Mariotti A, Peterschmitt E
J. E. DRED Biogéochimie isotopique, Université P. M. Curie-INRA, case courrier 120, 4 place Jussieu, 75252, Paris cedex 05, France.
Institut Français de Pondichéry, P.O. Box 33, 605001, Pondicherry, India.
Oecologia. 1994 May;97(4):475-480. doi: 10.1007/BF00325885.
In India, the stability of the forest savanna boundary (ecotone) has been questioned. To investigate the possibility of vegetation change at this boundary, we used the natural difference in the stable carbon isotope ratio (C/C, expressed as δC) of C (forest) and C (savanna) plants, which is preserved in the isotopic composition of soil organic carbon. Past changes in the position of the ecotone can thus be documented by C/C analysis of soil organic matter (SOM). Measurements were made on soil samples taken along a transect across the forest savanna boundary. In both ecosystems, δC values of SOM in upper soil layers appeared to be in equilibrium with the current plant community: SOM was near-14‰ under savanna cover, and near-28‰ under forest. By contrast, δC values of SOM from deep layers of soil profiles under forest cover near the ecotone, were less negative than would be expected for a C-dominated community. These results indicate that a change in ecosystem dominance occurred recently, and that forest has invaded an area occupied previously by a C plant community (savanna and cultivated grassland).
在印度，森林稀树草原边界（生态交错带）的稳定性受到了质疑。为了研究该边界处植被变化的可能性，我们利用了C₃（森林）植物和C₄（稀树草原）植物稳定碳同位素比率（¹³C/¹²C，以δ¹³C表示）的自然差异，这种差异保存在土壤有机碳的同位素组成中。因此，通过对土壤有机质（SOM）进行¹³C/¹²C分析，可以记录过去生态交错带位置的变化。我们沿着一条穿过森林稀树草原边界的样带采集土壤样本并进行测量。在这两个生态系统中，上层土壤中SOM的δ¹³C值似乎与当前的植物群落处于平衡状态：在稀树草原覆盖下，SOM的δ¹³C值接近-14‰，在森林覆盖下接近-28‰。相比之下，在生态交错带附近森林覆盖下的土壤剖面深层中，SOM的δ¹³C值比以C₃为主的群落预期的负值要小。这些结果表明，最近生态系统优势发生了变化，森林侵入了以前由C₄植物群落（稀树草原和人工草地）占据的区域。
