Study On Water Use Of Apple Trees-Grass Intercropping System With Isotope Tracer In Luochuan Loess Tableland

Luochuan loess tableland is located in the middle of the Loess Plateau,apple trees are planted in a large area.The implementation of apple trees-grass intercropping system promotes the redevelopment for local apple industry,but the water use pattern in this system is still unclear.Whereas the stable isotopes provide a possibility for its quantitative analysis.Through the carbon,hydrogen and oxygen isotope tracing and field monitoring,the adaptation mechanism of plant water use strategy to the ecological environment can be clarified,so as to provide a scientific basis for the selection of forage under apple trees-grass intercropping system,the optimization of orchard water management and the extensive promotion of the model in the Loess Plateau.We used the natural abundance of stable isotopic rations of carbon,hydrogen and oxygen to determine the seasonal changes in sources of soil water uptake and water use efficiency by apple trees-white clover/ryegrass intercropping system in Luochuan loess tableland.Results are as follows:（1）The analysis of precipitation,temperature and precipitation isotope composition in Luochuan loess tablelandDuring the experimental observation period,the isotopic composition of the precipitation fluctuated little,among them,isotopes were enriched in May and depleted in July,August and October.The local meteoric water line is:δD=10.50δ¹⁸O+24.54.（2）Soil moisture variations and plant water use in different systemsThere was no significant change in soil profile water content in different months among the three systems.The average soil water content of the three systems was the highest in July,followed by August.In the same month,the average soil water content also showed that the intercropping system was larger than the single cropping system,and the apple trees-ryegrass intercropping system had the highest water content,preserved soil moisture effectively.In July,affected by rainfall,apple trees mainly used shallow soil water and middle-layer soil water in the single apple trees system,the utilization ratio reached 71.50%.Apple trees and white clover mainly both used deep soil water in the apple trees-white clover intercropping system,the utilization ratio reached 48.00% and 98.50% respectively.Apple trees and ryegrass mainly both used shallow soil water in the apple trees-ryegrass intercropping system,the utilization ratio reached 80.50% and 52.00% respectively.And in other months,apple trees mainly uptook deep soil water（40¹00 cm）,forages mainly uptook surface water（0²0 cm）in the intercropping systems,it did not show competition for the utilization of soil moisture between apple trees and forages.（3）The seasonal variations ofδ¹³C in different systemsRaw grass has no significant effect on water use efficiency of apple tree leaves.With the increase of the month,theδ¹³C value of apple tree leaves showed a decreasing trend,and the white clover and ryegrass showed May>October>August>July in this three systems.And theδ¹³C value of the plant is not affected by precipitation and temperature alone.