Control of weeds and shrubs by the short-term intensive clearing on natural regeneration sites as related to their physiological properties of photosynthesis

点击翻译按钮获取中文摘要

1.Physiology of photosynthetic system1) Measurements of pulse-modulated chlorophyll fluorescence were useful for stress-diagnosis of regenerated leaves of weeds and shrubs after clearing. Diurnal drops in photosynthetic quantum yield were associated with photo-inhibition linked to water deficit ; water and nutrient conditions in leaves seemed to closely relate to photo-inhibition. 2) Establishment of photosynthetic system in cotyledons of tree seedlings was examined throughout changes in total-N and Rubisco contents after germination. Although photosynthetic system was established in a few weeks by rapid activation of N metabolism followed by germination, photosynthetic activity immediately decreased probably due to translocation of N to other organs and therefore highly stable stage was not observed. Nutrition condition in soil greatly influenced photosynthetic activity in cotyledons through effect of N contents.2.Vegetative propagation types for shrub speciesSeedlings of seven shrub species which had occurred after the cutting of a deciduous broad-leaved forest was investigated. Vegetative propagation by underground organs was divided into four types ; single sprouting, mulch-sprouting, horizontal root sprouting, subterranean stem sprouting ones. First subterranean stem sprouting types and secondarily horizontal root sprouting ones would act as tough competitors for tree seedlings because they are able to occupy the living space quickly at extremely high phytomass density.3. Ground treatment by machineryGround treatment by a small-sized excavator was made to reduce the regeneration of weeds and shrubs on a natural reproduction site. The mechanical treatment kept the reproduction site at low coverage condition for several months, delayed the bamboo grass development for a year, and restricted the shrubs development. Out of these three effects, the first one was considered to contribute most largely to the seedling establishment of objective tree species.