【Objective】【Objective】The water use strategy of apple trees indifferent planting years in the loess hilly
region wasdiscussed in this study,in order to provide a useful reference for water management and sustainable development
of apple orchards. 【Method】In this study,10-,15- and 22-year-old apple trees were selected as the object and the
natural and artificial deuterium isotope tracer techniques and MixSIR model were used to analyze the contribution ratio of
different moisture sources to apple trees growth to investigate the seasonal variation of its moisture source. 【Result】The
results indicated that the source of moisture utilization varied greatly among the three apple trees of different ages. The
main source of moisture of the 10-year-old apple trees changed from the middle and deep layers of flowering and fruit-
bearing stage(88. 9%)to the shallow layeratthe coloring and ripening stage (57. 9%). The main source of moisture for
the 15-year-old apple trees came from the middle layer during the blossoming and bearing fruits period and fruit expanding
stage; but in the coloring and ripening period,the apple tree mainly absorbed the shallow layer soil moisture. During the
whole growth period,the 22-year-old apple trees mainly used shallow and middle soil moisture (74. 34%,86. 07% and
87. 77% respectively),and the ratio of deep soil moisture utilization was decreased gradually. The significant increase in
deuterium isotopes in xylem samples of apple trees showed that apple trees could alleviate water stress by absorbing deepersoil moisture.【Conclusion】There was an obviously difference in water use source of three stand ages apple trees. The
water source was shallower gradually and more conservative with stand age increasing. Reasonable water management
measures should be adopted to effectively decrease nonproductive water consumption and extravagant water consumption to
realize sustainable and healthy development of orchards on the basis of water source seasonal variations for different stand
age apple trees.
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