Drought Adaptation Ecophysiological Mechanisms Of Geographical Substitute Caragana Species

With global climate change and intensifying human activity,drought has influenced the agriculture productivity and economic development in China.To discover how plants adapt to the water stress can help us to find ways to cope with threaten of drought.Genus caragana evolved from the same ancestor,but driven by these different climates,the Caragana species diversified,so that some species,such as C.microphylla and C.intermedia,thrived in arid and semiarid areas(annual precipitation less than 200 mm),while other species,such as C.stipitata,C.sinica,thrived in humid and semihumid areas(annual precipitation more than 1500 mm).Therefore,caragana species can provide good materials for researching plant drought strategies.This paper use genus caragana spreading in different rainfall areas to investigate their biomass allocation,stomatal conductance and leaf hydraulic conductance differentiate with the leaf water potential decrease,so as to reveal the mechanisms underlying plant distribution.The results obtained area as followings:1.There were no significant difference in stem destiny,LMA,root depth,and root/shoot of caragana species from arid and semi-arid areas and from humid and semihumid.So these characters could not explain the mechanism underlying genus caragana distribution in different habits.But as far as the relative root biomass distribute along root depth was concerned,the species from arid and semiarid areas had more biomass in deep soil,and the species from humid and semihumid areas had more biomass in shallow soil.2.Under water stress,species from humid and semihumid areas tended to have lower leaf water potential than species from arid and semiarid areas,but all species had leaf water potential less than-7MPa.which mean all species in this study had strong ability to tolerance drought stress.With the decrease in predawn water potential,the stomatal conductance and transpiration rate of species from arid and semiarid decreased rapidly,so as to reduce the water evaporation effectively,consequently,minimize the negative effect and improve the survival.While stomatal conductance and transpiration rate of species from humid and semi-humid areas declined relative slow.3.Leaf hydraulic conductance decreased with decline in the leaf water potential was different among Caragana species,the species from arid and semi-arid areas had lower P50(leaf water potential when 50%leaf hydraulic loss)and P80(leaf water potential when 80%leaf hydraulic loss)compared with species from humid and semihumid areas with the exception of C.stipitata,suggesting that species from arid and semi-arid areas had stronger ability to tolerate drought stress,to maintain leaf water transport and reduce the leaf hydraulic conductance losses,and to had lower hydraulic conductance vulnerability,than species from humid and semihumid areas.The interval from P50 to P80 is greater wide in species from in arid and semi-arid areas than from humid and semihumid areas,implying that the former had slowly rate of cavitation embolism.The leaf water potential when 80%stomatal conductance lose was higher in species from arid and semi-arid areas than from humid and semihumid areas,indicating that the stomatal conductance was relatively sensitive to the decrease in leaf water potential(?leaf)in arid and semiarid species.It would reduce prevent the leaf water potential from excessive decline under severe drought stress and protected vessel developing from cavitation embolism.