Abstract Excavation within the root-zone of urban trees is increasing rapidly in compact cities for the installation and repair of belowground infrastructures, but research on excavation damages is mostly limited to the assessment of their effects on growth and dieback, while effects on physiology and long-term stability are still elusive. This experiment was aimed to understand long-term mechanisms of tree response to root severance. Two urban tree species (Aesculus hippocastanum and Tilia x europaea) were subjected to two different root damage intensities by digging either one, or two parallel (either side of the root flare) trenches. An equal number of trees were left undamaged as control. Shoot elongation and DBH growth were measured at the end of each growing season for four years after severance. Root system area was measured after the excavation and four years later. Leaf gas exchange, water relations, and chlorophyll fluorescence were assessed during the growing seasons over a 51-month period after severance. The effects on tree stability were evaluated 2 and 44 months after root severance by conducting pulling-tests and by calculating a theoretical uprooting resistance index based on the size of the root system. Results showed that, even at the most severe root damage treatments, which removed up to 70% of the root system, tree survival, growth and physiology were little affected. CO2 assimilation declined by 16%−25%, mostly due to stomatal limitations, as also supported by a 0.7%−1.9% decrease in the maximum quantum yield of PSII (Fv/Fm). Excavation reduced stem diameter growth rate by 16%−28% and shoot elongation by 30%−41%, compared to control. Although the disturbance to tree physiology induced by excavation had a moderate intensity, the ability to recover from such damage over a 51-month period was scarce, particularly in Aesculus. Results indicate that root damage acts as a predisposing factor which reduces in the long term the capacity of trees to withstand co-occurring stresses by decreasing carbon availability for growth and defence. Similarly, the ability of trees to withstand uprooting was reduced by excavation, and no full recovery occurred in the following 44 months, when uprooting resistance was still 20%–66% lower in damaged plants compared to control, depending on the severity of the damage. A strong correlation (R2 = 0.822) was found between results of the pulling test and the uprooting resistance index. This study highlights the importance of integrating physiological parameters for a better prescription of tree preservation guidelines during excavation work.

中文翻译：

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在 51 个月内评估挖沟对两种城市树种的生长、生理和连根拔起抗性的影响

摘要 在紧凑型城市中，用于安装和维修地下基础设施的城市树木根区开挖正在迅速增加，但对开挖损害的研究大多仅限于评估其对生长和枯死的影响，而对生理和长期的影响。长期稳定性仍然难以捉摸。该实验旨在了解树木对根切断反应的长期机制。通过挖掘一个或两个平行（根耀斑的任一侧）沟槽，两种城市树种（Aesculus hippocastanum 和 Tilia x europaea）受到两种不同的根部损伤强度。相同数量的树木未受损作为对照。在切断后的四年内，在每个生长季节结束时测量枝条伸长率和 DBH 生长。在挖掘后和四年后测量根系面积。叶片气体交换、水分关系和叶绿素荧光在分离后 51 个月的生长季节进行了评估。在根部切断后 2 个月和 44 个月，通过进行拉拔试验和计算基于根系大小的理论拔根阻力指数来评估对树木稳定性的影响。结果表明，即使在最严重的根损伤处理中，去除了高达 70% 的根系，树木的存活、生长和生理也几乎没有受到影响。CO2 同化下降了 16%−25%，主要是由于气孔限制，PSII 的最大量子产率 (Fv/Fm) 下降了 0.7%−1.9%。挖掘使茎直径增长速度降低了 16%−28%，枝条伸长率降低了 30%−41%，与对照相比。尽管挖掘引起的树木生理干扰具有中等强度，但在 51 个月内从这种损害中恢复的能力很少，特别是在七叶树中。结果表明，根部损伤是一个诱发因素，从长远来看，它会通过减少用于生长和防御的碳可用性来降低树木承受同时发生的压力的能力。同样，开挖降低了树木承受连根拔起的能力，并且在接下来的 44 个月内没有完全恢复，此时受损植物的连根拔起抗力仍比对照低 20%–66%，具体取决于损坏的严重程度. 拉力测试结果与拔除阻力指数之间存在很强的相关性（R2 = 0.822）。