Limitations on the climatic and ecological signals provided by the delta C-13 values of phytoliths from a C-4 North American prairie grass

作者：Webb Elizabeth A^*; Longstaffe Fred J

来源：Geochimica et Cosmochimica Acta, 2010, 74(11): 3041-3050.

DOI：10.1016/j.gca.2010.03.006

Silica phytoliths, which are deposits of opal-A that precipitate in the intra- and intercellular spaces of plant tissues during transpiration, commonly contain small amounts of occluded organic matter. In this paper, we investigate whether the delta C-13 values of phytoliths from a C-4 grass, Calamovilfa longifolia, vary in response to climatic variables that can affect the carbon-isotope composition of plant tissues. There is no significant correlation (r(2) < 0.3) between climate variables and the delta C-13 values of C. longifolia tissues (average delta C-13, issue = -13.1 +/- 0.6 parts per thousand; n = 70) across the North American prairies. However, plant tissue delta C-13 values are lower for grasses collected in populated areas where the delta C-13 value of atmospheric CO2 is expected to be lower because of fossil fuel burning. Phytolith delta C-13 values are more variable (delta C-13 = -27.3 to -23.0 parts per thousand; average = -25.1 +/- 1.3 parts per thousand; n = 34) and more sensitive to changes in aridity than whole tissue delta C-13 values. The strongest correlations are obtained between the delta C-13 values of stem or sheath phytoliths and humidity (r(2) = 0.3), latitude (r(2) = 0.4) and amount of precipitation (r(2) = 0.5). However, use of these relationships is limited by the wide spread in delta C-13 values of phytoliths from different plant tissues at the same location. We have been unable to infer any relationship between delta C-13 values of phytoliths and expected variations in the delta C-13 values of atmospheric CO2. The C. longifolia phytoliths are depleted of C-13 relative to tissue carbon by 10-14 parts per thousand. This means that the phytoliths examined in this study have carbon isotopic compositions within the range reported previously for phytoliths from C-3 plants. This observation may further limit the usefulness of soil-phytolith assemblage delta C-13 values for identifying shifts in grassland C-3:C-4 ratios.

• 出版日期2010-6-1