Research On Model Simulation Of Water Use Efficiency And Carrying Capacity Of Typical Soil And Water Conservation Forest Land

The lack of water resources in the hilly and gully areas of the Loess Plateau is a key factor restricting the restoration and growth of plantations.Exploring the water use mode,efficiency and growth capacity of planted forests is an effective way to effectively use water and restore the ecology.It is also an urgent scientific problem to be solved for the sustainable restoration of vegetation and its ecological function.Therefore,this study selected the artificially planted Armeniaca sibirica,Hippophae rhamnoides,Pinus tabulaeformis,Populus simonii,Robinia pseudoacacia,Robinia pesudoacacia and Amygdalus davidiana mixed forest and Robinia pesudoacacia and Armeniaca sibirica mixed forests that were artificially planted and restored for 19 years in the Wuli Bay watershed of Ansai as the research objects,and compared and analyzed 0?100 cm,stability The vertical distribution of oxygen isotopes and the contribution rate of different soil layers to forest land;the Biome-BGC model is used to simulate the carbon and water flux and water use efficiency of different years;the bearing capacity model is used to estimate the soil water vegetation carrying capacity between forests,which is a cognition The water use characteristics and forest land carrying capacity at different levels of water and soil conservation forests in the hilly and gully regions of northern Shaanxi provide scientific basis for water and soil conservation forest configuration and tree species selection.The main findings are as follows:（1）The stable oxygen isotope distribution results show that there is an intersection point between the soil water and stem waterδ¹⁸O of the shrub Armeniaca sibirica forest at 0?20 cm.The soil water from 0～10 cm is mainly used,and the utilization ratio is 40.4%;The stem waterδ¹⁸O of Hippophae rhamnoides forest has two intersections at 0?10 cm and 80?100 cm.The water mainly comes from the soil layer of0?10 cm and 80?100 cm,and the utilization ratios are 27.4%and 65.5%,respectively.There is an intersection point between the soil water and stem waterδ¹⁸O of Pinus tabulaeformis forest and Robinia pseudoacacia forest in arbor forests at 0?20 cm.The water mainly comes from the 10～20 cm soil layer,and the utilization rate accounts for 45.2%and 67.3%of the total soil water respectively;Theδ¹⁸O values??of water and stem water of Populus simoniisoil forestare similar in distance,and the average value of soil water in the 0-100 cm soil layer is 16.7%.The soil water and stem waterδ¹⁸O of the mixed forest of Robinia pesudoacacia and Amygdalus davidiana have an intersection point at 10?20 cm.Mainly from 0～10 cm soil layer,the utilization rates of Robinia pseudoacacia and Amygdalus davidiana were 40.3%and 36.5%,respectively.The soil water and stem waterδ¹⁸O of the mixed forest of Robinia pseudoacacia and Amygdalus davidiana have an intersection point at 60?80 cm.The moisture mainly comes from the soil layer of 60～80 cm and 80-100 cm.The utilization rates of Robinia pseudoacacia and Armeniaca sibirica are 28.7%,28.5%and26.8,respectively.%,27.0%.This may be related to the distribution of plant roots.（2）Biome-BGC model simulation of water use efficiency of soil and water conservation forests in 1999?2020 shows that water use efficiency generally decreases with the increase of vegetation restoration,but the Armeniaca sibirica forest,the Pinus tabulaeformis forest,the Populus simonii forest and the mixed Armeniaca sibirica and Robinia pesudoacacia The maximum value of forest water use efficiency appeared in 2018,the minimum value of water use efficiency of Armeniaca sibirica forest and Robinia pseudoacacia forest appeared in 2000,and the minimum value of Pinus tabulaeformis forest appeared in 2003.The water use efficiency of shrub Hippophae rhamnoides in the water and soil conservation forests is the highest,with a range of 1.46?2.63 g C/kg H₂O;the arbor and Pinus tabulaeformis forest has the highest water use efficiency,with a range of 1.36?2.1 g C/kg H₂O.The average water use efficiency of shrubs in 2019 and 2020 is 1.86 g C/kg H₂O,1.33 g C/kg H₂O,and the average water use efficiency of arbor forests are 1.52 g C/kg H₂O,1.28g C/kg H₂O,which is lower than 18.3%of shrubs,3.8%.The differences in water use efficiency of different soil and water conservation forest lands are related to the characteristics of the plants themselves.（3）The estimation of soil water vegetation carrying capacity model shows that the soil water storage capacity of all forest lands is greater than the soil wilting water storage capacity,and the average effective water storage capacity of different soil and water conservation forests is 50.5mm.The water use efficiency for estimating carrying capacity is determined by the ratio of net primary productivity to evapotranspiration.The highest water use efficiency of Armeniaca sibirica forest and Populus simonii forest were 0.8 g C/kg H₂O and 0.84g C/kg H₂O,respectively.Followed by Robinia pseudoacacia forest,Robinia pesudoacacia and Amygdalus davidiana mixed forest and Robinia pesudoacacia and Armeniaca sibirica forest were 0.46 g C/kg H₂O,0.67 g C/kg H₂O and 0.77 g C/kg H₂O,and finally Hippophae rhamnoides forest and Pinus tabulaeformis forest were both 0.19 g C/kg H₂O.The single plant biomass range of the same soil and water conservation forest is 1.38 kg?55.86 kg,and the woodland biomass range is 3.04 t/hm²?45.92 t/hm².The surplus densities of different soil and water conservation forests to reach the maximum soil water carrying capacity were59 plants/ha and 85 plants/ha for shrubs,Armeniaca sibirica and sea buckthorn respectively;among arbor forests,Pinus tabulaeformis forest,Populus simonii forest,Robinia pseudoacacia forest,Robinia pesudoacacia and Amygdalus davidiana mixed forest mixed forest and Robinia pesudoacacia and Armeniaca sibirica forest The forest is 17?42plants/ha.The soil water vegetation carrying capacity of each water and soil conservation forest is 829 trees/ha in shrub forests and Armeniaca sibirica forests,2285 trees/ha in Hippophae rhamnoides forests;1833 trees/ha in arbor forests and Pinus tabulaeformis forests,followed by mixed forest of Robinia pesudoacacia and Amygdalus davidiana trees（917 trees/ha in Robinia pseudoacacia forest）.Hectares,Amygdalus davidiana forest is 458plants/ha),Robinia pesudoacacia and Armeniaca sibirica mixed forest（Robinia pseudoacacia forest is 339 plants/ha,Armeniaca sibirica forest is 1018 plants/ha）,Robinia pseudoacacia forest is 1224 plants/ha,and Populus simonii forest is minimum 841plants/ha.Based on the above analysis,different water and soil conservation forests mainly use soil water in the surface layer of the soil during the rainy season.The water use efficiency is decreasing year by year,and there are significant differences between forest lands.At the same time,the vegetation carrying capacity of soil moisture is surplus but close to saturation.