Abstract: Effects of rhizosphere acidification on Pefficiency in different poplar clones were conducted by the method of soil culture in greenhouse.Potassium dihydrogen phosphate was applied to furnish 0, 40, 80, and 120 mg P₂O₅ kg^-1.The experiment consisted of three replicatesof each treatment, with a pot of 40 kg soil in a randomized block.The results showed that high Pefficiency clones, such as S17, S19, and 105, could decrease their pHvalues in rhizosphere under P deficiency stress much stronger than clones 106, 797, 1-69, 1388, and 3244, which were low Pefficiency clones.The most decrement of pH for the former even accounted to 1.32 pHunits and the ratios of the decrements were over 10% in comparison with the pHvalues in bulk soil.Whereas for the latter less than0.21 pH units and 2.5% of the decreasing ratio respectively.In contrast to low P efficiency clones, high Pefficiency clones could acidify their rhizosphere through a kind of specific mechanism because the pH values in rhizosphere of high Pefficiency clones were gradually decreased corresponding with the intensity of Pdeficiency stress and vice versa.The amounts of available P in rhizosphere of clone S17, S19, and 105 reached 2.64, 3.27, and 3.28 mg穔g^-1, respectively, obviously higher than those of the other five low P efficiency clones, which all were below 2.00 mg穔g^-1 under Pdeficiency stress, and the summation percentages of available Pin rhizosphere were over 60% for all high Pefficiency clones, but less than 10% for low P efficiency clones.The amounts of P taken up by high P efficiency clones wore statistically greater than by low Pefficiency clones.Regression analysis also indicated that the increment of available Pin rhizosphere was closely correlated with the decrement of pHvalues in rhizosphere under Pdeficiency stress.This demonstrated the impact of rhizosphere acidification on availability of rhizosphere P, and identified that high Pefficiency clones could enhance their contents of available Pin rhizosphere, absorb more Pand thus grow better through rhizosphere acidification depended on deficiency stress.

Key words: Poplar, Clone, Phosphorus efficiency, Rhizosphere acidification, Available phosphorus in rhizo-sphcre