| In the Jiaodong hilly area,the soil layer is shallow,with thickness in some areas of less than 1 meter.The soil’s ability to retain water is insufficient,and water is an important limiting factor for the growth and development of deep-rooted crops in the hilly area.However,there is a lack of research on the dynamics and utilization of water in the weathered rock layer.Understanding the storage,consumption,supply,and utilization of soil water and rock water,and judging the effectiveness of water in the weathered rock layer,is of great significance for ecological hydrological processes.This study focuses on apple orchards growing on weathered rock（RP）and soil（CK）and combines apple orchards’water dynamics,spatial distribution of fine roots,and isotopic characteristics of different water sources to analyze apple tree adaptation strategies to the unique geological structure of the hilly area and quantify the contribution of rock（weathered layer）water to apple tree water.The main results are as follows:（1）The dynamic differences in soil structure and moisture in profiles were significant between different treatments.The bulk density(1.86 g·cm-3)and gravel content（40%）of rock regolith were significantly higher than those in deep soil(1.55g·cm-3,18%),and the saturation water conductivity was lower(RP:1.44 mm·h-1,CK:5.22 mm·h-1).In RP treatment,the soil volume water content at the interface of the soil-weathered rock layer is significantly higher than in CK treatment,but the available water is lower.Poor permeability of the weathered layer affects the redistribution of soil water,forming“permanent water”and becoming an important source of water for apple water use.（2）The weathering layer of the rocks significantly limits the root depth of the apple tree.More than 70%of fine roots are concentrated in the 0-40 cm soil layer,compared to 46%in CK.Fine root length density（FRLD）decreased overall with increasing soil depth,while specific root length（SRL）increased significantly in the rocky weathered layer（deep soil）.This indicates that the root structure of the apple tree has adapted to the unique geological structure of the weathering layer,and suggests the potential for effective use of rock water by the apple tree.（3）Theδ2H andδ18O of water in the weathered rock layer are significantly higher than those in the soil at the same depth,indicating that different soil structures affect the fractionation of water and may provide different sources of water for plants.The time variation of theδ2H andδ18O of xylem water reflects the difference in water utilization strategies of apple trees under different geological conditions and growing seasons.The intersection method and Mix SIAR model indicate that 40-200 cm is always the main source of water.The water contribution rate of weathered rock（RP）is 22-53%,with an average water contribution of 34%,which is lower than that of deep soil in CK（42%）,but it is still an important source of water absorption for apple trees.（4）The root system of the apple tree adapts to shallow soils by adjusting root configuration and water use strategy.The soil moisture content of 0～40 cm was unstable,and the high fine root length and biomass density increased the horizontal root distribution and realized the horizontal absorption of water in the 0～40 cm soil layer of the orchard.By increasing the length of fine roots in the regolith layer and increasing the proportion of very fine roots to whisker roots,34%of the water required for self-transpiration was absorbed by less than 7%of the root system.（5）Water storage in the 0-40 cm soil layer is the limit that limits root water absorption,and the number of roots in the rock regolith layer is the key to limiting water absorption. |
