Eco-physiological Effect Of Populus Davidiana-Quercus Liaotungensis Mixed Forests In Ziwuling Forest Area

In Ziwuling forest area of the Loess Plateau, there are three types of forests: Populus davidiana, Quercus liaotungensis, and Populus davidiana-Quercus liaotungensis mixed forests. They were studied in soil physical property, fine root distribution characteristic, plant diversity, chlorophyll content, leaf photosynthetic parameter and chlorophyll fluorescence dynamic parameter and so on. The results are as follows:(1) In 0~300cm soil layer, Populus davidiana mixed forest presented the highest soil moisture, but, in 200cm soil layer below groundsurface, Populus davidiana-Quercus liaotungensis mixed forest presented an obviously increased soil moisture which was higher than that of Quercus liaotungensis mixed forest by about 10.5% ~19.76%. In 0~60 cm soil layer, Populus davidiana mixed forest showed the highest soil bulk density and the lowest soil porosity, but Populus davidiana-Quercus liaotungensis mixed forest presented the lowest soil bulk density and the highest soil porosity; And both of them surpassed their corresponding pure forest in soil bulk density and soil porosity. These indicated that the mixed forests could make effective use of water in deeper soil and then obviously improved their soil physical and chemical properties.(2) The characteristics of the fine root of three types of forests: in 0-80cm soil layer, the fine root biomass, fine root length density and fine root surface area were all decreased with the increasing soil depth. And the characteristic of the total fine root biomass was: Populus davidiana-Quercus liaotungensis> Quercus liaotungensis> Populus davidiana.(3) The results showed that the vanguard community (Populus davidiana) to the climax community (Quercus liaotungensis) succession in the processes, the plant species richness index and plant diversity index assumes the drop tendency, but the mixed forest type is in the middle stage of succession, therefore its species richness index and plant diversity index is also between the two kinds of forest types, namely: Populus davidiana > Populus davidiana-Quercus liaotungensis mixed forest > Quercus liaotungensis. Each of the change of plant species richness index (Gleason index and Margalef index), diversity index (Shannon-Wiener index) in herbage layer,shrub layer and arbor layer assumes the drop tendency, namely: herbage layer (HL) > shrub layer (SL) > arbor layer (AL), the uniformity change tendency of the Pielou evenness index is consistent with the plant diversity. In the...