Diverse Litter and Suitable Tree Species Increased Activation Energy for Soil Respiration in Black Soils in China

Soil organic carbon (SOC) plays a critical role in regulating ecosystem functions and mitigating climate change. Understanding the factors that influence SOC dynamics, particularly the effect of activation energy (E_a) on SOC sequestration, is essential for predicting soil carbon responses to environmental changes. E_a refers to the minimum energy required for SOC decomposition to occur, and it is influenced by biotic and abiotic factors. This study investigated the effects of plant traits, geoclimatic and soil properties on E_a. A total of 540 soil samples from 1 m soil profiles beneath 10 plant species at seven sites were collected in black soil regions of China and analysed for E_a and other respiration parameters,including maintenance respiration (R₀), mean respiration rates (R_mean), temperature sensitivity (Q₁₀) and respiration variability (R_variability) measurements, under laboratory incubations. We also designed plant litter addition experiments (0, 1, 2, 4, 8 species) to identify litter diversity effects on these indices. Our findings revealed that litter diversity and plant species identity were the primary drivers of E_a variations, exerting 2.2-fold and 5.4-fold greater influences than geoclimatic and soil factors, respectively. Furthermore, litter addition significantly enhanced E_a by 33%, with increasing litter diversity positively correlated with elevated E_a values. Larix gmelinii exhibited 2.7-fold and 1.2-fold higher E_a than Populus xiaohei and Quercus mongolica, respectively. Structural equation modelling (SEM) testified that high E_a promotes elevated R₀ and R_mean, ultimately enhancing C accumulation in glomalin-related soil proteins (GRSP), which include glycoproteins produced by arbuscular mycorrhizal fungi in soil. Our findings highlighted that diverse litter returns to soils and afforestation with suitable species (e.g., L. gmelinii) could increase SOC sequestration, which depends on GRSP-C accrual induced by the increase in E_a.