Organic matter economy of Euphorbia adenochlora with special reference to its life cycle

The dry matter economy of Euphorbia adenochlora Morra et Decne was investigated in a moist tall grassland in the Tajimagahara nature reserve, which protects a riverside grassland on the Arakawa river in Saitama Prefecture, central Japan. Euphorbia adenochlora is a typical short clonal species in the flood plain meadows, but is listed as an endangered species. It starts to grow in late February, and grows fast in early April by using one-third to about half of the dry matter of the rhizomes, which are composed of annual segments up to 8–10 years of age. During the period of fastest growth in early April, the bulk density (g dry weight cm^–3) of the rhizomes attained the minimum value. By the end of May, it reached its maximum. When ¹³CO₂ was fed to the shoots by means of photosynthesis, the concentration of ¹³C-containing photosynthates was highest in the new rhizome segment; the older the segment the lower the concentration of ¹³C. Shoot-clipping of E. adenochlora in late April, when bulk density was near the minimum, greatly depressed shoot growth in the following year. At the beginning of June, all of the aerial shoots of E. adenochlora died out with the growth of tall grasses. These results suggest that E. adenochlora has a life cycle as a spring ephemeral.