| Strawberry plants( (Fragaria ananassa Duch.), Growing in field and pots were used in this experiment to the study effect of shading on the photosynthetic characteristics,chlorophyll fluorescence parameters, xanthophyll cycle, photorespiration, activity of protective enzymes, anatomical characteristics and effects of low temperature on photosynthesis characteristin at different vegetative growth phases.The results are as follows:1.In vegetative growth phases, light compensation point and saturation light intensity of photosynthesis in strawberry leaves were 48.0μmol·m-2·S-1 and 800umol.m-2.S-1, and CO2 compensation point and CO2 suturation point were 89 U mol/mol and 895 u mol/mol respectively.Diurnal variation of photosynthetics rate (Pn) of strawberry leaves in sunny day was a double peak curve , and the two peaks were at 10:30 and 13:30~14:00 respectively, there being a mid-day depression,Long time shading for strawberry had remarkable effects on its photosynthetic characteristics. Saturation light intensity, CO2 compensation point and CO2 suturation point declined after long time shading.Diurnal variation of Pn still was double peak curve, but the peak was earlier in the morning and later in the afternoon when compared with the Control(no shading).Photosynthetic rate (Pn) of mid-position leaf of strawberry was the highest, secondly in lower-position leaf, and lowest in upper-position, newly-spreaded leaf.The light compensation point of photosynthesis of upper, middle,lower-position leaves was 48.0, 49.1 and 36.7, and the saturation light intensity of photosynthesis in upper, middle and lower position leaves was 638,817,and 782μmol·m-2·S-1 respectively. CO2 compensation point in upper , middle and lower position leaves was 143.7,48.2 and 82.4μmol/molrespectively. CO2 saturation point in upper,middle and lower position leaves was 921,901 and 943 u mol/mol respectively.Moderate temperature of photosynthesis in strawberry leaves was 25℃.Pn, AQY, Fv/Fm and light saturation point under this temperature condition were higher .Within the range of 15~35 ℃, light compensation point, CO2 saturation point and CO2 compensation point raised as temperature raised.Midday-depression of photosynthesis in strawberry was affected by stomatal and non-stomatal limitation.Generally speaking, Ci increased as the shading level increased and Ls was opposite but CE declined as shading level increased.2.Photoinhibition of photosynthesis in strawberry leaves in the field and shading conditions was obvious, and the main characteristics of photoinhibition was that photosynthetic rate(Pn), apparent quantum yield(AQY) and photochemical etficiency of photosystem II (Fv/Fm of PS II) declined markedly under midday strong light stress.The extent of photoinhibition was serious due to stronger light stress in planting stage, and afterwards, the extent of photoinhibition reduced gradually.The degree of photoinhibition declined markedly under shading conditions.The more the shading, the gentlier the extent of photoinhibition was.Because CE declined after shading, photosynthetic rate (Pn) would declined as shading level increased.3. Using HPLG biochemical metheods and portable photosynthesic gas analysis system, we observed the diurnal changes of photo-respiration(Pr), xanthophylls(L)cycle and protective enzymes in strawberry leaves under shading and field conditions so as to study their role in protecting photosynthetic apparatus of strawberry leaves from photo-inhibition damage.The results shown that Pr of strawberry leaves in high light stress in mid-day increased markedly.When promoting Pr, it was favourable to raising AQY, Fv/Fm, reducing photoinhibition; Xanthophyll cycle started during high light stress, Xanthophyll cycle pool (A+Z+V) and its key component-content of zeaxanthin increased.It was advantageous to dissipate superfluous energy. The content of MDA in strawberry leaves in high light stress increased, at the same time, the activity of SOD, POD, CAT raised.After spreading DDTC(inhibitor of SOD), the activity of SOD,... |
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