Using SPIRAL (Single Pollen Isotope Ratio AnaLysis) to estimate C3- and C4-grass abundance in the paleorecord

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a r t i c l e i n f o a b s t r a c t C 3 and C 4 grasses differ greatly in their responses to environmental controls and influences on biogeochemical processes (e.g. water, carbon, and nutrient cycling). Difficulties in distinguishing between these two functional groups of grasses have hindered paleoecological studies of grass-dominated ecosystems. Stable carbon isotopic analysis of individual grains of grass pollen using a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer holds promise for improving C 3 and C 4 grass reconstructions. This technique, SPIRAL (Single Pollen Isotope Ratio AnaLysis), has only been evaluated using pollen of known C 3 and C 4 grasses. To test the ability of SPIRAL to reproduce the abundance of C 3 and C 4 grasses on the landscape, we measured δ 13 C values of N 1500 individual grains of grass pollen isolated from the surface sediments of ten lakes in areas that span a large gradient of C 3-and C 4-grass abundance, as determined from vegetation surveys. Results indicate a strong positive correlation between the δ 13 C-based estimates of % C 4-grass pollen and the abundance of C 4 grasses on the landscape. The % C 4-grass pollen slightly underestimates the actual abundance of C 4 grasses at sites with high proportions of C 4 grasses, which can be corrected using regression analysis. Comparison of the % C 4-grass pollen with C/N and δ 13 C measurements of bulk organic matter illustrates the distinct advantages of grass-pollen δ 13 C as a proxy for distinguishing C 3 and C 4 shifts within the grass family. Thus SPIRAL promises to advance our understanding of grassland ecology and evolution. Keywords: carbon isotopes pollen surface sediments Poaceae C 3 and C 4 grasses SPIRAL spooling wire microcombustion interface 1. Introduction Paleorecords are invaluable for assessing vegetational responses to varying environmental conditions, as well as the potential influence of vegetational change on important evolutionary and ecological processes , such as mammalian evolution and migration (Flessa et al., 2005). In grass-dominated ecosystems (e.g. prairie, steppe, and savanna), information about C 3 and C 4 plant variations …