Low Light's Effect On Photosynthesis And Mechanism Of Membrane Injury Of Peach Tree

Light is the necessary factor of plant upgrowth and developing. Low light become the main factor which restricts plant upgrowth, yield and quality in geeenhouse planting. The experiment takes late-maturing peach for material, which is normal planting breeding in Lan-zhou, and imitates low light in greenhouse by controlling light quantity artificially. Eventually, The experiment researchs the low light's affacts on photosynthetic characters, nutritious upgrowth, breeding upgrowth, metabolism of reactive oxygen species and responsing mechanism of peach tree. The main results as followings:1. In 400μmol/m2s low light treament, peach leaves'photosynthetic rate, stomatal conductance, intercellular CO2 concentration and evaporation rate are decreasing. The main reason is that stomatal conductance decreasing prevents H2O and CO2 exchanging between peach leaf and environment, which not only cause evaporation weakening, but affact CO2 offering so that lead to photosynthesis descending. It indicates that photosynthesis descending in 400μmol/m2s low light is related to stomatal factor mainly. Under 200μmol/m2s low light treament, peach leaves'photosynthetic rate, stomatal conductance and evaporation rate are decreasing, but intercellular CO2 concentration is increasing. It illustrates that photosynthesis descend under 200μmol/m2s low light mainly because of lower light quantity, which leads to intercellular CO2 concentration accumulation. In this condition, stomatal affacts photosynthesis indirectly.2. In 400μmol/m2s and 200μmol/m2s low light treament, total Chl. content in peach leaves is higher than 800μmol/m2s natural light, but Chl.a/b value is lowwer. And in 80μmol/m2s and 30μmol/m2s low light treament, total Chl. content in peach leaves is lower than 800μmol/m2s natural light, Chl.a/b value is higher. It implies that peach tree adapt to the environment by inducing light-capture ability and light-utilization efficiency enhancing in 400μmol/m2s and 200μmol/m2s low light conditions. And under 80μmol/m2s low light not only affects Chl.'s synthesim, but it also prevent Chl.a transforming to Chl.b, which lead to light-utilization efficiency decreasing.3. By contrast of 800μmol/m2s natural light condition, 400μmol/m2s low light has littie effects on leaf area, leaf fresh-weigh , leaf dry-weigh, time of fallen flowers and carborhybrate content, but fruit-settle efficiency enhance. 200μmol/m2s and 80μmol/m2s low light treament cause leaf area, leaf fresh-weigh and leaf dry-weigh increasing, value of dry-weigh/fresh-weigh, fruit-settle efficiency and carborhybrate content decreasing. 30μmol/m2s low light treament cause leaf-upgrowth stopping, flower withering and losing fruit-settle capability. Fruit-settle efficiency enhance in 400μmol/m2s low light maybe because high light's injury on flowers are reducing. 200μmol/m2s and 80μmol/m2s low light treament cause carborhybrate synthesis decreasing, prevent carborhybrate's transforming to flower, lead to fruit-settle efficiency reducing. 30μmol/m2s low light is close to light compensation point of peach tree, which cause nutrition lackness, lead to peach tree's mechanism declining eventually.4. By contrast of 800μmol/m2s natural light condition, 400μmol/m2s low light has littie effects on O2-. Production rate, H2O2 and MDA content, under 200μmol/m2s low light, the O2-. Production rate, H2O2 and MDA content increas with light quantity declining. In 400μmol/m2s, 200μmol/m2s and 80μmol/m2s low light, SOD and CAT acticity is higher than contrast, but 30μmol/m2s low light cause SOD and CAT acticity is lower. It indicate that 200μmol/m2s and 80μmol/m2s low light cause reactive oxygen species quick producing and SOD and CAT acticity enhance, but the latter's increasing cann't offset reactive oxygen species'quick producing, which lead to membrance peroxidize injury on peach tree. 30μmol/m2s low light's injury on peach tree mainly because reactive oxygen species'accumulation.In conclusion, it's a basic condition of greenhouse planting that keeping average diurnal light quantity is not lower than 400μmol/m2s.