The carbon isotopic composition of C₃ plant leaf tissue (δ¹³C_C3) provides insights into carbon cycling, climate, and vegetation at various spatiotemporal scales. By disentangling the competing influences of climatic and biological factors, modern δ¹³C_C3 calibrations can offer quantitative constraints on their applications. In this work, we examined the response of δ¹³C_C3 values to rainfall, temperature, and atmospheric CO₂ concentration (pCO₂) across wide range of ecosystem gradients. Towards this, we prepared a global database of bulk (δ¹³C_C3-Bulk, n = 737) and n-alkane (δ¹³C_C3-C29, n = 831) δ¹³C values from species-level C₃ plants for various plant functional types (PFTs). The δ¹³C_C3-Bulk and δ¹³C_C3-C29 values refer to carbon isotopic composition of total organic carbon and the C₂₉ homologue of n-alkanes in C₃ plant leaves, respectively. The PFTs were classified according to their leaf senescence (deciduous versus evergreen), seed cover (angiosperm versus gymnosperm), and growth forms (tree, shrub, herb, grass, forb, etc.). Though rainfall is commonly believed to be the major driver of the δ¹³C_C3 variability, our work demonstrated that, at the species level, it only influences δ¹³C_C3-Bulk values of evergreen shrubs (R² = 0.47, p < 0.05) and grasses (R² = 0.26, p < 0.05). Across a gradient from 251 to 398 ppm, pCO₂-effect is apparent only on the δ¹³C_C3-Bulk values of deciduous shrubs (R² = 0.32, p < 0.05), while δ¹³C_C3 values of other plant types are insensitive to low pCO₂ conditions. For the first time, we showed that both species-level δ¹³C_C3-Bulk and δ¹³C_C3-C29 values of many PFTs are affected by annual temperature. Our meta-analysis provided evidences for a weak yet significant temperature effect on the δ¹³C_C3 values of deciduous herbs (δ¹³C_C3-Bulk: R² = 0.18, p < 0.05; δ¹³C_C3-C29: R² = 0.11, p < 0.05) and evergreen angiosperm trees (δ¹³C_C3-Bulk: R² = 0.17, p < 0.05; δ¹³C_C3-C29: R² = 0.17, p < 0.05). We also observed that combined increase in annual rainfall and temperature can negatively drive the δ¹³C_C3 values of evergreen shrubs (δ¹³C_C3-Bulk: adjusted R² = 0.61, p < 0.05; δ¹³C_C3-C29: adjusted R² = 0.25, p < 0.05) and deciduous angiosperm trees (δ¹³C_C3-Bulk: adjusted R² = 0.32, p < 0.05; δ¹³C_C3-C29: adjusted R² = 0.38, p < 0.05), and δ¹³C_C3-Bulk values of grasses (adjusted R² = 0.61, p < 0.05). Overall, our results suggest the abiotic stressors (considered in this work) can explain 12–61% and 0–38% of the total variations in the δ¹³C_C3-Bulk and δ¹³C_C3-C29 values, respectively. We propose that using PFT-specific δ¹³C_C3 values-abiotic stressor relationship, instead of a generalized relationship that includes all types of C₃ plants, will add more certainty in paleoenvironment reconstructions and isotope-based PFT model preparation.

C ₃植物叶组织 (δ ¹³ C _C3 )的碳同位素组成提供了对不同时空尺度上的碳循环、气候和植被的见解。通过解开气候和生物因素的竞争影响，现代 δ ¹³ C _C3校准可以为其应用提供定量限制。在这项工作中，我们研究了 δ ¹³ C _C3值对降雨、温度和大气 CO ₂浓度 ( p CO ₂ )的响应，这些值在广泛的生态系统梯度范围内。为此，我们准备了一个全球批量数据库（δ ¹³ C_C3-Bulk , n  = 737) 和正烷烃 (δ ¹³ C _{C3 - C29} , n  = 831)不同植物功能类型 (PFT) 的物种水平 C ₃植物的δ ¹³ C 值。的δ ¹³ C ^ _C3-散装和δ ^13个Ç _{C3 - C29}值是指总的有机碳的碳同位素组成以及C ₂₉的同源物ñ -烷烃用C ₃分别种植叶子。PFTs 根据叶子衰老（落叶与常绿）、种子覆盖（被子植物与裸子植物）和生长形式（乔木、灌木、草本、草、杂草等）进行分类。尽管人们普遍认为降雨是 δ ¹³ C _C3变异的主要驱动因素，但我们的工作表明，在物种水平上，它仅影响常绿灌木的δ ¹³ C _C3-Bulk值（R ²  = 0.47，p  < 0.05 ) 和草 (R ²  = 0.26, p < 0.05)。在 251 到 398 ppm 的梯度范围内，p CO ₂ - 效应仅在 δ ¹³ C _C3-Bulk上很明显落叶灌木的 δ ¹³ C _C3值（R ²  = 0.32，p < 0.05），而其他植物类型的δ ¹³ C _C3值对低p CO ₂条件不敏感。我们首次表明，许多 PFT 的物种水平 δ ¹³ C _C3-Bulk和 δ ¹³ C _C3-C29值都受年温度的影响。我们的荟萃分析提供了证据，证明温度对落叶草本植物的 δ ¹³ C _C3值有微弱但显着的影响（δ ¹³ C _C3-Bulk : R ²  = 0.18, p  < 0.05; δ¹³ C _C3-C29 : R ²  = 0.11, p  < 0.05) 和常绿被子植物树 (δ ¹³ C _C3-Bulk : R ²  = 0.17, p < 0.05; δ ¹³ C _C3-C29 : R ²  = 0.17, p < 0.05）。我们还观察到，年降雨量和温度的综合增加会对常绿灌木的 δ ¹³ C _C3值产生负面影响（δ ¹³ C _C3-Bulk：调整后的 R ²  = 0.61，p  < 0.05；δ ¹³ C _C3-C29：调整后的 R ²  = 0.25，p < 0.05) 和落叶被子植物树（δ ¹³ C _C3-Bulk：调整后的 R ²  = 0.32，p  < 0.05；δ ¹³ C _C3-C29：调整后的 R ²  = 0.38，p < 0.05）和 δ ¹³ C _C3-Bul草的值（调整后的 R ²  = 0.61，p < 0.05）。总体而言，我们的结果表明，非生物压力因素（在本工作中考虑）可以分别解释 δ ¹³ C _C3-Bulk和 δ ¹³ C _C3-C29值总变化的 12-61% 和 0-38% 。我们建议使用 PFT 特定的 δ ¹³ C _C3价值-非生物应激源关系，而不是包括所有类型的 C ₃植物的广义关系，将在古环境重建和基于同位素的 PFT 模型制备中增加更多确定性。