Distribution and carbon isotopic composition of diploptene from epiphytic bryophytes in Wuhan, central China

Diploptene is a ubiquitous hopanoid in the geosphere, synthesized by all hopanoid-containing bacteria. Varia-tions in the concentration and stable carbon isotopic composition (813C) of diploptene in ancient peats and lignite can be used to reconstruct certain aspects of the wetland methane cycle in the past. However, the sources and mechanisms that control diploptene 813C values in wetlands are not fully constrained. To address this, here we determined the distribution and 813C values of diploptene, as well as n-alkanes, obtained from five genera of epiphytic bryophytes (non-vascular plants such as mosses) that occupy-three different habitats: soil, rock, and tree bark. Our data show that the concentrations of diploptene are highly variable with two order of magnitude differences between the various species. Mosses collected from the soil habitat had higher concentrations compared to those from rock and tree habitats. This suggests that the input from some habitats might dominate the sedimentary signal. The 813C values of diploptene (813Cdip) also vary between species with values ranging between -39.2%0 and -31.2%0. Generally, the 813C values of diploptene and long chain n-alkanes (i.e., C29 and C31) are similar (+/- 2%0) in most of the bryophyte species. This may suggest that diploptene is produced by heterotrophic bacteria that live in symbiosis with the mosses. However, for some bryophytes the 813Cdip values are much more 13C depleted (>-2%0) compared to long chain n-alkanes, implying that for some mosses bacterial methanotrophs or methylotrophs may contribute to the diploptene pool. Our findings expand our understanding of the biological sources of diploptene in terrestrial epiphytic bryophytes, which will allow for a more detailed interpretation of the long chain n-alkanes and diploptene (813C values) in past environmental and paleoclimatic reconstructions.