Water Uptake Of Pinus Sylvestris Var.mongolica Plantation In Horqin Sandy Land

The Three-North Shelterbelt Forest Program?TNSF?is an important ecological barrier in the west of Liaoning Province.The relationship between vegetation and water resources has always been the focus and difficulty to ecology research.In order to explore the water use process and law of Pinus sylvestris var.mongolica plantation in TNSF of the northwest of Liaoning Province,this study takes the P.sylvestris var.mongolica in Horqin Sandy Land in the northwest of Liaoning Province as the research object and analyzes the differences of the water source.The distribution of hydrogen and oxygen isotopic values of the soil and branch with different forest ages and deadwood degrees was studied.The seasonal variation of water source of P.sylvestris var.mongolica with different forest ages and deadwood degrees was quantitatively distinguished by direct comparison method and Iso-Source.The main conclusions were as follows:?1?.The variation range of precipitation?²H and?¹⁸O value were-127.24‰?-23.59‰and-16.95‰?-2.99‰,respectively.The variation range of?²H and?¹⁸O values of groundwater was small,and the distribution ranges of?²H and?¹⁸O were-73.77‰?-57.98‰and-10.81‰?-8.15‰,respectively.?2?In the observation period,the soil water content?SWC?of P.sylvestris var.mongolica forest land was different with different forest ages and different dry shoot degrees,which was fluctuates with seasons.The average SWC in dry season was significantly lower than that in rainy season.The SWC of forest land presents a downward trend with depth,with a larger decline in 0-80cm.Then it was declined in 80-200cm and maintaining a relatively stable range in 48 years old.There was a turning point in the range of 120-160cm.The average SWC of 12,19,34,48 and 58 years old of P.sylvestris var.mongolica were 2.78%,3.31%,3.90%,3.55%and 3.78%,respectively.The average soil moisture content of 1/4,2/4 and 3/4 in deadwood stands were 4.25%,3.89%,2.84%and 3.80%,respectively.?3?The?²H and?¹⁸O values of the branch water of Pinus sylvestris var.mongolica with different forest ages and different dry shoots changed alternately with the dry and rainy seasons.With the increase of soil depth,the?²H and?¹⁸O values of SWC were changed synchronously.And the change range of shallow soil water was larger than that of deep soil water.In April,May and June,the?²H and?¹⁸O values of SWC was gradually decreased with the depth in the sample plots of different forest ages.In July,the?²H and?¹⁸O values of SWC of Pinus sylvestris var.mongolica?19a and 34a?also showed a decreasing trend with the depth,but it showed an increasing trend with the depth in 12a,48a and 58a.However,In August September and October,both?²H and?¹⁸O values of SWC of Pinus sylvestris var.mongolica showed a tendency of enrichment with depth.The values of?²H and?¹⁸O in P.sylvestris var.mongolica increased with the depth in May,July and October,but it decreased with the depth in August September.The?²H and?¹⁸O values of SWC in 3/4 deadwood degrees of P.sylvestris var.mongolica all fluctuated and decreased with the increase of soil depth in the whole growing season.?4?The results of direct comparison method and Iso-Source showed that the water sources of P.sylvestris var.mongolica of different forest ages changed with the dry and rainy seasons.The P.sylvestris var.mongolica was used deeper water in the dry season,and uptake the shallower soil water in the rainy season,then it used deeper soil water after the rainy season.With the increase of age of P.sylvestris var.mongolica,its utilization ratio of deep soil water and groundwater gradually increased,while that of shallow soil water gradually decreased.In rainy season,the shallow 0-20cm soil water was mainly used for each forest age.In dry season,the main water sources used by P.sylvestris var.mongolica in 12,19,34,48 and 58 years old were soil water of 40-60cm,60-80cm,80-120cm,120-200cm,120-200cm and groundwater respectively.The water source of P.sylvestris var.mongolica in different dieback degree also alternated with dry and rainy seasons.With the increase of dieback degree,the utilization ratio of shallow soil water increased gradually,while that of deep soil water decreased gradually.The main water sources of P.sylvestris var.mongolica without litter,1/4,2/4 and3/4 were 120-200cm soil water,60-120cm,0-80cm and 10-60cm soil water,respectively.The main reason for the degeneration of P.sylvestris var.mongolica is the lack of water supply caused by the absorption of surface water.The long-term drought will lead to the obstruction of plant water transmission,the shortage of plant water or nutrient supply,and the degradation and even death of plants.