Interannual asymmetric transitions of gross primary productivity in the grasslands of Northern China

The gross primary production (GPP) asymmetry (A(GPP)) is an essential indicator for predicting carbon sink stability in grassland ecosystems. However, little is known about the response patterns and potential driving mechanisms of asymmetry over long-time series at the biome-scale. Here, we used three satellite-based GPPs, combined with climate-vegetation-soil factors to calculate the A(GPP), and then explored the transition characteristics and attributions of A(GPP) in the past 35 years. Our results showed that the temporal dynamics of A(GPP) followed a three-stage non-linear pattern (slow-declining stabilization period, fast-declining change period, and slow-increasing stabilization period) in the grasslands of Northern China. During the two stabilization periods, significant regional variations were observed among different ecological functional areas. I: humid and semihumid meadow grassland and meadow area and II: semi-arid grassland area shifted from negative to positive asymmetry, with a decreasing contribution ratio of mean annual precipitation (MAP). Conversely, III: warm shrub-grassland area, V: alpine meadow area, and VI: alpine grassland area shifted from positive to negative asymmetry, with mean annual temperature (MAT) being the dominant driving factor. We further showed that the overall A(GPP) of the grasslands in Northern China continues to exhibit a positive asymmetry under future climate scenarios, which means that interannual changes in A(GPP) favor the promotion of the future grassland carbon sink. These results contribute to predicting interannual variations in grassland carbon sink and formulating grassland management measures.