Linking In Situ Photochemical Reflectance Index Measurements With Mangrove Carbon Dynamics in a Subtropical Coastal Wetland

Abstract

Photochemical reflectance index (PRI) has been found to be closely related with vegetation photosynthetic phenology in many ecosystems including boreal evergreen, but its ability to track carbon dynamics in low‐latitude evergreen mangrove ecosystems has rarely been assessed. To fill up this gap, this paper explored potential mangrove PRI‐carbon links and their environmental controls across temporal scales (diurnal and seasonal), based on 1‐year continuous high‐resolution (half‐hourly) time series measurements of spectral signals, eddy covariance carbon fluxes, and multiple environmental factors at a subtropical mangrove wetland of southeastern China. The diurnal variation of half‐hourly mangrove PRI, a U‐shaped changing pattern, was consistent with previous PRI studies on boreal evergreen, while the seasonal variation of daily mangrove PRI did not experience a hump‐shaped changing pattern as in boreal evergreen. Diurnal and seasonal mangrove PRI variations were significantly correlated with meteorological (radiation and vapor pressure deficit) and carbon‐related parameters (gross primary productivity, net ecosystem exchange, and light use efficiency), and the strength of diurnal PRI‐carbon correlations varied with meteorological factors with stronger correlations at enhanced radiation and vapor pressure deficit. Our results further indicated that physiology‐related PRI performed better than conventional structure‐related normalized difference vegetation index in tracking mangrove photosynthetic parameters. To the best of our knowledge, this is the first study to explore the link between high‐frequency PRI and carbon dynamics across temporal scales in natural mangrove ecosystems. The PRI‐carbon linkage confirmed by this study will improve our understanding of temporal variations in photosynthetic carbon dynamics in mangrove ecosystems.

Response of Mangrove Carbon Fluxes to Drought Stress Detected by Photochemical Reflectance Index

“…The seasonal variation patterns of PRI0 and sunlit PRI were consistent across years (Figure 6), which implied that the size of the pigment pool was affected by seasonal variations of environmental factors [38], in particular for PAR. This is consistent with a previous study showing that PRI was radiation-dominated with additional effects from high VPD [42]. The typical seasonal variations of subtropical mangrove forests have higher and lower PAR in summer and winter, respectively [42], leading to similar seasonal variations of two components of PRI.…”

“…Although some attempts have been made to focus on this issue [40,41], most lack long-term continuous measurements that are necessary for clarifying the relationship between PRI and mangrove carbon fluxes at both seasonal and inter-annual time scales. Zhu et al [42] explored the link between PRI and mangrove carbon dynamics at a seasonal scale but they were not able to reveal any inter-annual variation pattern. Here, based on four-years of continuous measurement of mangrove PRI and EC-based ecosystem carbon fluxes, the purposes of this study are (1) to analyze the response of mangrove carbon fluxes to climate fluctuations and drought stress, (2) to examine the ability of PRI to track the response of the mangrove carbon cycle to climatic anomalies, and (3) to explore the complex mechanisms underlying PRI variations across different time scales.…”

How Land‐Sea Interaction of Tidal and Sea Breeze Activity Affect Mangrove Net Ecosystem Exchange?

“…Raw EC data were recorded by a CR3000 data logger (Campbell Scientific, Inc.) at 10 Hz. A typical EC pre-processing procedure, including flux calculations, corrections and quality controls (see Zhu, Song, et al (2019) for details), was implemented in the Ed-dyPro6.1 software (Li-COR Inc.) to produce half-hourly time series of NEE. Co-spectral analysis confirmed that the EC system was able to capture eddy fluxes of CO 2 across the whole range of frequencies (Figure S1).…”

Carbon Cycling in the World’s Mangrove Ecosystems Revisited: Significance of Non-Steady State Diagenesis and Subsurface Linkages between the Forest Floor and the Coastal Ocean

“…Here, the mass balance model of carbon flow through the world's mangrove ecosystems constructed by Alongi [2] is revised, using the data in Sections 2.1-2.3 and in Table 2, and newer data for soil + root burial [3,106], root production [107], mangrove gross primary production (GPP), POC, and DOC export [7,10], and canopy respiration (R c ) [19,66,[108][109][110][111][112][113][114], and extrapolated using the most recent estimate of global mangrove area [115]. The revised carbon flow model ( Figure 5) shows that ∼64% of GPP is respired by the canopy with NPP vested nearly equally in the litter, wood, and belowground root production.…”