Hydraulic Supply Characteristics In Leaves And Flowers Of Caragana Species Distributed In Geographic Substitution Pattern

In order to ensure growth and survival under stressed environments,it is necessary for plants to maintain hydraulic supply.Many studies have shown that the regulation of plant hydraulic system is basis for plants to adapt to complex environment.Under drought stress,the hydraulic system of roots,stem xylem and leaves will produce a series of reactions,which is the result of plant evolution and a long-term adaptation to environment.However,there are few studies shows how the hydraulic characteristics of same-genus-plants differentiate along the precipitation gradient.It should also be discussed whether there is a safety versus efficiency trade-off in hydraulic pathway of flowers.Caragana plants widely grow in arid,semi-arid,semi-humid and humid regions of China.They are typical materials to study above issues because these species show variable distribution along the precipitation gradient.We chose 17 species of Caragana species as plant materials to study how the photosynthetic and hydraulic characteristics of leaves differentiate along the precipitation gradient,besides the plasticity.We also studied the stoichiometric parameters of element and structural parameters in leaves.Under a drought stress simulation,the safety and efficiency in hydraulic pathway of flowers were also be studied.At the same time,we wanted to know if there was a safety versus efficiency trade-off in flowers.Finally we got some main conclusions:1.The leaf photosynthetic and hydraulic characteristics of Caragana plants differentiated along the precipitation gradient obviously.(1)Compared with the species from humid area,the species from arid area had higher photosynthetic rate,stomatal conductance and transpiration rate which decreased linearly with the increasing precipitation.Species from arid area had higher leaf hydraulic conductance,and the leaf hydraulic conductance showed an exponential decrease when the precipitation gradient increase.The species also had higher photosynthetic and hydraulic supply(which meant the ratio of hydraulic conductance to photosynthetic rate was higher,so as the ratio of hydraulic conductance to stomatal conductance).It showed an exponential decrease for both characteristics when the precipitation gradient increased.(2)The photosynthetic rate,stomatal conductance and transpiration rate of all species decreased at noon compared with what showed in the morning.The leaves of the species from arid area had higher photosynthetic supply(which meant the ratio of hydraulic conductance to photosynthetic rate was higher).It showed an exponential decrease when the precipitation gradient increased.(3)The study of plant plasticity(the difference between the characteristics in the morning and at noon)showed that,comparing with the species from humid area,the leaves of the species from arid area had a sharp decline of many characteristics including stomatal conductance,hydraulic conductance and water use efficiency.It meant that the plasticity decreased linearly when the precipitation gradient increased.(4)The analysis of leaf structure and element content showed that the leaves of the species from arid area showed smaler simple leaf area.The specific leaf weight,leaf carbon content and the ratio of carbon to nitrogen content was lower.The minor vein density was higher.The ratio of minor vein density to stomatal density was higher.These characteristics all changed along the precipitation gradient linearly.(5)The characteristics of species from Xinjiang were nearly the same with other species from arid area.Some were lower than them.The correlation coefficient and significance test of the regression analysis of leaf traits were changed after the addition of the species from Xinjiang.2.The flower hydraulic efficiency in species from arid area was lower.The water potential corresponding to the loss of 50% hydraulic conductance was more negative.Thus the hydraulic safety was higher.The species from humid area had higher flower hydraulic efficiency and lower hydraulic safety.Thus there was a safety vs efficiency trade-off in flowers of Caragana species.The analysis of allocation in biomass showed that the flowers of Caragana species from arid area had higher biomass(no matter the single anatomical structure or the whole flower).It suggested that plants would increase the investment in reproduction when they adapted to drought stress.The results showed that Caragana plants adapted to the arid habitat by strengthening the hydraulic and photosynthesis supply of leaves,enhancing the plasticity of leaf hydraulic and photosynthesis,reducing the hydraulic efficiency of flowers and increasing the hydraulic safety of flowers.