Abstract:

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.

Key words: Guangxi, ecological restoration area, mangrove, eddy covariance system, gross primary production, Path analysis

摘要：

红树林是海岸带生态系统中单位面积总初级生产力最高的植被生态系统。广西红树林总面积位居全国第二位，研究红树林GPP变化特征，深入探究其对气象因子的敏感性，以期为全面了解红树林碳循环动态和制定相应气候变化适应策略提供科学依据，为红树林的保育管理和生态修复提供参考。目前，尚未见有基于涡度相关技术开展广西红树林GPP研究的相关成果。以广西北海市沙生红树林为研究对象，研究区同时也是红树林生态修复区，采用涡度相关技术结合冠层实景观测技术，系统分析红树林GPP的月平均日变化特征、季平均日变化特征、月累积变化特征及年累积变化特征，并利用单因子相关分析和多因子通径分析，研究光合有效辐射、气温、地表5 cm温度、饱和水汽压差和降雨量在日、月尺度与GPP的响应模型。结果表明，GPP的平均日变化曲线在月和季尺度上呈倒“U”型分布，月累积年内呈现“双峰一谷”的变化趋势，春季和秋季为波峰，夏季为波谷；红树林冠层植被指数的分析表明，夏季波谷是由于虫害爆发导致GPP下降。2019－2022年GPP年累积分别为1.28×10³、1.29×10³、1.36×10³、1.38×10³ g∙m⁻²∙a⁻¹（以C计，下同），年累积量均值为1.33×10³ g∙m⁻²∙a⁻¹，GPP呈缓慢增加的趋势，但GPP显著小于东南沿海观测站点，这与研究区的土壤类型、群落结构以及观测站区域外部扰动有关。对红树林GPP产生直接影响最大的气象因子为光合有效辐射和气温，产生间接影响最大的因子为地表5 cm温度。综上，北海沙生红树林GPP与东南沿海相比较弱，随着生态修复工作的实施，GPP缓慢递增，但病虫害对红树林GPP影响较大，应及时开展病虫害防治工作，有利于红树林碳汇功能的提升。

关键词: 广西, 生态修复区, 红树林, 涡度相关系统, 总初级生产力, 通径分析