Abstract:
Root systems play an important role in the hydrological cycle by largely controlling water fluxes to the atmosphere and groundwater. Root distribution characteristic determines its water use strategy and has a direct effect on soil water depletion. In water-limited arid and semiarid regions, soil water is a critical factor affecting plant growth that may determine plant distribution pattern. The relationships between soil water and plant have been reported for a wide range. However, very limited information about the forest deep root and deep soil water has been reported. Little study has focused on the stand density effect on jujube plantation. Our study was conducted to determine the spatial distribution of fine root and soil profile water characteristic of the 12-year-old drip irrigated densely jujube plantation (Ziziphus jujube Mill.) with 2.4 m between trees and 2.4 m between tree rows, widely jujube plantation as control was not drip irrigated with 4 m between trees and 5 m between tree rows in the loess hilly region. Soil core method (Luoyang shovel) was used to obtain fine roots from 5 different horizontal positions in 0-5.4 m in densely jujube plantation and 4 different horizontal positions in 0-10.4 m in widely jujube plantation respectively, and soil water content was observed in 0-10.4 m at 0.2 m interval in the two jujube plantations. The results showed that: 1) Fine root dry weight density was decreased with soil depth and more than 50% of fine roots were concentrated in 0-0.8 m soil layer which was the dense root layer. It was 52.3% and 57.7% in the top four layers in densely and widely jujube plantations respectively. There were significant differences in the fine root dry weight density among the top four soil layers in the same sampling position, and no significant differences were observed among different horizontal positions. 2) Fine root dry weight density was increased with the increasing of the stand density, but the maximum fine root depth showed opposite tendency. The maximum fine root depth extended 5 m and the total fine root dry weight density was 2319.38 g/m3 in densely jujube plantation, while it was 10 m and 1969.06 g/m3 in widely jujube plantation respectively. When the soil water in the upper layer could not provide the jujube growth demand, root had to gradually move to deeper layer to absorb soil water. 3) The average of soil water content in 0~10.4 m was 8.34% and 6.68% in densely and widely jujube plantation respectively. Soil water content was greater in densely jujube plantation with drip irrigation than in widely jujube plantation. The low soil water content zone was concentrated in 1.6~3.0 m soil layer in densely jujube plantation while it was 2.2~4.6 m in widely jujube plantation. The soil depth of low soil water content zone moved up 1.6 m in densely jujube plantation than widely jujube plantation. Drip irrigation and densely plantation had an important effect on artificial forest root and soil water, drip irrigation could reduce the maximum rooting depth, and roots were shallower in densely jujube plantation which can alleviate deep soil water depletion.