Variation And Correlation Of Leaf Functional Traits Of Ulmus Pumila Across Precipitation Gradient Zone

From southeast to northwest of China,there is a precipitation gradient that spans several bioclimatic zones.It has extremely rich vegetation types and species diversity,and carries huge and diverse ecosystem services.As an important part of the study of plant traits,leaf functional traits are the bridge between plants and the environment.Their traits directly affect the basic behavior and function of plants,and reflect the adaptability of plants to the environment.Studies on the relationship between leaf functional traits of plants and their environmental factors in precipitation gradient zones are helpful to understand the morphological,physiological mechanisms and ecological adaptation strategies of plants in response to environmental changes.In this paper,10 research sample sites representing vegetation zonality are selected in the precipitation gradient zone,and U.pumila,which is distributed in all 10 sample sites,is taken as the research object.Adopt the combination of field investigation and laboratory test,measured the U.pumila stomatal character index(stomata density,stomata size,stomatal area fraction),Huber values,leaf mass per area,vein density,and photosynthetic physiological indexes(maximum stomatal conductance,net photosynthetic rate,water use efficiency).The mean annual temperature,mean annual precipitation,photosynthetically active radiation of growing season,aridity index,atmospheric vapor pressure deficit difference and relative air humidity were collected and calculated.The distribution and variation of functional characters of U.pumila leaves in precipitation gradient zone were analyzed,and the relationship between characters and environmental factors and the relationship between characters were explained.The main results are as follows:(1)The functional traits of U.pumila leaves vary greatly in the precipitation gradient zone.From southeast to northwest,stomatal density first decreased and then increased,stomatal size and stomatal area fraction first increased and then decreased.Leaf hydraulic traits(vein density and Huber value),economic traits(leaf mass per area)and photosynthetic traits(net photosynthetic rate and maximum stomatal conductance)increased from southeast to northwest.(2)The stomatal traits of U.pumila were mainly related to precipitation and the dryness index related to precipitation.The stomatal density first decreased and then increased with the decrease of precipitation,while the stomatal size and stomatal area fraction first increased and then decreased.Vein density,leaf mass per area and Huber value were significantly decreased with the increase of aridity index(p < 0.05).The net photosynthetic rate and the maximum stomatal conductance were significantly positively correlated with the photosynthetically active radiation in the growing season(p < 0.05),and increased first and then decreased with the aridity index.(3)The positive correlation between vein density and maximum stomatal conductance makes U.pumila have both high vein density and maximum stomatal conductance,which increases the water vapor exchange capacity of U.pumila.The negative correlation between water use efficiency and maximum stomatal conductance and between maximum stomatal conductance and stomatal area fraction indicated that the anatomical adaptation of maximum stomatal conductance and stomatal opening of U.pumila were independent and opposite.The higher maximum stomatal conductance indicates that the stomatal conductance adopted by U.pumila in arid region is radical,but the conservative adaptation strategies such as high Huber value,high vein density and high leaf mass per area make up for the hidden danger caused by the radical stomatal behavior(4)The environmental factors responding to the leaf functional traits of U.pumila were different under different habitat conditions.From the humid area to the mid-humid area,forest Fecosystem limits U.pumila stomatal traits and photosynthesis characteristic factor is the effectiveness of the light,from mid-humid zone to arid area,limiting factor by the light into the water,so the U.pumila stomatal character and photosynthetic properties(net photosynthetic rate,maximum stomatal conductance)in precipitation gradient belt is piecewise response to environmental changes.