Partitioning nocturnal respirations and their respective δ13C signatures in a wheat–maize rotation

Abstract

We conducted a four-year in situ experiment using chamber, eddy covariance, and mass spectrometry methods to partition nocturnal respiratory components (Fr, ecosystem respiration; Frs, soil respiration; Frsh, heterotrophic respiration; Fraa and Frab, above and below ground autotrophic respirations) and their respective carbon isotopic signatures (δr, δrs, δrsh, δraa, and δrab) in a wheat–maize rotation in the North China Plain. The annual patterns in Fr, Frs, Fraa, and Frab showed a bimodal curve in response to plant development, nitrogen fertilization, irrigation and precipitation events. Frs, Frsh, Fraa and Frab accounted for 43.4, 13.5, 56.6 and 29.9 % of Fr in the wheat season and 34.0, 15.2, 66.0 and 18.8 % of Fr in the maize season, respectively. The annual values of Fr, Frs, Frsh, Fraa, and Frab in the maize season were 2.18, 1.71, 2.45, 2.54, and 1.37 times those in the wheat season, respectively. In comparison, the annual values of δr, δrs, δrsh, δraa, and δrab in the wheat season were 5.84, 10.4, 9.84, 9.63, and 11.6 % more depleted than those in the maize season, respectively. The δraa and δrab means in the wheat (C3) season significantly depleted than those in the maize (C4) season due to the different photosynthetic carbon metabolisms in the two systems. Hysteretic response (2-3 hours) where soil temperature leads soil respiration was found, suggesting a causal role of temperature in the relationship. Higher soil temperature and water filled pore space (≥ 50 %) depleted δ13CO2 signatures. Overall, this study revealed the carbon balance of nocturnal respiratory components and their respective δ13CO2 signatures in a wheat-maize rotation.