Effects of Exogenous Ethylene and Cobalt Chloride on Root Growth of Chinese Fir Seedlings under Phosphorus-Deficient Conditions

Abstract

Studying the effects of different concentrations of ethephon on morphological and physiological changes in the roots of Chinese fir (Cunninghamia lanceolata Lamb. Hook.) seedlings under P deficiency can reveal the internal adaptive mechanisms of these plants under nutrient stress. Herein, we investigated the effects of different ethephon and cobalt chloride concentrations under normal P supply and P deficiency. A significant effect (p < 0.05) of exogenous additive application was observed on the development of Chinese fir root length, surface area, and volume. These root development indices showed maximum values when the ethephon concentration was 0.01 g kg−1 under normal P supply and P deficiency, and they were significantly different from those under 0.04 g kg−1 ethephon treatment. Similarly, the indices showed maximum values when CoCl2 concentration was 0.01 g kg−1 under P deficiency and was significantly different (p < 0.01) from those under 0.2 g kg−1 CoCl2 treatment. Under normal P supply, an increase in ethephon concentration caused superoxide dismutase (SOD; E.C. 1.15.1.1) activity to decrease and peroxidase (POD; E.C. 1.11.1.X) activity to increase gradually. Conversely, CoCl2 addition (0.01 g kg−1) promoted SOD and POD activities under P deficiency. There were no significant differences (p > 0.05) in malondialdehyde content of seedlings among ethephon or CoCl2 treatments. In conclusion, ethylene plays a significant role in adaptative mechanisms underlying stress resistance in plants, prompting them to respond to P starvation and improving seedlings’ tolerance to P-deficient conditions.