Study On Relative Pollen Productivities And Relevant Source Of Meadow Steppe Species In Inner Mongolia

The evidences of terrestrial ecosystem changes play an important role tounderstand the mechanism and the process of climatic changes and vegetationalsuccessions in the studies of past global changes. As a part of plant propagules, sporesand pollen become one of important index in simulating paleovegetation andpaleoclimate changes because their small size, huge pollen production, wide spread,hard ectotheca and easy preservation in sediments. However the complexity of pollenspread and pollen deposition makes the relationships between pollen and vegetationmore complex and changeable, which results the relationship becoming one of themost basic and difficult researche issues on palynology. So, studies on therelationships between pollen and vegetation, pollen and climate are very important toreconstruct the paleovegetation and paleoclimate.Nowdays the common used model in explaining the relationship between pollenand vegetation is ERV model (Extend R Value model), but when we use the ERVmodel we need calculating the relative pollen productivities (RPPs) and Relevantsource area of pollen (RASP) of major pollen species in study area.We calculated the pollen fall speed and then estimated the RPPs for commonpollen types of meadow steppe area using ERV models based on pollen analysis,pollen fall speed and vegetation survey from30sampling sites in East UjimqinBanner, Inner Mongolia. The results are presented as follow:In meadow steppe area, herbaceous pollen types are dominant in pollenassemblages including Chenopodiaceae, Poaceae, Artemisia, Compositae andCyperaceae etc, reflecting the steppe community appropriately. Duo to the influenceof surrounding vegetation, arbor pollen of Pinus, Quercus, Betula and so on also takea certain proportions in pollen assemblages.Pollen grain size plays a very important role in pollen fall speeds, in ellipsoidalpollen of Taraxacum has relative larger pollen grain size (average27.32975μm), andthen the Caryophyllaceae (average26.754μm), Poaceae (average23.84038μm), andThalictrum (average20.86175μm), while Chenopodiaceae pollen (average19.18538μm) has the smallest pollen grain size. In spherical pollen of Cirsium (averagelength×width:45.62822×32.65292μm) of Compositae family has relative largerpollen grain size, and then the Polygonum (average32.40125×22.6282μm), Cyperaceae (average28.21175×19.56325μm), Thymus (average27.44×19.4775μm),Aster (average24.74081×21.62820μm), Sanguisorba (average23.09125×18.92625μm) and Artemisia (average18.80427×16.57415μm), while Stellera (average17.18675×16.06111μm) has the smallest pollen grain size. So the alphabet of pollenfall speed is Compositae0.0374m/s (average of Taraxacum, Aster and Cirsium pollenfall speed)＞Polygonum0.0358m/s＞Cyperaceae0.02719m/s＞Thymus0.02553m/s＞Caryophyllaceae0.02165m/s＞Sanguisorba0.01723m/s＞Poaceae0.01719m/s＞Thalictrum0.01316m/s＞Artemisia0.01115m/s＞Chenopodiaceae0.01113m/s＞Stellera0.00893m/s。The RPPs of11common pollen types of meadow steppe estimated by ERVmodel using Poaceae as reference taxon in East Ujimqin Banner, Inner Mongoliashows that: Polygonum (42.51±2.49and33.59±2.03), Chenopodiaceae (33.81±5.41and30.35±4.96) have relative high RPPEs，Cyperaceae (22.08±0.26and19.77±0.22),Caryophyllaceae (19.83±2.61and26.98±2.95), Stellera (14.46±0.73and13.17±0.67)and Compositae (12.78±0.63and11.62±0.58) have moderate RPPEs, and then areArtemisia (7.64±0.57and5.66±0.51), Sanguisorba (4.81±0.57and5.16±0.59) andThalictrum (3.52±0.68and4.22±0.67)，while Thymus (1.60±0.17and1.79±0.18) hasthe lowest RPPEs which is similar to Poaceae (1). The estimated RSAP is about1000m which has little effect by wind speed, different estimated numbers of species andpollen fall speeds. The test of RPPs indicates that there are high consistency betweenthe estimated and actual vegetation abundance of Poaceae, Artemisia,Chenopodiaceae, Polygonum and Compositae, while Caryophyllaceae, Cyperaceae,Thalictrum, Sanguisorba, Stellera and Thymus estimated vegetation abundance arelower than actual ones, which means the RPPs was overestimated. The results suggestthat the pollen types should be considered with caution when we using RPPs inreconstructing the past vegetation.Comparing the RPPs result of meadow steppe in East Ujimqin Banner, InnerMongolia with other regions shows that the variations in vegetation structure andspecies composition, differences RPPs in Poaceae species and human activities indifferent areas may produce obvious changeable RPPs in different regions.