Study On The Physio-ecological Responses Of Hosta Ventricosa Under Lead Stress

Take the wild Hosta ventricosa (Salisb.) Stearn. as the experimental subject, study the effect of gradients stress under different Pb2+concentration which ranging from0mg/kg to2000mg/kg, on characteristics of seed germination, and nutrition growth of physiological ecology, analyse how the wild Hosta ventricosa react to different Pb2+stress, findig out their regular pattern, and the tolerance capacity to Pb2+stress, expecting to provide scientific basis for the application of City Greening, and lay the theoretical foundation for stuying the Hosta ventricosa’s mechanism resistance to lead. The main findings are as follows:(1) The effect of different Pb2+stress to the seed germination rate and germination energy of Hosta ventricosa shows under the low Pb2+concentration, the Pb2+stress can help raise the seed germination rate and germination energy. The seed germination rate reached the highest point when the Pb2+concentration was500mg/kg, and it increased by30.56%compared to the reference data. The seed germination energy reached the highest point when the Pb2+concentration was250mg/kg, and it increased by111.11%compared to the reference data. The seed germination rate went down the lowest when the Pb2+was1000mg/kg and2000mg/kg, with the germination rate lower than the original and germination energy0.(2) The root is more sensitive to Pb2+stress compared with the stem-leaf length. When the Pb2+concentration was lower than500mg/kg, the growth trend of the seedling root and stem-leaf length turned out to be in a "Hump" shape. The root length reached the longest under Pb2+concentration125mg/kg, and the stem-leaf length reached the max under Pb2concerntration250mg/kg. When the Pb2+concentration raning from1000mg/kg to2000mg/kg, the seedlings can not grewth well, and were not able to determine the index.(3) Pb2+stress would improve the biological accumulation of the Hosta ventricosa when the Pb2+concentration is less than500mg/kg. When the Pb2+concentration was lower than500mg/kg, the roots/shoot of Hosta ventricosa seedling was with the trend growth in "Humb" shape. And the roots/shoot reached the max vatue when the Pb2+concentration was125mg/kg, increasing30.06%compared with the reference data. The seedlings were either dead or undergrewth when the Pb2+concentration was between1000mg/kg and2000mg/kg, the index could not be determined.(4) The Pb2+concentration stress can contribute to the increasement of Uosta ventricosa leaves number and petiole length in a certain concentration range. Under the same Pb2+stress, the petiole length increased as the growth time went by, in a logarithmic function way, and the growth rhythm was fast first, and then got slow down. Determing in the same time, also under the different Pb2+stress gradient, the petiole length increased in a "Hump" shape, accompanied by the increasement of the Pb+concentration, and the petiole got the longest when the Pb2+was1000mg/kg. Under different Pb2+stress gradient, the leaf number of Host a ventricosa leaves increased were increased in an "Hump" shape. The leaf number was the most when Pb2" concentration reach125mg/kg, increased31.43%compared with reference data. Under Pb2+concentration ranging from250mg/kg to125mg/kg, the increase rate of leaf quantity got lower when the Pb2+concentration was increased.The Pb2+sress would increase the etiolation rate of all the first leaf.(5) Pb2+concentration had less impact on the soluble sugar content and malondialdehyde (MDA) content of the leaves. The Pb2+sress would increase the activity of antioxidant enzymes, The SOD activity was more sensitive compared with POD activity. MDA content surged in a high gradient when the Pb2+stress was52d. Under the same Pb2+stress, the SOD activity went high first, and then went down as the times went on. The SOD activity reached the max when the Pb2+stress was45d. Under the stress of the same Pb2+concentration, the peroxidase (POD) activity in leaves got increased as the Pb2+stress time went on, reaching the max when the stress arrive73d.(6) Pb2+stress helped increase the content of photosynthetic pigments.When the Pb2+stress time was ranging from59d to73d, the content of chlorophyll a, chlorophyll b, chlorophyll a+b, which under the different Pb2+stress gradient in the same period, were went up, as the Pb2+concentration got stronger, also in a "Hump" shape, reaching the max when the Pb2+concentration got1000mg/kg. Pb2+concentration can improve the photosynthesis when it ranging from0mg/kg to1000mg/kg. When the Pb2+concentration was2000mg/kg, photosynthetic rate, transpiration rate, and stomata conductance was lower than the reference data in the end of the vegetative growth. Experiments show that the intercellular CO2concentration closely related to the photosynthetic activity of mesophyll cells,but not stomatal conductance.The Pb2+stress had limited effect on the Fv/Fo and Fv/Fm in the early and mid-term of the vegetative growth, but it promoted the Fv/Fo and Fv/Fm values at the last stage.