The Adaptability Of Alternanthera Philoxeroides Grown In Different Habitats With Contrasting Water Conditions

Nowadays,China is a country with rapid economic development,but its biodiversity has been constantly threatened by invasive species.Alternanthera philoxeroides is one of the invasive species that seriously endangers the ecosystems of the country.Its strong adaptability and rapid propagation ability lead to the sharp decrease of native plant species,the blockage of waterway,the reduction of farmland production,the decline of community species diversity,and the destruction of primary ecosystems.The researches on A.philoxeroides in China are mostly focused on its harm and control,few on studying the differences of A.philoxeroides in different habitats which related the comparison of its anatomical structure.And the mechanism underlying its adaptation to different habitats remains unclear.Plant leaves respond rapidly to environmental changes and their higher water content can promote plant physiological activities.Therefore,taking the water relations of the leaves of A.philoxeroides as the breakthrough point,exploring the changes of the corresponding leaf hydraulic traits and other important physiological processes(such as photosynthesis and drought resistance)in both aquatic and terrestrial habitats is conducive to understanding the adaptation mechanisms of A.philoxeroides in different habitats,and providing theoretical basis for the prevention of the invasion of A.philoxeroides.In this study,A.philoxeroides grown in aquatic and terrestrial habitats were respectively selected in the South China Botanical Garden.Leaf water transport related functional traits(including leaf hydraulic conductance,instantaneous water use efficiency,turgor loss point,specific leaf area and gas exchange parameters)and structural traits(including leaf thickness,palisade tissue thickness and width,spongy tissue thickness,upper and lower epidermis thickness,cuticle thickness,stomatal size and density,and minor vein density)were measured systematically.In addition,the expression of A.philoxeroides plasma membrane instrinsic proteins(Ap PIPs)was analyzed.On the one hand,the changes of structural characters,water conductingability,drought resistance and photosynthetic capacity of A.philoxeroides in different habitats were analyzed,with an attempt to reveal the mechanism underlying its wide distribution patterns.On the other hand,the key water channel functional genes regulating the water relations of A.philoxeroides were identified to explore the regulation mechanism of water transport in different habitats.The results showed the physiological and ecological characters of A.philoxeroides in aquatic and terrestrial habitats were significantly different.For instance,compared with A.philoxeroides grown in aquatic habitat,leaf cuticle in terrestrial habitat is thicker,stomata are smaller and denser,while leaf palisade tissue and sponge tissue are relatively thinner.In addition,leaf hydraulic conductance,photosynthetic rate and drought resistance of A.philoxeroides grown in terrestrial habitat are higher than those grown in aquatic habitat.Furthermore,the expression of Ap PIP genes at the transcriptional level was observed by q RT-PCR method.It turned out that only Ap PIP2-3 gene displayed a higher expression level,when comparing plant grownin aquatic habitats with those grown in terrestrial habitat,and the expression of other Ap PIP genes were not significantly different in the two habitats.The results demonstrated that the leaf structure of A.philoxeroides in terrestrial habitat was beneficial to reduce water loss and enhance drought resistance,while that of A.philoxeroides in aquatic habitat was more inclined to water and resource storage.Furthermore,higher hydraulic conductance,photosynthetic rate and drought resistance of the leaves of A.philoxeroides grown in the terrestrial habitat indicated that it has stronger ability of resource acquisition and drought resistance,which might be conducive to its population dispersal.Although the up-regulation of Ap PIP2-3indicated it might play an important role in water transport A.philoxeroides grown in aquatic habitat,future work is in need to reveal how Ap PIP genes involved and to what extent they contributed to the regulation of water relations of A.philoxeroides in different habitats.In conclusion,the changes of leaf hydraulic related traits and the analysis of Ap PIP genes expression levels were integrated to reveal the mechanisms of the adaptation of A.philoxeroides under different habitats,thus providing some theoretical basis for the prevention and control of the invasion of A.philoxeroides.