Carbon mineralization and its temperature sensitivity under no-till and straw returning in a wheat-maize cropping system

Abstract

Soil organic carbon (SOC) mineralization is regulated by temperature and moisture. No-till (NT) and straw returning (SR) have been widely adopted to sequester SOC, but information about the effects of temperature and moisture on SOC mineralization in NT and SR is limited, particularly SOC mineralization in different aggregate size classes. To identify the responses of SOC mineralization to temperature and moisture in NT and SR, undisturbed soils were sampled from a factorial experiment of tillage (NT and plow tillage [PT]) and straw (SR and straw removal [S0]) in a wheat-maize cropping system and incubated at moisture levels of 40%, 70%, and 100% at 15 °C and 25 °C. The results showed that maize season increased SOC mineralization but decreased its temperature sensitivity (Q10) compared with the wheat season under different moisture levels. Because NT and SR promoted macro-aggregation and low mineralization was observed in macro-aggregates, NT significantly decreased the absolute (per unit soil) and specific (per unit SOC) mineralization compared with PT, regardless of the soil temperature, moisture, depth, and sample date (P < 0.05). The SR significantly increased absolute SOC mineralization; Whereas, there was no significant difference in specific mineralization and was even 24.4% lower at 5–10 cm depth in the maize season than that of S0 (P < 0.05). However, macro-aggregates had 13.6%-37.3% and 11.9%-19.9% higher Q10 values than the micro-aggregates in the wheat and maize seasons, respectively. This led to a higher Q10 under NT and SR at 40% moisture level, indicating that NT and SR constrained SOC accumulation under global warming. Increases in moisture ranging from 40% to 100% could decrease Q10, thus no significant difference between NT and PT, and SR and S0 at 100% level. Conclusively, NT with SR decreases SOC mineralization but increases its Q10, indicating that the loss of SOC is currently low but could accelerate under future warming. Our study also provided an effective approach that increased moisture could constrain the improvement of Q10 induced by NT with SR.