Phosphorus efficiency in pasture species. III. Correlations of dry matter accumulation with phosphorus pool sizes and their net transfer rate

Abstract

Results of an experiment over five solution P concentrations ( 1 , 2, 4, 8, 16 8M P) and five harvests were used in a response surface approach to determine the size and incorporation rates of major plant P pools in white clover (Trifolium repens cv. Ladino) and stylo (Stylosanthes hamata cv. Verano).At low P stylo had a greater total flux of P from the soluble P (inorganic P, ester P) pool to supply lipid and residue P (RNA, DNA, phosphoprotein) pools.At high P concentrations large soluble P pools in tops were associated with depressed dry weight accumulation in stylo compared to white clover. Possible reasons for this effect of soluble P, as related to photosynthetic rate, are discussed.Since both pool size and incorporation rate affected the efficiency of phosphorus use, the two measures were combined in a model of plant P use to assist in understanding reaction to high or low P. The model demonstrated the importance of maintenance of P supply to structural P pools, particulary phospholipids, at low P levels.Pool size and incorporation rate were combined as a transfer coefficient of P. RGR was best correlated with the transfer coefficients of structural (lipid, residue) pools in the roots rather than the tops. R2 values as high as 0.99 were obtained for relationships between structural P pools and dry weight. Strong correlations were also found when the data of both species were combined, including that the same factors were associated with RGR in different species. Selection for 'P efficiency' based on biochemical parameters is possible, but must take account of roots rather than simpler tops P concentrations.