| Climate warming has been the fact that does not dispute,the average global temperature increase at the same time presents the obvious seasonal asymmetry,global warming in winter was greater than the other seasons.And global winter is the most important indirect effects of climate change caused parts of soil freezing and snow cover and vanish,which result in the change of freezing and thawing cycle.Soil freezing-thawing not only affects soil physical and chemical properties and biogeochemical cycles,but also indirectly affects the physiological and ecological processes of plants through habitat stress or soil environment change,which may have an important impact on the productivity of vegetation ecosystem in widely distributed areas of frozen soil.Therefore,this paper takes niuxintaobao national wetland park in western jilin as the research area.By summarizing monthly meteorological data over the years,the conclusion was obtained that the winter minimum temperature increased by 2.881℃ and the maximum temperature increased by 1.307℃ in 67 years Based on this,three treatment groups were set(4℃ constant temperature treatment,"warming treatment in freeze-thaw period","normal freeze-thaw").According to the germination rate,survival rate,germination time and relative growth rate of the rhizome of reed,the effects of increasing temperature in freezing-thawing period on germination and spreading of reed seedlings were compared.The influence of temperature increase in freeze-thaw period on freeze-thaw cycle was studied by means of field in-situ cable heating.On the basis of this experiment,part of the soil and reed seedlings after in situ freezing-thawing warming treatment were moved to the indoor,and morphological indexes(plant height,thick stem,leaf length)and chlorophyll fluorescence parameters(Fo、Fm、Y(Ⅱ)、Fv/Fm、Fv/Fo、Y(NPQ)、Y(NO))were measured,so as to compare the effects of freezing-thawing warming on the leaf spreading and rapid growth of reed plantsThe increase of temperature significantly increased the frequency of soil freezing-thawing cycle in freezing-thawing period,and increased the soil temperature on layers of 15 cm,25 cm and 35 cm.Compared with the control group,the average soil temperature of each layer increased by 1.06℃,1.12℃ and 0.95℃,respectively.The increase of temperature significantly reduces the number of days of the complete freezing period,but increases the duration of the winter and spring thawing period,namely,increases the frequency of the permafrost permafrost thawing cycle.In the 15cm,25cm and 35cm soil layers,the temperature increase significantly reduced the duration of the complete freezing period by 16.4%,36.7%and 36.5%,and increased the freezing-thawing cycle frequency by 9,13 and 20 days,respectivelyFor the germination stage of reed seedlings,under the constant temperature treatment of 4℃(H),the seedlings began to bud earliest,4 d earlier than the two groups of freeze-thaw treatment,and grew at the fastest growth rate.Compared with"normal freeze-thaw’(C),the temperature of "warming treatment in freeze-thaw period"(W)increased by 1.3℃ to 2.9℃,and the average temperature of soil layer increased by 0.95℃ to 1.12℃,so that the germination period of reed seedlings was shortened and the leaf spreading period was advanced.The germination time of reed seedlings in "warming treatment in freeze-thaw period" was 1 week earlier than that in the "normal freeze-thaw".But the number of germination stopped to increase after 1 week of germination,while the number of germination in"normal freeze-thaw" still increased rapidly,and there was no significant difference between the two groups after 1 week.Obviously,increasing temperature during freezing-thawing period could not increase the germination number and germination rate of reed seedlings in the germination period."Warming treatment in freeze-thaw period" destroys plant cell membranes,thylakoids and chlorophyll.And the activity of antioxidant enzymes(APX,POD,CAT and SOD)was higher than "normal freeze-thaw" group,MDA content lower than "normal freeze-thaw",showed that reed leaves APX,POD,CAT and SOD activity content under "warming treatment in freeze-thaw period" after repeated freezing and thawing cycle experienced to slow the peroxidation damage of active oxygen and free radicals on cells and a quick adjustment,cell membrane injury although there is still a cell membrane structure has been the basic recovery.MDA and APX were significantly positively correlated in reed seedlings under constant temperature treatment,indicating that excessive accumulation of H2O2 under constant temperature treatment resulted in lipid peroxidation of cell membrane,leading to an increase in MDA content,indicating that APX was the main antioxidant enzyme for scavenging H2O2.The effect of increasing temperature in freezing-thawing period on morphological indexes and chlorophyll fluorescence parameters of reed plants was divided into stages.In terms of morphological indexes,plant height and stem thickness were significantly affected by "warming treatment in freeze-thaw period",except the leaf length of reed,which was not affected by "warming treatment in freeze-thaw period".In the leaf-spreading stage(1 week to 4 weeks after treatment,i.e.,April 9,solstice,May 21)(p<0.05),"warming treatment in freeze-thaw period"had a great influence on the stem thickness and a little influence on the plant height In the rapid growth stage(5 weeks to 15 weeks after treatment,that is,May 28,solstice,August 13),"warming treatment in freeze-thaw period" had a great influence on the plant height and a little influence on the stem thickness.In terms of chlorophyll fluorescence parameters,"warming treatment in freeze-thaw period" had significant effects on the initial fluorescence parameters(Fo),the maximum photochemical efficiency of PSⅡ(Fv/Fm),the actual photochemical efficiency of PSⅡ(Y(Ⅱ))and the potential activity of PSⅡ(Fv/Fo)of reed leaves in the leaf development period The photosynthetic indexes of leaves in the rapid growth period of reed were not significantly affected.In terms of plant elements,"warming treatment in freeze-thaw period" had a significant effect on the distribution of N P S elements in plant stems and leaves,but had no significant effect on roots. |
