Research On Sap Flow And Transpiration Water Consumption Characteristics Of Hippophae Rhamnoides In Pisha Sandstone Area Of Inner Mongolia

The Pisha sandstone area of Inner Mongolia is one of the areas with most severe water loss and soil erosion in Loess Plateau and even the world.Researches and practices of plant restoration and reconstruction in this area have been carried out for years.However,because the Pisha sandstone has the unique characteristics of"becoming mud when mixed with water,and becoming sand when there is wind",and this area has the environmental characteristics of dry climate and little annual average rainfall,the Pisha sandstone area of Inner Mongolia has become the main source of silt for downstream Yellow River.As a good tree species for water and land conservation,Hippophae rhamnoides has been widely used in the ecological recovery and reconstruction of the Pisha sandstone areas.However,due to the special soil properties and specific geological conditions of the Pisha sandstone area,as well as other factors such as drought and lack of water,after the Hippophae rhamnoides forest with large-area planting has grown to a certain period,it will show degradation and even death,while there is no in-depth discussion of the relationship between artificial vegetation and the environment in this area.For a long time,there have been no researches on or profound discussions of the environmental adaptability of Hippophae rhamnoides to the special erosion badland of the Pisha sandstone area,and whether current construction method of Hippophae rhamnoides forest is reasonable.In this work,from 2017 to 2019,with the Hippophae rhamnoides artificial forest at different growth stages in Erdos Soil and Water Conservation Science and Technology Demonstration Area of Inner Mongolia as the research objects,thermal property measurement system and automatic meteorological station were employed to continuously monitor the Hippophae rhamnoides sap flow and the environmental factors for 24h from May to October.We discuss the characteristics of Hippophae rhamnoides sap flow under different weather conditions and their response mechanism to the change of environmental factors,analyze the stand transpiration water consumption of Hippophae rhamnoides artificial forest and the interannual variation,and estimate the s Table.regulation density of Hippophae rhamnoides artificial forest sui Table.for the Pisha sandstone area based on the water resource carrying capacity.The main conclusions of our work are as follows:(1)Characteristics of Hippophae rhamnoides sap flow in the Pisha sandstone area and their relationship with environmental factorsBy comparing the sap flow rates of Hippophae rhamnoides of different stand ages,we find that the sap flow rate of 6-year Hippophae rhamnoides is slower than that of the 12-year and 20-year Hippophae rhamnoides,and the sap flow rates of 12-year and 20-year Hippophae rhamnoides are close.According to the sap flow rates of Hippophae rhamnoides in different months,the sap flow rates of Hippophae rhamnoides present relatively regular unimodal curves in May,June,September and October;in July and August,the sap flow rates of Hippophae rhamnoides demonstrate the curvilinear trend of peaks plus plateaus,and the peaks of flow rate curves also appear earlier than that in May,June,September and October.In accordance with the continuous monitoring from May to October,the sap flow rates of Hippophae rhamnoides in July and August reflect the special property of Hippophae rhamnoides sap flow rates in the Pisha sandstone area.Based on analysis of the change of soil moisture contents at soil layers of 0?20cm,20?40cm and 40?60cm,the equally spaced gradient change trends of soil moisture content curves at different soil layers correspond to the unimodal curves of Hippophae rhamnoides sap flow rates in May,June,September and October;the uneven distribution trends of soil moisture content curve at different soil layers corresponds to the peak plus plateau curve shape of Hippophae rhamnoides sap flow rates in July and August,and the soil moisture content curve at soil layer 20?40cm is close to that at soil layer 0?20cm.In May,June,September and October,the Hippophae rhamnoides sap flow rates change synchronously with the change of environmental factors such as the air temperature and solar radiation;in July and August,compared to the curves of environmental factors such as the air temperature and solar radiation,the peaks of the sap flow rate curves show move forward.By analyzing the process to select an optimal model,the prediction model of 12-year(peak stage of growth)Hippophae rhamnoides sap flow rate and environmental factor prediction model is selected as the representative model,and specifically,Y=2.265-0.214X₂(soil moisture content at 20?40cm)-0.134X₃(soil moisture content at 40?60cm)+0.183X₄(air temperature)+0.067X₅(solar radiation)+0.127X₈(vapor pressure deficit)(R²=0.85).The influences of various environmental factors on the Hippophae rhamnoides sap flow rate are in the following order:solar radiation>vapor pressure deficit>air temperature>soil moisture content at 20?40cm>soil moisture content at 40?60cm>soil moisture content at0?20cm.The sap flow model can provide a theoretical basis for estimation of Hippophae rhamnoides sap flow in the Pisha sandstone area.(2)Characteristics of Hippophae rhamnoides sap flow in the Pisha sandstone area under rainfall condition and their relationship with environmental factorsUnder rainfall condition,the sap flow rate curve of 12-year Hippophae rhamnoides basically coincides with that of 20-year Hippophae rhamnoides,and their sap flow rates are both higher than that of 6-year Hippophae rhamnoides.The sap flow rate curves of Hippophae rhamnoides all present obvious bimodal pattern,and show"noon break".Under different rainfall levels,the sap flow rates are:the sap flow rate under heavy rain is basically equivalent to that under moderate rain,and they are both higher than the sap flow rate under light rain.By analyzing the relationship between rainfall and sap flow rate in different months,we find that when the rainfall is above 15mm/12h,the daily change of Hippophae rhamnoides sap flow rate is very small,which indicates that the coincidence of sap flow rate curves under heavy rain and moderate rain has universality,and this phenomenon is a unique characteristic of Hippophae rhamnoides sap flow in the Pisha sandstone area.To explain the special change trend of Hippophae rhamnoides sap flow in the Pisha sandstone area under rainfall condition in mechanism,we focus on analyzing the soil moisture characteristic curve,the soil moisture content-rainfall relationship curve from May to October and the change of soil moisture content under Hippophae rhamnoides forest.The analysis results show that when the soil moisture content in the Pisha sandstone area is above30%,it is difficult for the soil moisture to migrate and infiltrate.Under heavy rain with short duration,the soil of the Pisha sandstone area cannot infiltrate excess rainfall,and the soil presents a mud state very soon.First,this will affect the sap flow rate of Hippophae rhamnoides,and further affect the transpiration efficiency;secondly,surface runoff will be formed,which will take the soil of the Pisha sandstone area,causing severe water loss and soil erosion.The Hippophae rhamnoides sap flow rate prediction model under rainfall condition is established:Y=1.547-0.185X₁(soil moisture content at 0?20cm)-0.215X₂(soil moisture content at 20?40cm)+0.278X₄(air temperature)+0.073X₅(solar radiation)+0.177X₈(vapor pressure deficit)(R²=0.88).Under rainfall condition,the influences of various environmental factors on the Hippophae rhamnoides sap flow rate are in the following order:soil moisture content at 20?40cm>soil moisture content at 0?20cm>solar radiation>vapor pressure deficit>air temperature>soil moisture content at 40?60cm.The sap flow model can provide a theoretical basis for estimation of Hippophae rhamnoides sap flow in the Pisha sandstone area.(3)Stand transpiration water consumption of Hippophae rhamnoides forest in the Pisha sandstone area and density regulationBased on the conditions that need to be met when selecting spreading parameters during calculation of transpiration water consumption,ground diameter,whole-plant biomass and above-ground biomass are finally chosen as the spreading parameters of Hippophae rhamnoides.However,considering the convenience of data acquisition,the ground diameter prediction model and above-ground biomass prediction model are more advantageous.From2017 to 2019,the monthly water consumption of Hippophae rhamnoides forest and the monthly average soil moisture content presented an exponential relationship:y=14758x^0.7592(R2=0.93);the accumulated water consumption of Hippophae rhamnoides forest and the accumulated rainfall also showed an exponential relationship:y=113.8x^0.8068(R2=0.93).In long term,rainfall has significant influence on the growth and development of plants,but such influence also shows an obvious lag effect,because the rain needs to become soil moisture first before being absorbed and utilized by plant.Based on the single-plant transpiration water consumption of Hippophae rhamnoides,the balance equation of water quantity is employed to estimate the stand s Table.density of Hippophae rhamnoides artificial forest in the exposed Pisha sandstone area,which is around2900 plants/hm².Due to the special rock-soil properties of the Pisha sandstone area,to enable the growth of Hippophae rhamnoides artificial forest to better adapt to the special environment of the Pisha sandstone area,so that the Hippophae rhamnoides forest can maintain a vigorous growth state,the planting density of Hippophae rhamnoides artificial forest should be adjusted properly during the vegetation construction period.Moreover,after the Hippophae rhamnoides forest has reached a s Table.stage,maintenance measures,such as intermediate cuttings and stumping,should be taken in a timely manner,so that the Hippophae rhamnoides forest in the Pisha sandstone area can maintain vigorous growth and continue to carry out its ecological and economic benefits.