Abstract: The relationship between leaf water potential of eight broadleaved and coniferous young trees in early morning and soil moisture content is studied. Mathematical equations expressing their relationship are deduced from large amounts of determination data, and critical values of soil moisture content for the normal growth of young trees of different species are calculated. Comparing these values under the same soil condition with drought resistance of young trees of different species,some new results are obtained,which can be of practical significance in guiding afforestation.

Key words: Aphis gossypii, Acyrthosiphon gossypii, high temperature stress, cumulative mortality, reproduction rate, complementary log-log model