Using isotope labeling to partition sources of CO2 efflux in newly established mangrove seedlings

Carbon dioxide (CO2) flux is a critical component of the global C budget. While CO2 flux has been increasingly studied in mangroves, better partitioning of components contributing to the overall flux will be useful in constraining C budgets. Little information is available on how CO2 flux may vary with forest age and conditions. We used a combination of 13C stable isotope labeling and closed chambers to partition CO2 efflux from the seedlings of the widespread mangrove Avicennia marina in laboratory microcosms, with a focus on sediment CO2 efflux in establishing forests. We showed that (1) above-ground part of plants were the chief component of overall CO2 efflux; and (2) the degradation of sediment organic matter was the major component of sediment CO2 efflux, followed by root respiration and litter decomposition, as determined using isotope mixing models. There was a significant relationship between C isotope values of CO2 released at the sediment–air interface and both root respiration and sediment organic matter decomposition. These relative contributions of different components to overall and sediment CO2 efflux can be used in partitioning of the sources of overall respiration and sediment C mineralization in establishing mangroves.