Functional significance of dauciform roots: exudation of carboxylates and acid phosphatase under phosphorus deficiency in Caustis blakei (Cyperaceae)

• Published in: The New phytologist 2006-01, Vol.170 (3), p.491-500
• Main Authors: Playsted, Cameron W.S, Johnston, Margaret E, Ramage, Carl M, Edwards, David G, Cawthray, Gregory R, Lambers, Hans
• Format: Article
• Language: English
• Subjects: acid phosphatase; Acid Phosphatase - metabolism; Acid soils; Biological and medical sciences; Carboxylates; carboxylic acids; Carboxylic Acids - metabolism; Caustis blakei; chelating agents; citrate; Citrates; Cyperaceae; Cyperaceae - enzymology; Cyperaceae - growth & development; Cyperaceae - metabolism; dauciform roots; Exudation; Fundamental and applied biological sciences. Psychology; malonate; Malonates; nutrient availability; organic acids; Organic soils; Phosphatases; phosphorus; Phosphorus - deficiency; Phosphorus - physiology; phosphorus uptake; Plant physiology and development; Plant roots; Plant Roots - anatomy & histology; Plant Roots - growth & development; Plant Roots - metabolism; Plants; root exudates; root growth; root systems; Soil - analysis; Soil horizons; soil nutrients; soil profiles; soil-plant interactions; Water and solutes. Absorption, translocation and permeability
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2006.01697.x

• Caustis blakei produces an intriguing morphological adaptation by inducing dauciform roots in response to phosphorus (P) deficiency. We tested the hypothesis that these hairy, swollen lateral roots play a similar role to cluster roots in the exudation of organic chelators and ectoenzymes known to aid the chemical mobilization of sparingly available soil nutrients, such as P. • Dauciform-root development and exudate composition (carboxylates and acid phosphatase activity) were analysed in C. blakei plants grown in nutrient solution under P-starved conditions. The distribution of dauciform roots in the field was determined in relation to soil profile depth and matrix. • The percentage of dauciform roots of the entire root mass was greatest at the lowest P concentration ([P]) in solution, and was suppressed with increasing solution [P], while in the field dauciform roots were predominately located in the upper soil horizons, and decreased with increasing soil depth. Citrate was the major carboxylate released in an exudative burst from mature dauciform roots, which also produced elevated levels of acid phosphatase activity. Malonate was the dominant internal carboxylate present, with the highest concentration in young dauciform roots. • The high concentration of carboxylates and phosphatases released from dauciform roots, combined with their prolific distribution in the organic surface layer of nutrient-impoverished soils, provides an ecophysiological advantage for enhancing nutrient acquisition.