土壤镉胁迫对檫木光合特性的影响

采用盆栽控制土培试验的方法,探讨不同浓度Cd胁迫对檫木(Sassafras tzumu Hemsl.)光合特性的影响。试验共设置5个镉处理水平(CK:0 mg·kg^-1,T1:5 mg·kg^-1,T2:20 mg·kg^-1,T3:50 mg·kg^-1,T4:100 mg·kg^-1)。分别测定每个处理下檫木叶片叶绿素含量、光合气体交换参数及光合—光响应曲线。结果表明:①随着处理Cd浓度的升高,檫木叶片叶绿素a、叶绿素b及叶绿素总量先增加后下降,T2处理下取达到最大值;②随着Cd浓度处理升高,叶片净光合速率(Pn)和气孔导度(Gs)均呈现下降趋势,各处理间胞间二氧化碳浓度(Ci)、蒸腾速率(Tr)差异不显著,檫木叶片光合速率主要受非气孔因素限制;③随着Cd浓度升高,檫木叶片的Pnmax(最大净光合速率)呈现显著下降趋势;T1处理条件下,檫木叶片的初始量子效率(α)值最大;檫木叶片的暗呼吸速率(Rd)、光补偿点(LCP)和光饱和点(LSP)总体呈现下降趋势。综上表明,在不同浓度Cd胁迫条件下,檫木叶绿素含量先增后减,在T1、T2处理下高于CK,体现了Cd胁迫“低促高抑”的效应;随着Cd浓度处理升高,光合气体交换参数及光合—光响应参数较CK总体上均呈现下降趋势,表明Cd胁迫对檫木光合作用产生了明显的抑制作用。

Photosynthetic Characteristics of Sassafras tzumu under Cadmium Stress in Soil

To explore the photosynthetic characteristics of Sassafras tzumu Hemsl.under Cd stress,the potted method was used.With 5 cadmium concentration levels(CK:0 mg·kg^-1,T1:5 mg·kg^-1,T2:20 mg·kg^-1,T3:50 mg·kg^-1,T4:100 mg·kg^-1)were set,Chlorophyll content,photosynthetic gas exchange parameters and photosynthetic-light response curve of S.tzumu leaves matching each treatment were measured respectively.The results showed that:①As the concentration of Cd increased,chlorophyll a,chlorophyll b and the total amount of chlorophyll in S.tzumu leaves increased first and then decreased,the maximum was in T2.②With the Cd concentration increased,the net photosynthetic rate(Pn)and stomatal conductance(Gs)of leaves showed a downward trend.There were no significant differences in the intercellular carbon dioxide concentration(Ci)and transpiration rate(Tr)between treatments.The photosynthetic rate of S.tzumu leaves was mainly limited by nonstomatal factors.③With the Cd concentration increased,Pnmax(maximum net photosynthetic rate)of S.tzumu leaves decreased significantly.Under T1 processing conditions,the initial quantum efficiency(α)of S.tzumu leaves got maximum value;The dark respiration rate(Rd),light compensation poin(t LCP)and light saturation poin(t LSP)of S.tzumu leaves decreased respectively.In conclusion,under the stress of different concentrations of Cd,the chlorophyll content of S.tzumu first increased and then decreased,which was higher than that of CK at T1 and T2,reflecting the“low promoting and high suppressing”effect of Cd stress.With the Cd concentration increased,photosynthetic gas exchange parameters and photosynthetic-light response parameters showed a downward trend compared with CK,indicating that Cd stress had an obvious inhibitory effect on S.tzumu photosynthesis.