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The influence of phosphorus (P) availability on growth and P uptake was investigated in South African Proteaceae: (1) Protea compacta R.Br., endemic on severely nutrient-impoverished colluvial sands; (2) Protea obtusifolia Bueck ex Meissner; and (3) Leucadendron meridianum I. J. Williams, the latter both endemic on comparatively fertile limestone-derived soils. Plants were grown hydroponically in 1000 L tanks at 0.01, 0.1 or 1.0 µm P for 14 weeks. Biomass accumulation was influenced by P availability, doubling as [P] increased from 0.1 to 1.0 µm. Total biomass was greatest for P. compacta, but L. meridianum and P. obtusifolia had two to four times greater relative biomass accumulation at 0.1 and 1.0 µm[P]. Proteoid root clusters developed at both 0.01 and 0.1 µm[P], but were suppressed at 1.0 µm[P]; this was a 10-fold lower [P] than previously reported to inhibit cluster root formation. Rates of net P uptake at 5 µm P decreased in response to increased P availability from 0.01 to 1.0 µm P. Significant between-species differences in rates of P uptake and capacity to down-regulate P uptake were observed: P. compacta < P. obtusifolia < L. meridianum. The species responses are discussed in terms of adaptation to mosaics in soil P availability and the high beta diversity in the natural habitat. [ABSTRACT FROM AUTHOR]

When grown in nutrient solutions of extremely low [P] (≤1.0 µm), the sedge Schoenus unispiculatus Benth. (Cyperaceae) develops dauciform roots, which are short and carrot shaped, and produce dense numbers of long root hairs. It has been suggested that dauciform roots of monocotyledonous sedges function to acquire P from nutrient-poor, P-fixing soils in a manner similar to that of cluster (proteoid) roots developed by some dicotyledonous species, but without evidence to substantiate this claim. To elucidate the ecophysiological role of dauciform roots, we assessed carboxylate exudation, internal carboxylate and P concentrations and O2 uptake rates during dauciform root development. We showed that O2 consumption was fastest [9 nmol O2 g−1 fresh mass (FM) s−1] and root [P] greatest (0.4 mg P g−1 FM) when dauciform roots were young and rapidly developing. Citrate was the most abundant carboxylate in root tissues at all developmental stages, and was most concentrated (22.2 µmol citrate g−1 FM) in young dauciform roots, decreasing by more than half in mature dauciform roots. Peak citrate-exudation rates (1.7 nmol citrate g−1 FM s−1) occurred from mature dauciform roots, and were approximately an order of magnitude faster than those from roots of species without root clusters, and similar to those of mature proteoid (cluster) roots of Proteaceae. Both developing and mature dauciform roots had the capacity to acidify (but not alkalinize) the rhizosphere. Anatomical studies showed that epidermal cells in dauciform roots were greatly elongated in the transverse plane; epidermal cells of parent roots were unmodified. Although structurally distinct, the physiology of dauciform roots in sedges appears to be analogous to that of proteoid roots of Proteaceae and Fabaceae, and hence, dauciform roots would facilitate access to sorbed P and micronutrients from soils of low fertility. [ABSTRACT FROM AUTHOR]

When grown at a low P supply, Hakea prostrata R.Br. (Proteaceae) develops dense clusters of determinate branch roots, termed ‘proteoid’ or ‘cluster’ roots and accumulates Mn in its leaves. The aim of this study was to vary the production of cluster roots and assess the relationship between Mn uptake and cluster-root mass. We collected native soil from a location inhabited by H. prostrata and amended this with ‘high’ and ‘low’ amounts of insoluble or soluble P. After 14 months, we measured the impact of the treatments on cluster-root development and the [P], [Mn], [Fe], [Zn] and [Cu] in young (expanding) and mature leaves. Dry mass and leaf area increased with increasing P availability in the soil, but growth decreased at the highest soluble [P], which caused symptoms of P toxicity. The [P] in young leaves (1.3–2.7 mg g−1 DM) exceeded that in older leaves (0.28–0.85 mg g−1 DM), except when plants were grown with soluble P (3.2–21 mg g−1 DM). Cluster-root formation was inhibited when leaf [P] increased; [P] in young leaves, rather than that in old leaves, appeared to be the factor that determined the proportion of the root mass invested in cluster roots. Old leaves of all treatments had [Mn] from 90 to 120 µg g−1 DM, except for plants grown at high levels of soluble P, when [Mn] decreased below 30 µg g−1 DM. The [Mn] and [Zn] in old leaves and the [Cu] in young leaves were positively correlated with the fraction of roots invested in cluster roots. These findings support our hypothesis that cluster roots play a significant role in micronutrient acquisition, and also provide an explanation for Mn accumulation in leaves of H. prostrata, and presumably Proteaceae in general. [ABSTRACT FROM AUTHOR]

• The incidence of species that develop specialised‘dauciform’ lateral roots, which are hypothesised to be important for phosphorus (P) acquisition, is uncertain. We investigated their occurrence in Australian reed, rush and sedge species, grown at low P concentration in nutrient solution, and studied the response ofSchoenus unispiculatus(Cyperaceae) to a range of P concentrations.• We assessed the fraction of root biomass invested in dauciform roots, their respiration and net P-uptake rate, and the P status of roots and leaves.• Dauciform-root development occurred only in particular genera of Cyperaceae when grown at low P supply. Increased P supply was associated with increased growth ofS. unispiculatusand increased leaf[P]. Dauciform-root growth was reduced by increased P supply, and reduced P uptake co-occurred with the complete suppression of dauciform roots.• The P-induced suppression of dauciform roots in Cyperaceae is similar to that observed for proteoid roots in members of Proteaceae andLupinus albus. The response of dauciform roots to altered P supply and their absence from root systems of some sedge species are discussed in terms of managed and natural systems.New Phytologist(2005)doi: 10.1111/j.1469-8137.2004.01283.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]