A study of the influence of climate and vegetation on the stable isotope chemistry of soils in grassland ecosystems of the Great Plains.

摘要

Prairie soils were characterized in the central and northern Great Plains to determine the relationship between climate/vegetation and soil ecosystem properties. Sites were selected along precipitation and temperature gradients in which landscape position and age and mineralogical composition of the parent materials differed little.; The influence of climate on soil properties was established by measuring selected chemical, morphological and biological properties of soils along each of the climatic gradients. The main focus was to determine the environmental influences on the stable isotope carbon ratios ({dollar}sp{lcub}13{rcub}{dollar}C/{dollar}sp{lcub}12{rcub}{dollar}C) of soil carbonate and opal phytoliths.; The stable C isotope composition of soil carbonate is controlled, to a large degree, by the isotopic composition of the initial parent material in low weathering, or relatively dry, environments. In higher weathering regimes, and moister regimes, dissolution and reprecipitation appear to greatly change the C isotope composition of soil carbonate and reduce the influence of the parent material values. The influence of vegetation on the stable C isotope composition of soil carbonate is complex due to mixing of atmospheric CO{dollar}sb2{dollar} with biologically respired CO{dollar}sb2{dollar}.; There is a strong relationship between the C isotope composition of a grass plant and the carbon in its opal phytoliths. The {dollar}sp{lcub}13{rcub}{dollar}C/{dollar}sp{lcub}12{rcub}{dollar}C ratios from opal phytoliths from surface soils reflect the current proportions of C{dollar}sb3{dollar} and C{dollar}sb4{dollar} plants in the standing biomass. Due to Holocene dust deposition, the age of the phytoliths is believed to increase with increasing soil depth. Consistent changes in carbon isotope composition of phytoliths with increasing soil depth at all the study sites indicates broad, climatically influenced, vegetation changes in the Great Plains during the Holocene epoch.