Abstract
Distribution patterns of two Drosera species (Droseraceae), D. rotundifolia and D. tokaiensis subsp. tokaiensis, are discussed in relation with the soil water conditions studied by continuous observation of soil water content and soil water qualities during the dry and wet seasons in summer in small-scale spring-fed marshes, Kani City, Central Japan. Soil water contents calculated from the electrical permittivity in fields correlated with the distribution pattern of two Drosera species; D. rotundifolia grew in wet areas over 0.4 m3m-3 water content and D. tokaiensis subsp. tokaiensis in dry areas under 0.1 m3 m-3 water content. The ion compositions of the water extracted from the soil differed; K+ and NH4+ were more abundant in the habitats of D. tokaiensis subsp. tokaiensis than those of D. rotundifolia, perhaps due to the difference in salt concentrations caused by drying off. Judging from the water content of the soil and the diurnal quantitative fluctuation and qualities of soil water, we deduce that, in dry seasons, habitats of D. rotundifolia are recharged by rainfall leaking out from the ground, and those of D. tokaiensis subsp. tokaiensis by sorption from the moister layers under impermeable layers or dewfalls.
