Large areas of the tropical peat swamp forests in Central Kalimantan were drained to be converted into rice fields and then abandoned. A change in the soil water level due to drainage in the forests must have had a big impact on the ecology and ecophysiology of the trees in the drained remnant forests. The leaf traits of these trees in particular may have been directly or indirectly affected by drainage because of their high sensitivity to environmental change. To understand the influence of drainage on leaf traits, we investigated leaf morphological and physiological differences between intact and drained peat swamp forests in Palangka Raya, Indonesia, using 14 species distributed over both types of forests. We compared the leaf mass per unit area (LMA), leaf toughness, leaf area- and mass-based nitrogen content (N_area and N_mass), carbon/nitrogen ratio, total phenolics, condensed tannin and lignin content and carbon isotope ratio (δ¹³C) of both types of forest trees. In the drained forest, trees had higher values in LMA, N_area, and δ¹³C than in the intact forest, suggesting that such trees adjust themselves to dry conditions to increase photosynthetic ability with high water use efficiency compared with those in intact forests. We also found an increase in condensed tannin content in drained forest trees, which may offset the drainage-induced acceleration of leaf decomposition to some extent.

In Yoron Island, cultivation of Sugarcane makes up 52% of the agriculture on the island, and it comes with extensive use of chemical fertilizers with ammonium sulfate. Moreover, as the main island is geographically formed from karst by the raised coral reef, precipitation smoothly flows to the sea through the underground. In this process, sulfate is brought to the sea as well. It is believed that potential hazards are then caused to the coral reef ecosystem. Considering this background, we aimed to evaluate the influence of sulfate on coral reef by analyzing the stable isotopes ratio of nitrogen (δ¹⁵N) and sulfur (δ³⁴S). Since the δ³⁴S of sulfate is 0‰, the same value would also be shown in coral skeleton if there were significant effect of inflows. Our result reveals that δ¹⁵N value in coral skeleton is similar to that of the chemical fertilizer. A contrary, δ³⁴S value obtained did not show similarity with that of the sulfate. However, from the analysis of the δ³⁴S in growth ring, we witness a decrease of 2‰ to 5‰ from 1979 to 2013 and from 1990 to 2013. The conclusive result is that the δ³⁴S value in coral skeleton is not significantly affected by that of the value of sulfate fertilizer. Nonetheless, the consistent decrease of δ³⁴S from 1979 to 2013 may possibly be related to the increase of inflow of land-substance with low δ³⁴S value to the sea.