Higher priming effect induced by stems than leaf and root litters

Soil organic carbon (SOC) decomposition can be influenced by plant litters via the priming effect (PE). While plant litters largely differ in biomass allocation, and chemical properties and thus decomposability, if and how PE varies with litter type is still unknown. We aimed to synthesize geographical generalities of the litter-induced PE across ecosystem types, and explore the relative importance of regulatorssuch as environmental conditions, litter and soil properties.We conducted a meta-analysis with 621 observationsfrom 118 publications, using multiple statistical approaches such as mixed-effects meta-regressions, variation partitioning analysisand structure equation modelling.Plant litter addition significantly enhanced SOC decomposition by on average 42.33% globally, i.e., an overall positive PE. Stem litters induced a higher PE than leaf and root litters, especially in soils from croplands, indicating the higher susceptibility of SOC decomposition in response to plant litter inputs than soils in natural ecosystems. Microbial biomass Cwas also significantly stimulated by average 45.40% acrossecosystem types, thus supporting the microbial co-metabolism hypothesis. Although environmental conditions had the highest relative importance followed by soil and litter properties, the effect size and direction varied with litter type. There was a higher positiveeffect and a lower negative effect of temperature on root and leaf litter-induced PE, respectively. Soil properties were more important for the root litter-induced PE than leaf litter-induced PE, with soil C:nitrogen ratio being a negative effect and soil pH being a positiveeffect, likely due to the lower decomposability of roots.We emphasize the importance of the specificity of litter type in regulating PE. Future studies should comprehensively investigate litter properties and interactions with environmental condition and soil property with long-term experiments to improveglobal predictions of SOC decomposition via PE.土壤有机碳（Soil organic carbon, SOC）的分解可通过激发效应（priming effect, PE）受到植物凋落物的调控。植物凋落物的生物量分配、化学性质乃至分解能力均存在显著差异，但激发效应是否随凋落物类型发生变化，以及其具体作用机制仍未明确。本研究旨在综合不同生态系统类型下凋落物诱导激发效应的地理共性，并探索环境条件、凋落物与土壤属性等调控因子的相对重要性。我们整合了118项已发表研究的621组观测数据，采用混合效应元回归（mixed-effects meta-regressions）、变异分割分析（variation partitioning analysis）及结构方程模型（structure equation modelling）等多种统计方法开展荟萃分析（meta-analysis）。全球范围内，植物凋落物添加可显著提升土壤有机碳分解速率，平均增幅达42.33%，即整体呈现正向激发效应。茎凋落物诱导的激发效应显著高于叶凋落物与根凋落物，尤其在农田土壤中，这表明农田土壤有机碳分解对植物凋落物输入的响应敏感性高于自然生态系统土壤。各生态系统类型下，微生物生物量碳（microbial biomass C）也被显著提升，平均增幅达45.40%，这一结果支持了微生物共代谢假说（microbial co-metabolism hypothesis）。尽管环境条件的相对重要性最高，其次为土壤属性与凋落物属性，但激发效应的效应量与作用方向均随凋落物类型发生变化。温度对根凋落物诱导的激发效应具有更强的正向调控作用，而对叶凋落物诱导的激发效应的负调控作用则更弱。土壤属性对根凋落物诱导的激发效应的影响重要性高于叶凋落物诱导的激发效应，其中土壤碳氮比呈负向调控效应，土壤pH呈正向调控效应，这可能与根凋落物较低的分解能力有关。我们强调了凋落物类型特异性在调控激发效应中的重要性。未来研究应通过长期实验，全面探究凋落物属性及其与环境条件、土壤属性的交互作用，以提升通过激发效应预测全球土壤有机碳分解的准确性。