The Effect Of Defoliation On The Growth And Photosynthetic Characteristics Of Cinnamomum Camphora Under Different Light Levels

In this paper, the effects of light intensity and leaf loss on biomass partitioning of plants were investigated. Two factors including light intensity and leaf loss were considered in the experiment. For the factor of light intensity, three light intensities were applied: full irradiance (100%), intermediate irradiance (43.5%) and low irradiance (6.74%); for the factor of leaf loss, plants were given defoliation (70% of total leaves removed) and non-defoliation treatment. The results of this experiment are as follows:(1) Defoliation and different light intensities changed the pattern of biomass partitioning of plants. Plants partitioned more biomass to the underground parts at high irradiance and more biomass to leaves at low irradiance. Biomass partitioned to roots and leaves of plants at intermediate irradiance went between those of plants at high and low irradiance. Defoliation of plants led to an increased partitioning of biomass to leaves, but the results were different at different time. Moreover, defoliated plants partitioned more biomass to leaves at low irradiance than defoliated plants at high irradiance.(2) The leaf efficiency of plants increased with increasing irradiance. For all three light levels, leaf efficiency of defoliated plants exceeded non-defoliated plants evidently. The quantity of increased leaf efficiency contributed to the aboveground biomass gain after defoliated are different at different irradiance. At the initial stage, the increased leaf efficiency of defoliated plants contributed more to biomass increment of aboveground under higher light level than those under lower irradiance. As the treatment time extended, the contribution to growth of increased leaf efficiencyof plants under intermediate light level went beyond those under full irradiancy. The result show that defoliation can't reduce but increase leaf efficiency, and moderate shade will improve plants' aboveground growth.(3) Both different light levels and defoliation caused changes of leaf nitrogen content. Generally speaking, leaf nitrogen content per unit leaf area increased under high irradiance and was significantly higher than those under low irradiance. On the contrary , nitrogen concentration decreased with increasing light levels. Defoliation led to lower leaf nitrogen content but higher nitrogen concentration contrasted with controlled plants. Researches showed that leaf nitrogen content and leaf nitrogen concentration change with different light and defoliation treatment. Both reduced irradiance and defoliation caused decreased SLM (specific leaf mass).(4) Generally, chlorophyll content and chlorophyll concentration increased with reduced light levels, the ratio of chlorophyll a to chlorophyll b of defoliated plants was higher than those of controlled plants, while in latter period, the results were contrary to that of the former period. The light saturation point was lower of defoliated plants than that of non-defoliated plants. With reduced light irradiance, light saturation point also decreased. Dark respiration changed with the same trend of light saturation point. But apparent quanta efficiency was not differentiated remarkably and need to be researched further.