库布齐沙漠中甘草对不同水分和养分供应的光合生理响应

PHOTOSYNTHETIC PHYSIOLOGICAL RESPONSES OF GLYCYRRHIZA URALENSIS UNDER DIFFERENT WATER AND NUTRIENT SUPPLIES IN KUBUQI DESERT,CHINA

为了解全球变化背景下在沙漠分布的豆科优势物种甘草(Glycyrrhiza uralensis)对多因素环境变化的适应性,该研究以第2年生长的甘草植株为对象,盆栽试验为手段,采用完全随机区组实验设计,人工模拟分别相当于库布齐沙漠当地自然年降雨量的3/8、1/2、1和2倍(W1～W4)的4个水分供应处理,以及4个养分添加处理(对照CK;N,83mg N.kg-1土;P,92mg P.kg-1土;NP,83mg N.kg-1土+92mg P.kg-1土),研究了库布齐沙漠中甘草的光合生理特性对于水分和养分供应变化的响应。结果表明:气体交换特征随测量时间表现出规律性变化。在实验处理条件下,每个植物功能性状参数随时间的变化趋势基本一致。当光合有效辐射(Photosynthetically available radiation,PAR)在11:00～13:00时段达到最高值时,大气温度也接近测量当天的最高值,净光合速率(Net photosynthetic rate,Pn)出现了明显的"午休"特征。第2年生长的甘草对于干旱胁迫表现出快速生理响应与气孔调节,尤其在极度干旱(W1)条件下,光合作用过程的控制在气孔限制与非气孔限制之间进行了多次转换。水分胁迫使Pn、气孔导度(Stomatal conductance,Gs)和蒸腾速率(Transpiration rate,Tr)等气体交换特征值下调,同时降低了最大净光合速率(Maximum net photosynthetic rate,Pmax)和表观量子效率(Apparent quantum yield,AQE)等光响应曲线特征参数。光合水分利用效率(Photosynthetic water use efficiency,PWUE)随着水分供应量减少而降低,并且养分添加也使其在水分供应良好(W4)的条件下降低,对于外界环境中水分利用的改变具有适应策略。另外,养分添加对于光合作用过程具有促进作用,尤其在水分供应良好的条件下,N素添加使Pn增加明显。在W1条件下,P素供应增加了Pmax、光饱和点(Light saturation point,LSP)并减小了光补偿点(Light compensation point,LCP),表明甘草物种对于P素的敏感性。研究结果表明,虽然养分添加能够调节水分胁迫条件下甘草对于光辐射的利用效率与适应性,但水分仍然是限制甘草光合生理的首要因素。

Aims Changes in precipitation pattern and increases in nitrogen deposition have been pre-dicted in previous studies of global change,and these may significantly affect plant growth in terrestrial ecosystems and the availability of resources such as water and nutrients for plant use. Our objective was to determine photo-physiological responses and adaptation of licorice （Glycyrrhiza uralensis）,a dominant legume species in the Kubuqi Desert,to different water and nutrient （N,P） supplies. Methods Using a completely randomized design,we subjected second-year licorice seedlings to water treatment at four supplement levels （3/8,1/2,1,and 2 times mean annual precipitation of the study area） and four nutrient treatments （CK,N：83mg N.kg-1 soil,P：92 mg P.kg–1 soil,and NP：83 mg N＋92 mg P.kg–1 soil） in 2005. We also determined diurnal changes of photo-physiological characteristics and lightresponse curves. Important findings Water supply and nutrient addition significantly affected licorice physiological characteristics. Water stress decreased gas exchange characteristics,such as net photosynthesis rate （Pn）,stomatal conductance （Gs）,and transpiration rate （Tr）,and down-regulated several A-PAR relationship curve parameters,such as maximum net photosynthetic rate （Pmax） and apparent quantum efficiency （AQE）. The major control of photosynthesis under severe water shortage （W1） varied between stomatal and non-stomatal limitation. Therefore,the second-year licorice seedlings performed a quick physio-logical response and corresponding regulation to water supply. Nutrient addition could increase Pn,especially under high-water supply,and phosphorus addition could also stimulate Pmax and light saturation point （LSP） and diminish light compensation point （LCP） under extremely low water supply. Shortage of water supply or nutrient addition combined with high water supply （W4） would decrease photosyn-thetic water use efficiency （PWUE）. Our results suggest that water supply is the primary limiting factor and nutrient addition is secondary for licorice photosynthesis in this desert area.