| Under the influence of global warming and increasing human activities,drought disasters occur frequently all over the world.When the terrestrial ecosystem is subjected to drought stress,there will be adaptive traits such as decreased plant photosynthesis and respiratory metabolism.Severe and long-term drought will affect the effective operation of its carbon sink system.This significantly affects the carbon and water exchange of terrestrial ecosystems.Gross primary productivity(GPP)is the total amount of organic carbon fixed by plants in the ecosystem through photosynthesis per unit time.As an important indicator of ecosystem function and an important negative feedback mechanism in carbon sink system,GPP represents the stability of terrestrial ecosystem.The ecological environment of Guizhou is highly sensitive and fragile.The negative impact of water shortage that drought causes in Guizhou on vegetation GPP is one of the main interference factors for the stability change of its ecosystem.Therefore,in-depth study of the temporal and spatial variation characteristics of ecosystem vegetation GPP and drought under climate change,and revealing the response relationship of vegetation to drought can provide scientific guidance for environmental protection,ecological repair,drought monitoring and prevention in this karst area.From the perspective of carbon water exchange in terrestrial ecosystem,this paper takes the response relationship between GPP and drought as the research theme,extracts the vegetation GPP data of Guizhou Province by using MODIS GPP products,calculates Standardized precipitation evapotranspiration index(SPEI)and standardized soil moisture index(SSI)respectively by using the meteorological data of Guizhou Province and the soil moisture data of GLDAS,so as to characterize meteorological drought and agricultural drought.Through time series decomposition method,trend analysis method,path analysis Correlation analysis and multiple regression analysis studied the temporal and spatial differences and change trends of vegetation GPP,SPEI and SSI on the monthly,seasonal,growing season and annual scales in Guizhou Province from 2000 to 2019,and systematically discussed the stability of vegetation GPP under drought stress on different monthly time scales,the path analysis between vegetation GPP and drought,and the sensitivity of vegetation GPP to meteorological factors and drought index,To understand the distribution of vegetation GPP and its response to drought changes in Guizhou Province from 2000 to 2019.The main conclusions are as follows:(1)From 2000 to 2019,the average monthly vegetation GPP was consistent with the change of vegetation growth,and the overall growth trend of seasonal vegetation GPP showed an upward trend,and its value size was summer > spring> autumn > winter,and its intra-year spatial change showed the distribution characteristics of west low,east high,north low and south high,spring,autumn and winter were mainly based on increasing trends,and summer was mainly decreasing trends.The overall growth season and annual vegetation GPP showed an upward trend,and the spatial change showed the distribution characteristics of gradually increasing from northwest to southeast,and its change trend showed the characteristics of gradual decline from northwest to southeast.The GPP of various vegetation types in spring,autumn and winter showed an upward trend,the mixed coniferous and broad-leaved forests and broad-leaved forests showed a downward trend in summer,and the GPP of meadow vegetation increased most significantly in the four seasons.The GPP of vegetation types at the growing season and annual scale showed an upward trend,with meadows being the most significant,and the interannual upward trend of mixed coniferous and broad-leaved forests,broad-leaved forests and coniferous forests was smaller than that of grasses,shrublands,cultivated vegetation and meadows.(2)SPEI-6 and SPEI-12 are more easily identifiable than SPEI-1 and SPEI-3 in wet and dry periods,and the area of aridization increases with the increase of the monthly time scale.In the past 20 a,the drought situation in spring and summer has increased,the drought trend in autumn and winter has weakened,the frequency of drought in summer and autumn is higher than that in spring and winter,and the spatial dry and wet changes of SPEI in different seasons are spring > summer> winter > autumn,and the drought situation in eastern and northern Guizhou is stronger.The aridization of the growing season is stronger than that of the annual scale,and the area of aridization is smaller than that of the annual scale.SPEI at different time scales is the driest in the Ridge Ridge Valley,the wettest in the Peak Forest Valley,the aridization of non-karst areas and peak cluster valleys is stronger than that of humidification,and the humidification of peak cluster depressions,peak cluster valleys and dissolved hill basins is stronger than that of drying.(5)SSI-1 and SSI-3 are dominated by mild droughts,while SSI-6 and SSI-12 are dominated by mild and moderate droughts.With the increase of time scale,the range of drought situation of SSI expanded,and the trend change formed a spatial characteristic of wet-dry-wet phase from south to north.The drought of SSI in spring and summer is strengthened,the drought situation in autumn and winter is weakened,the frequency of drought in SSI is winter> summer > autumn > spring,the drought situation in spring is smaller than other seasons,the area of drought in autumn and winter is less than that in spring and summer,the drying situation in western Guizhou is mainly arid in the scale of the season,and the humidification situation in the east and southeast is mainly humidified.The annual SSI drought is stronger than the growing season,and the spatial changes of the SSI in the west of central Guizhou and other areas are arid,and the areas east of the central region are humid.On different time scales,the Ridge Ridge Valley,non-karst areas,peak cluster valleys and dissolved hill basins are mainly humidified,and the peak cluster valleys,peak bush depressions and peak forest valleys are mainly arid.(4)In 2010,the GPP resistance of vegetation was SPEI-1> SPEI-12>SPEI-6> SPEI-3,which the increase of the monthly time scale,and the resilience of Western Guizhou was enhanced,and that of southern and Southeastern Guizhou was weakened.In 2011,the GPP resistance of vegetation was SPEI-6> SPEI-3> SPEI-12> SPEI-1,and the vegetation resilience of each region increased with the increase of the monthly time scale.Decreased drought intensity leads to a decrease in the resilience of ecosystem vegetation,which is less resilient and less resilient in wetter and drier states.The vegetation resistance of karst hill basin is stronger than that of its landform type,and its resilience is also higher,while the vegetation resistance of other landform types is weaker and its resilience is stronger.(5)The drought changes in the spring and autumn of 2000-2019 promoted vegetation GPP production as a whole,and the spatial changes were significant.Summer drought changes mainly inhibit vegetation GPP production.The response of winter vegetation GPP to drought change was mainly upward trend in SSI change and decreasing in SPEI change.The drought changes of the growing season and the annual scale of the nearly20 a mainly played a role in promoting the production of vegetation GPP,and the changes in the decline of vegetation GPP occurred in the growing season.(6)Vegetation GPP of summer landform types is strongly influenced by other factors than meteorological factors and drought index.The sensitivity of vegetation GPP to meteorological factors in non-karst areas,Ridge Valley,Karst hill basin,Peak Cluster Valley and Karst hill Depression in spring was higher than that of drought index,and SPEI and SSI in Spring Peak Cluster Valley and Peak Forest Valley had a promoting effect on GPP,and wind speed and air pressure inhibited it.The influence of climate change on vegetation GPP in autumn peaks and valleys and peak forest valleys exceeded other factors,and the contribution rate of temperature and air pressure was higher,respectively,and the SSI of dissolved hill depressions promoted vegetation GPP under the synergy of wind speed and precipitation.Vegetation GPP in non-karst areas,peak cluster depressions,ridge valleys,peak forest valleys,and dissolved hill depressions in winter is most sensitive to climate change.The vegetation GPP of the peak bush depression,peak bush valley,ridge valley,peak bush valley and dissolved hill depression in the growing season is mainly affected by the change of air pressure,while the vegetation GPP in the melt hill basin is mainly promoted by SPEI.On an annual scale,the vegetation GPP in non-karst areas,peak cluster depressions,ridge valleys,peak cluster valleys and dissolved hill depressions is mainly affected by climate change,which is promoted by temperature changes,inhibited by air pressure and wind speed,the average annual GPP of peak cluster valleys and peak forest valleys is mainly affected by drought changes,and SPEI and SSI both play a role in promoting vegetation growth. |
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