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

Abstract

Summary• 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.

Management of soil phosphorus and plant adaptation mechanisms to phosphorus stress for sustainable crop production: a review

“…Both proteoid and dauciform roots are covered with dense mat of root hairs, which markedly increase the surface area of the root system and are also specialized in efficient synthesis and secretion of organic anions (especially citrate and malate) and phosphatases, which help to solubilize insoluble P resources and hydrolyze organic P for plant uptake (Playsted et al, 2006;Lambers et al, 2006). Cluster roots grown under P deficiency exude 20-to 40-times more citrate and malate than those grown under sufficient P (Vance et al, 2003).…”

Methane Oxidation by Endophytic Bacteria Inhabiting Sphagnum sp. and Some Vascular Plants

“…This phenomenon probably results from the fact that many Cyperaceae species produce dauciform roots. It has been suggested that their function is to acquire P from nutrient-poor, P-fixing soils by means of excretion of compounds such as carboxylates, phenolics, and phosphatases, which facilitate access to the sorbed P (Playsted et al 2006). The high autumn EC may be explained by the changes in the soil water regimes, as the water table in this part of the year was much lower than in the previous months, thus resulting in a more concentrated soil solution.…”

Role of Root Clusters in Phosphorus Acquisition and Increasing Biological Diversity in Agriculture

“…Root clusters in species of the Casuarinaceae Reddell et al 1997), Cyperaceae (Shane et al 2005;Playsted et al 2006), Fabaceae Keerthisinghe et al 1998), Myricaceae ) and Proteaceae (Lamont 1982;Aitken et al 1992;Shane et al 2003a;2003b) are suppressed when adding P to the root environment. Feeding P to leaves also suppresses cluster-root formation in L. albus (Marschner et al 1986;Gilbert et al 2000;Shane et al 2003a), showing that the signal(s) that leads to suppression of cluster-root initiation and growth originate in the shoot, most likely in young leaves (Keerthisinghe et al 1998).…”

“…Though morphologically and anatomically very distinct, dauciform roots function in a way very similar to proteoid roots (Davies et al 1973;Lamont 1974;Shane et al 2005;Playsted et al 2006). That is, dauciform-root formation is suppressed when plants have a relatively high P status (Shane et al 2005;Playsted et al 2006) and carboxylates (e.g., citrate) are released during a brief interval once the dauciform root has matured ( Figure 1D, Shane et al 2005;.…”

“…That is, dauciform-root formation is suppressed when plants have a relatively high P status (Shane et al 2005;Playsted et al 2006) and carboxylates (e.g., citrate) are released during a brief interval once the dauciform root has matured ( Figure 1D, Shane et al 2005;. This brief time interval when large amounts of carboxylates are released from the roots is considered important to mobilize P before microbial activity builds up.…”