关键词: 刺槐, 种子大小, 盐胁迫, 干旱胁迫, 种子萌发, 幼苗特征

Abstract:

Objective: This paper aims to study the germination regularity of R. pseudoacacia seeds with different sizesunder salt and drought stresses, and propose suggestions on the selection of suitable seed sizes and degree of the stress, in order to provide a theoretical basis for the cultivation of excellent seedlings of R. pseudoacacia. Method: The seeds of R. pseudoacacia were divided into three categories of sizes (large, medium and small) with the soil sieve, and the range of seed size, thousand grain weight and the imbibition rate of each category were determined. NaCl andpolyethylene glycol 6000 (PEG6000) (iso-osmotic conditions of 0, -0.05, -0.15, -0.30and -0.49 MPa)were prepared to simulate salt and drought stress. Seeds of different sizes were placed in the light incubator for germination test. In this way, the germination characteristics, seedling biomass and root growth of seeds of different sizes were analyzed, and the plasticity indexes of those seeds were compared. Result: 1) The imbibition rate of large seeds and medium seeds was significantly higher than that of small seeds, and the thousand grain weight of medium and small seeds were reduced by 22.01% and 61.72% respectively compared with large seeds.2)With the increase of stress degree, the germination rate, germination index and vigor index decreased significantly, and the mean germination time increased significantly. The water content, biomass, root length, root surface area, specific root length and specific root surface area of seedlings decreased significantly with the osmotic potential decreasing. Under salt stress, the germination rate, germination index, vigor index and water content of seedlings were higher than those under drought stress. The root dry weight, root shoot ratio, root length, root surface area, specific root length, and specific root surface area under salt stress were lower than those under drought stress.3)In the whole germination process, the large and medium seeds had higher germination rate, germination index, vigor index and seedling biomass compared with the small seeds, but they werenot as good as the small seeds in seedling water content and root development. In addition, seed size had significant interaction with salt and drought stress on seed germination. Compared with small seeds, large and medium seeds had higher germination ability and seedling biomass under stress conditions, though such advantage gradually decreased with the decline of osmotic potential.4)In terms of plasticity index, the total plasticity indexes of large and medium seeds were greater than that of small seeds under both salt and drought stress. The total plasticity index under salt stress was lower than that under drought stress. Conclusion: Salt and drought stresses significantly inhibit the seed germination, seedling growth and root development of R. pseudoacacia, those impacts under drought stress are more obvious than those under salt stress. Large seeds and medium seeds have obvious advantages in germination and seedling growth, but such advantages are affected by the type and degree of the stress. Therefore, both the seed size and stress conditions affect the seed germination and seedling growth of R. pseudoacacia. It is suggested to choose large and medium seeds in sowing and raising seedlings of R. pseudoacacia in arid and saline areas.

Key words: Robinia pseudoacacia, seed size, salt stress, drought stress, seed germination, seedling characteristics