中文摘要：

选用内蒙古科尔沁沙地1年生植物狗尾草（Setaria viridis）和沙米（Agriophyllum squarrosum）为材料,采用盆栽方法研究了它们在不同土壤水分处理下的光合参数和水分利用效率的日变化特征及其与环境因子的相关关系。结果表明,狗尾草和沙米的净光合速率日变化曲线在充分供水条件下均呈单峰型,在轻度干旱胁迫下均呈双峰型,而在重度干旱胁迫下分别呈双峰型和左偏单峰型。狗尾草和沙米的蒸腾速率在不同水分处理下都近似呈双峰型曲线,然而变化程度却不相同。重度干旱胁迫下,狗尾草日平均净光合速率（11.52μmol.m^-2.s^-1）和蒸腾速率（3.62 mmol.m^-2.s^-1）分别比相应充分供水处理增加7%和43%,而沙米的日平均净光合速率（7.07μmol.m^-2.s^-1）和蒸腾速率（5.56 mmol.m^-2.s^-1）则分别较相应充分供水处理降低13%和36%。重度干旱胁迫下,狗尾草水分利用效率（2.84 mmol.mol^-1）比相应充分供水处理降低3.1%,而沙米水分利用效率（1.14mmol.mol^-1）则较充分供水处理提高了34%。光合速率下降在充分供水条件下主要是由气孔调节,但在轻度干旱胁迫和重度干旱胁迫处理下非气孔因素调节却起到十分重要的作用。在重度干旱胁迫下,狗尾草仍具有显著高于沙米的的净光合速率和水分利用效率,这可能是其仍然能够在固定沙地分布的原因之一。

英文摘要：

Net photosynthetic rates, transpiration rates, stomatal conductance and water use efficiencies of two annuals, Setaria viridis and Agriophyllum squarrosum, were studied by a LI-6400 Portable Photosynthesis System under different water treatments. The results revealed that the photosynthetic rate of S. viridis and A. squarrosurn under wet treatment presented a single-peak curve. In contrast, light drought treatment showed a double-peak curve,and in serious drought condition,photosynthetic curve of A. squar- rosum presented a single-peak curve but S. viridis showed a midday depression of photosynthesis. Compared with wet treatment,the average daily photosynthetic rate of S. viridis in serious drought treatment （11.52 μmolCO2.m^-2.s^-1） increased by 7% ;average daily transpiration rate （3.62 mmol H2O.m^-2.s^-1） increased by 43% and average daily water use efficiency （2.84 mmolCO2.mol^-1H2O） decreased by 3.1%. However,with the dramatic decrease of average daily transpiration in serious drought treatment, average daily photosynthetic rate of A. squarrosum was 7.07 μmol CO2 . m^-2 .s^-1 and decreased by 13% compared with wet condition,which resulted the water use efficiency in serious drought treatment （1.14 mmolCO2.mol^-1 H2O） increased by34%. In addition,through the correlation analysis,in wet condition, the decrease of stomatal conductance was mainly responsible for decrease of photosynthetic rate, but in light and serious drought treatment, high light intensity in research area might induce the depression of photosynthesis. S. viridis showed higher photosynthetic rate and water use efficiency than A. squarrosum under serious drought condition, which might be one of the reasons of its strong competition ability and wide distribution.