Carboxylic acid distribution patterns of temperate C3 and C4 crops

Agricultural grasses cover a major part of the land surface in temperate agro-ecosystems and contribute significantly to the formation of soil organic matter. Crop-derived lipids are assumed to be responsible for fast carbon turnover in Soils. Differences in lipid distribution patterns between crops following C-3 and C-4 photosynthesis pathways have rarely been described, but could be useful for source apportionment of crop-derived input into soils or sediments. The distribution of long chain n-carboxylic acids (C-22, C-24, C-26) reveals significant differences between crop plants following either the C-3 or the C-4 photosynthetic carbon fixation pathway. The plant compartments leaves, stems and roots of C-4 plants contain relatively large proportions (> 40%) of n-C-24 carboxylic acid when compared to C-3 plants. These reveal larger relative proportions of n-C-22 and /1-C-26 acids, whose relative abundance is subject to change between different plant compartments and during, the growing season. The carboxylic acid ratio [CAR = n-C-24/(n-C-22 + n-C-26) carboxylic acids] provides distinct ratios for C4 (> 0.67) and C-3 crops (< 0.67) and can thus be used as a molecular marker for the differentiation of crop plant biomass. In combination with the bulk stable carbon isotopic composition (delta C-13) the CAR can be used as a tool for the estimation of the C4 derived carbon proportion in soils or sediments. (c) 2006 Elsevier Ltd. All rights reserved.