Effects Of Day- And Night-time Warming On Global Vegetation Greenness

The increasing rate of global land-surface daily minimum temperature(T_min)over the past five decades is 1.4 times that of daily maximum temperature(T_max).This asymmetric warming is expected to affect carbon assimilation and consumptions in plants,given that photosynthesis in most plants occurs during the daytime and thus is more sensitive to T_max.Whereas plant respiration occurs throughout the whole day,and is therefore influenced by both T_maxax and T_min.In this study,we analyzed the response of vegetation growth to day-and night-time warming in global vegetation-covered area based on normalized difference vegetation index?NDVI?,vegetation type,and climate data.Specifically,it includes the following contents:?1?To explore asymmetric warming impact on vegetation dynamics and analyzed the response of the global and different latitude interval zone's vegetation for day-and night-time warming in the yearly and seasonal scale;?2?To analyze the strength of the relationship between the inter-annual/inter-seasonal variability of NDVI and T_maxax and T_min.?3?To examine the different effects of asymmetric warming on different vegetation types and analyze the dynamic of the relationships between the all kinds of vegetation's NDVI and T_maxax and T_min.The main conclusions of this paper were obtained:?1?The effect of day-and night-time warming was relatively weak on global vegetation NDVI.The influence degree of daytime warming and night warming was different on global vegetation NDVI.Different latitude interval vegetation NDVI showed different response to day and night temperature increase.The effect of day and night warming on vegetation activity was significantly different in different seasons.The influence of spring was the largest on global vegetation activity,while the influence degree of autumn was the lowest.The effect of the vegetation in different latitude zones is different from that of day and night.On the whole,the effect of day and night warming is greater on the northern latitudes.?2?The variation trend of the correlation between vegetation dynamics and day and night warming was obvious in different latitudes.Southern hemisphere mid-latitudes vegetation had a negative correlation with the temperature during the day.The correlation of vegetation between the northern hemisphere and low latitudes in the southern hemisphere and night temperature presented a negative trend.However,the correlation between the southern hemisphere mid-latitudes vegetation and the night temperature had a positive trend.In different seasons,the variation trend of the correlation between vegetation dynamics and day and night warming was obvious.?3?It was different about the response of vegetation NDVI in different types to the asymmetry of the rate of day and night warming.The rise of daytime temperature had a significant positive effect on the desert vegetation,while the rise of night temperature had a significant positive significance to the vegetation dynamic.There is obvious heterogeneity in the characteristics of the correlation between different types of vegetation and the day and night temperature increase.The correlation between vegetation dynamics and daytime temperature in grassland,evergreen coniferous forest and deciduous coniferous forest showed a negative trend.The correlation between the vegetation dynamics of the multi tree and the Savannah and the daytime temperature indicated a positive trend.The correlation between vegetation dynamics and night air temperature in evergreen broad-leaved forest,mixed forest,deciduous broad-leaved forest,woody savanna,savanna and crop/natural vegetation showed a negative trend,but the correlation between vegetation dynamics and night temperature in evergreen coniferous and deciduous coniferous forests was a positive trend.The purpose of this study is to explore the effects of day and night temperature increasing on the global vegetation ecosystem.It is of great significance to reveal the influence of the asymmetric temperature increasing on the global terrestrial vegetation ecosystem and clarify the adaptability of vegetation ecosystem to global warming in the context of global climate change.Moreover,it can provide a theoretical basis in order to understand the long-term dynamics of global carbon cycle.It also plays an important role in enhancing the ability to adapt and mitigate climate change.