荒漠植物白刺对模拟增雨的光合响应机制

Photosynthetic Response Mechanism of a Desert Plant Species Nitraria tangutorum to Rain Addition

【目的】研究不同增雨条件下白刺叶片的光合作用和叶绿素荧光特性,从光合生理角度探讨白刺对增雨的响应机制。【方法】以乌兰布和沙漠东缘地区典型荒漠植物白刺为研究对象,设置不同的增雨梯度(增加年均降水量的0,25%,50%,75%和100%),对自然生长的白刺沙包进行人工模拟增雨,利用Li-6400xt便携式光合测定系统分析仪(USA,LI-COR)测定不同增雨条件下白刺叶片净光合速率(Pn)日动态变化、光响应曲线、CO2响应曲线以及叶绿素荧光参数,并根据Pn日变化曲线和响应曲线计算叶片日光合总量(∑Pn)以及各光合生理参数。【结果】1)75%和100%增雨对日均Pn和∑Pn影响显著,日均Pn比CK分别高32.74%和37.64%,∑Pn比CK分别高32.01%和38.43%,说明增雨使白刺光合能力增强,日光合产物的积累增加。2)增雨使白刺表观量子效率(AQY)和光饱和点(LSP)升高,25%,50%,75%和100%增雨的AQY比CK分别高17.24%,31.03%,37.93%和24.14%,LSP比CK分别高14.6%,6.0%,3.0%,26.1%,说明白刺叶片利用弱光的能力增强,对强光的利用范围增加,光能转化效率提高,有利于光合作用的高效进行。3)随着增雨量的增加,羧化效率(CE)呈现出逐渐增加的趋势,其中,100%增雨的CE比CK高5.73%;增雨使CO2饱和点(CSP)升高,50%,75%和100%增雨的CSP显著高于CK,分别比CK高23.67%,28.35%和29.13%,说明白刺叶片Ru BP羧化酶和光合碳循环酶的活性增强,对高CO2浓度的利用范围增加。4)增雨使白刺叶片的原初光化学量子效率(Fv/Fm)、实际光化学量子效率(ФPSⅡ)、电子传递速率(ETR)和光化学猝灭系数(qP)提高,说明增雨有利于白刺叶片PSⅡ反应中心活性增强、开放比例提高,有利于叶片把所捕获的光能转化为生物化学能,并将更多的光能用于推动光合电子传递。【结论】白刺能够调节光合机构的功能、改变自身生理特性、增强对环境资源的利用能力来适应增雨的变化。

Objective][Objective]This research was carried out to investigate the photosynthesis and chlorophyll fluorescence characteristics and explore the response mechanism in terms of photosynthetic physiology of Nitraria tangutorum under different rain addition treatments. [Method]Field plots were set and a typical desert plant,Nitraria tangutorum,was used as the research object at the eastern margin of the Ulanbuh Desert. The species were subjected to five water regimes by adding extra rainfall （ increased 0,25%,50%,75% and 100% of the local mean annual precipitation,respectively）. A Li-6400xt portable photosynthesis measurement system was used to determine the dynamic changes of net photosynthetic rate,the light and CO2 response curve,and the chlorophyll fluorescence parameters. Total daily photosynthesis and photosynthetic parameter were calculated according to the net photosynthetic rate daily dynamic curve,the light response curve and the CO2 response curve under five rain addition treatments. [Result]1） Average and total daily photosynthesis increased significantly under 75% and 100% rain addition treatments. The average daily photosynthesis of N. tangutorum treated with 75% and 100% rain addition was higher than those in control by 32. 74%and 37. 64%,respectively. The total daily photosynthesis of N. tangutorum with 75% and 100% rain addition was higher than those in control by 32. 01% and 38. 43%,respectively. The results indicated that photosynthetic capacity and daily photosynthesis accumulation were enhanced after rain addition. 2） With the increase of precipitation,apparent quantum yields （ AQY） and light saturation points （ LSP） increased gradually. AQY under 25%,50%,75% and 100% rain additions were 17. 24%,31. 03%,37. 93% and 24. 14% higher than control,respectively,and the corresponding LSP increased by 14 . 6%,6 . 0%,3 . 0% and 26 . 1%. These results suggested that rain additions promoted the capacity of utilizing optical energy at low light levels,the utilization of bright light,and conversion efficiency of light energy of N. tangutorum,which would improve the efficiency of photosynthesis. 3） With the increasing of precipitation,carboxylation efficiency （ CE ） increased gradually. The CE under 100% rain addition was significantly higher than control and the increment rate was 5. 73%. The CO2 saturation points （ CSP） were greater in watered plots than in control plots. The CSPs in 50%,75% and 100% rain additions were approximately 30. 31%,26. 56%,and 50. 94% higher than control, respectively. These results suggested that rain addition enhanced the activities of photosynthetic carbon cycle enzymes and increased utilization amplitude of high carbon dioxide concentration for the desert plant. 4 ） Rain addition led to the increase of primary photochemical quantum efficiency （ Fv/Fm ） ,PSⅡquantum yield （ФPSⅡ） ,electron transport rate （ ETR） and photochemical quenching （ qP ） of N. tangutorum. The results indicated that rain addition was conducive to increase the activity and opened proportion of PSⅡ reaction center,which should be beneficial to transform the captured light energy into biochemical energy for N. tangutorum leaves and make more energy used to promote photosynthetic electron transport.[Conclusion]Thus,under global change scenario,N. tangutorum would mediate the function of photosynthetic apparatus,change the physiological characteristics and enhance the ability of utilization environmental resources to adapt to precipitation pattern variation in the future.