Abstract: Borszczowia aralocaspica, an annual halophyte, is an endemic species in the Central Asian deserts, whose dimorphic seeds are differed in color (black and brown), shape and size. The present study was to compare the differences in the physiology and biochemistry materials and seed coat structures of dimorphic seeds of B.aralocaspica, and reveal the effect of reproductive allocation on the ecological adaption mechanism of dimorphic seeds. The seeds were collected in natural populations from Fukang county in Xinjiang. A total of 1000 grains of dimorphic seeds of B.aralocaspica were respectively selected and weighted for black and brown seeds. The seed coat structures were observed by scanning electron micrographs (SEM). The soluble sugar, soluble protein and nutrient element of dimorphic seeds were also tested. Black seeds had two layers of seed coat compared to single layer in brown seeds. The structures of both seeds were found to be totally different. Brown seeds are bigger than black ones, and the weight distribution was mostly focused on 2.1 to 3 mg. The contents of soluble sugar, soluble protein, total nitrogen, total phosphorus, K⁺, Na⁺, K⁺/Na⁺ and Mg²⁺/Na⁺ in brown seeds were significantly higher than those in black seeds. In the process of reproduction, the resource allocations of the maternal plant to brown seeds and black seeds are different, which leads to the distinct differences in dormancy and germination mechanism. This will help it to adapt to the unstable desert environment, and to maintain the stability of the B.aralocaspica population.

Key words: Borszczowia aralocaspica, dimorphic seeds, halophyte, reproductive allocation, SEM