Abstract: We measured the isotope ratios of δ¹³C and δ¹⁵N in cave animals and their organic carbon sources in Mawan cave of Fenggang, Guizhou, and further analyzed trophic level relationship and food sources of the cave ecosystem. The results showed that the values of plant δ¹³C in the cave ranged from -41.78‰ to -38.80‰, which is lower than that of plants out the cave. The δ¹⁵N of plants in the cave ranged from -1.31‰ to 1.23‰, which is within the range of terrestrial organic matter. The δ¹³C of soil organic matter in the cave ranged from -31.09‰ to -24.95‰, while the δ¹⁵N of soil organic matter in the cave ranged from -1.08‰ to 7.72‰. The δ¹³C of cave animals ranged from -30.41‰ to -12.02‰, while their δ¹⁵N ranged from 2.07‰ to 8.94‰. The contribution rate of cave soil organic matter to animals was more than 72%, being higher than that of plants, indicating that soil organic matter was the main food source for cave animals. There were four trophic levels in the food web. Plants were the first trophic level. Tipula sp., Gastropoda, and Diolopoda were the second trophic level. Distrammena sp., Mecistocephalus sp. were the third trophic level. Most of Araneae groups were the third or fourth trophic level. Our results indicate that the trophic levels of most animals were relatively stable in the cave. A few animals from same species have different trophic levels in different light zones, whereas different species belonging to the same group would be at different trophic levels in the same light zone.

Key words: coastal wetland., carbon storage, Tamarix chinensis, biomass