Abstract: To investigate the effects of interspecific relationships and precipitation changes on photosynthetic characteristics of mixed plant communities,the C₃ plant Reaumuria soongarica and C₄ plant Salsola passerina were selected as research objects,photosynthetic parameters of single and mixed R. soongarica and S. passerina were measured along the natural precipitation gradients. The results showed that mixed growth increased the net photosynthetic rate (Pn),transpiration rate (Tr) and stomatal conductance (Gs) of R. soongarica,which increased by 12.3%,13.7% and 20.4%,respectively;On the contrary,S. passerina decreased by 5.5%,14.1% and 28.9%,respectively. With the decrease of precipitation,the photosynthetic rate of mixed R. soongarica and S. passerina did not increase significantly,which indicated that the reciprocity between R. soongarica and S. passerina had not been strengthened with the increase of environmental stress,and the stress gradient hypothesis was not supported. On the whole,the values of Pn,Tr and Gs of R. soongarica in arid and semi-arid regions of Northwest China were higher than those of S. passerina,the average increase by 6.6%,36.9% and 27.8%,respectively,but its WUE was lower than that of S. passerina,which decreased by 13.9%. The above research showed that R. soongarica made better use of nutrient resources to adapt to interspecific competition and drought stress environment through interspecific reciprocity,and the competition of mixed S. passerina was strengthened. R. soongarica was mainly adapted to arid environment by increasing photosynthetic rate in arid and semi-arid areas of Northwest China,and S. passerina maintained growth by increasing its water use efficiency.

Key words: Change of precipitation, Reciprocity, Competition, Photosynthetic characteristics, Reaumuria soongarica, Salsola passerina

摘要： 为探明种间关系和降水变化对混生植物群落光合特性的影响，以C₃植物红砂（Reaumuria soongarica）和C₄植物珍珠（Salsola passerina）为研究对象，沿自然降水梯度测定单生和混生红砂与珍珠光合参数。结果表明：混生可提高红砂的净光合速率、蒸腾速率、气孔导度，平均分别增加12.3%，13.7%，20.4%；而珍珠相反，平均分别减少5.5%，14.1%，28.9%。随降水的减少，混生红砂与珍珠的光合速率并没有显著提高，表明随干旱胁迫梯度增加其互惠作用并没有得到加强，并不支持胁迫梯度假说。西北干旱区和半干旱区红砂的净光合速率（Net Photosynthesis Rate，Pn）、蒸腾速率（Transpiration Rate，Tr）和气孔导度（Stomatal conductance，Gs）整体高于珍珠，平均分别增加6.6%，36.9%，27.8%，但其水分利用效率（Water Use Efficiency，WUE）低于珍珠，降低13.9%。研究表明，红砂可通过种间互惠更好地利用养分资源适应种间竞争及干旱胁迫环境，而混生珍珠竞争作用加强，在我国西北干旱和半干旱区红砂主要是通过提高光合速率来适应干旱环境，珍珠则通过提高水分利用效率来维持生长。

关键词: 降水量变化, 互惠, 竞争, 光合特征, 红砂, 珍珠