Plant can accelerate or slow down the soil organic carbon (SOC) decomposition by the rhizosphere priming effect (RPE). In forest ecosystems, the change of light availability due to canopy gap formation strongly influences growth of young trees and rhizosphere microbial activities in soil. However, the responses of RPE of forest young trees to light availability and its driving mechanisms remain elusive. We investigated the effects of about 60% shading on RPE of two dominant forest tree species (i.e., shade-tolerant species maple and photophilic species oak) over the four months of the growing season using the ¹³C natural tracer approach. Our results showed that the effects of shading on RPE were not dependent on the tree species. Under natural light, negative RPE on SOC decomposition prevailed during the experimental period (The loss of soil carbon via CO₂ was 31.9% lower in planted soil than in unplanted soil). RPE under shading was 71.1% more positive than that under natural light. Under natural light mineral nitrogen (N) content and microbial biomass nitrogen (MBN) were lower in planted soil than in unplanted soil, suggesting that N competition between roots and microbes due to N uptake by plants may be responsible for the negative RPE. The results of two-way ANOVA showed that although shading only had the tendency of increasing MBC, it significantly increased MBN and C-acquiring enzyme activities. These changes contributed to more positive RPE under shading. The main reason for this result may be the alleviation of root-microbes competition, the higher demand of available substrates from SOC by microbes and the higher soil moisture conditions under shading. Our study also highlights the importance of soil microbial biomass and enzyme activity when studying the mechanisms of the responses of RPE to shading or other environmental changes.

植物可以通过根际启动作用（RPE）加速或减缓土壤有机碳（SOC）的分解。在森林生态系统中，由于树冠间隙的形成而导致的可用光的变化强烈影响幼树的生长和土壤中的根际微生物活动。但是，林木幼树的RPE对光可利用性的响应及其驱动机制仍然难以捉摸。我们调查了在生长季节的四个月中，约60％的遮荫对两种主要林木树种（即耐荫树种枫树和亲光树种橡树）的RPE的影响，使用了^13种C自然示踪法。我们的结果表明，遮光对RPE的影响不取决于树木。在自然光下，在实验期间，RPE对SOC的分解作用为负（CO ₂引起的土壤碳损失）种植土壤比未种植土壤低31.9％）。阴影下的RPE比自然光下的正值高71.1％。在自然光下，种植土壤中的矿质氮（N）和微生物生物量氮（MBN）低于未种植土壤，这表明由于植物吸收氮而导致根与微生物之间的氮竞争可能是负RPE的原因。双向方差分析的结果表明，虽然阴影仅具有增加MBC的趋势，但它显着增加了MBN和C吸收酶的活性。这些变化使阴影下的RPE更加积极。该结果的主要原因可能是根微生物竞争的减轻，微生物从SOC获得的可用底物的需求增加以及遮光条件下土壤湿度的升高。