Natural 13C and 15N abundance of moss-substrate systems on limestones and sandstones in a karst area of subtropical China

Abstract

Epilithic mosses (EM) and organic substrates (OS) constitute a special ecosystem developing on rocks and a critical interface regulating rock-atmosphere interactions and biological weathering. Carbon (C) and nitrogen (N) are critical elements influencing biotic-abiotic interactions in EM-OS systems. However, the dynamics of C and N in EM-OS systems and their differences among rock types remain unclear. This study investigated contents ([C], [N]) of C and N and their isotope compositions (δ13C, δ15N) in EM and OS layers on limestones and sandstones in Huanjiang karst observatory of Guangxi, China. Significant higher [C]EM (by ca. 5.0%) and lower δ13CEM values (by ca. 3.0‰) on sandstones than on limestones might reflect a lower water use efficiency in mosses on sandstones. Differences in δ13C values between EM and OS correlated positively with those in C contents, elucidating increasing 13C discriminations with the C decomposition in substrates. The δ15NEM and δ15NOS values were correlated positively, indicating mosses as a major contributor of organic N in OS. The [N]EM did not differ between two rock types, but significant lower [N]OS and higher δ15NOS values (by ca. 0.2% and 1.5‰, respectively) occurred on limestones than on sandstones, suggesting larger N losses and 15N enrichments in OS on limestones. These results underscore that elemental and isotopic signatures can elucidate different C and N dynamics in the EM-OS ecosystems as a function of rock types.