Sedge Stomatal Responses To Altitudinal Gradient At High Elevations

The uplift history of extensive plateaus and huge mountain ranges, such as theTibet and Andes, remains one of the most interesting topic in geosciences. For theCenozoic climates, extensive plateaus and huge mountain have profound effects onregional and global climate by constraining atmospheric circulations. Therefore,reconstructing paleoelevation is particularly important for further understandingclimate evolution of the Cenozoic.The paleoaltimetry to infer paleoelevation largely involves qualitative andquantitative methods. Qualitative methods mainly take the significant changes ofEarth’s lithosphere, surface environment and climate as indicators to estimate theuplift history of plateau in geological time. However, due to different qualitativeproxies of these methods, both application and reliability among these methods weredifferent.Comparison to qualitative paleoaltimetries, quantitative ones are able to achievemore accurate data. At present, measurements to reconstruct paleoelevation mainlyinclude vesicular basalt-derived paleoaltimetry, stable isotope-based paleoaltimetry, organic hydrogen isotope paleoaltimetry, and palaeobotanical method. According tovesicle size and distribution in basalt flow, paleoelevation could be estimated byvesicular basalts-based measurement. The climate-independent approach constrainson a simple emplacement history of lava and is restricted to basalt. Stable isotopicmethod fixes the disadvantage of material; however, that is sensitive to climate andevaporation. On the basis of the stable isotope-based paleoaltimetry, the newclumped-isotope carbonate thermometer is presented (Δ47as an indicator ofpaleoaltimetry), which is climate-independent and is affected by fewer factors. Butthis method has several disadvantages, most importantly, the analytical techniquesinvolved in a clumped isotope paleotemperature estimate are slow and requiredprogrammed and standardized. Organic hydrogen isotope paleoaltimetry has potentialto deduce paleoelevation by using the relationship between n-alkane δD values (δDwax)of deposited higher plant and δD values of predicted precipitation (δDp) and altitudegradient. This method has high resolution, and the fractionation between source waterand plant lipid alkane D is less affected by temperature，that may make error small.However, the relationship between δDwaxand δDpis not clear in higher elevation andthe potential to rebuild paleoelevation is required to further validated.Among paleobotanical approaches, the co-existence method is highlytaxon-depended and sensitive to local climate. Moreover, when distribution rangewithin taxa altered under the paleoenvironmental changes in deep time, this approachwould cause big error. While the CLAMP (Climate Leaf Analysis MultivariateProgram)—enthalpy paleobarometer is more accurate, but it requires plant fossils to live in the similar latitude of the same period. In addition, CLAMP-moist staticenergy has a high requirement on fossils. Stomata frequency paleoaltimetry makes abig progress on those problems, based on the inverse relationship between stomataldensity and CO2partial pressure along the increased elevation, which isclimate-independent and relative accurate. However, stomatal response to altitude ispoorly known in the high elevation regions.Here, stomatal responses to altitude gradient are reported based on Kobresiaroyleana (Nees) Boeckeler in high elevation widely over the northernQinghai-Tibetan, which devided from the G109National Highway, from Golmud toLhasa and Namtso. The stomatal densities vary from286.64±37.84mm-2to542.03±81.75mm-2(r2=0.607; p=0.000) with altitudes ranging. This negative relationship isalso apparent along Namsto transection (r2=0.681; p=0.043). However, theepidermal density and stomatal index do not show statistical significance with theelevation in both transections. It appears that the negative stomatal response of K.royleana to altitudinal gradient, instead of positive correlation in many species, islikely to be driven by high UV-B irradiation at high elevation. These results clearlyshow the negative relationship between stomatal density and elevation is highlyspecies-specific, rather than the positive correlation in all species. Hence therelationship between the stomatal density and elevation of a taxon should be validatedbefore it is employed to reconstruct the paleoelevation, especially dealing with apotential high paleoelevation of the fossil site.