Effects of soil temperature on root growth and on phosphate uptake along Pinus radiata roots

Abstract

At 3 weeks, uptake of phosphate along roots of seedlings grown in soil at 25°C was greatest in the apical centimetre and decreased sharply along the roots. By contrast uptake was markedly more sustained along the roots of seedlings grown in soil at 14°C and here the greatest uptake occurred several centimetres behind the apex. No one pattern of ion uptake along roots can be assumed to hold for all conditions of growth when constructing mathematical models of ion uptake from soil. Increasing soil temperature from 15°C to 25°C approximately doubled total root length of 3-week seedlings of Pinus radiata; primary root length was increased but the main effect was due toa marked increase in the number and length of lateral roots. Lateral root growth of the 3-week seedlings was almost completely suppressed in the soil at 11°C. Roots of 3-week sterile seedlings growing in phosphate-deficient nutrient solution were considerably smaller than those of pine grown in complete nutrient solution at 15°C but not at 25°C. This interaction of temperature and phosphate deficiency did not occur with soil grown seedlings. The sustained phosphate uptake along roots grown at the low soil temperature did not compensate for greater root growth (and therefore soil exploration) at higher temperatures, for P content of 3-week seedlings grown in soil at 25°C was considerably greater than that of seedlings grown in soil at 15°C. In phosphate poor soils low temperature depression of root growth will seriously restrict phosphate uptake. A modification of the scanning method for uptake sites along roots showed translocation to occur from all parts of the root with rather less translocation from the apical centimetre than from other parts.