Carbon Addition Modified the Response of Heterotrophic Respiration to Soil Sieving in Ectomycorrhizal-Dominated Forests

Soil heterotrophic respiration (R-h) is an important pathway of carbon (C) dioxide release from terrestrial soils to the atmosphere. It is often measured using sieved soil in a laboratory, but the uncertainty of how it is influenced by soil sieving persists, which limits the accuracy of predicting soil organic C dynamics in C models. To address how soil sieving during laboratory incubation affects R-h and its response to increased carbon availability, we investigated R-h in sieved and intact soil cores and its response to C-13-glucose addition. This was conducted through a 27-day laboratory incubation in four forests, including two ectomycorrhizal-dominated (ECM) forests and two arbuscular mycorrhizal-dominated forests. The significant influence of soil sieving on R-h in all forests was not observed during incubation when glucose was not added. After adding glucose, the R-h in the sieved soils on the 5th day of incubation was averaged 27.2% lower than that in intact soils in ECM forests. On the 27th day it was 22.1% lower in the Pinus massoniana forest, but 78.0% higher in the Castanea mollissima forest. Strong relationships were detected between R-h in sieved and intact soils (r(2) = 0.888), and in soils both with and without the addition of glucose (r(2) = 0.827). The measured soil variables explained 74.7% and 49.7% of the variation in R-h on the 5th and 27th day of incubation, and the role of soil nutrients and microbial PLFA groups in regulating R-h varied temporally. Our findings suggest that plant mycorrhizal types influenced the role of increased C availability to microbes in regulating the response of R-h to sieving in forest ecosystems.