Data from: Vegetation type controls root turnover in global grasslands

Abstract: Aim: Root turnover is an important process determining carbon and nutrient cycling in terrestrial ecosystems. It is an established fact that root turnover is jointly regulated by climatic, edaphic, and biotic factors. However, the relative importance of these forces in determining the global patterns of root turnover time is far from clear. Location: Global. Time period: 1946–2017. Major taxa studied: Grasslands. Methods: We compiled a database of 141 sites with 433 observations on root turnover time and applied structural equation modelling (SEM) to investigate the relative contribution of climate, soil properties, and vegetation type to the observed variations in root turnover time. Results: Root turnover time was 3.1 years on average across the global grasslands and differed significantly among grassland types (tropical grassland & savanna, temperate grassland & meadow, alpine grassland & meadow, tundra, and desert). It decreased with mean annual temperature, mean annual precipitation, and Palmer Drought Severity Index but increased with soil organic carbon content, total nitrogen content, and carbon: nitrogen ratio. Soil bulk density and soil texture also significantly affected root turnover time, with clay content negatively correlating to root turnover time and explaining more variations than bulk density and sand content. The SEM showed that climatic factors had dominant effects on root turnover time when vegetation type was not considered. Vegetation type became the primary driver when it was included in the SEM. Main conclusions: Our results highlight that the influences of climatic and edaphic factors on root turnover time are predominantly manifested through vegetation type. The critical role of precipitation as revealed for the first time in this study challenges our current understanding of climate impacts on root turnover time. The findings necessitate accurate representation of vegetation type in Earth system models to predict root function dynamics under global change.

摘要：研究目的：根系周转是调控陆地生态系统碳循环与养分循环的核心过程。已有研究证实，根系周转受气候、土壤及生物因子共同调控，但上述因子对全球尺度根系周转时间格局的相对重要性仍未明确。研究区域：全球。时间跨度：1946–2017年。研究类群：草地生态系统。研究方法：本研究整合了覆盖141个样点、共计433条根系周转时间观测数据的数据库，并采用结构方程模型（Structural Equation Modelling, SEM），探究气候因子、土壤属性与植被类型对根系周转时间变异的相对贡献。研究结果：全球草地生态系统的根系周转时间平均为3.1年，且在不同草地类型间存在显著差异，包括热带草原与稀树草原、温带草原与草甸、高寒草原与草甸、冻原以及荒漠。根系周转时间随年平均气温、年平均降水量及帕尔默干旱严重指数（Palmer Drought Severity Index）的升高而降低，但随土壤有机碳含量、全氮含量以及碳氮比的升高而升高。土壤容重与土壤质地同样对根系周转时间存在显著影响：黏粒含量与根系周转时间呈负相关，且其对周转时间变异的解释度高于土壤容重与砂粒含量。结构方程模型结果显示，当未纳入植被类型时，气候因子对根系周转时间起主导调控作用；当模型纳入植被类型后，植被类型则成为首要驱动因子。主要结论：本研究结果表明，气候与土壤因子对根系周转时间的影响主要通过植被类型实现。本研究首次揭示了降水的关键调控作用，这一发现挑战了当前学界对气候因子调控根系周转时间的认知。研究结果提示，在地球系统模型（Earth System Models）中准确表征植被类型，是精准预测全球变化背景下根系功能动态的必要前提。