Response Of Leaf Water Use Efficiency Of Prunus Armeniaca To Slope Aspects

Plant water-use efficiency（WUE）as a key element of the plant-soil carbon and water cycle is an important composite indicator of plant growth adaptability under drought conditions.Soil erosion and desertification are very serious in the Loess Plateau region,and the ecological environment is very fragile,while afforestation/grass planting is an important means to combat soil degradation,improve the ecological environment and promote the recovery of damaged ecosystems.Therefore,it is of great significance to study the difference and influencing factors of leaf water use efficiency（LWUE）of Prunus armeniaca across different terrains,the main plant species in afforestation projects on the Loess Plateau region.To study the water use efficiency and the factors influencing the water use efficiency of the leaves of Prunus armeniaca,a major tree planting species in the Loess Plateau region,under different slopes,South-facing and North-facing,were used as the environmental change gradients,and the water use efficiency of the leaves of the mountain apricot was characterized by its stable carbon isotope(δ¹³C),in terms of the effects on the water use efficiency of the leaves of Prunus armeniaca.The results of the environmental gradients were used to determine the stable carbon isotopes of Prunus armeniaca leaves and the functional properties（including leaf water content（LWC）,leaf dry matter content（LDMC）,leaf mass per area（LMA）,leaf area（LA）,specific leaf area（SLA）,leaf carbon（LC）,leaf nitrogen（LN）,leaf phosphorus（LP）,ratio of leaf carbon to nitrogen（LC:LN）,ratio of leaf carbon to phosphorus（LC:LN）and ratio of leaf nitrogen to phosphorus（LN:LP））and soil physicochemical properties（including soil organic carbon（SOC）,soil total nitrogen（STN）,soil total phosphorus（STP）,ratio of soil carbon and nitrogen content（SOC:STN）,ratio of soil carbon and phosphorus content（SOC:STP）,ratio of soil nitrogen and phosphorus content（STN:STP）,soil available phosphorus（SAP）,soil available nitrogen（SAN）,soil bulk density（SBD）,soil temperature（ST）,soil potential of hydrogen（p H）and soil water content（SWC））in the regional environment were compared.The results showed that:（1）The functional traits of Prunus armeniaca leaves in the study area vary with slope as follows:leaf water content,leaf mass per area,leaf area,leaf nitrogen content,leaf phosphorus content,ratio of leaf carbon to nitrogen content,ratio of leaf carbon to phosphorus content and ratio of leaf nitrogen to phosphorus content on the North-facing slope were all higher than those on the South-facing slope,while leaf dry matter content,specific leaf area and leaf carbon content showed opposite trends.（2）The variation of soil physicochemical properties with slope in the study area were:soil organic carbon,soil total nitrogen,soil total phosphorus,soil available phosphorus,soil available nitrogen and soil water content on North-facing slope were higher than those on South-facing slope,while the ratio of soil carbon and nitrogen content,ratio of soil carbon and phosphorus content,ratio of soil nitrogen and phosphorus content,soil bulk density,soil potential of hydrogen and soil temperature were opposite.（3）The leaf stable carbon isotope and water use efficiency of Prunus armeniaca leaves on the South-facing slope was significantly higher than those on the North-facing slope of the study area.（4）The main factor affecting the leaf water use efficiency of Prunus armeniaca leaves was soil total nitrogen,while the secondary factors were specific leaf area,soil water content and soil bulk density.The specific leaf area,leaf area,soil water content and ratio of soil carbon and nitrogen content were the direct factors,while soil total nitrogen,soil available nitrogen and soil bulk density were the indirect factors.These results suggest that,with changes in slope aspects,Prunus armeniaca modulates its leaf water use efficiency by changing its functional traits to adapt to the relatively dry habitat caused by changes in environmental factors.Consequently,the study of the changes in leaf water use efficiency in the context of leaf functional traits and environmental factors can provide a reference for the conservation and ecological benefits of the main afforestation and greening tree species of Prunus armeniaca in the Loess Plateau replacing farmland with forest/grass project,and provide a scientific and theoretical basis for local revegetation,restoration,ecological adaptation strategies and response mechanisms.