Abstract:

Objective: To verify that the addition of exogenous ethylene can promote the root growth of Chinese fir seedlings under phosphorus stress and improve the utilization rate of phosphorus to adapt to adversity. Method: The seedlings of Chinese fir from No. 25 half-sib family cultivated at the seed garden of Wuyi National Forest Farm in Zhangping, Fujian Province, which were selected as experimental materials. Two phosphorus(P) levels of low P supply(P₀: 0 mmol·L^-1 KH₂PO₄) and normal P supply(P₁: 1 mmol·L^-1 KH₂PO₄) were set. Three reagent treatments were designed at different P levels(E+: 200 mg/L ethephon, 0:no additive reagent, E-: 5 mol·L^-1 ethylene synthesis inhibitor CoCl₂). After 30 days of treatment, ethylene in roots was collected by headspace method, and indexes such as seedling height, ground diameter, root morphology, P content and dissolution rate of cortex cells in Chinese fir seedlings were measured. Result: 1) Phosphorus stress and exogenous ethylene both promoted the increase of endogenous ethylene in the roots of Chinese fir seedlings, and the ethylene content in roots treated with exogenous ethylene(E+) was higher than that of other treatments at different phosphorus supply levels, With the increase of endogenous ethylene content, the ability of seeking phosphorus in the roots of Chinese fir seedlings is enhanced, the phosphorus content in the shoots and roots is significantly increased, and the phosphorus utilization rate is improved. 2) Under phosphorus stress, the increment of seedling height in the treatment with exogenous ethylene(E+) was significantly lower than that in the treatment with ethylene inhibitor(E-) and the treatment without ethylene inhibitor(CK), while the increment of ground diameter was the opposite.3) The addition of exogenous ethylene treatment(E+) increased the growth of root length, average root diameter and root volume increment of Chinese fir seedlings, and each index was positively correlated with the absorption of available phosphorus in soil by roots, which promoted the absorption of phosphorus in soil by roots of Chinese fir seedlings. 4) Under phosphorus stress, the addition of exogenous ethylene treatment(E+) increased the lytic rate of the root cortex, and the three treatments reached an extremely significant level, while the difference was not significant under normal phosphorus supply environment. Conclusion: Under phosphorus stress, the content of ethylene in roots of Chinese fir treated with exogenous ethylene had a significant correlation with the morphological growth of roots, and the ground diameter, root length, average root diameter and root volume of Chinese fir increased significantly. Under phosphorus stress, the addition of exogenous ethylene increased the phosphorus content and root ethylene content of Chinese fir seedlings and increased the lytic rate of root cortex cells. In order to further reveal the mechanism of exogenous ethylene as the key factor of phosphorus regulation on the growth of Chinese fir seedlings under phosphorus stress.

Key words: exogenous ethylene, Chinese fir, phosphorus stress, seedling growth index, chemical volatiles