SEPARATING THE EFFECTS OF LITTER QUALITY AND MICROENVIRONMENT ON DECOMPOSITION RATES IN A PATTERNED PEATLAND

Decomposition rates, measured as proportion of original ash-free dry m ass lost from litter bags, were studied on four microhabitats of an om brogenous peatland in southwestern Scotland: a Racomitrium lanuginosum hummock (HR), a Sphagnum capillifolium hummock (HS), a Sphagnum papil losum lawn (L), and a Sphagnum cuspidatum hollow (H). Reciprocal trans plant experiments, in which litter bags were swapped among depths both within and among microhabitat types, separated the effects of litter quality (litter type and degree of humification of the peat) and micro environment (water table position and microhabitat type). All were imp ortant determinants of mass loss. Decomposability of the litter from d ifferent microhabitats increased in the order HR < HS < L < H. Chemica l 'ageing' of the peat reduced rates of decay in highly humified peat, although a history of decay was associated with maximum decomposabili ty of peat from HR hummocks. The suitability of hollows for decay was significantly less than for HR and HS hummocks and lawns. Feat lost ma ss most slowly when placed below the lowest water table, but the highe st mass losses were for peat placed in, or slightly above, the zone of water table fluctuation. Mass loss decreased with depth for peat deca ying in its natural position in hollows and lawns and the oxic layer o f HS hummocks. A peak in mass loss occurred within the zone of water t able fluctuation in HS hummocks, and just above the highest water tabl e in HR hummocks. The results support earlier suggestions that differe nces due to chemical ageing of peat contribute to differences in decom position rates between hummocks and hollows, and that hummock species are intrinsically more resistant to decay than hollow species. The pat tern was complicated further, however, by the effects of water table p osition and microhabitat type. The combined effects of litter quality (species composition and degree of humification of the litter) and env ironment (microhabitat of incubation and position of incubation relati ve to water table) are complex, and these complexities must be incorpo rated into models of decomposition.