Estimation Of Total Primary Productivity Of Forest Ecosystem In Qiannan, Guizhou And Its Response To Climate Chang

Gross primary productivity（GPP）determines the initial material and energy entering the terrestrial ecosystem,and is an important index for the study of carbon cycle and climate change.Forest ecosystem is the main body of terrestrial ecosystem.Forest GPP estimation can provide basic data for understanding regional forest carbon background and evaluating carbon absorption capacity.As the city（prefecture）with the leading forest coverage rate in Guizhou Province,it is of vital significance to clarify the temporal and spatial variation characteristics of GPP in Qiannan.Therefore,based on remote sensing images and meteorological data,this study estimated the forest ecosystem GPP in Qiannan from 2000 to 2020 with P model inversion,and revealed the spatial and temporal distribution pattern of GPP in Qiannan with P model estimation results verified by accuracy,analyzed the change trend of forest GPP and predicted future changes.The response of GPP to climate factors such as temperature,precipitation and VPD was also discussed.The results of this study are helpful to understand the dynamic development of terrestrial carbon,clarify regional carbon absorption capacity,and clarify the main limiting factors affecting vegetation growth in this region,so as to promote the sustainable development of regional forestry.The results show that:（1）From 2000 to 2020,the annual average GPP of forests in Qiannan was 1238.81±107.82 g C·m^-2·a^-1,which fluctuated several times under different climatic conditions,but showed an upward trend,with a rate of 6.08 g C·m^-2·a^-1..and the vegetation GPP in growing season was much higher than that in non-growing season.Interestingly,the growth trend of forest GPP in Qiannan in the past 21 years was mainly contributed by non-growing season GPP.（2）From 2000 to 2020,forest GPP decreased from south to north and from west to east,and showed significant spatial heterogeneity.According to the Hurst index analysis results,in the future,more than 70%of the regional forest GPP in Qiannan will have a certain degree of increase-weak anti-sustainability,which indicates that the regional GPP will probably not maintain a sustainable growth trend in the future,mainly because the relatively high forest coverage rate has been achieved in Qiannan.GPP also reached a relatively high peak,and a small increase in forest area in the future did not lead to the same significant increase in GPP as before.（4）The partial correlation between forest GPP and temperature in southern Guizhou showed an insignificant positive correlation,with an average partial correlation coefficient of 0.10.Among them,the positive correlation area accounted for 64.05%,mainly distributed in Changshun County,Huishui County,Sandu Shui Autonomous County,Libo County.The negative correlation area accounted for 35.95%,mainly concentrated in most parts of Guiding County,Fuquan City and northern Pingtang County.The effect of precipitation on the interannual variation of forest GPP in southern Guizhou was positively correlated with that of temperature,with a partial correlation coefficient of 0.11,which was stronger than that of temperature,indicating that precipitation was the main limiting climate factor for the variation of forest GPP in southern Guizhou,followed by temperature.About 70.47%of regional forest GPP was positively correlated with precipitation in Qiannan,and it was distributed in most areas of Pingtang County,Guiding County,Longli County and Sandu Shui Autonomous County.it was negatively correlated between forest GPP and VPD.The negative correlation area accounted for 51.40%,mainly distributed in Luodian,Pingtang,Dushan and Libo counties,etc.91.11%of the negative correlation showed an insignificant negative correlation.The results showed that the increase of VPD had an insignificant inhibitory effect on GPP.In conclusion,during 2000-2020,forest GPP in Qiannan showed significant differences in interannual,annual,growing season and non-growing season.The results of partial correlation analysis showed that precipitation was the main influencing factor in this region,followed by temperature,and VPD showed a negative correlation.The effects of climate change on the temporal and spatial changes of forest ecosystem GPP can provide theoretical basis for assessing regional carbon absorption capacity and carrying out forest resource protection.In particular,it is of great significance to coordinate the ecosystem composition structure to increase vegetation productivity under the background that Hurst index predicts a certain degradation trend of forest GPP in Qiannan region in the future.