Vegetation Phenology And Its Driving Mechanism In The Northern Hemisphere Based On Multiple Remote Sensing Variables Under Climate Change

Vegetation phenology records the start of growing season(SOS)and end of growing season(EOS)and the length of growing season(LOS),which plays an important role in reflecting plant photosynthesis and terrestrial ecosystem response to climate change.However,the research on the response of phenology to climate factors is not clear,and the impact of phenology on photosynthetic capacity is helpful for us to understand the vegetation carbon cycle.So this paper,the phenological characteristics of different vegetation types at 66 FLUXNET sites in the Northern Hemisphere from 2007 to 2014 were tracked by solar induced chlorophyll fluorescence(SIF),leaf area index(LAI),normalized difference vegetation index(NDVI)and enhanced vegetation index(EVI).And then based on SIF,the spatial pattern and temporal trend of vegetation phenology in Northern Hemisphere from2001 to 2018 were analyzed,and the impacts of climatic controls on different phenological indicators were quantitatively investigated.At last,based on the SIF and different characteristic parameters of phenology in the Northern Hemisphere,the spatial and temporal characteristics of SIF and the influence of different phenological parameters on vegetation photosynthetic capacity was analyzed quantitatively.The main conclusions are as follows:(1)The four remote sensing variables have different characteristics in tracking vegetation phenology.Among the three vegetation types of deciduous broad-leaved forest,evergreen coniferous forest and mixed forest,LAI and SIF have higher accuracy in tracking vegetation phenology,while EVI or NDVI are more suitable for tracking vegetation phenology of grassland and farmland.In addition,shortwave radiation is the main factor affecting phenology in most of the 66 stations.(2)Temporal and spatial characteristics of vegetation phenology in the Northern Hemisphere.The average distribution of SOS,EOS,LOS and T-SIFmax in Northern Hemisphere was 127 DOY,259 DOY,132 days and 189 DOY,respectively.During the period of 2001-2018,SOS showed a significant advanced trend,LOS shows a significant extended trend,and day of the max of SIF showed a significant delayed trend,while EOS only showed a delayed trend during 2001-2008.(3)The response of vegetation phenology to climate factors in the northern hemisphere.The increase of shortwave radiation and temperature in the preseason of spring led to the advance of SOS,while the increase of precipitation led to the delay of SOS.However,the increase of mean radiation and temperature during the growing season caused the delay of T-SIFmax,while the increase of precipitation caused the advance of T-SIFmax.In addition,The environmental factors in the preseason of autumn and all year had no significant effect on EOS and LOS.(4)Impact of vegetation phenology on photosynthetic capacity in northern hemisphere.The results showed a significant upward trend from 2001 to 2018.The results showed that the influence of SOS on SIF was significant,and the advance of SOS promoted the growth of SIF.In addition,the delay of EOS,the advance of day of the max of SIF and the extension of LOS all promoted the growth of SIF.This study systematically analyzed the vegetation phenology from multi-source remote sensing variables in the Northern Hemisphere,and explored the response of vegetation phenology to environmental factors.In addition,the impact of phenological changes on photosynthetic capacity changes in recent years was analyzed.These results are of great significance for the establishment of dynamic detection model of vegetation in the Northern Hemisphere.