Influences of Drought Stress on Photosynthesis in Flaveria bidentis

[Objective] Through the discussion of diurnal changes of photosynthesis of Flaveria bidentis at the seedling stage under different soil moisture conditions,photosynthetic physiological basis of Flaveria bidentis to adjust to drought stress is investigated in order to provide a theoretical basis for prevention of further invasion. [Method] The seeds of Flaveria bidentis were planted in plastic buckets laid within all-transparent canopy. It was set with 3 soil moisture treatments,that is,the soil relative water contents （SRWC） were 80% （CK）,60% （T1）,30% （T2） of field maximum moisture capacity. Photosynthetic parameters and diurnal changes of relevant ecological factors of Flaveria bidentis at the seedling stage were measured and the differences between different treatments were compared. [Result] Under CK treatment,the diurnal changing curve of Pn of Flaveria bidentis was basically in a ＂bimodal＂ shape,while under T1 and T2 treatment,Pn was a ＂unimodal＂ curve. At about 11：30 am,CK reaches its first peak value of 31.83 μmol/（m2·s） and its second peak value of 23.34 μmol/（m2·s） appears at 15：30. At 13：30 T1 and T2 have their peak values. The diurnal changes of Tr of Flaveria bidentis leaves in the three treatments are all in a unimodal curve. There are no significant differences between CK and T2 treatments,while the diurnal water use efficiency in T1 treatment is obviously below the ones in CK and T2 treatments. [Conclusion] Drought stress reduces Pn,Tr,Sc and other physiological indices of Flaveria bidentis. The reason why Pn is reduced is due to both stoma and non-stoma factors. Drought stress also postpones the appearance of Pn peak value. Proper drought can efficiently promote water use efficiency of Flaveria bidentis and cause its anti-drought reaction.

The Extraction,Isolation and Identification of Exudates from the Roots of Flaveria bidentis

Large amounts ofFlaveria bidentis＇s root culturing solution were obtained by using DFT （deep flow technique） equipment and these solution which was vacuum concentrated （10, 20 mg mL-~） can have a certain inhibition on Triticum aestivum, Cucumis sativus, Raphanus sativus, Amaranthus retroflexus, Setaria viridis, Chenopodium album, Echinochloa crusgalli and Chloris virgata. This outcome suggested some active compounds in the root exudates ofFIaveria bidentis can inhibit the germination, seedling elongation and root length. The dichloromethane extract of root exudates was identificated by GC-MS, and 29 kinds of compounds, including esters, hydrocarbons, ketones, thiazole, amines, etc. were obtained and the phthalate n-octyl ester, phthalate 2-ethylhexyl ester were proved to be allelochemicals. The culturing solution of root exudates was separated through the resin column and silica gel column and a component inhibiting seedling height, root length and fresh weight of wheat was got. There were 6 kinds of organic compounds in this component including dioctyl phthalate, 1,2-phthalate, mono（2-ethylhexyl） ester by GC-MS.

Bacillus promotes invasiveness of exotic Flaveria bidentis by increasing its nitrogen and phosphorus uptake

The effect of exotic plants on Bacillus diversity in the rhizosphere and the role of Bacilli in exotic or native plant species remain poorly understood.Flaveria bidentis is an invasive grass in China.Setaria viridis is a native grass and occurs in areas invaded by F.bidentis.Our objectives were(i)to examine the differences in the Bacillus communities between F.bidentis and S.viridis rhizospheres soil,and(ii)to compare the effects of Bacilli from F.bidentis and S.viridis rhizospheres on the competitiveness of the invasive species.Flaveria bidentis monoculture,mixture of F.bidentis and S.viridis and S.viridis monoculture were designed in the field experiment.Bacillus diversity in their rhizosphere was analyzed using 16S rRNA.One of the dominant Bacilli in the rhizosphere soil of F.bidentis was selected to test its effect on the competitive growth of F.bidentis in a greenhouse experiment.Bacillus diversity differed in F.bidentis and S.viridis rhizosphere.Brevibacterium frigoritolerans was the dominant Bacilli in the rhizosphere of both F.bidentis and S.viridis;however,its relative abundance in the F.bidentis rhizosphere was much higher than that in the S.viridis rhizosphere.In addition,B.frigoritolerans in the F.bidentis rhizosphere enhanced the growth of the plant compared with that of S.viridis by improving the nitrogen and phosphorus levels.This study showed that F.bidentis invasion influenced Bacillus communities,especially B.frigoritolerans,which,in turn,facilitated F.bidentis growth by increasing the levels of available nitrogen and phosphorus.

Isolation and Structural Identification of Herbicidal Active Substance from Root of Flaveria bident(L.) Kuntze

In order to understand the composition and structure of herbicidal active substance from the root of Flaveria bidentis （L.） Kuntze, the isolation and structural identification were researched in this paper. The crude extract from the root ofF. bidentis （L.） Kuntze was extracted by petroleum ether, ethyl acetate, and water saturation of n-butyl alcohol, respectively, and the extraction fluid was separated by using the method of TLC, then the main fraction was separated by HPLC, and the structure of the herbicidal active substance was analyzed by LC-MS, elemental analysis and ~H-NMR. The results showed that the petroleum extraction had the strongest herbicidal activity, and the purple blue stripe separated by TLC had the strongest effect on Digitaria sanguinalis. The herbicidal active substance was identified as ct-terthienyl according to the data of LC-MS, elemental analysis and 1H-NMR.

气候变化情景下中国外来入侵植物黄顶菊潜在分布区模拟与早期预警

20世纪90年代外来植物黄顶菊(Flaveria bidentis)入侵中国,威胁我国的农业生产和生态安全,现已在河北省8个地级市、天津市、河南省6个地级市、山东省5个地级市、山西省长治市广泛分布,并呈迅速扩散蔓延趋势,预测黄顶菊在中国的潜在分布区可为阻断其传播和早期预警提供参考.本文基于黄顶菊在南美洲原产地的分布数据和环境变量构建本土生态位模型,投影至我国并预测当前和未来气候情景下黄顶菊的潜在分布格局.结果表明:①黄顶菊潜在分布范围涵盖华北平原、东北平原、黄土高原和云贵高原.与黄顶菊实际分布区相比,山东省中部、北京市中南部、辽宁省南部、山西省南部、陕西省中部具有较大面积的中-高潜在适生区,黄顶菊在中国尚未达到其最大潜在分布范围,仍有可能继续扩散.②全球变暖导致黄顶菊潜在适生区明显向北扩张、向南收缩,分布中心由华北中纬度地区向东北高纬度地区迁移.③综合比对黄顶菊实际分布状况及其在不同气候情景下潜在分布的变化趋势,结合国家和地方的管控需求,以地级及以上城市行政区为管控单元划定重点管控区、重点监测区和重点预防区,建议在黄顶菊扩散前缘区加强监测阻截力度,逐步消除黄顶菊发生区的生态影响,重点监测其潜在适生分布,抑制其向邻近地区进一步扩散蔓延.研究显示,黄顶菊在我国仍具有较大的潜在分布空间,全球变暖加剧其向东北高纬度地区迁移,基于黄顶菊的潜在适生区变化趋势制定分级监管策略在一定程度上可提升防控效率,以防止其进一步扩散.