Comparison of the response to phosphorus deficiency in two lupin species, <scp><i>L</i></scp><i>upinus albus</i> and <scp><i>L</i></scp><i>. angustifolius</i>, with contrasting root morphology

<jats:title>Abstract</jats:title><jats:p>White lupin (<jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>upinus albus</jats:italic>) produces cluster roots, an adaptation to low soil phosphorus (<jats:styled-content style="fixed-case">P</jats:styled-content>). Cluster roots exude large levels of <jats:styled-content style="fixed-case">P</jats:styled-content>‐solubilizing compounds such as citrate and malate. In contrast, narrow leaf lupin (<jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic>) is closely related to <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. albus</jats:italic>, but does not produce cluster roots. To examine the different strategies for <jats:styled-content style="fixed-case">P</jats:styled-content> acquisition, we compared the growth, biomass allocation, respiratory properties and construction cost between <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. albus</jats:italic> and <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> under <jats:styled-content style="fixed-case">P</jats:styled-content>‐deficient conditions. Both <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>upinus</jats:italic> species were grown in hydroponic culture with 1 or 100 <jats:italic>μ</jats:italic><jats:styled-content style="fixed-case">M P</jats:styled-content>. Under the <jats:styled-content style="fixed-case">P</jats:styled-content>‐deficient regime, <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. albus</jats:italic> produced cluster roots with little change in biomass allocation, while <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> significantly increased biomass allocation to roots. The rate of cyanide‐resistant <jats:styled-content style="fixed-case">SHAM</jats:styled-content> (salicylhydroxamic acid)‐sensitive respiration was high in cluster roots and very low in roots of <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic>. These results suggest a low alternative oxidase (<jats:styled-content style="fixed-case">AOX</jats:styled-content>) activity in <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> roots, and thus, <jats:styled-content style="fixed-case">ATP</jats:styled-content> would be produced efficiently in <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> roots. The construction cost was highest in cluster roots and lowest in <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> roots. This study shows that under <jats:styled-content style="fixed-case">P</jats:styled-content> deficiency, <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. albus</jats:italic> produces high‐cost cluster roots to increase the <jats:styled-content style="fixed-case">P</jats:styled-content> availability, while <jats:styled-content style="fixed-case"><jats:italic>L</jats:italic></jats:styled-content><jats:italic>. angustifolius</jats:italic> produces large quantities of low‐cost roots to enhance <jats:styled-content style="fixed-case">P</jats:styled-content> uptake.</jats:p>