The mangrove blue carbon sink potential: Evidence from three net primary production assessment methods

Abstract Mangrove forests are among the highest carbon (C) sinks in the tropics and subtropics worldwide. Net primary productivity (NPP) is estimated by the permanent plot method with litterfall plus incremental growth (LG) and has great significance for the evaluation of the carbon sequestration capacity of forests. Here, we developed a new high-resolution method, sap flow investigation (SF), for the evaluation of carbon sequestration capacity. We also compared the forest carbon sequestration capacity estimated using two NPP estimation methods, stand water use using SF and light attenuation/gas exchange (LA), with traditional permanent plots using the LG method in four typical mangrove forests in the Futian Mangrove Reserve of Shenzhen City, China. The LG results showed that mangrove forests had NPPs ranging from 7.67 to 11.87 Mg C ha−1 yr−1, with species-specific differences. Among the three methods, the LG method is the most widely used, although it is costly and difficult to implement in the field. The LA results showed seasonal variation of NPP, with 4.69 g C m−2 d-1 in summer and 2.02 g C m−2 d-1 in winter. The LA method is relatively simple, but it requires a homogeneous canopy structure with a simple canopy extinction coefficient, which is suitable for mangroves with homogenous canopy structures. Although costly, the most convenient and efficient method is the SF method, which can realize continuous and high-precision dynamic NPP monitoring at the stand scale. After standardization by the LG method, the two high-resolution NPP methods could be used in mangrove forests with different time scales. For the global scale, after modification by the correction method provided in our study, the error caused by the determination method could be eliminated, which could make the global database more plentiful and accurate.