Plant Distribution in Relation to Mineral Nutrient Availability and Uptake on a Wet-Heath Site in South-West England

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Abstract
Chemical analyses of peat samples from a grid of ninety-seven sample points in wet-heath vegetation at Aylesbeare Common, Devon, show trends significantly at the 1% level in third-order trend-surfaces for pH and extractable Ca, Mg, K, Mn, P and NH4-N. Ca, Mg and pH are closely correlated (and K and Mn moderately so) with one another and with the first component of a principal-component analysis of the measured peat variables. The major vegetation contrast between species-poor wet heath and acid Sphagnum carpet communities on the one hand, and species-rich wet health and Molinietum on the other, correlates closely with the distribution of Ca, Mg and pH. Molinia performs best in areas with higher pH, Ca, Mg and K, and where there is active water movement. Leaf (or green shoot) material of eight species.sbd.Molinia caerulea, Ulex gallii, Trichophorum cespitosum, Eriophorum angustifolium, Narthecium ossifragum, Cirsium dissectum, Succisa pratensis and Serratula tinctoria.sbd.from points on the sampling grid was analysed for Ca, Mg, K, Na, Mn, Fe, N and P. In mean percentage chemical composition, Cirsium, Succisa and Serratula are relatively higher in Ca, Mg and K, Cirsium and Succisa in Na, Molinia and Ulex in Fe, Molinia, Narthecium and Serratula in Mn, Molinia and (especially) Ulex in N, and Ulex, Cirsium, Succisa and Serratula in P. Narthecium contains higher levels of most elements than the other monocotyledons. The concentration of an element in a plant species is best predicted by the concentration of the same element in the peat in only a few instances: Ca in Cirsium, Succisa and Serratula; Mg in Trichophorum; K in Molinia; Fe in Ulex, Eriophorum and Succisa; Mn in Ulex, Trichophorum, Eriophorum and Cirsium. More commonly the uptake of one element is most strongly related to the concentration of another element in the peat. Thus K in Trichophorum and Succisa is positively correlated with peat Ca; Ulex Mg and K, and Cirsium Mg and Na, are negatively correlated with peat Ca. The pattern of uptake for every species and every element is different. This could be taken as evidence of niche differentiation between species in relation to nutrient uptake, and may be a factor in their stable coexistence.