Abstract:

Objective: This study aims to understand the effects of propagation methods on root biomass allocation and growth of different order roots of Chinese fir seedlings, which is helpful to reveal the differences in individual root development status and growth strategies of Chinese fir seedlings. Method: One-year Chinese fir seedlings cultivated by seed germination, tissue culture and cutting were used to examine the differences in root biomass, morphological traits and tissue carbon and nitrogen content at different order levels, and analyze the relationships among the measurement indexes of root biomass at different order levels, so as to explore the differences in the influence of propagation methods on root growth strategies of Chinese fir seedlings. Result: 1) There were significantly differences (P<0.05) in the root: shoot ratio of Chinese fir seedlings cultured by different propagation methods, with the order as cutting > seedlings > tissue culture seedlings. In terms of the distribution of root biomass in the same order, the biomass [(0.68±0.13)g per plant] of the first order roots of cuttings was 4.31 times that of seedlings and 1.09 times that of tissue culture seedlings. The biomass of 2^th-4^th order roots of tissue culture seedlings was significantly greater than that of seedlings and cuttings, with values of (1.19±0.21)g per plant, (1.63±0.19)g per plant and (1.82±0.27)g per plant, respectively The biomass accumulation of different order roots of tissue culture seedlings and cuttings was greater. 2) Seedlings promoted 1-2 order root extension through 4 order root growth, and their 4-order root biomass and 1-2 order root specific surface area were significantly larger than those of tissue culture seedlings and cuttings (P<0.05). However, the root average diameter and specific root length of the 1-order roots of tissue culture seedlings and cuttings were significantly greater than those of seedlings, showing a strategy to enhance resource absorption efficiency by increasing diameter and length. 3) There were differences in the C and N contents in different order roots of seedlings, tissue culture seedlings and cuttings. The N content of 1-2 order roots of tissue culture seedlings and cuttings was significantly higher than that of seedlings (P<0.05), but the N content of 3-4 order roots was significantly lower than that of seedlings. The C content of 1-4 order roots of tissue culture seedlings was significantly lower than that of seedlings and cuttings. The C/N ratio of the 1-order roots of tissue culture seedlings and cuttings was significantly lower than that of seedlings. 4) The root biomass of seedlings was significantly correlated with tissue N content in grade 1 order roots, morphological traits of 2-3 order roots, and morphological traits and tissue C content in 4 order roots (P<0.05). For tissue culture seedlings and cuttings, there was significant correlation between root biomass and 1-2 order root morphological traits, 3-4 order root morphological traits, as well as tissue C content, reflecting that there was the ecological trade-off relationship between morphological construction and resource acquisition efficiency at different root order levels. Conclusion: There are significant differences in the root development level and growth strategy of Chinese fir seedlings cultivated by different propagation methods. The root system of seedlings shows the growth strategy of exploring and searching for soil space resources. In contrast, the root morphology construction characteristics and growth strategies of tissue culture seedlings and cuttings are more similar, showing a growth strategy to enhance the absorption and utilization efficiency of occupied space resources.

Key words: Cunninghamia lanceolata, propagation methods, root orders, biomass allocation, morphological structure characteristics, growth strategy