Root of edaphically controlled Proteaceae turnover on the Agulhas Plain, South Africa: phosphate uptake regulation and growth

The influence of phosphorus (P) availability on growth andP uptake was investigated in South African Proteaceae:(1) Protea compacta R.Br., endemic on severely nutrientimpoverishedcolluvial sands; (2) Protea obtusifolia Bueckex Meissner; and (3) Leucadendron meridianum I. J.Williams, the latter both endemic on comparatively fertilelimestone-derived soils. Plants were grown hydroponicallyin 1000 L tanks at 0.01, 0.1 or 1.0 mM P for 14 weeks.Biomass accumulation was influenced by P availability,doubling as [P] increased from 0.1 to 1.0 mM. Total biomasswas greatest for P. compacta, but L. meridianum and P.obtusifolia had two to four times greater relative biomassaccumulation at 0.1 and 1.0 mM [P]. Proteoid root clustersdeveloped at both 0.01 and 0.1 mM [P], but were suppressedat 1.0 mM [P]; this was a 10-fold lower [P] than previouslyreported to inhibit cluster root formation. Rates of net Puptake at 5 mM P decreased in response to increased Pavailability from 0.01 to 1.0 mM P. Significant betweenspeciesdifferences in rates of P uptake and capacity todown-regulate P uptake were observed: P. compacta <P.obtusifolia <L. meridianum.The species responses are discussedin terms of adaptation to mosaics in soil P availabilityand the high beta diversity in the natural habitat.