A soil texture manipulation doubled the priming effect following crop straw addition as estimated by two models

Crop straw is often incorporated with soil tillage to maintain soil organic carbon (SOC). Both the crop straw addition per se and its associated soil structure changes can stimulate SOC decomposition, known as the priming effect. Yet no attempt has been made to isolate their effects. In addition, the priming effect is usually estimated by using uniformly labeled plant litters in the laboratory, and the impacts of non-uniform labeling on the estimation of the priming are poorly understood. The objectives of this study were 1) to isolate the effects of crop straw addition and soil structure changes on SOC decomposition and microbial community composition and 2) to evaluate the effects of the addition of pulse-labeled straw on estimation of the priming effects. The labeled 13C content and its δ13C abundance in the labile fractions of the straw sequentially extracted by ethanol, water and 0.1 M HCl were similar, but were much larger than those in the stable fractions exacted by 0.1 M NaOH. To identify the effects of soil structure changes, the soil texture of a surface soil was manipulated by adding fine sized particles (<53 μm from the subsoil) into the soil. After straw addition, >74 μm macroporosity of the texture-manipulated soil (MMS1) increased, causing strong shifts in microbial community composition characterized by phosphorus lipid fatty acid profiling compared to non manipulated soil (NMS1) during a 56-day incubation. The dynamics and total priming effects estimated using the end mixing model (EMM) based on the δ13C abundance in the labeled straw and the improved priming model (PRIM) based on first-order SOC decomposition agree well. Total straw decomposition and total priming effect in the treatment MMS1 were larger than those in the treatment NMS1 by 175% and 170% with the EMM model, respectively. Our findings highlight the importance of understanding abiotic and biotic interactions underlying SOC turnover in the detritusphere of arable ecosystems.