Soil phosphorus fractionation and phosphorus-use efficiencies of tropical rainforests along altitudinal gradients of Mount Kinabalu, Borneo

We studied soil phosphorus (P) fractionation and P-use efficiencies (PUEs) of rainforests along altitudinal gradients (700-3100 m) on two types of par ental rocks (sedimentary versus ultrabasic) on Mount Kinabalu, Borneo. Sedi mentary rocks were known to contain more quartz (which does not adsorb P) t han ultrabasic rocks. The pool (top 30 cm) of total P was always greater on sedimentary (ranging from 34.9 to 72.6 g m(-2)) than on ultrabasic (9.0-29 .2 g m(-2)) rocks at comparable altitudes. Accordingly, the pools of organi c P and labile inorganic P were always greater on sedimentary than on ultra basic rocks. The pool of primary mineral, calcium P increased upslope from 1.7 to 4.3 g m(-2) on sedimentary rock, suggesting that the altitudinal seq uence of the sites reflected a decreasing magnitude of soil weathering upsl ope. The pool of calcium P on ultrabasic rock did not vary consistently wit h altitude (1.2-2.8 g m(-2)), probably reflecting the greater between-site variability of primary mineral P in parent rocks. When all sites were compa red, the pool of most labile, bicarbonate-extracted inorganic P increased ( ranging from 0.02 to 1.85 g m(-2)) with increasing calcium P. Calcium P was therefore considered to be an important P source to the biota on Kinabalu. Gross patterns in the variation of PUE (indexed as the reciprocal of the P concentration in litter) were best explained by the pool size of actively cycling P (total P minus occluded inorganic P). PUE, however, demonstrated distinct altitudinal patterns to generate an intricate conrol of P use patt ern by soil P pools and altitude.