Calcium-mediated adaptive responses to low phosphorus stress in Chinese fir

Abstract

Ca2+ induces adaptive response to low P stress through increased root growth and expansion, but plays minor or no role in remobilization of P in leaf tissues or in maintaining membrane integrity. The role of calcium (Ca2+) in signaling environmental stress has been demonstrated; however, its role in signaling low phosphorus (P) stress and subsequent adaptive responses in trees are largely unexplored. The aim of this study was to examine the effects of Ca2+ application on root growth and expansion, seedling growth, remobilization of P, and maintaining membrane integrity in leaf tissues. Thus, a sand culture experiment was set up with five Ca2+ concentrations (0, 1, 3, 5, and 10 mmol/L Ca(NO3)2·4H2O) under two P treatments (0.0 and 1.0 mmol/L KH2PO4). After 4 months, growth attributes, P and Ca2+ accumulations, and biochemical responses were determined. Results showed that (1) low P seedlings supplied with 5 mmol/L Ca2+ produced longer roots, larger root surface area, higher root diameter, and larger root volume than the control; (2) seedling height and root collar diameter were positively affected by addition of 3 and 5 mmol/L Ca2+ into the growing media, and whole plant biomass of low P seedlings supplied with 5 mmol/L Ca2+ was significantly higher than the control; (3) whole plant P accumulation was higher in 3 and 5 mmol/L Ca2+ treatments in low P seedlings, whereas whole plant Ca2+ accumulation increased linearly with increasing Ca2+ concentration; and (4) the effects of Ca2+ on malondialdehyde and soluble protein contents and acid phosphatase activity did not show consistent trend with increasing or decreasing Ca2+ concentration. In conclusion, Ca2+ induces adaptive response to low P stress through increased root growth and expansion, but plays minor or no role in remobilization of P in leaf tissues or in maintaining membrane integrity.