Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Increasing nitrogen supply stimulates phosphorus acquisition mechanisms in the fynbos species Aspalathus linearis

Pravin M. Maistry A , A. Muthama Muasya A , Alex J. Valentine B and Samson B. M. Chimphango A C

A Department of Biological Sciences, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.

B Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.

C Corresponding author. Email: samson.chimphango@uct.ac.za

Functional Plant Biology 42(1) 52-62 http://dx.doi.org/10.1071/FP14100
Submitted: 31 March 2014  Accepted: 2 July 2014   Published: 20 August 2014

Abstract

We investigated the physiological basis for tolerance of limiting P supply and for enhanced growth with simultaneous addition of N and P in Aspalathus linearis (Burm. f.) R. Dahlgren. It was hypothesised that increasing N supply would stimulate P acquisition mechanisms and enhance plant growth with high P supply. In sand, plants received 100 μM, 300 μM, 500 μM and 700 µM N at a low P level of 10 µM and a high P level of 100 µM. In solution, plants received 200 μM and 500 µM N at a low P level of 5 µM and a high P level of 15 µM. Cluster roots formed only in plants with low P supply. Roots showed greater citrate and malate production and phosphatase activity at 5 µM P than at 15 µM P. At 10 µM P, greater N supply enhanced cluster root formation to 60% of root biomass, and increased the phosphatase activity of noncluster roots and succinate release by both root types. At a high P supply of 15 µM, greater N supply stimulated phosphatase activity of roots by 50%, increasing P uptake and plant growth. With increased resource partitioning towards P acquisition due to greater P demand, A. linearis is tolerant of low P supply and highly responsive to combined addition of N and P.

Additional keywords: cluster roots, colimitation, organic acids, phosphatase.


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