TY - JOUR
T1 - Carbon-isotopic analysis of individual pollen grains from C3 and C4 grasses using a spooling-wire microcombustion interface
AU - Nelson, David M.
AU - Hu, Feng Sheng
AU - Mikucki, Jill A.
AU - Tian, Jian
AU - Pearson, Ann
N1 - Funding Information:
We thank Ed Cushing and David Seigler for providing pollen samples. Neeraj Joshi and Daniel Scholes assisted by picking pollen grains. Sunita Shah helped build the SWiM-IRMS at Harvard. Susan Carter provided laboratory assistance. Earlier drafts of the manuscript were improved by comments from Andrew Henderson, Melissa Farmer, Gina Clarke, Denise Devotta, Kevin Wolfe, and Carolyn Barrett. Daniel Gavin, Philip Higuera, and Adam Martinsek provided helpful statistical advice. We thank Alex Sessions, Magnus Eek, and two anonymous reviewers for their constructive comments. This work was supported by Packard Fellowships in Science and Engineering (F.S.H. and A.P.), NSF ATM-0318404 (F.S.H.), and NSF EAR-0311937 (A.P.), and NSF ANT-0528710 (J.A.M.).
PY - 2007/8/15
Y1 - 2007/8/15
N2 - Pollen grains from grasses using the C3 and C4 photosynthetic pathways have distinct ranges of δ13C values that may be used to estimate their relative abundance in paleorecords. We evaluated a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer (SWiM-IRMS) for δ13C analysis of individual grass-pollen grains. Pollen from four C3 and four C4 grass species was isolated through micromanipulation and analyzed as single grains suspended in water. A carbon yield greater than the 2σ range of the carbon content of blanks containing only water was used to distinguish samples containing pollen ("pollen present") from those not containing pollen. This criterion resulted in the exclusion of ∼45% of the 946 samples applied to the wire. The average δ13C values (±1σ) of the remaining samples were -26.9‰ (±6.3‰) and -11.5‰ (±9.6‰) for C3 grasses and C4 grasses, respectively, after blank-correcting the δ13C data. These results suggest that the SWiM-IRMS system can be used to distinguish C3 from C4 grass pollen. The high variability in measured δ13C values is likely caused by a combination of factors. These include natural isotopic variability among individual pollen grains; the relatively poor precision that can be obtained when determining δ13C values of such small samples; and the uncertainty in the magnitude, isotopic composition, and stability of the analytical blank. Nonetheless, high percentages of individual pollen grains were correctly classified as being of either C3 or C4 origin. On average, 90% (range = 78-100%) of pollen grains from C3 grasses had δ13C values more negative than the cutoff threshold of -19.2‰; while 84% (range = 77-90%) of pollen grains from C4 grasses had δ13C values more positive than -19.2‰. Compared with analysis using an elemental analyzer interfaced with an IRMS (EA-IRMS), the number of pollen grains required for δ13C-based evaluation of C3/C4 grass composition is many times lower with the SWiM-IRMS. Additionally, δ13C data from the SWiM-IRMS does not need to be incorporated into a mixing model to derive estimates of the abundance of C3 and C4 grass pollen. Carbon-isotopic analysis of individual grass-pollen grains using the SWiM-IRMS system may help improve our understanding of the evolutionary and ecological significance of grass taxa in the paleorecord.
AB - Pollen grains from grasses using the C3 and C4 photosynthetic pathways have distinct ranges of δ13C values that may be used to estimate their relative abundance in paleorecords. We evaluated a spooling-wire microcombustion device interfaced with an isotope-ratio mass spectrometer (SWiM-IRMS) for δ13C analysis of individual grass-pollen grains. Pollen from four C3 and four C4 grass species was isolated through micromanipulation and analyzed as single grains suspended in water. A carbon yield greater than the 2σ range of the carbon content of blanks containing only water was used to distinguish samples containing pollen ("pollen present") from those not containing pollen. This criterion resulted in the exclusion of ∼45% of the 946 samples applied to the wire. The average δ13C values (±1σ) of the remaining samples were -26.9‰ (±6.3‰) and -11.5‰ (±9.6‰) for C3 grasses and C4 grasses, respectively, after blank-correcting the δ13C data. These results suggest that the SWiM-IRMS system can be used to distinguish C3 from C4 grass pollen. The high variability in measured δ13C values is likely caused by a combination of factors. These include natural isotopic variability among individual pollen grains; the relatively poor precision that can be obtained when determining δ13C values of such small samples; and the uncertainty in the magnitude, isotopic composition, and stability of the analytical blank. Nonetheless, high percentages of individual pollen grains were correctly classified as being of either C3 or C4 origin. On average, 90% (range = 78-100%) of pollen grains from C3 grasses had δ13C values more negative than the cutoff threshold of -19.2‰; while 84% (range = 77-90%) of pollen grains from C4 grasses had δ13C values more positive than -19.2‰. Compared with analysis using an elemental analyzer interfaced with an IRMS (EA-IRMS), the number of pollen grains required for δ13C-based evaluation of C3/C4 grass composition is many times lower with the SWiM-IRMS. Additionally, δ13C data from the SWiM-IRMS does not need to be incorporated into a mixing model to derive estimates of the abundance of C3 and C4 grass pollen. Carbon-isotopic analysis of individual grass-pollen grains using the SWiM-IRMS system may help improve our understanding of the evolutionary and ecological significance of grass taxa in the paleorecord.
UR - http://www.scopus.com/inward/record.url?scp=34547544985&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2007.06.002
DO - 10.1016/j.gca.2007.06.002
M3 - Article
AN - SCOPUS:34547544985
SN - 0016-7037
VL - 71
SP - 4005
EP - 4014
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 16
ER -