Data Sheet 1_Technical note: methodological choices influence root carbon exudation measurements.pdf

Root exudation is an important pathway of belowground carbon (C) allocation in forest ecosystems, with profound implications for soil processes, nutrient cycling, and ecosystem functioning. Despite its importance, quantifying root exudation from mature trees in situ remains technically challenging, and methodological inconsistencies among studies hinder synthesis and upscaling. In this technical note, we systematically evaluated how variations in commonly used exudate collection protocols influence measured C fluxes. Specifically, we tested the effects of root resting, trap moisture, and trap solution composition on exudation rates in two contrasting biomes: a temperate forest in Germany and a Mediterranean forest in Israel. By incorporating both inter- and intraspecific root combinations, we also accounted for potential species interaction effects. Our results reveal several methodological sensitivities. Omitting a root-resting phase can streamline sampling without compromising measurements. Moisture conditions within cuvettes strongly influenced flux estimates, with saturated traps yielding up to six-times higher values than moist traps. Root exudation was further affected by trap solution composition, with initially increased exudation under P-deficient solutions in both biomes. Roots showed an adaptive response to the syringe environment, particularly to differences in trap-solution composition and moisture conditions; with effects partially diminishing after 48 hrs when a second flush was collected. However, the magnitude and direction of these responses differed between biomes. Within our experimental framework, first-flush sampling using a standard trap solution provided the most consistent basis for cross-biome comparison of root exudation fluxes. Species mixing had no detectable effect on exudation rates. Together, these findings emphasize that methodological variation can substantially alter root exudation C flux rates. Standardized approaches – or, at a minimum, transparent and detailed reporting – are essential to improve comparability across studies. Addressing methodological challenges will allow more accurate quantification of root exudation, strengthen its integration into terrestrial C models, and ultimately refine our understanding of belowground C allocation under global change.根系分泌物分泌（root exudation）是森林生态系统地下碳（C）分配的重要途径，对土壤过程、养分循环及生态系统功能具有深远影响。尽管其重要性不言而喻，但原位定量成熟树木的根系分泌物分泌仍面临技术瓶颈，且不同研究间的方法学差异阻碍了研究结果的综合与外推。在本技术简报中，我们系统评估了常用分泌物收集方案的变异对测得碳通量的影响。具体而言，我们在两种截然不同的生物群落——德国温带森林与以色列地中海森林——中，测试了根系静置期、采集阱湿度及采集液组成对根系分泌速率的影响。通过纳入种间与种内根系组合，我们同时考量了潜在的物种互作效应。本研究结果揭示了多项方法学敏感性特征。省略根系静置期可简化采样流程且不会影响测定结果。采集容器内的湿度条件对通量估算具有显著影响：饱和采集阱的测得值最高可达湿润采集阱的6倍。采集液组成同样会影响根系分泌物分泌：在两种生物群落中，缺磷溶液条件下的初始分泌速率均有所提升。根系对采集装置环境表现出适应性响应，尤其对采集液组成与湿度差异的响应显著；在采集第二次淋洗液时，这些效应在48小时后会部分减弱。不过，这些响应的强度与方向在不同生物群落间存在差异。在本实验框架内，采用标准采集液进行第一次淋洗采样，是开展跨生物群落根系分泌物碳通量比较的最可靠一致的基准。物种混合对根系分泌速率无显著可检测影响。综上，本研究结果表明，方法学差异可显著改变根系分泌物碳通量的测定结果。标准化的实验方法——或至少做到透明且详细的方法报告——对提升不同研究间的可比性至关重要。解决方法学难题，将有助于更精准地定量根系分泌物分泌，加强其在陆地碳模型中的整合应用，并最终深化我们对全球变化背景下地下碳分配的认知。