Achieving grain security and carbon neutrality: Challenges from carbon allocation

Abstract

Climate change and management practices influence crop allocation of carbon (C), and consequently can alter grain yield and the magnitude of C sequestration (or release) from agroecosystems. However, few in situ longitudinal studies are available to quantify these changes. Here, we combined the results from 13 years (from October 2007 to September 2020) of eddy covariance data and detailed crop production measurements to investigate changing climate and C allocation in a typical wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping agroecosystem in the North China Plain. We found that the agroecosystem on average acted as a slight C sink, i.e., net ecosystem carbon balance (NECB) is 36 g C m−2 yr−1) across the study period. Increased CO2 led to a rising trend of gross primary production (GPP, 72 g C m−2 yr−2), ∼35% of which led to increased NECB (the slope is 25 g C m−2 yr−2). However, concomitant increases in temperature and decreases in surface soil moisture caused higher partitioning of GPP to autotrophic respiration, leading to lower increases in net primary production and grain yield. Summer maize experienced a greater risk of C source increase, as well as greater grain yield reduction than winter wheat, most likely due to higher temperatures and drought in summer. Overall, our observational evidence suggests that current management and ongoing climate change increase the ability of the agroecosystem to increase NECB, but does not enhance crop production in this intensively managed high yield agroecosystems. However, C allocation strategies are unlikely to maintain constant in the future as multiple climate change factors act on the agroecosystem.