| The reproductive allocation rules and strategies of eelgrass in three sites(According to the submerged depth of eelgrass,three sites were selected in depth 0,0.5 and lm respectively at maximum low tide)in Shuangdao Bay were studied.Population density,biomass,and ecological stoichiometry of nitrogen and phosphate were investigated or measured from March in 2016 to February in 2017.The results showed clonal growth was the more important reproductive means for this eelgrass population,and more allocation of population density,biomass,and N and P nutrients are contributed to clonal ramets rather than reproductive ramets.Therefore,clonal reproduction is the main maintenance way for this eelgrass population regeneration and stability.The main results are sunmmarized as follows:From March in 2016 to February in 2017,the population density and ramet density among one clonal fragment of eelgrass and the effectiveness of the two reproductive means in three sites were studied.The results are:1)Clonal ramets were the main contributors to population density for eelgrass population in three sites in Shuangdao Bay?and they survived the whole year in the population,while the reproductive ramets and seedlings existed only form February to July and form February to June respectively.During its sexual reproduction,the ratio of the number of clone ramets accounted for 85 to 93%of the total population number,and the ratio of reproductive ramets was only 6.2?7.90%.The proportion of seedling for site SDW2 was the highest(9.7%).and the corresponding ratio for the other two sites was less than 5%.2)Four indices of eelgrass clonal reproductive effectiveness(the density of young clonal ramets,the ratio of young clonal ramets density to population density,density of regenerating clonal ramets and the ratio of regenerating clonal ramets density to population density)in three sites were highest in autumn and winter,lowest in summer with the highest effectiveness in site SDW1.The order of mortality of clonal ramets was SDW1>SDW3>SDW2,the peak was in summer and autumn,and the mortality was up to 48.4 ±10.5%.The effectiveness of sexual reproduction:seed yield ranked as SDW3>SDW2>SDW1.The seed abortion rate was lowest in site SDW2(19.2 ±1.6%).The field seed germination rate was less than 2%and the mortality of seedlings in three sites was 100%.3)During the sexual reproduction,the number of clonal ramets per clonal fragment in site SDW1,SDW2 and SDW3 clones were 8.5±13.4 ramets/shoots,4.9±2.1 ramets/shoots and 2.6±1.3 ramets/shoots respectively,and their difference was significant.The number of eelgrass daughter generation ramets per clonal fragment was more than granddaughter generation ramets in site SDW1 and SDW2,but site SDW3 produced only granddaughter generation ramets.From March in 2016 to February in 2017,the allocation of population biomass and ramets biomass among one clonal fragment and biomass allocation among different organs of one clonal ramet in three sites were studied.The results are:1)Clonal ramets biomass was the main contributors to population biomass for eelgrass in three sites in Shuangdao Bay,and the deeper water was,the greater the biomass was allocated.During sexual reproduction period,the average biomass allocation ratio of clonal ramets was 84.3%?88.6%and 91.2%in three sites,while the ratio was 100%during the non-sexual reproduction period.2)The above/belowground biomass and aboveground/rhizome biomass of eelgrass clonal ramet significantly changed with month in three sites,and the annual average ratios ranged from 118 to 287%and 181 to 436%respectively.In addition,the deeper water was,the aboveground biomass allocation was more prominent to belowground and rhizome biomass.The rhizome/root biomass in three sites did not change significantly with month,and the rhizome biomass was more than 2 times to that of root.In addition?the biomass of rhizome was allocated as heavy as 5 times to that of root in autumn and winter.3)The biomass of one clonal fragment in three sites ranked as SDW3>SDW2>SDW1,and biomass of leaves of clonal ramets and reproductive ramets was the main allocation for each clonal fragment with the equal allocation of both.The biomass of per clonal fragment was mainly assigned by parental generation ramets and daughter generation ramets in three sites,and it was equal for two generation ramets.However,there was limited biomass allocation for granddaughter generation ramets in each site.From March in 2016 to February in 2017,the N and P ecological stoichiometry in different eelgrass organs,the reproductive allocation of N and P content of eelgrass population and clonal fragment in three sites were studied.The results are:1)The contents of N and P in the organs of eelgrass were not significantly different among three sites in Shuangdao Bay.The seasonal changes of N,P contents in eelgrass leaves,rhizomes and reproductive ramets were most obvious in different sites,while there was no significant difference in N,P contents of root between the month.The N/P ratio of eelgrass different organs in each sites ranged from 9.8 to 16.4,and hence it was implied that N element limitation occurred for eelgrass in Shuangdao bay.2)The content of N and P of clonal ramets was the main contributor for the populations in three sites.The annual average content of N was 687?2181 mg/m2,and that of P was 119?370 mg/m2,while the allocation of N and P of eelgrass reproductive ramets was limited with the 230?407 mg/m2 average content of N,and that of P was 48?91 mg/m2 in three sites.The allocation proportion of N and P in rhizomes was the highest in SDW1(31.8%and 28.9%respectively),and the allocation proportion in three sites increased significantly in autumn and winter.3)The contents of N and P in clonal fragment were highest in site SDW3(45.0 mg/shoot and 10.3 mg/shoot,respectively),and the N and P contents of leaves of clonal ramets and reproductive ramets were the main allocation for each clonal fragment with the equal allocation of both.The N and P contents per clonal fragment were mainly assigned by parental generation ramets and duaghter generation ramets in three sites,and it was equal for two generation ramet.However,there was limited N and P content allocation for granddaughter generation ramet in each site. |
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