Large spatial variation and stagnation of cropland gross primary production increases the challenges of sustainable grain production and food security in China.

Sustainable crop grain production and food security is a grand societal challenge. Substantial investments in China's agriculture have been made in the past decades, but our knowledge on cropland gross primary production in China remains limited. Here we analyzed gross primary production (GPP), solar-induced chlorophyll fluorescence (SIF), terrestrial water storage, crop grain production, and agricultural investment and policy during 2000-2018. We found that based on croplands in 2000, approximately 52 × 10 ha (~37%) had continuous increasing trends in GPP during 2000-2018, which were mainly located in northern China. GPP for 63% of croplands was stagnant, declined, or had no significant change. At the national scale, annual cropland GPP increased during 2000-2008 but became stagnant in 2009-2018, which was inconsistent with the interannual trend in the crop grain production data for 2009-2018. The spatial mismatch between crop production and water availability became worse. The major grain exporting provinces, mostly located in water-stressed regions, experienced increased water resource constraints, which posed a challenge for sustainable grain production. The stagnant cropland GPP and increasing water resource constraints highlight the urgent need for sustainable management for crop production and food security in China.