Lycoris radiata, a winter-green geophyte has about a 4-month leafless period from early June in Kanto region of Japan. The species maintains an active root function during the leafless period. The aim of the present study is to examine effects of nitrogen uptake during the leafless summer on winter growth of the plants.

We carried out experiments to compare biomass among plants with different regimes of nitrogen supply. Plants were potted individually in April, kept outdoors in Kawasaki, Japan, and harvested to measure biomass about 2 and 3 months after leaf emergence.

The plants supplied with nitrogen in leafless summer attained larger biomass than those supplied with nitrogen after leaf emergence in autumn or control plants without nitrogen supply. Although the plants with autumn nitrogen supply had higher concentrations of nitrogen in leaves and higher photosynthetic activities, their biomass was not significantly different from that of the control plants. In addition, the plants supplied with nitrogen only in summer attained biomass not significantly different from those supplied with nitrogen both in summer and autumn. These results suggest that summer nitrogen uptake is crucial to biomass production of the species at least in the early stage of the growing period.