Interannual variation in soil respiration and its components across cropland, grassland, and pasture in the agro-pastoral ecotone of Northern China

Abstract

Quantitative understanding of the temporal patterns of soil respiration (Rs), its components (i.e., autotrophic respiration (Ra) and heterotrophic respiration (Rh)), and their controlling factors is essential to estimate grassland carbon sequestration under various land use practices. However, the sensitivity and magnitude of seasonal Rs patterns associated with these practices remain poorly understood. We conducted an experiment in the agro-pastoral ecotone of Northern China across three land-use types, including two perennial pastures composed of either Medicago sativa or Bromus inermis, two annual croplands planted with either Avena sativa or Solanum tuberosum, and two natural grasslands that had been either fenced or clipped annually. We measured Rs and its components along with a suite of biotic and abiotic factors over three growing seasons (2021–2023). Mean Rs over the growing seasons for pastures was 224–270 mg m⁻² h⁻¹, which was significantly (P < 0.05) higher than croplands (188–190 mg m⁻² h⁻¹) and grasslands (192–197 mg m⁻² h⁻¹) in ²022 and 2023. While 53–72 % of the variation in Rs between cropland and pasture was attributable to Ra, Rh and Ra each accounted for 50 % of the variation in Rs between grassland and pasture. For grasslands and croplands, interannual variation in Rs did not exceed 50 mg m⁻² h⁻¹, yet for pastures it ranged from 75–122 mg m⁻² h⁻¹, with 60–80 % of this variation attributed to Rh. This key difference among land-use types was mainly driven by greater belowground biomass and temperature sensitivity of Rh in pastures. These results contribute important knowledge of Rs and its components in the agro-pastoral ecotone of northern China and provide insights into how interannual variation in Rs among land-use types may impact the regional carbon balance.