Using isotope labeling to partition sources of CO 2 efflux in newly established mangrove seedlings

Carbon dioxide (CO 2 ) flux is a critical component of the global C budget. While CO 2 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 CO 2 flux may vary with forest age and conditions. We used a combination of 13 C stable isotope labeling and closed chambers to partition CO 2 efflux from the seedlings of the widespread mangrove Avicennia marina in laboratory microcosms, with a focus on sediment CO 2 efflux in establishing forests. We showed that (1) above‐ground part of plants were the chief component of overall CO 2 efflux; and (2) the degradation of sediment organic matter was the major component of sediment CO 2 efflux, followed by root respiration and litter decomposition, as determined using isotope mixing models. There was a significant relationship between C isotope values of CO 2 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 CO 2 efflux can be used in partitioning of the sources of overall respiration and sediment C mineralization in establishing mangroves.