The Fruit-set Pattern And Reproductive Allocation Of Dimorphic Seeds Of The Euhalophyte Suaeda Salsa

Suaeda salsa L. is an annual euhalophyte with high salt tolerance. Up to now, the study of dimorphic seeds in the species mainly focus on seed germination.There is no information about fruit-set pattern and reproductive allocation in S. salsa. Therefore, the present study investigated these aspects in the species. 1. Effect of salinity on production and salt tolerance of dimorphic seeds of S. salsa in an indoor experimentThe effect of salinity on brown seeds/black seeds ratio, seed weight, endogenous hormone concentrations, and germination of brown and black seeds in S. salsa from inland saline soils was investigated in this experiment. The brown seeds/black seeds ratio, seed weight of brown and black seeds and the content of protein increased at 500 m M Na Cl compared to low salt condition(1 m M Na Cl). The germination percentage and germination index of brown seeds from plants cultured in 500 m M Na Cl were higher than those cultured in 1 m M Na Cl, but it was not true for black seeds. The concentrations of IAA(indole-3-acetic acid), ZR(free zeatin riboside) and ABA(abscisic acid) in brown seeds were much greater than those in black seeds, but there was no difference in the level of GAs(gibberellic acid including GA1 and GA3) regardless of the degree of salinity. Salinity during plant culture increased the concentration of GAs, but salinity had no effect on the concentrations of the other three endogenous hormones in brown seeds. Salinity had no effect on the concentration of IAA but increased the concentrations of the other three endogenous hormones in black seeds. Accumulation of endogenous hormones at different concentrations of Na Cl during plant growth may be related to seed development and to salt tolerance of brown and black S. salsa seeds. These characteristics may help the species to ensure seedling establishment and population succession in variable saline environments.2. Effect of salinity on fruit-set pattern and reproductive allocation of S. salsa under saline conditionThe effect of salinity on reproductive allocation and fruit-set pattern was investigated in S. salsa from an intertidal zone under saline condition. The reproductive allocation and fruit-set pattern were investigated after plants were treated with 1 or 500 m M Na Cl for 120 days in a glasshouse. The results showed that high salinity(500 m M Na Cl) decreased the shoot dry weight, but increased the reproductive allocation,i.e., the reproductive allocation at 500 m M Na Cl was 3.6 times of that at 1 m M Na Cl. This indicated that S. salsa can allocate more resources to the reproductive organs at high salinity. High salinity significantly reduced the number of secondary branches, but had no significant effect on the number of primary branches. High salinity decreased the percentage of unfilled grains, increased the number of fruits and seeds in each node of primary and secondary branches. The characteristics of reproductive allocation and fruit-set pattern may ensure the establishment of the population of S. salsa in saline environment.3. The reproductive allocation and fruit-set pattern of S. salsa from an intertidal zone in fieldThe soil water content and salt content were measured in soils where S. salsa from an intertidal zone occurs. The results showed that salt content was higher and nutrition content was lower in soils of upper tidal line than those in lower tidal line. The biomass of plants collected from upper tidal line was lower than that from lower tidal line, but the opposite trend was true in the reproductive allocation. The brown seeds/black seeds ratio increased but the percentage of unfilled grains decreased for the plants from upper tidal line compared to that in lower tidal line. The number of branches(especially secondary branches), nodes and the distribution of fruits and seeds in S. salsa from upper tidal line were higher than those from lower tidal line in different levels of branches. The number of nodes in different levels of branches progressively decreased in plants from either upper or lower tidal line. Therefore, more resources may be allocated to primary branches in order to produce a greater number of secondary and tertiary branches and to produce more fruits. The distribution of fruits decreased from the bottom to the top in all levels of branches. More seeds were produced at the bottom and middle of all levels of branches, and there were only 1 or 2 brown seeds and almost no black seeds were found at the top of branches. There were more fruits and brown seeds in plants of S. salsa from upper tidal line than plants in lower tidal line. There was no significant difference in the number of black seeds in secondary and tertiary branches between plants in upper and lower tidal line, except that the number of black seeds in primary branches was higher in lower tidal line than that in upper tidal line. The mainly reason may be that plants may preferentially ensure the production of brown seeds, and allocate surplus resources to the production of black seeds. The reproductive allocation and fruit-set pattern traits will ensure S. salsa in an intertidal zone to establish its population in harsh saline environments.