Spatio-temporal distribution of soil respiration in dune-meadow cascade ecosystems in the Horqin Sandy Land, China

This study investigated soil respiration (Rs) in adjacent ecosystems with a cascade distribution in the semi-arid region of the Horqin Sandy Land (HSL) and determined the spatio-temporal distribution of Rs as well as its relationship with the influencing factors.Four ecosystems with a cascade distribution (i.e., cascade ecosystems) were selected from the dune–meadow area of the HSL, including sandy bare ground (SBG), a sandy Caragana microphylla community (SCC), transitional artificial Populus forest (TPF), and a meadow Phragmites communis community (MPC). In 2014 and 2015, Rs, soil temperature (Ts) and soil moisture content (Ms) were measured every 10–15days during the growing season, and 24-h continuous observations were carried out during the early, middle and late stages of growth. In addition, landforms, soil properties, vegetation characteristics and groundwater table depths of the cascade ecosystems were surveyed.The Rs values of the cascade ecosystems showed significantly different seasonal variations (P<0.05). During the growing season, the mean, coefficient of variation, and temperature sensitivity of Rs were in order of SBG<SCC<TPF<MPC, which was consistent with landforms, soil properties and vegetation characteristics. Due to the differences in landforms, soil properties, vegetation characteristics and groundwater table depth, the Rs values of SBG and SCC were significantly positively correlated with Ms. but not with Ts. TPF had the optimum Ms. for Rs, while the Rs value of MPC was significantly negatively correlated with Ms. Further, the Rs values of TPF and MPC were significantly positively correlated with Ts. Ts and Ms. together explained 49.9%, 74.8%, 79.5%, 92.1% of Rs in the cascade ecosystems(SBG, SCC, TPF, MPC). At the diurnal scale, the Rs values of SBG, TPF and MPC had different relationships with Ts and Ms. during different stages of the growing season. The Rs values of SBG and TPF also had different diurnal patterns during these stages.The critical factors that led to the spatial variation of Rs in the cascade ecosystems in the study area were root biomass, vegetation cover, soil organic matter and Ms. These factors also resulted in the complex relationships of Rs with its influencing factors. The critical factors that led to the temporal variation of Rs in the cascade ecosystems were Ts, Ms. and plant growth. Cascade ecosystems should be considered when estimating the terrestrial carbon balance, and caution must be taken to select the appropriate relation between Rs and its influencing factors. Results of this study will contribute to the accurate estimation of terrestrial carbon emissions and our understanding of the carbon cycle process.