Shoot regrowth and age-specific rhizome storage dynamics of Phragmites austrails subjected to summer harvesting

摘要

Shoots of a monospecific wetland stand of Phragmites australis (Cav.)Trin.ex Steud.in Central Japan were harvested during two summer months in June (June-cut stand)and July (July-cut stand)and their effects on the stand morphology,above- and below-ground biomass and rhizome storage level (in terms of age-specific rhizome bulk density,sigma_(rhiz)),were investigated between themselves and to an uncut control stand.Both harvesting treatments increased leaf production and decreased shoot height,stem diameter,and the storage accumulation capacity of older rhizome age categories,the June-cut stand showing the lowest sigma_(rhiz).Even though the year-end age-specific rhizome reserve level did not reach to that of uncut stand values,both treatments accelerated the post-harvest rhizome reserve accumulation rates (i.e.rate of sigma_(rhiz)increment)stimulated by shoot harvesting,especially in younger rhizomes and were negatively and linearly correlated with rhizome age.The study identified the seasonal changes of the rhizome reserve quality as essential for proper vegetation management.July or August is the appropriate harvesting time for plant stands used in phytoremediation and wastewater treatment,where a larger shoot-bound nutrient stock is removed,while preserving a healthy stand for the subsequent years.A harvest in May to June would be more effective in reducing the growth,and repeated June-cutting may likely weaken the stand beyond repair after several years.