黄土高原植被NEP时空变化及对气温降水和退耕还林(草)的响应OA

[Objective]Net ecosystem productivity(NEP)is a key indicator for measuring the carbon budget of terrestrial ecosystems.Quantitatively assessing NEP and its influencing factors is of great importance for deeply understanding the regional carbon cycle and its driving mechanisms.[Methods]Taking the Loess Plateau as the study area,the research used data products such as MOD13A1 NDVI,MOD17A3 NPP,climate data(temperature and precipitation),digital elevation model(DEM),and land cover data.The Carnegie-Ames-Stanford-Approach(CASA)model,Theil-Sen trend analysis,Mann-Kendall significance test,and correlation analysis were employed to analyze the spatiotemporal distribution changes of vegetation NEP on the Loess Plateau from 2001 to 2022 and to explore its responses to temperature,precipitation,and the implementation of the Grain-for-Green Program.[Results]1)From 2001 to 2022,the multi-year mean vegetation NEP on the Loess Plateau was 327.06 g/m²(in terms of C),showing a significant increasing trend at a rate of 7.51 g/(m²·a)(p<0.05).Among land cover types,grassland had the fastest growth rate.2)Spatially,vegetation NEP on the Loess Plateau mainly exhibited an increasing trend.Significantly increasing areas accounted for 77.38%of the total,primarily distributed in the central part of the loess tableland gully region and the central part of the loess hilly gully region.Significantly decreasing areas accounted for only 0.98%,primarily located in the western part of the rocky mountainous and river valley plain region,the southwestern part of the sandy land and agricultural irrigation region,and the western part of the loess tableland gully region.Among the subregions,the loess hilly gully region had the highest proportion of areas where vegetation NEP showed a significant increasing trend,accounting for 93.00%of its total area.3)Vegetation NEP on the Loess Plateau was overall positively correlated with both mean annual temperature and annual precipitation.Areas showing significant positive correlation accounted for 6.28%and 26.38%of the total area,respectively.The former concentrated in the southern part of the loess tableland gully region,while the latter was mainly distributed in the northern part of the loess tableland gully region and the eastern part of the loess hilly gully region,the central and northeastern parts of the sandy land and agricultural irrigation region,and the northeastern part of the rocky mountainous and river valley plain region.Areas showing significant negative correlation accounted for 1.38%and 0.13%,respectively,and were primarily distributed in the western and northwestern parts of the loess plateau gully region.Among different subregions,the proportion of areas where the vegetation NEP of cropland,forest,and grassland showed a significant positive correlation with annual precipitation was higher than that with mean annual temperature.The relationship between vegetation NEP and annual precipitation was most pronounced in the sandy land and agricultural irrigation region.4)In areas of the Loess Plateau with slopes greater than 25°,the increase rate in vegetation NEP was higher in areas where cropland had been converted to forest or grassland than in areas where cropland remained unchanged.[Conclusion]The implementation of the Grain-for-Green Program and the warming-wetting climate play critical roles in increasing vegetation NEP on the Loess Plateau.