Effect Of Soil Layer Thickness On Growth And Fine Root Distribution Of Jujube Tree

In arid and semi-arid areas such as Loess Plateau,rainfall is scarce,and plants absorb deep soil water through deep root system when rainfall cannot meet their own water consumption demand.Deep soil water storage becomes a key factor affecting soil water and growth and development of local plants.As a key property of soil,soil thickness determines a series of conditions affecting plant growth,such as root distribution space and soil water storage capacity.Plants develop a series of adaptive growth strategies in the face of different growth environments.In order to study the growth strategies of jujubes in the face of differences in deep soil water resources storage at different soil thicknesses,this paper constructed soil spaces of different depths from 2 to 6 m for long-term localized observation experiments with jujubes as the research object.We investigated the effects of soil thickness on soil moisture,water consumption,fine root distribution and biomass of jujube trees in jujube forests.The following conclusions were obtained:（1）Jujube trees growing in shallower soil have poor soil moisture.During the 5th to 7th year of growth of jujube trees,the soil moisture of jujube forest gradually approached the withering humidity in the soil layer thickness of 2-4m,and was still at a relatively high level in the soil layer thickness of 5-6m.In the 4-6m thick soil layer,the main water absorption depth and rainfall infiltration recharge depth of jujube tree roots were greater than the shallow soil layer of 2-3m.The interannual trends of shallow soil moisture,soil storage and jujube water consumption in different soil thickness plots were consistent with those of annual rainfall,and the shallow soil moisture,soil storage and jujube water consumption in 2-3m shallow soil thickness plots had stronger positive correlation with annual rainfall than those in4-6m thick soil thickness plots.（2）The water consumption characteristics of jujube trees in different soil thickness plots were as follows:in years with high soil moisture,the water consumption of jujube trees showed an increasing trend as the soil thickness decreased;in years with insufficient soil moisture,the water consumption of jujube trees was mainly influenced by the deep soil water storage,and the water consumption of jujube trees showed an increasing trend as the soil thickness increased and the deep soil water storage increased;as the age of the trees grew,the deeper the soil layer,the better the growth condition of jujube trees,and the water consumption of jujube trees also increased.The deeper the soil layer,the better the growth condition of jujube trees,and the water consumption of jujube trees also increased.（3）In the soil depth of 2-6m,fine roots of jujube trees were concentrated in 0-0.6m soil,and with the increase of soil depth,the overall trend of change was first increased and then decreased.The decrease in soil layer thickness significantly increased the proportion of fine root distribution in soils below 0.6m compared with the naturally growing jujubes in the 6m soil layer thickness area.The total root length and the total root dry weight of jujube showed an increasing trend with the decrease of soil layer thickness.（4）The average diameter of fine roots of jujube tree is the smallest in the soil layer thickness of 6m,and the length of fine roots is the largest.The length of jujube fine roots in2-3m shallow soil layer(7.2-8.1 m·g^-1)was significantly lower than that in 4-6m thick soil layer(8.8-9.3 m·g^-1),indicating that the physiological function of jujube fine roots growing within 2-3m soil layer may be weakened in absorbing water and nutrients.There was a highly significant positive correlation between fine root length of jujube and soil moisture in all plots.Among the fine root morphological parameters,the fine root ratio root length had a stronger correlation with soil moisture.（5）With the decrease of soil layer thickness,the growth indexes and aboveground biomass of jujube trees showed a downward trend,while the biomass and yield water use efficiency of jujube trees showed a downward trend.With the decrease of soil layer thickness,jujube tree will choose to inhibit the aboveground part and strengthen the growth of underground roots.The aboveground biomass decreases,the root biomass increases,and the root-shoot ratio of jujube tree presents an increasing trend.