Xylem Hydraulic Characteristics Of Robinia Pseudoacacia And Acer Truncatum In Response To The Soil Moisture

In the context of global climate change,the response of plant xylem hydraulic characteristics to soil water conditions has become an important content and been a hot spot in the study of plant drought resistance.In this paper,the two kinds of drought tolerance strategy species of Robinia pseudoacacia Linn and Acer truncatum Bunge were studied,to explore xylem hydraulic characteristics of two tree species in response to the different soil moisture,in order to provide theoretical basis for drought tolerant plants adapt to the physiological and ecological characteristics of arid environment.The annual seedlings of R.pseudoacacia and A.truncatum water treatments were carried out in different degree,and divided into well-watered group(A),moderate stress group(B)and severe stress group(C).We used Cochard cavitron centrifuge to determine the embolism vulnerability(P50),to calculate the xylem embolism vulnerability.Vessel diameter,intervessel wall thickness,conduit wall span and vessel length was measured by staining techniques and Silica gel injection.The hydraulic conductivity and the loss of hydraulic conductivity under natural conditions were measured by “Low Pressure Flow Meter”,and then determined the embolism degree.Pressure chamber was used to calculate the leaf water potential,portable photosynthesis system was used to determine the diurnal variation of photosynthetic physiological index.Analyse the changes in vulnerability,xylem structure,hydraulic characteristics and physiological indexes caused by different species in the same degree of water stress and the same tree species in the different degrees of water stress,and the interaction among these changes,to explore the response of plant xylem hydraulic characteristics to soil moisture conditions.The main conclusions are as follows:1.The embolism vulnerability of two tree species were in the order of A>B>C.For the same species,antithrombotic resistance of group C was stronger than group A and group B,it has the highest drought resistant.For R.pseudoacacia and A.truncatum,the amplitude of variation of embolism vulnerability between A and C were 58.50% and 31.62%,respectively.The influence of soil moisture changes for A.truncatum was smaller than R.pseudoacacia,therefore,the adaptability of A.truncatum's embolism vulnerability to soil water condition was stronger than R.pseudoacacia.2.Before watering,at dawn and noon,the amplitude of variation of R.pseudoacacia stem water potential between A and C was less than A.truncatum,but after watering the amplitude of variation of R.pseudoacacia was greater than A.truncatum.The influence of change of soil water condition to R.pseudoacacia was greater than to A.truncatum.The adaptability of A.truncatum stem water potential to the soil moisture change was stronger.3.For R.pseudoacacia and A.truncatum,the amplitude of variation of hydraulic conductivity between A and C were 57.66% and 19.48%,respectively.The influence of soil moisture changes of A.truncatum was smaller than R.pseudoacacia,and the adaptability to soil water condition was stronger.There was a significant difference among the three groups of R.pseudoacacia(p<0.01),but for A.truncatum,there was no significant difference in embolsm level among three groups(p>0.05).The response of R.pseudoacacia to the soil moisture is more sensitive than A.truncatum.The influence of soil moisture changes to embolism level of A.truncatum was smaller than R.pseudoacacia,and the adaptability of A.truncatum is stronger.4.The vulnerability curve of R.pseudoacacia is "R" shape,it's adapted to soil moisture conditions through the change of vessel length and xylem density.The vulnerability curve of A.truncatum is "S" shape,it's adapted to soil moisture conditions through the change of vessel diameter,intervessel wall thickness and conduit wall span.5.The daily mean net photosynthetic rate of A.truncatum and R.pseudoacacia were both in order of A>B>C,it's decreased with the reduction of soil water content.The decline range of daily mean net photosynthetic rate for R.pseudoacacia and A.truncatum were 35.71% and 32.42%,and the amplitude of variation of A.truncatum was smaller,the adaptability of A.truncatum to the soil moisture change was stronger.For the embolism vulnerability,stem water potential,hydraulic conductivity,embolism level and daily average net photosynthetic rate of A.truncatum,the influence to different soil water conditions was smaller than R.pseudoacacia,that's to say,the adaptability to the soil water change of A.truncatum was stronger.