| This study was based on the three main plantation types of pure forest of Pinus tabulaeformis and Hippophae rhamnoides,mixed forest of Pinus tabulaeformis and Hippophae rhamnoides which in loess hilly.Based on continuous sampling and analysis of hydrogen stable isotopes of soil water,trees branchlets,Use the MixSIR model to quantified the water sources of Pinus tabulaeformis and Hippophae rhamnoides,analysed the water sources seasonal variation of Pinus tabulaeformis and Hippophae rhamnoides,and determined the relationship of two species of water sources,and investigated the effect of mixed forest of Pinus tabulaeformis and Hippophae rhamnoides.The sap flow density(Js)of Pinus tabulaeformis and Hippophae rhamnoides in three forest stand were used the thermal diffusion probe(TDP)to observe continuously,and used the automatic weather station to observe environmental factors continuously(0n May 1-October 30,2016).The influencing factors of sap flow density of Pinus tabulaeformis and Hippophae rhamnoides were analyzed systematically,and the average water consumption of growing season of each forest stand was also estimated.At the same time used the xt LI-6400 portable photosynthesis system and water potential measuring to determined leaf photosynthesis and water potential of two species and also analyzed the influence factors of water potential.Based on the above research,we expect provides a more scientific basis for the selection of suitable afforestation species and the evaluation of soil water suitability in the region.The main results are as follows:1)The main water sources of Pinus tabulaeformis and Hippophae rhamnoides were determined by means of hydrogen stable isotope,in initial growth stage,the soil water of 20-100 cm soil layer was mainly used in the pure forest of Pinus tabulaeformis,while the soil water of 100-200 cm soil layer was mainly used in early fast growth stage,and the soil water of 20-100 cm soil layer was used in the later fast growth stage.In late growth stage,the soil water of 0-20 cm surface was mainly used.Pinus tabulaeformis in mixed forest in early stage of initial growth stage,the soil water of 100-200 cm was mainly used,and in later stage of initial growth stage and in fast growth stage and in late growth stage,the soil water of 0-20 cm was mainly used.In pure forest of Hippophae rhamnoides in initial growth stage,the soil water of0-20 cm surface was mainly used.In early stage of fast growth stage,the soil water of 0-20 cm and 100-200 cm was mainly used,but in later stage of fast growth stage,the soil water of 20-100 cm was mainly used,in late growth stage,the soil water of 0-20 cm was mainly used.Unlike Hippophae rhamnoides in pure forest,Hippophae rhamnoides in mixed forest in initial growth stages,the soil water of 0-20 cm was mainly used.In early stage of fast growth stage,the soil water of 0-20 cm was mainly used,but in later stage of fast growth stage,the soil water of 100-200 cm was mainly used.In late growth,the soil water of 0-20 cm was mainly used.Soil water competition existed in 0-20 cm between Pinus tabulaeformis and Hippophae rhamnoides in mixed forest.2)There were differences in water consumption of each forest stand in different periods.The total water consumption in pure forestof Pinus tabulaeformis in the growing season was higher than that in mixed forestof Pinus tabulaeformis,but there was no significant difference.Unlike Pinus tabulaeformis,the water consumption in pure forest of Hippophae rhamnoides in different periods of growing season was significantly lower than in mixed forest of Hippophae rhamnoides(p<0.01),the water consumption of Pinus tabulaeformis was significantly higher than Hippophae rhamnoides.In different periods of growing season,the sap flow density in pure forest and mixed forest of Pinus tabulaeformis and Hippophae rhamnoides showed obvious diurnal variation rhythm,the two species were all showed a single peak trend.In the pure forest and mixed forest the Js of Pinus tabulaeformis at 6:00 in the morning began started,and at noon 11:00-15:00 reached the maximum,and at 18:00 began to decline.In the pure forest and mixed forest the Js of Hippophae rhamnoides at 8:00 in the morning began started,and at noon 11:00-14:00 reached maximum,and at 16:00 began to decline.In the growing season the chang of Js in pure forest and mixed forest of Pinus tabulaeformis were maintained high sap flow density in initial growth stage,and maintained lower sap flow density in late growth,the sap flow density in mixed forest of Pinus tabulaeformis was higher than that of Pinus tabulaeformisin pure forest(there was no significant difference).In the growing season,the meteorological factors was the main influence factor of sap flow density in pure forest of Pinus tabulaeformis.Ininitial growth stage,the meteorological factors was the main influencefactor of sap flow density in mixed forest of Pinus tabulaeformis,which explained 15.01%.But in fast growing stage the soil volumetric water content(SWC)was the main influence factor,which explained 39.36%.In late growth the meteorological factors was the main factor,which explained 24.33%.In initial growth stage,the sap flow density of Hippophae rhamnoides in two forest stands were all reached highest,and were all reached lowest in late growth.The sap flow density of Hippophae rhamnoides in mixed forests was significantly higher than that in pure forest.In growing season the soil volumetric water content was the main influencefactor of sap flow density in pure forest ofHippophae rhamnoides,the interpretation in the three periods were 2.35%,9.05% and 2.35%,respectively.In the initial growth stage and late growth stage the ssoil volumetric water content was the main influence factor of sap flow density in mixed forest of Hippophae rhamnoides,which explained 8.97% and 23.02%,while in the fast growth stage the meteorological factors is the main influence factor,which explained 16.10%.The Js of Pinus tabulaeformis in growing season was significantly higher than that of Hippophae rhamnoides(p<0.01).3)In the growing season,the daily change of leaf water potential of Pinus tabulaeformis and Hippophae rhamnoides were all showed a trend of "V" curve,and the two species were all reached a peak in 6:00-7:00 in the morning,then reached a minimum in12:00-16:00 p.m.,then began to pick up.The change of leaf water potential in pure forest of Pinus tabulaeformis was mainly influenced by relative humidity.The temperature and relative humidity were the main influence factors of leaf water potential in mixed forest of Pinus tabulaeformis and Hippophae rhamnoides in the growing season.According to the change of leaf water potential margin,we concluded that Hippophae rhamnoides was more prone to water deficit than Pinus tabulaeformis.The daily change of leaf water use efficiency(WUE)Pinus tabulaeformis in growing seasons was showed double peak.And in Hippophae rhamnoides was showed single peak and double peak two types,but the changes of WUE of Hippophae rhamnoides in mixed forest,except the single peak and double types,also appeared irregular change curve.The WUE magnitude sequence in pure forest of Pinus tabulaeformis in different periods was: WUE10month>WUE8 month>WUE6 month>WUE9 month>WUE7 month>WUE5 month.The WUE in mixed forest of Pinustabulaeformis in different periods the magnitude sequence was: WUE10month>WUE9 month>WUE7 month>WUE8 month>WUE6 month>WUE5 month.The WUE in mixed forest of Hippophae rhamnoides in different periods the magnitude sequence was: WUE6 month>WUE9 month>WUE7 month>WUE10 month>WUE8 month >WUE5 month.The WUE in mixed forest of Hippophae rhamnoides in different periods the magnitude sequence was: WUE9month>WUE10 month>WUE8 month >WUE7 month WUE6 month >WUE5 month. |
PDF Full Text Request