Acid phosphatase activity of intact roots and phosphorus nutrition in plants. III. Its relation to phosphorus garnering by wheat and a comparison with leaf activity as a measure of phosphorus status

Eight wheat cultivars, selected on the basis of their root phosphatase (E.C. 3.1.3.4.1) activities to provide a range of phosphorus garnering abilities, experienced difficulty in taking up phosphorus from a nutrient solution containing 1 �M phosphorus, a level frequently found in the soil solution. Under the experimental conditions, total phosphorus uptake by the plants was not affected by root weight, length or fineness, nor by early plant vigour as indicated by relative leaf expansion rates during the first 3 days. With this low phosphorus source, standard root phosphatase activity was not related to phosphorus uptake but was related to total phosphorus content of the plants (r = -0.736; P < 0.01). When root phosphatase activity and total phosphorus content were determined on the same plants, the correlation was improved (r = -0.914; P < 0.001), which suggests that root phosphatase activity is a good indicator of the present phosphorus status of a plant. This suggestion was tested further by determining leaf and root phosphatase on wheat plants which were responding in yield and in phosphorus uptake to four levels of phosphorus supply. In actively growing plants, leaf phosphatase (E.C. 3.1.3.4.1) activity was better related to total phosphorus uptake (r = -0.963; P < 0.001) than was root phosphatase activity. At a second stage, where yields continued to increase but there was little change in the phosphorus content of the plant other than in its redistribution between component parts, root phosphatase was better related to total phosphorus uptake (r = -0.910; P < 0.001). Nevertheless leaf phosphatase activity was still significantly related to total phosphorus uptake (r = -0.853; P < 0.001), and could prove to be a useful measure of the phosphorus status of the growing plant. In all cases total phosphorus content and total yield were positively related (r = +0.94; P < 0.001).