Study On The Anatomical Structures And Physiological Adaptation Of The Exotic Plant Gaura Parviflora Dougl

Gaura parviflora is a biennial herbaceous plant of Onagraceae Gaura, originating from the prairie of North America. It has escaped into natural environments and become a weed after introduction and cultivation. It is adapted to a wide range of environmental conditions, which can live in the roadside, brae, ridge and even in the poor soil of alkaline land. Now it has spread fast in Henan, Hebei, Shandong, Anhui, Jiangsu, Hubei, Fujian and Zhejiang Provinces. If it over spreads, it will seriously damage the ecological systems, and affects the biodiversity of aboriginal communities. Furthermore, once an invasive species becomes firmly established, its control could often be difficult and eradication is usually impossible. Presently, the research reports on Gaura parviflora are very poor, mainly about the aboveground biomass dynamics, dissection structure of flowers, allelopathy and karyotype analysis,etc.The studies on invasion mechanisms are still relatively lack, the studies on physiological adaptation and anatomical structure of vegetative organs has not been reported yet.In order to reveal the structure and physiological basis of invasion and spread of Gaura parviflora, the anatomical structure of vegetative organs and physiological index response to stress were studied. This information could improve our understanding of the adaptive mechanism of Gaura parviflora and provide theory basis for effectively controling this weed. Followings were main study content: the anatomical structure of roots, stems and leaves; the dynamic changes of physiological indices, including the contents of free proline, malonaldehyde (MDA) and chlorophyll, superoxide dismutase (SOD) activity under heat, cold, drought and low salt stresses. The main results as follows:(1) In the secondary structure of the roots of Gaura parviflora,there was a larger proportion of secondary xylem, about two thirds of the entire cross section, the number of vessels averaged 138.25, and the lumen diameter was 85.37μm;(2) The cork of the roots and stems were both developed, which was composed of 6 to 7 layers of flat cells; there were many parachyma cells containing needle crystals in the secondary phloem;(3) The leaves of Gaura parviflora had the typical characteristics of xerophytes leaves: the multiple epidermis; the stomata existed in both upper and lower epidermis,whose densities were 180/mm 2 and 266/mm 2 respectively; the palisade tissue was two-side palisade which included 2 to 3 layers of cylindrical cells in the upper side, with a lot of chloroplasts.(4) In comparison with Brassica campestris, Gaura parviflora could maintain high SOD activity and low rates of membrane lipid peroxidation, so its cell membrane system was harmed lightly. In addition, the recovery speed of physiological function was fast after rewater treatments, which indicated that Gaura parviflora had stronger stress resistance and recovery than field crops.(5) The physiological response of temperature stress showed: Gaura parviflora had broader niche of temperature which could adapt itself to 38℃and 5℃temperatures. According to the four measured physiological indices, Gaura parviflora had more strong resistance to low temperature of 5℃than high temperature of 38℃.This may relate to Gaura parviflora originating from the prairie of North America and long-term adaptation to low temperaturegrowth environment.(6) The physiological response of low salt stress showed: under low NaCI stress, as for Gaura parviflora, the SOD activity and free proline contents obviously increased, the chlorophyll contents rised slightly, the MDA contents had small fluctuation, all these indicated that Gaura parviflora was insensitive to low concentration NaCI and had higher salt-resistance.(7) According to above results, developed conducting tissue and typical xeromorphic structure of Gaura parviflora were the basis of morphological structure for its invasion and spread; Under drought, heat, cold and low salt stresses, Gaura parviflora had strong defense ability for activate oxygen and low membrane lipid peroxidation, meanwhile, it can maintain normal water demand and chlorophyll contents, which suggested it had stronger anti-adversity ability, all these were the physiological basis for its invasion and spread.