Effects Of Different Groundwater Depth On The Photosynthetic Characteristics Of Phragmitesaustralisin At North Shore Of Bosten Lake In Yanqi Basin

In recent years, the changing groundwater level greatly in Bosten Lake influenced much on the growth of Phragmites australis in south Xinjiang. Ascertained response of photosynthetic characteristics and growth on different groundwater depths would preliminarily base for nursing wetland vegetation and restoring environment. In May, July and August 2014, we selected four samples for controlling experiments, and measured the photosynthetic and growtn parameters of Phragmites australis living in different groundwater depths(just as 0cm, 40 cm, 80 cm and 105cm), just like net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance(Gs), intercellular CO2 concentration(Ci), as well as the environment parameters, including photosynthetic active radiation(PAR), air temperature(Ta) and relative humidity(RH), and the concentration of CO2(Ca),using Li-6400 XT, a portable photosynthetic system.The results showed that:(1) The net photosynthetic rate of Phragmites australis’ leave has two peaks of the curves about diurnal variations and those are the phenomena of “midday depression” at 14:00 in different groundwater(0cm, 40 cm, 80 cm and 105cm). The anova analysis showed that there is significant difference of mean net photosynthetic in different groundwater depths(p = 0.000 <0.01). The order of Pn integrated value by 1 to 7 of PAR was 97.77(105cm)> 89.71(0cm)> 81.96(80cm)> 79.52(40cm).(2) Photosynthetically active radiation and relative humidity are the dominant factors of photosynthesis(net photosynthetic rate, intercellular CO2 concentration) when the groundwater depth is 0cm. Relative humidity is the dominant factor of photosynthesis(intercellular CO2 concentration), when the groundwater depth 40 cm. The same, photo-synthetically active radiation and relative humidity are the dominant factors of photosynthesis(net photosynthetic rate, intercellular CO2 concentration) when the groundwater depth is 80 cm. Photo-synthetically active radiation, relative humidity and leaf temperature are both the dominant factors of photosynthesis(net photosynthetic rate, intercellular CO2 concentration) when the groundwater depth is 105 cm.(3) In Spring(May), net photosynthetic rate in the groundwater depth 40 cm is significantly higher than the values of other groundwater(p <0.001); In summer(July), net photosynthetic rate in the groundwater depth 40 cm, 80 cm and 105 cm are significantly higher than the values of other groundwater(p <0.001). In autumn(August), net photosynthetic rate in the groundwater depth 105 cm are significantly higher than the values of other groundwater(p <0.001).(4) Photosynthetic-light response curve is fitted by non-rectangular model. The order of maximum photosynthetic rate is 22.89(105cm) > 19.92(80cm) > 17.49(0cm) > 15.79 μmol CO2·m-2·s-1(40cm). The light saturation point in groundwater depth of 0cm, 40 cm, 80 cm and 105 cm is 1183.94、810.51、1402.74 and 1809.53 μmol CO2·m-2s-1, while the light compensation point is 16.83、13.54、44.13 and 48.19 μmol CO2·m-2·s-1. About all, the most adaptable to light environment is the situation with groundwater depth 105 cm.(5) Photosynthetic-CO2 response curve is fitted by non-linear model. The order of maximum photosynthetic rate is 48.19(105cm)> 44.13(80cm)> 16.83(0cm)>13.54 μmol CO2·m-2·s-1(40cm). The CO2 saturation point in groundwater depth of 0cm, 40 cm, 80 cm and 105 cm is 1082.4、963.6、1333.2 and 2107.6 μmol·m-2·s-1, while the CO2 compensation point is 52.8、74.8、37.9 and 29.7 μmol·m-2·s-1. About all, the most adaptable to light environment is the situation with groundwater depth 105 cm.(6) In whole day(08:00-20:00), the anova analysis showed that there is significant difference of fluorescence parameters at different groundwater depths(0cm, 40 cm, 80 cm and 105cm)(p=0.000 <0.01). The order of F0 is 333.2±6.1(105cm) > 318.5±4.6(80cm) > 308.6±6.4(40cm) > 240.5±9.6(0cm), and the order of Fm is 1892.6±49.3(105cm) > 1807.4±27.4(80cm) > 1719.6±31(40cm) > 1268.3±49.2(0cm), the same, the order of Fv/F0 is 4.67±0.078(105cm) > 4.50±0.023(80cm) > 4.57±0.025(40cm) > 4.28±0.061(0cm).(7) In May, July and August, the anova analysis showed that there is significant difference of mean plant height at different groundwater depths(0cm, 40 cm, 80 cm and 105cm)(p = 0.000 <0.01). In May, the order of plant height is 31.4 ± 0.6cm(40cm) > 27.1±2.6cm(80cm) > 21.9±0.4cm(105cm) > 15.6±0.3cm(0cm); In July, the order of plant height is 100.7±2.3cm(40cm) > 77.4±3.6cm(80cm) > 72.8±2.7cm(105cm) > 63.7±1.3cm(0cm); In August, the order of plant height is 119.69±3.7cm(105cm) > 118.31±1.6cm(40cm) > 106.50±4.5cm(80cm) > 95.38±2.3cm(0cm). In October, the order is 197.6±0.7cm(105cm) > 174.8+1.2cm(80cm) > 155.5±0.8cm(40cm) > 131.4±0.5cm(0cm). In May and July, plant height in the groundwater depth 40 cm is significantly higher than the values of other groundwater(p <0.001). In August, plant height in the groundwater depth 105 cm are significantly higher than the values of other groundwater(p <0.001). In October, plant height(historical height) in the groundwater depth 105 cm are the highest.Conclusion: In a word, the groundwater depth of 105 cm favored to the growth of Phragmites australis at north shore in Bosten Lake.