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

1)脉冲调制的叶绿素荧光测量有助于杂草和灌木清除后再生叶片的逆境诊断。光合作用量子效率的昼夜下降与缺水引起的光抑制有关；叶片中的水分和营养状况似乎与光抑制密切相关。2)通过萌发后全氮和Rubisco含量的变化，研究了树苗子叶中光合作用系统的建立。虽然光合作用系统在几周内通过快速激活氮代谢和萌发而建立，但光合作用活性立即下降，可能是由于氮素向其他器官的转移，因此没有观察到高度稳定期。土壤营养条件通过N含量对子叶的光合作用有很大的影响。2.灌木树种的无性繁殖类型调查了7个灌木树种的苗木采伐落叶阔叶林后的苗木生长情况。地下器官营养繁殖可分为4种类型：单芽型、地膜型、水平根型、地下茎发芽型。首先是地下茎萌发类型，其次是水平根萌发类型，因为它们能够在极高的植物量密度下迅速占据生存空间，是树苗的有力竞争对手。机械地面处理用小型挖掘机进行地面处理，以减少自然繁殖场地上杂草和灌木的再生。机械处理使繁殖地处于低盖度状态数月，使竹草发育延迟1年，限制了灌木发育。在这三个效应中，第一个效应被认为对目标树种的成苗贡献最大。

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.