Phosphorus efficiency in pasture species. II. Differences in the utilization of P between major chemical fractions

Abstract

A solution culture experiment was conducted over a range of initial solution P concentrations (1-16 8M P) to investigate differences in P utilization of a tropical and temperate pasture legume. The species used were white clover (Trifolium repens cv. 'Ladino') and Caribbean stylo (Stylosanthes hamata cv. 'Verano'). Incorporation of solution 31P and a pulse of 32P into the soluble (inorganic, ester P), lipid and residue (phytin RNA, DNA, phosphoproteins) fractions of roots and tops was monitored over five harvests. At low P concentrations the major finding was that clover reduced its incorporation of 31P and 32P into root phospholipids at the final harvest. The reduction in P concentration in phospholipids coincided with reductions in relative growth rate of the whole plant by the final harvest, which were discussed in the first paper of this series.At high P concentrations, dry weight accumulation was related to the extent to which absorbed P was incorporated from the soluble to the lipid and residue fractions. While clover had higher dry weights and a greater incorporation capacity at high P.Correlation coefficients between dry weight and biochemical parameters showed that the best correlations between dry weight and any biochemical parameter was for the relationship between dry weight and residues P or lipid plus residue P content. A relationship between P uptake rate and root soluble P concentration indicated that root soluble P may have a feedback effect on P uptake. The negative feedback effect was greatest in stylo at high solution P concentration.