Abstract：Taking Chinese cabbage〔 Brassica campestris L. ssp. pekinensis（Lour）Olsson〕cultivars‘Defeng No.1’（tolerance to low potassium）and‘Fengkang 70’（sensitive to low potassium）as experimental material，studies the response made by dry matter accumulation during seedling stage and root system parameter of Chinese cabbage with different tolerance to potassium deficiency through hydroponics experiment．The results showed that under potassium deficiency（0.3 mmol·L-1），the root dry weight，plant dry weight，and root to shoot ratio in‘Fengkang 70’declined significantly，while there were no marked changes in‘Defeng No.1’．On the other hand，the length and surface area of thin roots（Φ ≤ 0.2 mm）and the proportion between thin root surface area and total root system surface area were significantly increased in‘Defeng No.1’，while there were no changes detected in‘Fengkang 70’．All these results indicated that under low potassium stress，the increase of thin root length and surface area of Chinese cabbage cultivar with low potassium tolerance might increase the propotion of thin root length and its surface area，thus strengthen its tolerance to potassium deficiency．
