Using eDNA to determine the source of organic carbon in seagrass meadows

Abstract

Seagrasses sequester globally significant amounts of carbon (C), which is stored mainly in the sediment. BothC fixation by the seagrass (autochthonous) and the trapping of organic matter that is derived from outside theecosystem (allochthonous)contribute to seagrass sediment organic C (OC). However, due to limitations incurrent methods we do not yet fully understand which sources of C are most important to blue C ecosystems.We used environmental-DNA (eDNA) to identify and estimate the contribution of floral sources to seagrass sedi-ment OC sampled from three sites in Moreton Bay, Australia that differ in potential levels of autochthonous andallochthonous OC inputs. Using the plant barcode generbcLand a next-generation sequencing platform we iden-tified 150 plant operational taxonomic units in the sediment samples. We found that seagrass DNA composedon average 88% of the eDNA pool in the sediment samples. Allochtonous sources were primarily mangrove, salt-marsh, and freshwater marsh species, but the proportional contribution of other sources varied among meadows.Carbon and nitrogen (N) stable isotope mixing models suggested a lower autochthonous contribution than theeDNA data, but had high ambiguity due to indistinguishable isotopic values among some of the sources. Ourstudy shows that eDNA can be an effective tool for identifying sources to sediment OC in blue C ecosystems andcan be used in conjunction with stable isotope analysis to reduce ambiguity. Identifying the sources of OC to thesediments of blue C ecosystems is crucial for building robust and accurate C budgets for these systems.