摘要
植被生长峰值是反映陆地生态系统对气候变化响应的重要指标,其动态直接影响生态系统固碳能力和大气CO_(2)浓度的季节波动。北半球多年冻土区正经历显著升温,冻土融化过程通过改变土壤环境间接调控植被功能与碳汇效应。目前,该区域气候因子与冻土融化对植被生长峰值的综合作用仍缺乏量化评估。本研究基于遥感产品、气象及冻土数据,系统分析了2001—2018年北半球多年冻土区植被生长峰值的时空变化特征及其对气候和冻土融化的响应机制。结果表明,植被绿度峰值和生产力峰值呈显著上升趋势,年均增长率分别为0.11%和0.05%,且在75%的研究区域二者同步增加。两个峰值指标变化主要受温度驱动(相对重要性为60%、54%),其次是水分(15%、17%)和辐射(11%、13%),而冻土融化(8%、12%)与大气CO_(2)浓度(4%、6%)的影响相对较弱。结构方程模型揭示,多年冻土融化通过调控土壤水热条件间接影响植被生长峰值。春季土壤融化期(SOT)提前对峰值增加具有正向作用,而活动层厚度(ALT)的影响则因冻土类型不同而异:在连续和不连续多年冻土区促进峰值增加,在零星和岛状多年冻土区则因加剧土壤水分下渗而产生抑制作用。此外,土壤温度是连续多年冻土影响峰值的主导中介变量,而其他多年冻土区由土壤湿度中介的路径占比更高。研究成果将有助于深入理解高纬度生态系统对气候变化的适应策略,并为准确预测多年冻土区碳循环模式和制定区域生态保护政策提供科学依据。
Functioning as a pivotal link between the atmosphere and the pedosphere,vegetation is essential for regulating surface energy exchanges,maintaining ecosystem processes,and facilitating global biogeochemical cycling.Peak vegetation growth serves as a critical indicator of how terrestrial ecosystems respond to climate change,directly influencing their carbon sequestration capacity and the seasonal dynamics of atmospheric CO_(2) concentrations.Permafrost regions in the Northern Hemisphere have been undergoing significant warming,leading to deepening of the active layer and shortened soil freezing durations.These thawing processes indirectly regulate vegetation function and carbon sink potential by altering subsurface thermal and hydrological conditions.However,a comprehensive quantitative assessment of the combined effects of climate drivers and permafrost thaw on peak vegetation growth remains limited in these regions.In this study,multi-source remote sensing products,reanalysis meteorological data,and permafrost parameters,including active layer thickness(ALT)and the start of spring soil thaw(SOT)were integrated to systematically investigate the spatiotemporal dynamics of peak vegetation growth and its response mechanisms to climate and permafrost thaw across the permafrost regions of the Northern Hemisphere from 2001 to 2018.The results revealed widespread and significant upward trends in both peak normalized difference vegetation index(NDVImax)and peak near-infrared reflectance of terrestrial vegetation(NIRvmax).The annual average increase rates were 0.11% for NDVImax and 0.05% for NIRvmax.Notably,75% of the study region exhibited synchronous increases in both peak indicators,indicating a widespread enhancement of peak ecosystem function in permafrost-affected landscapes.Using an explainable machine learning analysis,it was found that temperature was the primary driver of changes in both NDVImax(60%)and NIRvmax(54%),followed by moisture(15% and 17%)and radiation(11% and 13%).In contrast,the influence of permafrost thaw was relatively weaker(8% for NDVImax and 12% for NIRvmax),as was that of atmospheric CO_(2) concentrations(4% and 6%).Across different vegetation types,peak growth indicators were generally positively correlated with temperature,precipitation,and CO_(2) concentrations,but negatively correlated with radiation.However,in broadleaf forests,mixed forests,and shrublands,NIRvₘₐₓexhibited a negative correlation with precipitation and a positive correlation with radiation,contrary to the overall trends.The ALT in permafrost regions exhibited an overall increasing trend during the study period,with 77% of the area showing thickening and a regional mean rate of 0.53 cm per year.The SOT generally advanced,with 65% of the area experiencing earlier thawing and a regional average advancement rate of 0.11 days per year.Furthermore,piecewise structural equation modeling was applied to identify the pathways through which permafrost thaw affected vegetation peak growth.The results showed that permafrost thaw primarily exerted indirect effects by altering soil thermal and moisture regimes.Earlier SOT had a positive effect on peak vegetation growth.In contrast,the impact of ALT varied by permafrost type.It promoted peak growth in continuous and discontinuous permafrost regions,but suppressed growth in sporadic and isolated permafrost zones.The negative effects were attributed to enhanced soil water percolation and drainage,which led to root-zone moisture deficits during the growing season.Moreover,mediation pathway analysis indicated that the dominant variable mediating the influence of permafrost thaw differed across regions.In continuous permafrost zones,soil temperature was the primary mediator linking permafrost thaw to peak vegetation growth.In contrast,in other permafrost types,particularly sporadic and isolated zones,the dominant mediation pathway was through soil moisture.These findings underscore the complex and spatially heterogeneous effects of permafrost thaw on high-latitude vegetation dynamics.Such variability highlights the importance of incorporating soil thermal-hydrological feedbacks and permafrost heterogeneity into evaluation of ecosystem responses to climate change.By capturing these interactions,the results provide a scientific basis for improving predictions of carbon cycling processes and for guiding policy decisions related to ecosystem conservation and climate mitigation in permafrost-affected regions.
作者
于涵
吴谋松
YU Han;WU Mousong(International Institute for Earth System Science,Nanjing University,Nanjing 210023,China)
出处
《冰川冻土》
2025年第5期1459-1474,共16页
Journal of Glaciology and Geocryology
基金
国家重点研发计划项目(2024YFF0810900)资助。
关键词
植被生长峰值
北半球多年冻土区
气候变化
冻土退化
peak vegetation growth
permafrost regions of the Northern Hemisphere
climate change
permafrost degradation
