不同城市绿地类型碳源/汇的城乡梯度格局——以杭州市为例

探究城市化对绿地空间碳源/汇的空间分布格局的影响,对评估城市生态系统的碳足迹和制定相应的碳收支管理措施具有重要意义。以净生态系统生产力(NEP)做为碳源/汇的反映指标,基于净初级生产力和土壤呼吸估算杭州市主城区绿地碳源/汇的空间分布格局,关注城乡梯度对不同绿地类型碳源/汇水平的作用。基于净初级生产力和土壤呼吸数据综合获得绿地空间NEP,通过土地利用数据和Fragstats软件进行景观格局分析,采用多元线性回归模型和逐步回归模型筛选影响NEP的景观、植被和气象因子,最后利用广义加性模型探讨NEP与各因子之间的关系。此外,分别比较了相同统计过程在不同城乡梯度和不同绿地类型之间的模型差异。结果表明:杭州市绿地空间NEP分布及其影响因子存在显著的城乡梯度与绿地类型差异。2019-2022年杭州市主城区绿地空间,整体表现为碳源,年均NEP为-0.277 kg C m^-2 a^-1;其中表现为碳汇的绿地主要分布在杭州市主城区的西部,而碳源绿地主要分布在中部和东部。整体绿地空间的NEP大小与绿地斑块面积、乔木盖度和灌木盖度呈正相关,与灌木物种丰富度和气温呈负相关。NEP随城区、城郊结合部、郊区的城乡梯度逐步增强;城区NEP与乔木盖度呈正相关,与景观多样性和气温呈负相关;城郊结合部NEP与乔木物种丰富度和灌木盖度呈正相关,与绿地斑块密度和气温呈负相关;郊区NEP则与聚集度指数、乔木盖度和灌木盖度呈正相关。公园、农田、自然植被的NEP依次增大并受到不同因素的调控。公园NEP与聚集度指数、乔木盖度和灌木盖度呈正相关,与景观分割指数、灌木物种丰富度和气温呈负相关;农田NEP与聚集度指数和灌木盖度呈正相关,与气温呈负相关;而自然植被NEP则与乔木盖度呈正相关,与景观多样性指数和气温呈负相关。研究进一步揭示了城市化对绿地空间碳源/汇的影响,为城乡碳收支的差异化管理提供了一定的理论和数据支持。

Patterns of carbon source/sink across urban-rural gradient and urban green space types: A case study of Hangzhou City

To effectively evaluate the carbon footprint of urban ecosystems and appropriately manage urban carbon budget, it is crucial to investigate how urbanization affects the spatial pattern of carbon source/sink of green space. This study employed net ecological productivity (NEP) as an indicator for carbon source/sink, evaluating by the integration of net primary productivity and soil respiration. Then we formed the carbon source/sink distribution of urban green spaces, and analyzed the impact of the urban-rural gradient on carbon source/sink levels across different types of green spaces in Hangzhou City. Following the landscape pattern analysis with the land use data using Fragstats, we applied multiple linear regression and stepwise analysis to pre-examined the effects of landscape, vegetation, and microclimatic factors on NEP. A generalized additive model was then employed to analyze the relationship between NEP and each factor. Furthermore, the different performances of these factors across the urban-rural gradient and greenspace types from the same statistic process were compared. The results showed that there were significant variations of NEP distribution and its influencing factors across green space types and urban-rural gradient. From 2019 to 2022, the whole carbon budget of main urban area in Hangzhou was carbon source, with annual average NEP -0.277 kg C m^-2 a^-1 carbon sink greenspace mostly located at the western part of Hangzhou, while the carbon source greenspace at the central and eastern part. NEP of the entire green space was positively correlated with patch area, tree coverage, and shrub coverage, but negatively correlated with shrub richness and temperature. Furthermore, NEP increased gradually with urban, sub-urban and rural gradient. Urban NEP was positively correlated with tree coverage, but negatively correlated with Shannon''s diversity index and temperature. Sub-urban NEP displayed a positive correlation with tree richness and shrub coverage, but a negative correlation with patch density and temperature. Rural NEP showed a positive correlation with the aggregation index, tree coverage and shrub coverage with different driving factors. Aggregation index, tree cover, and shrub cover were all positively connected with park''s NEP, while negatively correlated with temperature, shrub richness, and landscape division index. Farmland''s NEP had a negative correlation with temperature and a positive correlation with the aggregation index and shrub coverage. The natural vegetation''s NEP had a positive correlation with tree cover and a negative correlation with both temperature and Shannon''s diversity index. Our findings highlighted the impact of urbanization on the carbon source/sink of green space, and provided theoretical and empirical support for differentiated managements of urban and rural carbon budget.