庙岛群岛南五岛生态系统净初级生产力空间分布及其影响因子

净初级生产力(NPP)估算对于海岛碳源/汇研究具有重要意义。以庙岛群岛南五岛为例,结合CASA模型和区域特征构建NPP估算模型,借助RS和GIS技术进行NPP估算,进而分析南五岛NPP空间分布特征及其影响因子。结果表明:南五岛NPP总量为11043.52 t C/a,平均密度为340.19 g C m~(-2)a~(-1),处于全国平均水平,高于同纬度的西部地区,低于东部沿海大陆地区;夏季NPP总量占全年的80%左右,春季和秋季分别占11%和7%,冬季仅占1.3%;不同海岛的NPP平均密度由大到小依次为大黑山岛、北长山岛、庙岛、南长山岛和小黑山岛,各岛NPP平均密度与建设用地比例呈明显负相关;不同地表覆盖类型的NPP平均密度由大到小依次为阔叶林、针叶林、农田、草地、建设用地和裸地,林地具有较高的NPP值,说明南五岛的人工林建设具有重要生态作用;NDVI和地表覆盖类型是NPP最主要的影响参数,地形参数通过影响NDVI和地表覆盖类型间接作用于NPP结果;NPP与土壤p H、有效磷、全磷、全钾呈显著负相关,与全氮、总碳、总有机碳呈显著正相关,与含水量、速效钾和含盐量之间相关关系不明显。

The spatial distribution and impact factors of net primary productivity in the island ecosystem of five southern islands of Miaodao Archipelago

Island ecosystems are characterized by self-containment and vulnerability due to their limited and isolated areas. They are also important for biodiversity maintenance, freshwater conservation, and other basic ecological functions. Moreover, island ecosystems play important roles in global carbon cycle, which makes the estimation of net primary productivity (NPP) more significant for ecological construction and the study of carbon source and sink on islands. The rapid development of RS and GIS technologies provides a practical method for NPP estimation. In this study, five southern islands of Miaodao Archipelago were examined and an NPP estimation model was established based on the Carnegie-Ames-Stanford Approach (CASA) and regional characteristics. To characterize each season, 4 temporal remote sensing images were utilized. The normalized difference vegetation index (NDVI) and land cover types were extracted, and these constituted the data used for the NPP estimation model, along with meteorological and topographical data. The NPP values for different seasons, islands, and land cover types were calculated using GIS methods. The linear correlations between NPP values and various parameters including NDVI, altitude, slope, aspect, and land cover types were obtained to determine the importance of each parameter. Finally, the relationships between 10 soil environment-chemical properties and NPP at 36 sampling sites were analyzed. The total NPP for the five islands was 11043.52 t C/a. The mean density of NPP (MDN) was 340.19 g C m^-2 a^-1, which was higher than that of western regions at a similar latitude (e.g., Gansu Province and Qinghai Province) and lower than that of coastal zones in the eastern region (e.g., Guangdong Province, Jiangsu Province, and Panjin City in Liaoning Province). NPP in the summer accounted for approximately 80% of the total yearly NPP, followed by spring (11%), autumn (7%), and winter (1.3%), indicating that NPP in the northern area differed greatly among seasons. The total NPP was highest for Nanchangshan Island, followed by Beichangshan Island, Daheishan Island, Miao Island, and Xiaoheishan Island, and the total NPP was positively correlated with island area. MDN was highest for Daheishan Island, followed by Beichangshan Island, Miao Island, Nanchangshan Island, and Xiaoheishan Island, and was negatively related to the proportion of construction land. The land cover types included broad-leaf forest, coniferous forest, farmland, grassland, construction land, and bare land, in descending order based on MDN. The high NPP for forest land indicated that the plantations on the five southern islands were of great ecological significance. NDVI and land cover types were the most important parameters with respect to the spatial distribution of NPP, and topographical parameters indirectly affected NPP via their effects on NDVI and land cover type. NPP had a significant negative relationship with soil pH (P < 0.01), available phosphorus (P < 0.01), total phosphorus (P < 0.01), and total potassium (P < 0.05), and a significant positive relationship with total carbon (P < 0.01), total organic carbon (P < 0.01) and total nitrogen (P < 0.05). No significant relationships with water content, available potassium, or salinity were observed.