Scots pine (Pinus sylvestris L.) is one of the most important conifers in Northern Europe. In boreal forests, over one-third of net primary production is allocated to roots. Pioneer roots expand the horizontal and vertical root systems and transport nutrients and water from belowground to aboveground. Fibrous roots, often colonized by mycorrhiza, emerge from the pioneer roots and absorb water and nutrients from the soil. In this study, we installed three flatbed scanners to detect the daily growth of both pioneer and fibrous roots of Scots pine during the growing season of 2018, a year with an unexpected summer drought in Southern Finland. The growth rate of both types of roots had a positive relationship with temperature. However, the relations between root elongation rate and soil moisture differed significantly between scanners and between root types indicating spatial heterogeneity in soil moisture. The pioneer roots were more tolerant to severe environmental conditions than the fibrous roots. The pioneer roots initiated elongation earlier and ceased it later than the fibrous roots. Elongation ended when the temperature dropped below the threshold temperature of 4 °C for pioneer roots and 6 °C for fibrous roots. During the summer drought, the fibrous roots halted root surface area growth at the beginning of the drought, but there was no drought effect on the pioneer roots over the same period. To compare the timing of root production and the aboveground organs’ production, we used the CASSIA model, which estimates the aboveground tree carbon dynamics. In this study, root growth started and ceased later than growth of aboveground organs. Pioneer roots accounted for 87% of total root productivity. We suggest that future carbon allocation models should separate the roots by root types (pioneer and fibrous), as their growth patterns are different and they have different reactions to changes in the soil environment.

中文翻译：

---

芬兰南部赤松 (Pinus sylvestris L.) 根系日常生长的温度和湿度依赖性


欧洲赤松（ Pinus sylvestris L.）是北欧最重要的针叶树之一。在北方森林中，超过三分之一的净初级生产力分配给根部。先锋根扩展了水平和垂直根系，并将养分和水分从地下输送到地上。须根通常被菌根定殖，从先锋根中出现并从土壤中吸收水分和养分。在这项研究中，我们安装了三台平板扫描仪来检测 2018 年生长季期间欧洲赤松先锋根和须根的每日生长情况，这一年芬兰南部出现了意外的夏季干旱。两种根系的生长速率均与温度呈正相关。然而，根伸长率与土壤湿度之间的关系在扫描仪之间和根类型之间存在显着差异，表明土壤湿度的空间异质性。先驱根比须根更能耐受恶劣的环境条件。先锋根比须根更早开始伸长，并且更晚停止伸长。当温度降至先锋根 4 °C 和须根 6 °C 的阈值温度以下时，伸长结束。在夏季干旱期间，须根在干旱开始时停止了根表面积的生长，但同期对先锋根没有干旱影响。为了比较根系生产和地上器官生产的时间，我们使用了 CASSIA 模型，该模型估计了地上树木的碳动态。在这项研究中，根生长的开始和停止晚于地上器官的生长。先锋根占总根生产力的87%。 我们建议未来的碳分配模型应按根类型（先锋根和纤维根）将根分开，因为它们的生长模式不同，并且对土壤环境变化有不同的反应。