不同栽植年限小叶杨与胡杨杂交种（小×胡杨）光合响应特性比较

了解不同光强对小×胡杨气体交换参数的影响，可为进一步评价小×胡杨新品种适应性提供基础数据，为乌兰布和沙漠东北部防护林体系的更新及造林树种选择提供一定的理论依据。利用Li-6400xt便携式光合仪测定了不同光强下小×胡杨的光合生理参数，利用非直角双曲线模型，拟合植物叶片净光合速率（P_n）与光合有效辐射（PAR）的关系，计算光饱和速率（A_max），光饱和点（LSP），光补偿点（LCP），表观量子效率（AQY），暗呼吸效率（RD）等光合生理参数。结果表明，在光合有效辐射（PAR）0～1 500 μmol·m^-2·s^-1范围内，不同栽植年限小×胡杨净光合速率均随着光合有效辐射（PAR）的增强而增加，当光合有效辐射（PAR）为1 500 μmol·m^-2·s^-1时，曲线处于缓慢上升趋势，小×胡杨还没有达到光饱和点。不同光合有效辐射，净光合速率值均表现为3年>2年>1年生，1年、2年、3年生小×胡杨之间的净光合速率差异显著（P<0.05）。3年生小×胡杨的光饱和速率（A_max）、光饱和点（LSP）、光补偿点（LCP）、表观量子效率（AQY）最高。1年生小×胡杨的暗呼吸速率最大，3年小×胡杨的暗呼吸速率最小。在光合有效辐射（PAR）0～1 500 μmol·m^-2·s^-1，不同栽植年限小×胡杨气孔导度（G_s）均随光合有效辐射（PAR）的增加而增加，而胞间CO₂ 浓度（C_i）均呈逐步下降的趋势；随着有效光辐射的逐步增强，不同栽植年限小×胡杨蒸腾速率逐渐增加，变化趋势都较缓慢平稳，蒸腾速率对光合有效辐射（PAR）的变化并不敏感。当光合有效辐射<600 μmol·m^-2·s^-1，1年、2年、3年生小×胡杨水分利用效率增加迅速，当光合有效辐射>600 μmol·m^-2·s^-1，随着光强的增强，3年生小×胡杨水分利用效率继续缓慢上升，但1年、2年生的小×胡杨水分利用效率趋于平缓甚至下降。综合分析，1年、2年、3年生小×胡杨具有高光合，高水分利用效率和相对较低的蒸腾速率的特点，表现出了对当地生态气候的良好适应性。

Comparison of Photosynthetic Response Characteristics of Populus simonii×P.euphratica with Different Planting Years

To understand the effects of different light intensities on gas exchange parameters of a hybrid between Populus simonii×P.euphratica to provide basic data for further evaluation of the adaptability and certain theoretical basis for the renewal of the shelter forest system and the selection of afforestation tree species in the northeast of Ulan Buh Desert.The photosynthetic physiological parameters of the hybrid under different light intensities were measured by the Li-6400xt portable photosynthesis instrument.The relationship between the net photosynthetic rate (P_n) of plant leaves and photosynthetically active radiation (PAR) was fitted by using a non-right-angle hyperbolic model,while photosynthetic physiological parameters were calculated,such as light saturation rate (A_max),light saturation point (LSP),light compensation point (LCP),apparent quantum efficiency (AQY),and dark respiration efficiency (RD).The photosynthetic rate of the hybrid with different planting years increased with the increase of PAR in the range of 0-1 500 μmol·m^-2·s^-1.The curve was in a slowly rising trend after PAR was 1 500 μmol·m^-2·s^-1,indicating that the light saturation point of the hybrid had been not yet reached.The P_n values of the hybrid planting with different years were in the order of 3-year>2-year>1-year for different PARs,and the differences of P_n values were significant (P<0.05).The values of A_max,LSP,LCP,and AQY of the 3-year-old hybrid were the highest.The dark breathing rate of 1-year-old hybrid was the largest,and the dark breathing rate of 3-year-old hybrid was the smallest.In the range of PAR was 0-1 500 μmol·m^-2·s^-1,the stomata conductance (G_s) of the hybrid at different planting years increased with the increase of PAR.While the intercellular CO₂ concentration (C_i) showed a gradual decrease trend with the increase of PAR.The transpiration rate increased slowly,indicating that the transpiration rate was not sensitive to the change of PAR.The water use efficiency increased rapidly when the values of PAR were less than 600 μmol·m^-2·s^-1.When the values of PAR were greater than 600 μmol·m^-2·s^-1,the water use efficiency of 3-year-old hybrid continued to rise slowly,while the water use efficiency of 1- and 2-year-old hybrid tended to be stable or even decline.Comprehensive analysis shows that 1-,2- and 3-year-old Populus hybrid have the characteristics of high photosynthesis,high water use efficiency and relatively low transpiration rate,indicating good adaptability of the spices to the local ecological climate.