Effect of calcium and potassium nutrition on yield, ion content, and salt tolerance of Brassica campestris (rapa)

When plants encounter salinity, growth is reduced initially by water stress and subsequently by toxic levels of ions and by interference with nutrient acquisition and translocation. Calcium (Ca2 +) in particular seems to have an important role in salt tolerance and there are reports of a beneficial effect of increasing Ca2 + availability. Higher potassium (K+) concentrations in plants may also improve salinity tolerance as sodium (Na)+/K+ ratios have been shown to be important. Previous work with a range of Acacia species has suggested that endogenous seed Ca2 + and K+ concentrations might influence salinity tolerance at germination, but this has not previously been tested with a single species. The objectives of this investigation were thus to determine whether (1) altered Ca2 + and K+ nutrition of Brassica campestris (rapa) L. plants affects the yield and ion content of their seeds, and (2) seeds with different Ca2 + and K+ contents differ in their salinity tolerance. Plants were grown in a growth room or greenhouse in (1) Gem® horticultural sand (2) Silvaperl® perlite and sand (2:1), or (3) Shamrock® Medium General Purpose Irish Sphagnum Peat and Vermiperl® vermiculite (1:1). Plants in each growth substrate were supplied with nutrient solutions based on a modified Hoagland's solution as a control, low Ca2 + and low K+ solutions containing those elements at half the control strength, but all other mineral elements as far as possible at control strength, and high Ca2 + and high K+ solutions containing those elements at double control strength but all other mineral elements, as far as possible, at control strength. An increase in substrate available Ca2 + and K+ resulted in increased Ca2 + and K+ concentration in seeds, respectively, and was accompanied by a reduction in seed K+ and Ca2 +, respectively. The Ca2 + and K+ concentrations of seeds affected their salinity tolerance. Increases in seed Ca2 +, K+ or Ca2 ++ K+ concentrations decreased salinity tolerance at germination. The results, especially in terms of Ca2 + nutrition, contradict previous results of an increased salinity tolerance with increased Ca2 + and/or K+ concentrations.