| The hydro-fluctuation zone of the three gorges reservoir area is a typical ecologically fragile area,where resident's lives and economies were affected with the frequently geological and meteorological disasters,decreased biodiversity,seriousness non-point source pollution,intensified channel silt deposit,increased floats.In recent years,vegetation restoration and reconstruction has been widely used in the elimination area due to its low cost,sustainable and improved ecological environment.Although vegetation can improve the environment,it is still to be studied whether it is really adapted to the environment and whether the local plants are threatened.In this paper,the study was conducted on the Betula nigra of 170 m and 175 m,(1)taking time as a variable factor,the soil physical properties and soil chemical properties of different soil layer,the growth characteristics of Betula nigra were investigated in May 2015,May2016 and May 2017.Photosynthetic characteristics of the leaf of Betula nigra were investigated in May 2014,May 2015 and May 2016.Which can indicate the response of the hydro-fluctuation zone of the three gorges reservoir area on Betula nigra,the adaptability of Betula nigra to the hydro-fluctuation zone of the three gorges reservoir area.(2)The diversity of plant species was investigated in May 2017,take the root and leaf of Betula nigra as research material,take common herbs of Lolium perenne L.,Paspalum notatum Flugge and Trifolium repens L.in the hydro-fluctuation zone of the three gorges reservoir area as the receptor plants,which can reveal the effects of different concentration of root and leaf extract of Betula nigra on the growth of Lolium perenne L.,Paspalum notatum Flugge and Trifolium repens,and study the ecological invasion risk of Betula nigra simultaneously.The following results are mainly obtained:1.Betula nigra has a better adaptability to the hydro-fluctuation zone of the three gorges reservoir area.(1)The soil bulk density under Betula nigra forest had a content order of2015>2016>2017 with the variable time,soil water content and soil porosity had a content order of 2015<2016<2017,and the degree of influence increases with time.The reduction range of soil bulk density in the 0-10 cm,10-20 cm and 20-30 cm of the soil layer under Betula nigra forest was 1.30%~20.98% in the altitude of 170 m and175m,the amplication range of soil water content and soil porosity were30.73%~145.72% and 15.13%~90.64% respectively.The order of soil p H,organic matter,total nitrogen,total phosphorus,alkali-free nitrogen,effective phosphorus and instant potassium in the 0-10 cm,10-20 cm and 20-30 cm of the soil layer were 2017>2016>2015 in both two kind of altitude under Betula nigra forest.The greater the time interval,the greater the difference in the chemical properties of the soil.The variation range of soil p H,organic matter,total nitrogen,total phosphorus,alkali-free nitrogen,effective phosphorus and instant potassium were 2.54%~12.55% ? 8.26%~84.47% ?14.90%~47.92% ? 12.98%~99.51% ?-0.97%~+19.92% ? 42.89%~97.30% ?47.07%~81.00%,respectively.(2)The variation trend of height,chest diameter,crown length and width of Betula nigra was 2017>2016>2015,the amplication range of height,chest diameter,crown length and width of Betula nigra were 25.1%~130.5%,5.6%~85.1%,30.8%~71.1%,21.2%~130.5%,respectively.The variation trend of net photosynthetic rate of Betula nigra in both two altitude was 2014<2015<2016,meanwhile,which were 23.07% and22.84% higher in 2016 than it in 2014.Stomatal conductance and intercellular The variation trend of CO2 concentration were 2014 > 2015 > 2016,however,the transpiration rate and stomatal limit value were not obvious.The content of chlorophyll showed with 2014 < 2015 < 2016.There had a significant impact on the electron transfer rate,maximum photochemical efficiency,photochemical quenching coefficient,non-photochemical quenching coefficient and the actual photochemical efficiency were studied(P<0.05),and with nonuniform regular.To sum up the above(1)and(2),Betula nigra planting can improve the physical and chemical properties of the soil,it can normal growth in hydro-fluctuation zone of the three gorges reservoir area,and its photosynthesis gradually increases with the increase of the age,which indicating that Betula nigra has a better adaptability to the hydro-fluctuation zone of the three gorges reservoir area.2.Introduction plant Betula nigra is not ecological invasive.(1)There were found 29 herbs under Betula nigra forest in both two altitudes,and there was 15 herbs in the elevation of 170 m,14 herbs in the elevation of 175 m,therealso no plantlet of Betula nigra was found in the Betula nigra forest.The sum importance values of Lepidium and Juncus effusus L were 38.32%,which as dominant species under Betula nigra forest in the altitude of 170 m,the sum importance values of Lepidium and Vicia hirsuta(Linn.)S.F.Gray were 50.08%,which as dominant species under Betula nigra forest in the altitude of 175 m.Shannon-Wiener diversity(H?)of undergrowth Betula nigra forest were 2.414,2.120,respectively in both altitude.Pielou's evenness index(Jw)of undergrowth Betula nigra forest were 0.871,0.783,Alatalo dominance index(Ea)of undergrowth Betula nigra forest were 0.749,0.527.Based the evaluation of plant diversity threshold,Betula nigra in altitude of 170 m belong to III which had a better diversity,Betula nigra in altitude of 175 m belong to II which had a rich diversity.(2)Concentration of 0.075 of leaf of Betula nigra made germination number and height of Lolium perenne L.increased by 1.18% and 1.18% respectively,the rest concentration of leaf extract has reduced the germination number,height,root length and maximum reduction of 42.35%,32.78%,65.64% and 42.35% respectively.Each concentration of root extract reduced germination number,height and root length but promoted maximum reduction.Concentration of 0.075,0.100,0.150,0.250 of root of Betula nigra has reduced the germination number of 47.35%,48.82%,48.82%,47.35%,reduced height of 6.60%,5.87%,1.19%,11.48%,reduced the root length of 0.17%,19.43%,38.49%,79.07%,and increased maximum reduction of 3.82%,14.12%,6.76%,2.35%.The synthesis effect(ASE)of root and leaf extract of Betula nigra was negative to Lolium perenne L.,the ASE decreased with the increase of concentration..Root and leaf extract had an inhibiting effect on germination number,height,root length and maximum reduction of Paspalum notatum Flugge,ASE of root and leaf extract was negative.Except that there had a promoting effect on root length of Trifolium repens in altitude of 175 m,and there had a significant influence on germination number,height and maximum reduction of Trifolium repens,the amplication range of which were31.28%~63.35%,0.16%~34.38%,11.11%~44.44%,respectively.The ASE of leaf extract of Betula nigra was negative to Trifolium repens.To sum up the above(1)and(2),introduction plant Betula nigra is not ecological invasive,and becausre of high concentration,root and leaf extract had an inhibiting effect on Lolium perenne L.,Paspalum notatum Flugge and Trifolium repens. |
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