Soil Seedbank And Its Correlations With Aboveground Vegetation In Damaged Ecosystem Of Wenchuan Earthquake Area

The devasting Wenchuan Earthquake struck Sichuan Province,Southwestern of China,with a magnitude of 8.0 at 14:28:01.42 CST on May 12,2008 and killed at least 68,00 people.This finally caused a serious of secondary disaster with great intensity,huge distructive force,wide affected area,massive loss and serious ecological degradation.Geo hazards are the main limiting factor for ecological recovery in several affected areas,which is full of complexity and arduousness,but their influences are still poorly understood.Soil seed bank is the foundation of vegetation recovery,which could indicate the recovery potential and succession direction of the damaged ecosystem.To determine the characteristics of soil seed banks and their relationships with aboveground vegetation and soil environmental factors in different climate zones,field surveys backed up with laboratory experiments were conducted in a typical ecological restoration zone in Weizhou Township(Wenchuan County),Beichuan county(Aba prefecture)and Hanwang Township(Mianzhu City)of Sichuan Province.This zone was the epicenter of the massive Wenchuan Earthquake on May 12,2008.Further evaluation of the recovery potential of damaged ecosystem was also performed.The studying results are reflected in the following aspects:(1)Germination dynamic and spatial distribution characteristics of Soil seed bank under differerent climate types.In the process of soil seed germination,both undamaged areas and destruction areas had a typical germination peak.While the peak of undamaged sample plots last longer.The density peak of soil seed bank appeared during February and March.Density of soil seed bank in September showed that undestroyed sample plots in subtropical humid monsoon climate areas(HMU)>destroyed sample plots in subtropical humid monsoon climate areas(HMD)>destroyed sample plots in semi-arid dry warm river valley climate areas(DHD)>(undestroyed sample plots in semi-arid dry warm river valley climate areas(DHU).And in March it tended to be undestroyed sample plots>destroyed sample plots.Seed banks in different climate areas had different germination potentials at different soil depths,but both had obviously phenomenon of "table chgesion".(2)Species composition and and life pattern distribution of Soil seed bank under different climate types.A total of 61 species,57 genuses and 36 families were identified in the 63 soil seed bank samples using the germination method and herbaceous plants had the most significant advantage.Species of Compositae,Gramineae and Leguminosae had wider distribution,accounting for 26.2%,16.4%,6.6%respectively.However,species of Compositae,Gramineae and Chenopodiaceae had higher germination rates,accounting for 42.95%,24.19%,5.47%respectively.Dominant species is given priority to pioneer species.Compositae had the most distribution in undamaged area and Gramineae had the most distribution in destruction area.Viola verecumda universally existed in the soil seed bank of both types.Different sample plots in different climate types had unique species,but the main life pattern was herbsThere wasn't significant difference of the diversity indexes of different sample types.In the same climate types the Simpson index,Shannon index,Richness index tended to be undamaged are>destruction area,while the Evenness index tended to be small difference(3)Soil environmental interpretation of the soil seed bank species' spatial distributionCCA analysis indicated that TK,Ca,OM and TN had great influence on seed bank species distribution in destruction areas.While TK and Ca had great influence on that in undamaged areas(4)Construction of prediction model of soil seed bank densityMultivariate linear regression technique and Principal component regression techniques were applied to set up the soil seed bank density fitting model with environmental factors y1k=0.14(Z11X1k+Z21X2k+...Zi1Xik+...Z201Z20k)-0.26(Z14X1k+Z24X2k+...Zi4Xik+...Z204X20k)+3.03Zij:Score coefficient values of index i corresponding to the principal component j,i belongs to 1?20,j belongs to 1?5.Xik:Original data of index j of plot k,kbelongs to 1?N(N:the number of sample plot).(5)Community characteristics of aboveground vegetation of different climate typesA total of 120 species,100genuses and 51 families were recorded in sample plots.WW had 29,WZ had 14,LW had 36,LZ had 36,HW had 42,HZ had 33,MW had 23.Different types of plots had different plant species significantly.The unique species of undamaged areas were more than those in destruction areas.Compositae,Rosaceae,Gramineae and Leguminosae accounted for significant advantage with a percentage of 41.67 in total.The aboveground vegetation communities were composed of herbage primarily except DHU.The proportion of shrub communities and Perennial-biennial herb communities both presented that undamaged areas>destruction areas.While Annual herb community showed a opposite trend.In semi-arid dry warm river valley climate area,the Simpson index,Shannon index,Richness index and Dominance index tended to be DHU>DHD which was similar to that in subtropical humid monsoon climate area.(6)Relationships of soil seed bank with aboveground vegetation in different climate typesBoth the S(?)rensen and Jaccard similarity coefficients of species composition between soil seed bank and aboveground vegetation showed that undamaged areas>destruction area and all were in the medium level.And the similarity coefficients in semi-arid dry warm river valley climate area were lower generally.In semi-arid dry warm river valley climate area the SBES(seed bank endemic species)>SAVS(eed bank aboveground vegetation species),while in subtropical humid monsoon climate area SBES?SAVS.SBES and SAVS in undamaged area were higher than those in destruction area generally.The total proportion of Annual and a biennial herb of seed bank endemic species presented a trend that destruction areas>undamaged areas.While the total proportion of perennial herb and shrub plant cane of seed bank endemic species indicated that undamaged areas>destruction areas.However,seed bank aboveground vegetation species had a opposite trend.(7)The comprehensive evaluation index of ecological restoration zone of Wenchuan Earthquake RegionThe comprehensive evaluation i of ecological restoration effect indicated that MW(6.95)>WW(6.74)>HW(6.01)>LW(5.86)>LZ(5.59)>WZ(5.43)>HZ(5.41).