|Abstract or Summary
- The effects of soil temperature and soil water suction on the
uptake of calcium, magnesium, and potassium by wheat (Triticum
aestivum VILL., Host) were studied. Companion studies on uptake of
nitrogen and phosphorus provided background for discussion of the
results. Plants were grown in perlite slabs separated from an
osmotic solution by a semi-permeable membrane. Five week old
seedlings were used for the measurements made at root temperatures
of 10.0, 18.3, 23.9, and 32.2°C, and soil water suctions of 0.35 and
2.5 bars. Air temperature remained constant at 23.9°C during these
experiments. The dry weight of shoots and roots was determined at
two-day intervals. Plant material extract was analyzed by atomic
absorption spectrophotometry for concentrations of calcium,
magnesium, and potassium.
Rates of dry weight accumulation for both shoots and roots were
highest when temperature of the root environment was about 24°C.
The rate of growth was higher at a soil water suction of 0.35 bar than
at 2.5 bars for all root temperatures tried. Concentrations of potassium,
nitrogen, and phosphorus increased with increasing root temperature
in both shoots and roots. By contrast, concentrations of
magnesium were minimally affected by temperature differences; concentration
increased slightly in the roots as temperature increased
but remained the same in the shoots. Concentration of calcium in both
shoots and roots decreased as temperature increased. This was
attributed to a combination of ion interaction and temperature effects.
The rate of uptake for all five elements, i. e. , calcium, magnesium,
potassium, nitrogen, and phosphorus increased to a maximum rate
and then decreased with increasing root temperature.
The translocation of ions to the shoots was lowest for calcium.
The fraction of total uptake translocated to the shoots was for:
magnesium, 69%; potassium, 83%; nitrogen, 74%; phosphorus, 72%;
and calcium less than 50%. Calcium content in the shoots was less
than in the roots. The limited translocation of calcium to the shoots
was attributed to its high degree of immobility. It was retained by the
roots in relatively high concentration.
The mineral concentration of plants grown at soil water suctions
of 0.35 and 2.5 bars were not significantly different statistically while there was a significant reduction in the rate of plant growth at a
soil water suction of 2.5 bars. As a result of the reduced growth rate
at the higher suction the rate of ion uptake was also reduced even
though the concentrations in the plant tissue at the two suctions were
the same. Under the conditions of these experiments water availability
affected plant growth apparently more by its effects on plant physiological
functions other than mineral uptake.