The Characteristics Of Carbon Isotope Composition Of Modern Plants In Dajiuhu Peat Bog And Its Environmental Significance

Due to the need of quantitative research on peat paleoclimatology,Much attention have payed to the study about the environmental and ecological significance of stable carbon isotope of organic matter in peat.The main source of sedimentary organic matter in peat is vegetation on the ground.The dead or living parts of plants were buried in the place and deposited with peat year after year.The fibrous tissue of plants are composed of carbon chain,and carbon atoms in carbon chains are not involved in the exchange of carbon with the outside environment.The carbon isotopic composition would't be changed when fibrous tissue is decomposed.The information of environmental conditions and carbon isotopic fractionation effects when it was formatted were well recorded and preserved by cellulose in plants.However,the indicator significance of cellulose ?13C in peat sediment remains controversial,and this limits its application in the study of paleoclimate.The reasons for this situation is the lack of research about how the modern plants in peatland response to environmental factors,which serves as an important guideline for paleoclimatic studies.The water use efficiency of plants and the carbon isotopes composition of plants have common key control factors(stomatal conductance?photosynthetic efficiency).Thus,the?13C of plant can be used to reveal its ecological adaptability and the relationship between carbon and water.At present,research about the relationship between WUE and the ?13C value of plant in China focused on the arid and semiarid areas,yet such research is less in tropical and subtropical regions.Dajiuhu is located in the subtropical regions and exists the typical subalpine peat bogs which are well preserved.In the area peat bog was formed typically and peatland plant species are diverse.It is an ideal area for studying how the ?13C of modern plants in peatland response to environmental factors.In four period of plant growth(Apr?Jun?Jul?Sep),typical plants were collected,including herbs,shrubs and trees(a total of 68 samples).Holocellulose and a-cellulose were extracted,then the value of ?13C were measured and the relevant analysis with meteorological data in the same period were done.The sensitivity of different plants responding to meteorological factors were discussed and WUE was evaluated.The results are as follows:(1)The main factor affecting the ?13C values of majority of plants is atmospheric relative humidity.There are no significant differences of sensibility in response to the change of relative humidity in recent month between 813C of holocellulose and 813C of?-cellulose.Therefore,813C of holocellulose can be considered to reconstruct relative humidity change in this area.(2)The carbon isotope of sixty-eight samples we collected was fractionated through the C3 pathway.Among this four months,plants which have the minimum value of 813C were plants that was aquatic or with strong water-holding ability.Different plant had the different features of seasonal variation of WUE.(3)?13C of Polytrichum commune and Carex argyi are sensitive to daily average relative humidity of the period from entering into the growth to the date of the samples were collected.?13C of Polytrichum commune was positively correlated with it,while 813C of Carex argyi was negatively correlated with it.It is consistent with the result of previous studies about the indicator significance of a single plant residues ?13C in peat deposits.Environmental implications of moss and Carex ?13C is relatively clear.When information of palaeoclimate from peat sediment in Dajiuhu are extracted,Polytrichum commune and Carex argyi may be good choices which is sensitive to relative humidity and has more content of residue.