低钾胁迫对苹果砧木M9T337幼苗光合荧光特性及13C吸收分配的影响

Effects of Low Potassium Stress on Photosynthetic Fluorescence Characteristics and 13C Absorption and Distribution of M9T337 Seedlings

以1年生苹果砧木M9T337幼苗为试材,采用叶绿素荧光分析和13C同位素示踪技术,水培条件下研究了不同供钾水平(0.02、0.5、2和6 mmol·L^-1)对幼苗光合生理特性、叶绿素荧光特性以及13C光合产物积累和分配的影响。结果表明:与正常供钾(6mmol·L^-1K^+)对照处理相比,低钾胁迫下苹果砧木M9T337幼苗各器官生物量、净光合速率(Pn)和气孔导度(Gs)均显著下降,胞间CO2浓度(Ci)先下降后上升。低钾胁迫下幼苗叶片的光化学猝灭系数(qP)、PSⅡ实际光化学效率(ΦPSⅡ)、PSⅡ电子传递速率(ETR)和PSⅡ最大光化学效率(Fv/Fm)均显著下降,基础荧光(F0)和非光化学猝灭系数(NPQ)显著升高,且低钾胁迫程度越大,叶绿素荧光参数变化幅度越大。随着处理时间的延长,低钾胁迫处理下的RuBP羧化酶(Rubisco)和碳代谢酶活性逐渐降低,35 d后酶活降至最低水平。13C示踪试验结果表明,低钾胁迫显著影响了碳素同化物的积累和分配。两年平均,13C标记结束6 h后0.02、0.5、2 mmol·L^-1 K^+处理的幼苗根系13C积累量分别为对照的15.59%、26.62%和59.72%;标记结束72 h后,0.02、0.5、2 mmol·L^-1 K^+处理下的幼苗叶片13C分配率高达70.44%、67.61%、66.02%,分别较对照提高14.00%、9.44%、6.87%,而根系的13C分配率为10.54%、11.84%、13.34%,分别为对照的61.87%、69.50%、78.31%。结果显示,低钾胁迫降低叶片气孔导度,破坏PSⅡ反应中心,降低光反应阶段还原力的供应以及碳同化能力,从而抑制光合作用及碳素向根系的运输,并且抑制程度与低钾胁迫时间和程度显著相关。

Hydroponic culture method was used with M9 T337 dwarf rootstock seedlings as tested materials,the chlorophyll fluorescence analysis and track technology of 13C were used to study the effect of different potassium supply levels(0.02,0.5,2,6 mmol·L^-1)on photosyntheticphysiological characteristics,chlorophyll fluorescence characteristics and 13C photosynthate accumulation of seedlings.The results showed that compared with 6 mmol·L^-1 K^+treatment,the biomass of all organs,net photosynthetic rate(Pn)and stomatal conductance(Gs)of M9 T337 seedlings significantly decreased under low potassium stress while the intercellular CO2 concentration(Ci)first decreased and then increased.The coefficient of photochemical quenching(qP),PSⅡactual photochemical efficiency(ΦPSⅡ),PSⅡelectron transport rate(ETR)and PSII maximum photochemical efficiency(Fv/Fm)in leaves of M9 T337 seedlings dropped significantly under low potassium stress,based fluorescence(F0)and the coefficient of photochemical quenching(NPQ)significantly increased,and the greater the degree of stress,the greater the change in chlorophyll fluorescence parameters.With the prolongation of treatment time,the activities of RuBP carboxylase(Rubisco)and carbon metabolic enzyme decreased gradually under low potassium stress,and reached the lowest level after 35 days.The results of 13C tracer test showed that low potassium stress significantly affected the accumulation and distribution of carbon assimilates.Six hours after 13C labeling,the accumulations of 13C in roots of seedlings under 0.02,0.5 and 2 mmol·L^-1 K^+treatment were 15.59%,26.62%,59.72%of that under 6 mmol·L^-1 K^+treatment,respectively.After 72 h,the 13C distribution rates of seedling leaves under 0.02,0.5 and 2 mmol·L^-1 K^+treatment were as high as 70.44%,67.61%,66.02%,respectively,14.00%,9.44%,6.87%higher than 6 mmol·L^-1 K^+treatment;while the 13C distribution rates of 0.02,0.5 and 2 mmol·L^-1 K^+treated seedling roots were 10.54%,11.84%,13.34%,respectively,which were 61.87%,69.50%,78.31%of 6 mmol·L^-1 K^+treatment.The result showed that low potassium stress can reduce stomatal conductance of leaves,destroy PSⅡreaction center,reduce the supply of reducing power and carbon assimilation ability in photoreaction stage,thus inhibiting photosynthesis and carbon transport to roots of seedlings,and the degree of inhibition is significantly related to potassium stress time and degree.