Contrasting effects of irrigation practice on soil respiration and carbon turnover in wheat and maize season

Irrigation plays a pivotal role in regulating soil respiration (RS) in agricultural ecosystems. Currently, the effects of traditional surface irrigation on RS are well-documented, but the influence of subsurface drip irrigation remains poorly understood, even though this knowledge is critical for global carbon budgeting. To address this gap, we conducted an irrigation experiment in a winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) agroecosystem, which dominates the North China Plain's cropping systems. The study evaluated three treatments—no irrigation (NI), surface irrigation (SI), and subsurface drip irrigation (SSDI)—to compare their effects on RS and its components. Our results showed that both SI and SSDI significantly increased RS compared to NI, but RS peaks under SSDI occurred later than under SI during the wheat season. Specifically, during the wheat season, SI and SSDI treatments increased RS by 28 % and 13 %, respectively, compared to NI (570 ± 44 g C m−2). This reduction in RS under SSDI compared to SI was attributed to decreased rhizospheric respiration. Notably, SSDI led to the highest RS during the maize season due to elevated heterotrophic respiration (RH), while annual RS under SI and SSDI were similar, as seasonal differences balanced out. However, SSDI caused faster carbon turnover and higher annual RH than SI, suggesting that its water efficiency gains may accelerate soil carbon loss and weaken carbon sink potential. These findings highlight that irrigation practice induced variations in RS and its components should be considered for regional carbon budget assessments and the development of optimized irrigation management strategies.