Abstract:

The quantitative assessment of net ecosystem productivity (NEP) and its influencing factors is helpful to further understand the regional carbon cycle and its driving mechanism. As one of the sensitive regions to climate change, the study on temporal and spatial variation characteristics of NEP in the Yellow River Basin and its climate driving factors is of great significance for clarifying the characteristics of terrestrial carbon sink pattern in northern China. Therefore, based on estimation model of NEP, the spatiotemporal evolution characteristics of NEP in the Yellow River Basin and its driving mechanisms from 2000 to 2020 were analyzed by trend analysis, correlation analysis, cluster analysis and other methods in this study. Results were shown as follows: (1) the annual average NEP in the Yellow River Basin was 92.7 g·m^-2, showing carbon sink as a whole. For the spatial distribution, the NEP in the Yellow River Basin showed an increasing trend from the west to the east. There was an obvious spatial aggregation effect on NEP in the Yellow River Basin, in which the high-value and low-value aggregation areas accounted for 32.6% and 41.7% of the basin area, respectively. (2) The NEP in the Yellow River Basin had generally increased since 2000, with an average annual increase of 4.7 g·m^-2. In particular, 62.4% of the regions had a significant increase in NEP, and the carbon sequestration capacity of vegetation had been significantly improved. In different regions, the increase rate of NEP in the middle reaches of the Yellow River was the largest, with an average annual increase of 7.8 g·m^-2. For different vegetation types, the NEP of evergreen forest increased most significantly, and the proportion of area with a significant increasing trend was the highest, reaching 82.8%. (3) From the perspective of future trends, the average Hurst index of NEP in the Yellow River Basin was 0.74, which was characterized as strong sustainability. The NEP showed a significant increase trend, and the proportion of the area that would maintain strong sustainability in the future would reach 56.2%, indicating that the carbon sequestration capacity in most areas of the Yellow River Basin would continue to increase in the future. (4) From the climate correlation analysis, NEP in the Yellow River Basin was positively correlated with precipitation and negatively correlated with sunshine hours. However, the impact of temperature on NEP was not significant. In terms of the influence range of key climatic factors, the precipitation had the largest influence area (70%), followed by sunshine (19.3%), and temperature (10.7%). Therefore, the precipitation was considered to be the dominant climatic factor determining the spatial distribution of NEP in the Yellow River Basin.

Key words: net ecosystem productivity, carbon sink, spatial-temporal dynamics, climate response characteristics, soil heterotrophic respiration, Yellow River Basin

摘要：

净生态系统初级生产力（Net Ecosystem Productivity，NEP）及影响因素的定量评估研究，有助于深入理解区域碳循环及其驱动机制。作为气候变化敏感区域，黄河流域净生态系统生产力的时空变化特征及其气候驱动因子的研究，对阐明中国北方陆地碳汇格局特征具有重要意义。因此，该研究基于NEP的估算模型，采用趋势分析、相关分析、聚类分析等分析方法，对2000-2020年黄河流域NEP时空演变特征及其驱动机制进行分析。结果表明，（1）黄河流域年均NEP为92.7 g·m^-2，总体上表现为碳汇。在空间分布上，NEP呈现从西向东逐步递增的分布特征，并存在明显的空间聚集效应，高值和低值聚集区域分别占流域面积的32.6%、41.7%。（2）2000年以来黄河流域NEP总体呈增加趋势，平均每年增加4.7 g·m^-2，其中有62.4%的地区NEP增加趋势达到显著水平，植被固碳能力提升明显。在不同分区中，黄河中游地区NEP增加速率最大，平均每年增加7.8 g·m^-2；在不同植被类型中，常绿林NEP提升最为显著，具有显著增加趋势的面积占比最高，达到82.8%。（3）从未来变化特征看，黄河流域NEP的Hurst指数平均为0.74，未来变化趋势具有强可持续性特征。其中NEP呈显著增加趋势，且未来保持强持续性的区域面积占比达到56.2%，说明未来黄河流域大部地区固碳能力仍将保持提升趋势。（4）从气候相关分析看，流域NEP多与降水呈正相关性，与日照时数呈负相关性，而气温影响不显著。在关键气候因子的影响范围方面，降水影响面积最大，占比达到70%；日照时数次之（19.3%）；气温影响范围最小（10.7%）。因此，降水是影响黄河流域NEP空间分布的最主要气候因子。

关键词: 净生态系统生产力, 碳汇, 时空特征, 气候响应, 土壤异养呼吸, 黄河流域