The Effects of Phosphorus Supply on The Rates of Intake of Phosphorus and Nitrogen and Upon Certain Aspects of Phosphorus Metabolism in Gramineous Plants

Abstract

SummaryFor experiments previously described, new data are presented relating to the intake of phosphorus by gramineous plants, its distribution within the plant, and its partition in the leaves between alcohol-soluble, nucleic-acid, and "residual" phosphorus.Major determinants of the rate of intake of phosphorus by the plant are: ( a) the demand set up by the growth and normal functioning of various plant parts, and (b) the concentration of the nutrient in the medium.It is considered that the indirect effect of phosphorus treatment on growth, and hence on demand, is more important than the direct effects of external concentration of phosphorus on the rates of intake of that nutrient.Even when growth is not limited by the supply of phosphorus, the rate of intake is limited by the maximal capacity of successive plant parts for accumulation.For the oat experiment, rates of intake of phosphorus and nitrogen are expressed per unit weight of root system. With nitrogen, the supply of which was the same for all treatments, large initial effects of phosphorus treatment on the rates of intake are accounted for in terms of differences in the ratios of roots to shoots.Phosphorus-deficient oat plants derived only 30 per cent. of their inflorescence phosphorus from other plant parts; those with an excessive supply derived no less than 93 per cent. of their inflorescence phosphorus from these sources.The percentage phosphorus contents of the stems, leaves, and roots fell ultimately to lower values with a moderate supply of phosphorus than they did with the deficient supply. A more efficient re-utilization of phosphorus in the plants receiving the greater supply is favoured as an interpretation of this "dilution" effect.From an examination of the data for protein-nitrogen and nucleic-acid phosphorus in the leaves of young plants, it is concluded that the effects of phosphorus treatment on protein-nitrogen content at this stage are due primarily to variation in nucleoprotein content.With phosphorus deficiency, oat seedlings soon exhausted their seed reserves of phosphorus, and this was followed by a drastic change in the partitioning of leaf phosphorus, such that absolute nucleic-acid phosphorus was reduced to one-fifth of the value obtaining eleven days earlier, alcohol-soluble phosphorus decreased slightly, and the water-soluble fractions represented by "residual" phosphorus increased by 30 per cent. Total phosphorus was virtually unchanged in amount. During this same period of eleven days, the whole of the phosphorus intake from the medium was retained by the roots, and there was a stimulation of root growth relative to leaf growth. These facts suggest that the high root weight ratios found with phosphorus deficiency may be due to the fixation in organic forms of a greater proportion of the absorbed phosphorus, so that relatively little is available for shoot growth. The literature relating to the partitioning of phosphorus within plant tissues is discussed and, where comparisons are relevant, this is in substantial agreemen...

Nutrient Uptake and Distribution in Subterranean Clover During Recovery from Nutritional Stresses I. Experiments with Phosphorus

“…Although the demand set up by each of the organs is usually met in part, if not entirely, by uptake from the medium, the rate of intake by the roots can be restricted to the extent that the nutrient is more readily available within the plant itself. This point was illustrated (Williams 1948) with results of an experiment with oat plants grown at different phosphorus levels. Deficient oat plants derived 30% of their inflorescence phosphorus from other plant parts, whereas plants grown with a high phosphorus supply derived no less than 93% of their inflorescence phosphorus from other plant parts.…”

Interaction Between Potassium and Calcium in Their Absorption by Intact Barley Plants. II. Effects of Calcium and Potassium Concentration on Potassium Absorption

“…Rates of K absorption per gram fresh weight of roots were calculated between successive harvests using \Villiams' formula (22) which makes allowanice for increasing root weight as described in the previous paper (10).…”

Effects of Temperature On Growth and Nutrient Uptake In Subterranean Clover During Recovery From Phosphorus Stress

“…A comparison between plants of different sizes or growth rates is facilitated by expressing the nutrient uptake per unit root weight in unit time (Williams 1948). Below is shown the nutrient uptake by PI and P 2 plants raised at t2 for the 7 days after transfer to TI, T2, and T3, expressed as micrograms of phosphorus per milligram root weight per day: Nutrient uptake by:…”