In warming climates, soil water content (SWC) may act as an important factor in determining belowground carbon dynamics in boreal forests. Here, we estimated the respiration and nonstructural carbohydrate (NSC) concentrations of tree roots in a mature Scots pine (Pinus sylvestris L.) stand in southern Finland during two growing seasons with contrasting weather conditions. Root respiration was estimated with four different methods: 1) incubating excised roots, 2) partitioning forest floor respirations with root exclusion, or 3) based on temperature response functions and 4) modelling with the whole-tree carbon model ‘CASSIA’. In addition, we conducted a drought experiment in a greenhouse to determine the effect of reduced soil-water availability on respiration by incubating soil and roots of Scots pine saplings.

We observed that the respiration of incubated roots of Scots pine saplings and soil decreased with drying after excluding the effect of temperature on respiration (R_RES), soil being more sensitive to drought than roots. Similarly, R_RES of incubated roots in the field was significantly decreased by lowered SWC, whereas respiration of the entire root system estimated with other methods was clearly higher in dryer and warmer than moister and cooler year. Nevertheless, incubated roots excavated from the topsoil are most affected by drying soil, which might not reflect the response of the entire root system. R_RES of incubated roots was negatively associated with root fructose and glucose concentrations. At the same time, root fructose, glucose and sucrose concentrations were negatively associated with SWC due to their role in osmoregulation. Thereby it seems that R_RES does not directly follow the changes in NSCs despite the apparent correlation. Our study highlights the responsive nature of root carbon dynamics in varying weather events that should be taken into account in estimating and modelling the impacts of warming climate.

在气候变暖的情况下，土壤含水量 (SWC) 可能是确定北方森林地下碳动态的重要因素。在这里，我们估计了成熟的苏格兰松 ( Pinus sylvestris ) 中树根的呼吸和非结构性碳水化合物 (NSC) 浓度L.) 位于芬兰南部的两个生长季节，天气条件截然不同。用四种不同的方法估计根呼吸：1) 培养切除的根，2) 用根排斥划分森林地面呼吸，或 3) 基于温度响应函数和 4) 用全树碳模型“CASSIA”建模。此外，我们在温室中进行了一项干旱实验，通过培育苏格兰松树树苗的土壤和根部来确定土壤水分可用性降低对呼吸的影响。

_{我们观察到，在排除温度对呼吸的影响（R RES} ）后，苏格兰松树苗和土壤的孵化根和土壤的呼吸随着干燥而降低，土壤比根对干旱更敏感。类似地，田间培养根的 R _RES因降低 SWC 显着降低，而用其他方法估计的整个根系的呼吸在干燥和温暖的年份明显高于潮湿和凉爽的年份。然而，从表土中挖出的孵化根受干燥土壤的影响最大，这可能无法反映整个根系的反应。R _RES培养根的数量与根果糖和葡萄糖浓度呈负相关。同时，根果糖、葡萄糖和蔗糖浓度与 SWC 负相关，因为它们在渗透压调节中起作用。因此，尽管存在明显的相关性，但似乎 R _RES并不直接跟随 NSC 的变化。我们的研究强调了根系碳动力学在不同天气事件中的响应性质，在估计和模拟气候变暖的影响时应考虑到这些性质。