Effect of litter on soil respiration in a man-made Populus L. forest in a dune-meadow transitional region in China’s Horqin sandy land

Human disturbance and climate change both influence the input quantity of plant litter, significantly affecting soil respiration (Rₛ). However, what leads to a change of relationship between Rₛ in on-litter input (Rₛ(NL)) and natural litter input (Rₛ(CL)) is not yet fully understood. This study selected a man-made Populus forest in a dune-meadow transitional region to observe Rₛ(NL) and Rₛ(CL), soil temperature and soil moisture at a depth of 0–10 cm, groundwater depth between April and October in 2014 and 2015, and diurnal variations were carried out during the early, middle, and late stages of the growing seasons. Complex Rₛ diurnal patterns were observed in different growth stages. The soil moisture beyond field capacity inhibited root respiration and soil microbial activities, thus making Rₛ(NL) smaller than Rₛ(CL). When soil moisture was below field capacity with the increase of groundwater depth, dry air and low litter moisture content resulted in the shielding effect of the litter on Rₛ beyond its decomposition, thus making Rₛ(NL) consistently larger than Rₛ(CL). The temperature sensitivity was significantly affected by soil moisture. These results indicate that interactions among the quantity of litter, soil temperature, soil moisture and groundwater, which cause diurnal variations in Rₛ were diverse. Negative litter respiration may not be a measurement error, but caused by soil moisture which changes the relationship between Rₛ(NL) and Rₛ(CL). Thus, this study shows that plant litter has a significant influence on Rₛ in the dune-meadow transitional region. The findings of this study will provide useful information to understand these fragile ecosystems and the terrestrial carbon cycle.