
%0 Journal Article
%A Barrett, Damian J. 
%A Gifford, Roger M. 
%T Increased C-gain by an endemic Australian pasture grass at elevated atmospheric CO<sub>2</sub> concentration when supplied with non-labile inorganic phosphorus
%J Functional Plant Biology
%D 1999/08/27
%V 26
%N 5
%P 443-451
%K Carbon dioxide, global change, citrate, carbon, biomass, phosphorus, photosynthesis, root efflux.
%R https://doi.org/10.1071/PP98153
%U https://www.publish.csiro.au/paper/PP98153 
%X Limited phosphorus (P) availability in Australia's highly weathered soils may constrain an increase in terrestrial net primary productivity (NPP) with the globally increasing atmospheric CO 2 concentration. We examined whether an Australian temperate pasture grass (Danthonia richardsonii) grown in sand culture and supplied solely with virtually insoluble Al- and Fe-phosphate was able to increase C-gain when exposed to elevated (731 &micro;mol mol &minus;1 ) compared with ambient (379 &micro;mol mol &minus;1 ) CO 2 concentrations. When supplied with 8 mg kg &minus;1 insoluble P concentration, total citrate efflux by root systems (&micro;mol h &minus;1 ), plant P uptake, shoot photosynthesis rates and plant mass were all significantly greater at elevated than at ambient CO 2 after a growth period of between 55 and 63 days. In this treatment, although the P concentration of the rooting medium limited growth at ambient CO 2 , elevated CO 2 increased P-uptake from the non-labile source, increased photosynthesis rates per unit shoot soluble-P and increased plant mass. At P concentrations lower than 8 mg kg &minus;1 , plant mass, specific citrate efflux and maximum leaf carboxylation rates were limited by the amount of P available in the rooting medium and no CO 2 effect was observed. In all treatments, carbon supply did not appear to limit citrate efflux. Where an increase in P uptake at elevated CO 2 was achieved, it was due to an increase in root mass (indicative of a potentially larger soil volume explored) rather than to increased specific rates of citrate efflux. Above 8 mg kg &minus;1 , the supplied P concentration was sufficient that minimal rates of specific citrate efflux alone solubilised enough P for growth and a strong CO 2 effect on plant mass, photosynthesis and P uptake was observed. 
