Differences of soil carbon pools and crop growth across different typical agricultural fields in China: The role of geochemistry and climate change.

Carbon storage and the aboveground biomass of farmland provide practical significance for understanding global changes and ensuring food production and quality. Based on soil carbon storage, aboveground biomass, climate, geochemistry, and other data from 19 farmland ecological stations in China, we analysed the distribution characteristics of farmland carbon storage in topsoil and aboveground biomass. We notably revealed the response direction and degree of climate and geochemical factors to farmland carbon storage in topsoil and aboveground biomass. The results indicated that the average carbon stocks of farmland in different regions ranged from 0.28 to 7.91 kg m, the average fresh weight of the aboveground biomass (FAB) ranged from 1370.64 to 5997.28 g m, and the average dry weight of the aboveground biomass (DAB) ranged from 119.95 to 852.35 g m. The least angle regression (LARS) and the best subsection selection regression (BSS) showed that evapotranspiration and extreme low temperatures were significant climatic factors affecting carbon sequestration and aboveground biomass on long-time scales. The linear mixed-effects model (LMM) further showed that AN and AP had significant long-term effects on carbon sequestration and aboveground biomass (p < 0.05), with AN having the highest contribution to SOC FAB, and DAB. The structural equation model (SEM) showed that carbon sequestration and aboveground biomass in agricultural fields were significantly positively correlated (p < 0.05). Moreover, the climate had a less direct contribution to carbon sequestration and above-ground biomass compared to geochemistry (PC < 0.1<PC), and its effect was more indirect. When the geochemical variables were removed, the correlation between climate and carbon and aboveground biomass variables decreased significantly. We conclude that it is possible that extremes climate and geochemistry control carbon sequestration and above-ground biomass in long-term cropland through interactions in the context of global change, which provides new insights into the evolution of soil organic carbon in long-term cropland and the scientific formulation of policies to increase food production and preserve quality.