Abstract: We investigated the relationship between the growth characteristics and the change of endogenous hormone contents in needles and root tips of Chinese fir (Cunninghamia lanceolata) with different phosphorus (P) use efficiency under lower P condition, to provide a basis for further understanding of the mechanism of responding to the P stress.[Method] Two half-sib families of Chinese fir (No.4 and No.41, respectively with low and high P use efficiencies under no P supply condition) were treated with three different P levels (P₁:no P supply, 0 mmol·L^-1 KH₂PO₄; P₂:low P supply, 0.5 mmol·L^-1 KH₂PO₄; P₃:normal P supply, 1.0 mmol·L^-1 KH₂PO₄) and cultured in sand medium indoor to investigate the growth of seedlings under different P levels, and the contents of cytokinins (ZT), gibberellins (GA₃), growth hormone (IAA) and abscisic acid (ABA) in needles and roots.[Result] 1) Under no P supply condition, the increments of the average length, surface area and diameter of roots, and the root to shoot ratio of family No.41 were significantly higher than those of family No.4 (P<0.05). 2) Under low P supply condition, the contents of ZT and IAA in the needles of family No.4 were significantly higher than those of family No.41; the content of ZT in roots of the two families were lower than those of normal P level (P<0.05), but both of IAA and ABA contents were significantly increased; the content of ABA in family No.41 seedlings roots was higher than that in family No.4 (P<0.05). 3) Under normal P supply condition, there was no significant correlation between the contents of endogenous hormones and the growth characteristics of the seedlings. Under low P supply condition, the contents of IAA and GA₃ in family No.4 both were negatively correlated with the root length increment (P<0.05); for family No.41, the content of ZT in needles was positively correlated with root length increment, like as root surface area increment (P<0.05), and the content of IAA was positively correlated with the height increment, which was negatively correlated with ABA (P<0.05). Under no P supply condition, the content of IAA in needles of family No.4 was positively correlated with the height increment (P<0.01), whereas the content of ABA in the roots was negatively correlated with the increments of root length, root surface area and root diameter respectively (P<0.05); for family No.41, only the root diameter increment was significantly correlated with the content of ZT, like as GA₃. The seedlings treated with low P and normal P levels displayed no significant correlation between the endogenous hormone contents in needles and the root to shoot ratio; the contents of ZT and GA₃ in roots of family No.4 was positively and negatively correlated with the root to shoot ratio respectively, while the ZT content of family No.41 was negatively and positively correlated with the root to shoot ratio respectively (P<0.01).[Conclusion] Under low P supply condition, compared with family No.41 with higher P use efficiency, the root growth of family No.4 with lower P use efficiency was significantly inhibited. Under no P supply condition, the contents of ABA in needles and roots of the two families with different P use efficiencies (No.4 and No.41) were both significantly increased, but the content of ZT in roots significantly decreased; moreover, there was positive correlation between the ZT content and the root to shoot ratio in seedlings of family No.4, or negative correlation in seedlings of family No.41 which had a high P use efficiency. This is probably related to the capacities of different families with different P use efficiencies in diluting and releasing P nutrient by the aerenchyma of the roots under low P condition.

Key words: Cunninghamia lanceolata, low phosphorus condition, root morphology, plant hormones, regulatory role