海南岛红树林生态系统总初级生产力分布格局及形成机制

Distribution patterns of gross primary productionof mangrove ecosystems in Hainan Islandand their driving mechanisms

红树林具有较高的光合速率和较低的光补偿点,表现出较高的总初级生产力(gross primary production,GPP),是“蓝碳”的重要组成。准确估算区域红树林生态系统GPP,并量化其限制因素贡献对于我国实现“双碳”目标具有重要意义。该文以海南岛红树林生态系统为研究对象,利用哨兵-2(Sentinel-2)影像和环境因子数据,基于红树植被光合作用-光能利用效率(MVP-LUE)模型估算了2016—2020年期间海南岛红树林生态系统GPP,并探究其时空分布格局及形成机制。结果表明:(1)在研究期间,海南岛红树林生态系统年GPP呈现出增长趋势,在空间上呈现出东部高于西部、北部高于南部的分布格局。(2)在形成机制上,海南岛红树林生态系统月均GPP时空分布格局受到多气象因素的综合影响,年内季节性上GPP在“旱→雨”过渡期随着空气温度(air temperature,T air)的限制降低和光合有效辐射(photosynthetically active radiation,PAR)与海水温度的促进作用,展现出较高的GPP;旱季中期T air低,对GPP限制严重,但随着纬度的降低,红树林生态系统GPP受T air限制的程度被减弱;雨季则因较高的云覆盖而使PAR成为GPP的限制因素。该研究结果为评估区域红树林对全球碳循环的贡献提供了基础数据,为揭示影响红树林生态系统碳动态的关键环境因素提供了理论支撑。

Mangrove forests,characterized by high photosynthetic rate and low light compensation point,exhibit high gross primary production(GPP),an important component of“blue carbon”.Accurate estimation of regional GPP and quantification of its limiting factors are greatly significant for China to achieve its carbon peaking and carbon neutrality goals.In this paper,the GPP of mangrove ecosystems in Hainan Island from 2016 to 2020 were estimated based on the mangrove vegetation photosynthesis-light use efficiency(MVP-LUE)model using Sentinel-2 imagery and environmental data,and the spatiotemporal distribution pattern of GPP and its driving mechanism were explored.The results were as follows:(1)During the study period,the annual GPP of mangrove ecosystems on Hainan Island showed an increasing trend,with higher GPP in the eastern regions than western regions,and northern regions than southern regions.The mangroves distributed over a large area in northeastern Hainan Island dominate the temporal variation patterns at the whole island scale.However,distinct differences exist in the temporal dynamics across different regions of the mangrove ecosystem in Hainan Island.(2)In terms of the formation mechanism,the spatiotemporal distribution pattern of GPP of mangrove ecosystems on Hainan Island was driven by a combination of multiple meteorological factors.Seasonally within each year,during the transition from the dry season to rainy season,GPP was higher due to lower limitation from air temperature(T air),and the promoting effects of photosynthetically active radiation(PAR)and sea surface temperature.In the middle of the dry season,low T air imposed a serious limitation on GPP,but this T air limitation was weakened with decreasing latitude.In the rainy season,higher cloud cover resulted in PAR becoming a limiting factor for GPP.At the end of the paper,we discussed the uncertainties and limitations of MVP-LUE,and the spatiotemporal distribution patterns of mangrove ecosystem GPP not only be constrained by environmental factors,but also species composition and forest age structure can also be driving factors.The results of this study provide basic data to assess the contribution of regional mangrove forests to the global carbon cycle,and theoretical support to reveal the key environmental factors affecting mangrove ecosystem carbon dynamics.