Changing Characteristics of Gross Primary Production for Typical Sandy Mangrove in Guangxi and Its Response to Meteorological Factors
Among all coastal ecosystems,mangrove is the vegetation ecosystem with the highest Gross Primary Production(GPP)per unit area.Under the global climate change,carbon cycle process is quantitatively explored.The total area of mangroves in Guangxi ranks second in China.In this study,we aimed to illuminate the GPP change characteristics of mangroves and to explore the sensitivity of GPP to meteorological factors.Our results would be helpful for understanding the carbon cycle dynamics of mangrove,assisting local policy-makers in taking initiatives to combat climate change,and providing scientific basis for conservation management and ecological restoration of mangrove.Until now,there have been few studies on mangroves GPP in Guangxi which used eddy covariance technology.This study focused on the sandy mangrove in ecological restoration area,located in Beihai,Guangxi.Using eddy covariance technology combined with canopy-based observation technology,we analyzed the monthly average daily changing characteristics,seasonal average daily changing characteristics,monthly cumulative changing characteristics,and annual cumulative changing characteristics for mangrove GPP.In addition,the response models of photosynthetically active radiation,air temperature,surface temperature at 5 cm depth,vapor pressure deficit,and rainfall to GPP at daily and monthly scales were explored using single-factor correlation analysis and multi-factor path analysis.Results showed that the daily average changing curve of GPP presented an inverted"U"shape at monthly and seasonal scales.The monthly cumulative GPP showed a"two-peak and one-trough"trend,with peaks in spring and autumn and troughs in summer.The mangrove canopy vegetation index results indicated that the troughs in summer were due to the outbreak of insect pests.The annual cumulated GPP showed a slow increasing trend,and was 1284.11,1286.67,1362.10 and 1382.19 g∙m-2∙a-1 in 2019-2022,respectively.The average annual cumulated GPP was 1328.77 g∙m-2∙a-1 from 2019 to 2022,and was significantly lower than that of the southeast coastal observation stations,resulting from the soil type,community structure and external disturbance in the study area.Photosynthetically active radiation and air temperature had the greatest direct impact on mangrove GPP,while 5 cm soil surface temperature had the greatest indirect impact on mangrove GPP.Overall,the GPP of sandy mangroves was lower than that of the southeast coastal areas.With the implementation of ecological restoration projects,the GPP increased slowly,but pests and diseases had a great impact on mangroves GPP.Thus,implementations of pest control-related projects are necessary for the improvement of the carbon sink function for mangroves.
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