket bog, and lowest in the poor-fens. (5) Plant analyses suggested greater availability of Fe and Mn in the wet heath and poor-fen sites, but otherwise did not closely reflect the peat analyses. (6) A factorial nutrient-addition experiment with Carex echinata grown on peats from the six sites showed that N and P were limiting growth on all six. N was more strongly limiting on the wet heath peats and P on the blanket bog. Both N and P appeared more freely available in the poor-fen peats. (7) K appeared to be in at least adequate supply in all but the blanket-bog peat; it showed no significant main-effect response, but there were significant interactions with N, P and Site. These suggest differences in processes of N supply and uptake in the wet heaths and blanket bog on the one hand, and the poor-fens on the other.