关键词: 苹果, 砧木, 低钾胁迫, 光合, 荧光, 13C 吸收, 分配

Abstract: Hydroponic culture method was used with M9T337 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 M9T337 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 M9T337 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.

Key words: apple, rootstock, low potassium stress, photosynthetic, fluorescence, 13C absorption, distribution