NPP在欧洲生态系统变暖和干旱条件下调节气候-土壤碳路径的双重作用

摘要(中文译文)

土壤碳动态对气候变化的响应对于全球碳循环和生态系统恢复力具有关键意义。净初级生产力（NPP）作为土壤碳输入的主要来源，具有双重功能：它通过碳输入通量介导气候效应，并通过改变气候对土壤碳影响的强度来调节这些效应。本研究汇集了2009年和2018年欧洲地区8147个重复采样点的土壤有机碳（SOC；以下简称OC）及其组分——颗粒有机碳（POC）和矿物结合态有机碳（MAOC）的数据集。采用结构方程模型，结合联合中介和调节分析，在三种主要土地利用类型中，我们识别出NPP两种功能上不同且依赖于情境的作用。NPP作为中介变量：有利气候增加地下输入并促进OC积累，主要通过MAOC的形成和稳定化实现。NPP也作为调节变量：它放大了温度对土壤碳的负面影响，其中POC对增温最为敏感。NPP对气候湿度与土壤碳关系的影响表现出非线性反转：在湿润条件下，NPP主要减少分解驱动的碳损失，而在干旱条件下，它增强输入驱动的碳积累。相比之下，土壤湿度始终表现出稳定的正向影响，持续支持碳输入和积累。跨生态系统比较表明，森林更强烈地依赖NPP驱动的输入和调节途径，而在农田中，NPP的中介和调节作用相对较弱，使土壤碳更直接地受到气候影响。总体而言，NPP在气候-土壤碳路径中发挥双重作用：既是输入增强的来源，也是边际放大因子，代表了气候变化情景下的功能性权衡。

Abstract

Soil carbon dynamics in response to climate change hold critical implications for global carbon cycling and ecosystem resilience. Net primary productivity (NPP), the dominant source of soil carbon inputs, serves dual functions: it mediates climate effects via carbon input fluxes and moderates them by altering the intensity of climate impacts on soil carbon. In this study, we assembled a dataset of soil organic carbon (SOC; hereafter OC) and its fractions-particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)-from 8147 repeated sampling sites across the European region in 2009 and 2018. Using structural equation modeling with joint mediation and moderation analysis across three major land uses, we identified two functionally distinct, context-dependent roles of NPP. NPP acts as a mediator: favorable climate increases belowground inputs and promotes OC accumulation, primarily through the formation and stabilization of MAOC. NPP also acts as a moderator: it amplifies temperature's negative impacts on soil carbon, with POC being most sensitive to warming. The effects of NPP on the relationship between climatic moisture and soil carbon exhibited a nonlinear reversal: under humid conditions, NPP mainly reduced decomposition-driven carbon loss, whereas under drought conditions, it enhanced input-driven carbon accumulation. In contrast, soil moisture consistently showed a stable positive influence, continuously supporting carbon inputs and accumulation. Cross-ecosystem comparisons show that forests rely more strongly on NPP-driven input and regulatory pathways, whereas in cropland the mediating and moderating roles of NPP are comparatively weaker, making soil carbon more directly influenced by climate. Overall, NPP plays a dual role in the climate-soil carbon pathway: as both a source of input enhancement and a marginal amplifier, representing a functional trade-off under climate change scenarios.

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