Adaptability Of Plants Under Environmental Stresses At Seedling Stage

Tree species selection is most important for the construction of forestry ecological projects in Heilongjiang Province. The principles and methods for tree species selection are much different due to the various climatic conditions, site conditions, and afforestation purposes in different regions. A study on plant restoration on coal-gangue pile, improvement of saline-alkali land, water conservation, and superior tree species selection for dry and barren soil was conducted to meet the needs of the forestry ecological project construction in Heilongjiang Province.Potted plant tests were conducted to study the following items:the enrichment characteristics of soil heavy metal elements in Hippophae fhamnoides, Ulmus pumila, Spiraea blumei, Pinus sylvestris var. mongolica, Medicago sativa, and Melilotus suaveoolens grown on coal-gangue pile; the physiological responses of Syringa oblata Lindl, Caragana arborescens (Amm.) Lam., Hippophae fhamnoides, and Suaeda glauca Bge. to salt stress under four different salinity concentrations; the transpiration regularities and water use efficiency of Populus suaveolens, Fraxinus mandshurica Rupr., Quercus mongolica, Tilia americana, Be tula platyphylla, and Betula maximowicziana Regel, and the drought resistance abilities of the six tree species under different intensities of water stress.Heavy-metal absorption by the six species of seedlings from the coal-gangue pile, having stopped discharging the gangue since 1977, shows that the main existing forms of Cu, Zn, Cd, and Cr in the coal-gangue soil before and after planting plants are not totally consistent, and certain differences in proportions of Cu, Zn, Cd, and Cr were also observed. The total amount of heavy metal elements in the coal-gangue soil decreased after planting plants. The herbage plants are superior in removal effects of Cu, Zn, and Cd compared with the woody plants, while the removal effect of Cr for the woody plants is better than that for the herbage plants. All the plants exhibit excellent removal effects on Cu. The absorption ability and enrichment of heavy metals for H. fhamnoides and P. sylvestris var. mongolica are the best, and then followed by U. pumila, M. sativa, M. suaveoolens, and S. blumei.The physiological responses of C. arborescens, H. fhamnoides, S. glauca, and S. oblata to salt stress show that the growth and development of the plants are inhibited by salinity stress. H. fhamnoides exhibits the strongest salinity tolerance, followed in a decreasing order by S. glauca, C. arborescens, and S. oblata judged by their morphological changes. Activities of superoxide dismutase (SOD) and peroxidase (POD) in the plants remained at high level under salinity stress, which could well protect the membrane system by free radical scavenging. As a whole, SOD activities of different species of plants show S. oblata, C. arborescens, H. fhamnoides, and S. glauca, and POD activities exhibit S. oblata, H.fhamnoides, S. glauca, and C. arborescens from high to low. The contents of soluble protein in S. oblata, C. arborescens, and H. fhamnoides decrease in the early stage of salinity stress, but the contents of soluble protein exhibit an increasing tendency with the increasing salt concentration and the prolonged salinity stress. The soluble protein content of S. glauca is higher than that of the control during salinity stress. The cell membrane permeability of S. oblata, C. arborescens, and H. fhamnoides is higher than that of the control, while the effects of salt concentration on cell membrane permeability are different. The MDA contents of C. arborescens, H. fhamnoides, S. glauca, and S. oblata in different stages of salinity stress increase with salt concentration increasing, and the changing ranges of different treatments are various. The damage of salinity stress to the plants under low salt concentration is slight due to the lower free radical accumulation and membrane lipid peroxidation in the plants, while the damage to the membrane system of the plants become severe with the increasing salt concentration and the prolonged salinity stress. The photosynthesis of S. oblata, S. glauca, and C. arborescens is inhibited under salinity stress, but the photosynthetic rate of H. fhamnoides increases. No obvious regularity was found in the transpiration rates of different plants with increasing salt concentration. Different plants show different water use efficiencies under salinity stress. The water use efficiencies of S. oblata, S. glauca, and C. arborescens manifest a decreasing tendency, while that of H. fhamnoides exhibits an increasing tendency. Aa a whole, the water use efficiency of H.fhamnoides is the highest, and then followed by S. oblata, S. glauca, and C. arborescens from high to low. The salt tolerances exhibit S. glauca, H. fhamnoides S. oblate, and C. arborescens from high to low judged by all the above indexes under sodium bicarbonate stress.Results of transpiration characters and drought resistance of six species of plants showed that, in June, the diurnal variations of leaf transpiration (TR) of P. suaveolens, Q. mongolica, T. americana, and B. platyphylla could be well described by double-peak curves and that of F. mandshurica and B. maximowicziana by single-peak curves; in July, the diurnal variations of TR of P. suaveolens, F. mandshurica and T. americana exhibit single-peak curves, those of B. platyphylla and B. maximowicziana exhibit double-peak curves, and that of Q. mongolica belongs to a middle type; in August, the diurnal variations of TR of P. suaveolens, T. americana, and B. platyphylla show single-peak curves and B. maximowicziana, and those of Q. mongolica, and T. Americana belong to middle types; in September, the diurnal variations of TR of P. suaveolens, Q. mongolica, F. mandshurica and T. Americana display double-peak curves, and those of B. maximowicziana and B. platyphylla belong to middle types. The peaks of transpiration rate and their occurrence time are various for different seedling species and determination periods. The water use efficiencies of the six species of seedlings are various in different months, and increase with prolonged time, except that the water use efficiency of P. suaveolens in July is lower than that in June. The water use efficiency of Q. mongolica is the highest, and then followed by F. mandshurica, P. suaveolens, B. maximowicziana, B. platyphylla, and T. americana. F. mandshurica and B. maximowicziana are species with medium leaf transpiration and medium water use efficiency, B. platyphylla with medium leaf transpiration and low water use efficiency, and T. Americana with low leaf transpiration and low water use efficiency. Relative water contents of all the six species of seedlings indicate a decreasing tendency with prolonged water stress, among which the leaves of P. suaveolens, Q. mongolica, and B. platyphylla have stronger water retention abilities compared with B. maximowicziana and T. Americana, while F. mandshurica leaves show the weakest water retention ability. The soluble protein contents in leaves of P. suaveolens, Q. mongolica, T. Americana, and B. platyphylla under water stress in treatment No.2, No.3 are higher than those of treatment No.1, and that of treatment No.4 is lower than that of No.1. The soluble protein contents in leaves of F. mandshurica and B. maximowicziana tend to increase under different treatments. The soluble sugar contents in leaves of F. mandshurica, F. mandshurica, B. platyphylla and B. maximowicziana tend to decrease, while that of Q. mongolica is always higher than that of the control. The contents of dissociative proline of all the six species of seedlings increase with increasing salt concentration and prolonged salinity stress. The net photosynthetic rates of different species of seedlings are various under different water stress. The net photosynthetic rates of Q. mongolica and T. americana first increase and then decrease with the prolonged water stress. The decreasing range of Q. mongolica is the lowest, followed by B. maximowicziana, F. mandshurica and B. platyphylla, and P. suaveolens shows the highest decreasing range. The transpiration rates of the seedlings decrease under different water stress treatments, but the decreasing ranges are various. The decreasing ranges for B. platyphylla and P. suaveolens are the highest, and that for Q. mongolica is the lowest. The water-adjustment capacity of Q. mongolica is the strongest, followed by T. americana, B. maximowicziana and F. mandshurica, and those of P. suaveolens and B. platyphylla are the weakest. The changes in stomatal conductance of the seedlings are various with the prolonged water stress. Responses of Q. mongolica, F. mandshurica, T. americana, B. platyphylla and B. maximowicziana to water stress are sensitive, while P. suaveolens is not sensitive to slight water stress. Intercellular CO2 concentrations in leaves of different tree species increase to different degrees, among which the increasing range for Q. mongolica is the largest and that for B. maximowicziana is the smallest. The water use efficiencies of seedlings in all the treatments increase to different degrees, except that the water use efficiencies of P. suaveolens and F. mandshurica in treatment No.2 are lower than those of treatment No.1. The drought resistances of F. mandshurica is the highest, and then followed by T. americana, P. suaveolens, B. platyphylla, and B. maximowicziana.