Influence of shade timing on an Equisetum arvense L. population

Equisetum arvense L. is a perennial pteridophyte that grows in open sites. In Tokyo, the plant has photosynthetic shoots from late March to November. However, in some populations, these shoots are lost before summer because of shading by taller plants. To investigate the contribution of shoots that remain on the plant for a certain duration, in terms of the maintenance of the E. arvense population, tubers were cultivated under different light conditions and the dry weight of growth, photosynthetic rates and respiration rates were measured. Individual growth was simulated on the basis of matter production and its partitioning. Biomass at the start of the next growing season (the initial size) was seriously decreased by shading before July. However, shading after July had little effect on the initial size of the next season plants. Thus, E. arvense can maintain its population if its shoots are retained until summer.