AOBPreview originally published online on October 13, 2005
Annals of Botany 2005 96(7):1275-1282; doi:10.1093/aob/mci279
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Cluster Roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) Take Up Glycine Intact: An Adaptive Strategy to Low Mineral Nitrogen in Soils?
1 Department of Botany, Private Bag, University of Cape Town, 7701, South Africa and 2 Centre for Ecosystem Management, School of Natural Sciences, Edith Cowan University, Joondalup 6027, Western Australia
* For correspondence. E-mail hhawkins{at}botzoo.uct.ac.za
Received: 19 May 2005 Returned for revision: 27 June 2005 Accepted: 7 September 2005 Published electronically: 12 October 2005
• Background and Aims South African soils are not only low in phosphorus (P) but most nitrogen (N) is in organic form, and soil amino acid concentrations can reach 2·6 g kg–1 soil. The Proteaceae (a main component of the South African Fynbos vegetation) and some Fabaceae produce cluster roots in response to low soil phosphorus. The ability of these roots to acquire the amino acid glycine (Gly) was assessed.
• Methods Uptake of organic N as 13C–15N-Gly was determined in cluster roots and non-cluster roots of Leucadendron laureolum (Proteaceae) and Lupinus albus (Fabaceae) in hydroponic culture, taking account of respiratory loss of 13CO2.
• Key Results Both plant species acquired doubly labelled (intact) Gly, and respiratory losses of 13CO2 were small. Lupin (but not leucadendron) acquired more intact Gly when cluster roots were supplied with 13C–15N-Gly than when non-cluster roots were supplied. After treatment with labelled Gly (13C : 15N ratio = 1), lupin cluster roots had a 13C : 15N ratio of about 0·85 compared with 0·59 in labelled non-cluster roots. Rates of uptake of label from Gly did not differ between cluster and non-cluster roots of either species. The ratio of C : N and 13C : 15N in the plant increased in the order: labelled roots < rest of the root < shoot in both species, owing to an increasing proportion of 13C translocation.
• Conclusions Cluster roots of lupin specifically acquired more intact Gly than non-cluster roots, whereas Gly uptake by the cluster and non-cluster roots of leucadendron was comparable. The uptake capacities of cluster roots are discussed in relation to spatial and morphological characteristics in the natural environment.
Key words: Amino acid, cluster roots, 13C–15N-Gly, Leucadendron laureolum, Lupinus albus, Fynbos, Proteaceae, organic nitrogen
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