Abstract
The photochemical reflectance index (PRI) has been often used as a physiology-based remote sensing indicator of ecosystem carbon fluxes. However, the assessments of PRI in tracking long-term carbon fluxes with climatic anomalies in mangroves are very limited. In this study, four-year (2017–2020) continuous time series measurements from tower-based eddy covariance and spectral systems in a subtropical mangrove were used to explore the ability of PRI in tracking the response of mangrove carbon fluxes to climate fluctuations and drought stress. The results showed that the temporal dynamics of daily PRI and carbon fluxes shared similar variation patterns over the study period, experiencing simultaneously decreasing trends under drought stress. Compared with the first three years, annual mean values of NEE in 2020 decreased by 10.7% and PRI decreased by 29.0%, correspondingly. PRI and carbon fluxes were significantly correlated across diurnal, seasonal, and annual time scales with better fitness under drought stress. Dark-state PRI (PRI0), the constitutive component of PRI variation due to seasonally changing pigment pool size, showed similar temporal variation as PRI in response to drought stress, while delta PRI (ΔPRI), the facultative component of PRI variation due to diurnal xanthophyll cycle, showed no response to drought stress. This study confirms the ability of PRI to track temporal dynamics of mangrove carbon fluxes on both short-term and long-term scales, with the temporal variation of PRI largely affected by the long-term constitutive pigment pool size. This study highlights the potential of PRI to serve as an early and readily detectable indicator to track the response of the mangrove carbon cycle to climatic anomalies such as drought stress.
Highlights
Mangrove wetland is one of the most important coastal ecosystems in the world, well known for its high carbon assimilation rates and strong carbon sink potential [1,2,3,4]
The responses of photochemical reflectance index (PRI) and carbon fluxes to climate fluctuations and drought stress were examined in a subtropical mangrove forest with continuous highfrequency time-series measurements from 2017 to 2020
The ability of PRI to track temporal dynamics of mangrove carbon fluxes was confirmed at both short-term and longterm scales
Summary
Mangrove wetland is one of the most important coastal ecosystems in the world, well known for its high carbon assimilation rates and strong carbon sink potential [1,2,3,4]. With high gross ecosystem production and a low respiration rate, mangrove forests can sequester more carbon than nearby terrestrial forests [5]. The net primary production of mangrove forests was conservatively estimated to be ~218 ± 72 TgC year−1 [2]. Mangrove forests play an important role in the global carbon cycle [6], they are disappearing at a rate roughly equivalent to the declining rate of tropical rainforests [7]. The carbon sink strength of mangrove wetland could reduce in response to global warming in the future through the temperature-carbon cycle feedback [8]. More research is needed to better understand the response of the mangrove carbon cycle to global climate change
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
