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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.

Mangrove species have developed uniquely efficient water-use strategies in order to survive in highly saline and anaerobic environments. Herein, we estimated the stand water use of two diffuse-porous mangrove species of the same age, Sonneratia apetala Buch. Ham and Sonneratia caseolaris (L.) Engl., growing in a similar intertidal environment. Specifically, to investigate the radial patterns of axial sap flow density (Js) and understand the anatomical traits associated with them, we measured axial sap flow density in situ together with micromorphological observations. A significant decrease of Js was observed for both species. This result was accompanied by the corresponding observations of wood structure and blockages in xylem sapwood, which appeared to influence and, hence, explained the acute radial reductions of axial sap flow in the stems of both species. However, higher radial resistance in sapwood of S. caseolaris caused a steeper decline of Js radially when compared with S. apetala, thus explaining the latter's more efficient use of water. Without first considering acute reductions in Js into the sapwood from the outer bark, a total of ~55% and 51% of water use would have been overestimated, corresponding to average discrepancies in stand water use of 5.6 mm day-1 for S. apetala trees and 2.5 mm day-1 for S. caseolaris trees. This suggests that measuring radial pattern of Js is a critical factor in determining whole-tree or stand water use.

The global distribution and diversity of mangrove forests is greatly influenced by the frequency and intensity of winter air temperature extremes. However, our understanding of how different mangrove species respond to winter temperature extremes has been lacking because extreme freezing and chilling events are, by definition, relatively uncommon and also difficult to replicate experimentally. In this study, we investigated species‐specific variation in mangrove responses to winter temperature extremes in China. In 10 sites that span a latitudinal gradient, we quantified species‐specific damage and recovery following a chilling event, for mangrove species within and outside of their natural range (i.e., native and non‐native species, respectively). To characterize plant stress, we measured tree defoliation and chlorophyll fluorescence approximately one month following the chilling event. To quantify recovery, we measured chlorophyll fluorescence approximately nine months after the chilling event. Our results show high variation in the geographic‐ and species‐specific responses of mangroves to winter temperature extremes. While many species were sensitive to the chilling temperatures (e.g., Bruguiera sexangula and species in the Sonneratia and Rhizophora genera), the temperatures during this event were not cold enough to affect certain species (e.g., Kandelia obovata, Aegiceras corniculatum, Avicennia marina, and Bruguiera gymnorrhiza). As expected, non‐native species were less tolerant of winter temperature extremes than native species. Interestingly, tidal inundation modulated the effects of chilling. In comparison with other temperature‐controlled mangrove range limits across the world, the mangrove range limit in China is unique due to the combination of the following three factors: (1) Mangrove species diversity is comparatively high; (2) winter air temperature extremes, rather than means, are particularly intense and play an important ecological role; and (3) due to afforestation and restoration efforts, several species of non‐native mangroves have been introduced beyond their natural range limits. Hence, from a global perspective, mangroves in China provide valuable opportunities to advance understanding of the effects of freezing and chilling temperatures on mangroves. Within the context of climate change, our findings provide a foundation for better understanding and preparing for mangrove species‐specific responses to future changes in the duration and intensity of winter temperature extremes.