Interactive drivers of root decomposition in restored and natural mangroves

The allocation of blue carbon credits needs to constrain the contribution of autochthonous and allochthonous carbon. In mangroves, live roots turnover to form dead roots, which decompose into autochthonous carbon stored in sediments. However, limited data on root decomposition are available for mangroves, which hinders a comprehensive understanding of carbon dynamics in these ecosystems. This study used 210 litter bags to examine the variation in root decomposition for restored and natural mangroves while considering local environmental factors. This is among the first studies to examine interactive biotic–abiotic drivers of root decomposition in restored mangroves. Data were also combined with published studies on root decomposition to explore global patterns and identify potential drivers of decomposition rate constants. The final remaining root mass was significantly less in restored mangroves due to higher root decomposition rate constants (2.5 × 10 −3 ± 2.2 × 10 −4 day −1 , n = 18) than those in natural mangroves (2.2 × 10 −3 ± 3.8 × 10 −4 day −1 , η 2 = 4 × 10 −2 , 95% CI: [0, 1], n = 24). Fine roots decompose slower (1.7 × 10–3 ± 1.3 × 10–4 day‐1, n = 21) than coarse roots (2.9 × 10 −3 ± 4.2 × 10 −4 day‐1, η 2 = 1.1 × 10 −1 , 95% CI: [0, 1], n = 21). Fine root decomposition rate constants were also controlled by other local factors, including species, litter C/N, porewater salinity and sediment nutrients. However, no clear pattern was observed for root decomposition rate constants along latitudes and longitudes, suggesting that local factors dominate over global trends. Stable carbon isotopes of roots showed site‐ and morphology‐dependent variation, suggesting distinct decomposition pathways. Synthesis and applications : Root decomposition in mangroves is controlled by interactive local factors rather than global factors, highlighting the need for site‐specific management strategies. Our results underscore the importance of making site‐specific decisions to harness the autochthonous carbon related to mangrove roots effectively. Furthermore, uncertainties in stable carbon isotopes of roots and litter should be carefully considered to better constrain autochthonous carbon. Methodologies for blue carbon credits can be improved by incorporating stable carbon isotopes of roots into isotope mixing models, which can better constrain the contribution of autochthonous carbon.