Studies On The Responses Of Seed Germination And Seedling Growth Of Deyeuxia Angustifolia, Phragmites Communis To Environmental Factors

Sanjiang plain is the largest freshwater marsh wetland in China. However, waterlevel in Sanjiang plain was decreased because of reclamation in large areas andinfluences of altered climate. And these changed environments made wetland areasshrinked and damaged remained sight. It was clear that decreased water level andother altered environments would affect succession and regeneration of vegetationalcommunity, and affect structure and function of ecosystem in wetland according to therelationship of water level and vegetational regeneration. For example, Deyeuxiaangustifolia, the mian species in the Sanjiang plain was decreased, so, it wasnecessary for plant regeneration. Some investigations showed that seed germinationand seedling growth were significant for vegetation regeneration, and decided thetrend of vegetational succession. So, in this study, we choose D. angustifolia, an mainmarsh species in the. Sanjiang plain and Phragmites communis, an satellite plant forsubjects, and performed a series of experiments to investigate effects ofenvironmental factors on seed germination and seedling growth, in order to explainthe mechanism of forming and maintaining distribution pattern of D. angustifolia andP. communis. The results showed that:Seed of D. angustifolia and P. communis could germinate in desinged conditions(light of 0,2500 lx; temperature ranged from 7 to 38℃; saturated water). Light hadinsignificant differences on seed germination of D. angustifolia and had significantdifferences on seed germination of P. communis, indicating that D. angustifolia was ~light-insensitive plant and P. coJnmunt~s was light-sensitive plant. D. angustifolia cangerminate in a wide range of temperature, from 10 to 35 ~C, and the suitabletemperature was 20-30 ~C. And P communis can germinate in a narrow range oftemperature, from 20 to 35 ~C, and the suitable temperature was 20 ~C. At same lightand temperature treatment, germination percantage of D. angustifolia was higher thanthat of P. communis, indicating that seed of D. angustifolia had a stronger ability togermination in contrast with P ~ommultis. Effects of simulated substrate type and burial depth on seed germination showed that: seeds of D. angustifolia could germinate at 1-, 2-, 4-ram sand, and at 1-, 2-mmmud, and seeds of P. communis could germinate at 1-, 2-, 4-mm sand, and onlygerminate at 1-mm mud. For the same substrate, the time for staring to germinateincreased and germination percentage of two species decreased with increasing burialdepth. At the same burial depth, germination percentage of two species was higher insand than in mud. Enhanced water depth inhibited seed germination of two species.Seeds of D. angustifolia could germinate at two designed oxygen concentration (21%,7%), but seeds of P. communis could not germinate at low oxygen concentration, andlow oxygen concentration inhibited seed germination of two species. So, seedgermination of two species were significant affected by soil environments, and seedgermination of P. communis was more sensitive to soil environments in contrast withD. angustifolia. And these responses of seed germination to soil environments werethe main factor for low germination percentages of two species in wild and for widedistribution areas of D. angustifolia and narrow distribution areas of P. communis.Light intensity had significant effects on seedling survive and growth of twospecies. The time for seedling starting to death increased and seedling mortality oftwo species decreased with increasing light intensity ranged from 100 lx to 1000 lx.At the same light intensity, seedling mortality of D. angustifolia was lower than thatof P. communis, indicating that D. angustifolia had a stronger ability to survive inlight stress than P. communis, and this was an important reason accounting for widedistribution areas of D. angustifolia and narrow areas of P. communis in wild. Lighthad significant influences on seedling biomass accumulation and allocation pattern oftwo species. Root, stem, leaf biomass, total biomass, growth rate and net assimilationrate significantly increased with increasing light intensity. But leaf area ratio, leafmass ratio and lamina area per unit lamina mass significantly increased withincreasing light intensity, indicating that more investments were taken intoptoto-tissure to make leaves thin and increase ptoto-areas, and it was an effectivestrategy for seedlings of D. angustifolia and P. communis to accommodate light stress.The influences of light and water on seedling asexual propagation and seedlinggrowth of two species were significant. Seedling total tamet number of two species increased with light intensity and decreased with water depth. At the same water leveltreatment, root, stem, leaf biomass, total biomass, leaf number, growth rate, height,elongation rate of two species were all significantly increased with increasing lightintensity, indicating that light was an important factor for biomass accumulation andstem elongation. At the same light treatment, root, stem, leaf biomass, total biomassand other growth parameters of D. angustifolia had insignificant difference by waterlevel, indicating that seedling growth of D. angustifolia did not affect by water level.However, enhanced water level inhibited seedling biomass accumulation and stemelongation of P. communis. These data indicated that seedling growth of D.angustifolia and P. communis had different response to water level.D. angustifolia had stronger abilities to accommodate environment in contrastwith P. communis. These were main reasons why D. angustifolia could become one ofthe main species and P. communis could become satellite species in the Sanjiangplain.