## 1 Introduction  
Primary production is a fundamental ecological process, representing the first step in the capture, storage, and transfer of matter and energy. Photoautotrophs, such as mangroves and various types of algae, produce the food needed for metabolism, growth, and reproduction by incorporating carbon dioxide into organic matter using energy from sunlight. These primary producers require nutrients such as nitrogen (N) and phosphorus (P) to construct biomolecules, such as nucleic acids and proteins [1]. Nutrient uptake and cycling occur in tandem with primary production and the ratio with which they are used influences other ecological processes, including biogeochemical cycles. In forests, the canopy photosynthesizes and produces fixed carbon, leading to the formation and accumulation of tree foliage, branches, wood, and roots. Many factors are important in regulating primary production, especially light, temperature, salinity, nutrients, water availability, and sediment characteristics, such as grain size and percentages of sand, silt, and clay. Recently, a light-use efficiency model revealed that the annual mean gross primary production (GPP) of tropical vegetation ranges from 7.1 to 7.6 g C m\({}^{-2}\) d\({}^{-1}\), with an apparent increasing trend from 2001 to 2020 [2]. Inland vegetation was affected mostly by precipitation, whereas coastal wetlands were mainly influenced by temperature; land cover changes that reduced the forest area significantly influenced the rates of GPP, illustrating that global environmental change is the dominant driver affecting tropical GPP. Net primary production (NPP), in contrast, has exhibited a significant decline in drought-affected areas of southern Africa, central Asia, India, South America, and Australia; tropical Asia suffers little from drought, but nearly all global vegetation has been negatively affected by climate change [3]. Mangrove forests are often described as the most productive ecosystems on Earth [4]. And while this statement is true in many coastal settings [5], not all mangroves are highly productive, especially in environments where high salinity and temperature, low rainfall, and anoxia prevail. Until recently, most estimates of mangrove primary production have been empirical measurements of litterfall rates, as it is relatively easy to collect litter beneath the canopy using litter traps. Both gross and net primary production are very method-dependent, with significantly different rates among methods [6; 7]. For example, it is well known that litterfall accounts for only a fraction of the total mangrove net primary production [4; 8], as litter is composed of leaves, twigs, and reproductive parts that fall from the canopy, but does not account for wood or root production. Other photoautotrophs contribute significantly to the total forest primary production. Chlorophytes, diatoms, phytoflagellates, and cyanobacteria living on the sediment surface and as epiphytes on leaves, decomposing wood, bark, and on living roots, as well as macroalgae living on the aboveground roots of most mangrove species, are important additional sources of fixed carbon. Wood and roots constitute a large proportion of the total forest net primary production. The estimation of wood (or stem) production typically involves repeated measurements of the stem diameter and the application of allometric equations to estimate increases in biomass over time. Increments are summed for all trees within a stand surviving an appropriate time interval (1-3 y) to estimate wood production. The production of belowground roots is of considerable significance to sediment formation and the gain of surface elevation, making significant contributions to carbon processes due to the high proportion of biomass allocated belowground relative to the aboveground biomass. Knowledge of root production is limited by difficulties associated with measuring the root growth, mortality, and longevity of complex root structures [4; 9].