Towards a stomata based atmospheric CO2 reconstruction using Pinus sylvestris and Abiesalba remains

A number of species (i.e.: Quercus, Betula, Pinus, Tsuga?), which leave/needle remains have been preserved in different deposits along the Earth and, therefore, they have been used to reconstruct past atmospheric conditions. Still, plant atmospheric responses are species and site specific, and calibration with present or recent past material is needed prior to estimate any atmospheric parameter. Recent palaeobotanical researches in the Pyrenees and in the Iberian Central System, conducted under a coordinated project funded by the Spanish Ministerio de Ciencia, Innovación y Universidades (CSO2015- 65216-C2-1-P/2-P), have given light to numerous Abies alba and Pinus sylvestris-uncinata type Late Pleistocene needle remains. Here we present the preliminary stomatal-atmospheric CO2 calibration performed on Pinus uncinata, Pinus sylvestris and Abies alba altitudinal transects sampled during 2013 and 2017 on six Pyrenean populations (Irati?Navarra, Mata de Valencia?Lérida, Virós-Lérida, Maçarent de Cabrenys?Gerona, Montseny?Barcelona), and an additional P. sylvestris Central System population (Cotos ? Madrid). Five to nine needles per altitude, sampled every 100 m altitudinal increase (from 900 to 2600 m a.s.l.) were macerated and skilled to analyse cuticle parameter (stomata density, stomatal length, stomatal band width and length and pore length) responses to CO2 atmospheric partial pressure changes.