Abstract High resolution measurements of trunk diameter fluctuations (TDF) provide a means to study short-term and long-term stem radial variations and response to water stress of fruit trees. There is a lack of information, however, on the performance of TDF measurements on fast-growing poplar trees. To both clarify the intra-annual and inter-annual growth patterns and to diagnose water status of young poplar trees, we monitored TDF, leaf area index, soil matric potential, midday stem water potential (Ψstem) and main meteorological variables in a plantation with 3- and 4-year-old Populus tomentosa trees over two growing seasons (2016 and 2017). We had two irrigation treatments, well-watered (WW) and water-stressed (WS). For the first time for this species, we identified accurately and quantitatively the seasonal growth pattern and associated parameters (growth initiation and cessation time, growing season duration, maximum growth rate, etc.) of young P. tomentosa with four clear stages, based on the growth rate for both treatments. We identified that stage II (mid-April to mid-June), when trees showed the most active growth rate and less rainfall was recorded, is the most crucial stage for irrigation management, especially as trees grow larger and have a greater water demand. In the two experimental years, irrigation did not affect the timing of growth initiation and cessation. However, maximum growth rate was significantly higher and occurred earlier in the WW trees than in the WS trees. From the tested trunk diameter fluctuation indicators, trunk growth rate (TGR) showed a greater potential for assessing tree water stress than both maximum daily shrinkage (MDS) and daily growth (DG), being even more sensitive to the onset of water stress than midday Ψstem. We conclude that high resolution trunk dendrometers are useful to track growth and determine water stress, which make them a good candidate to schedule irrigation in fast-growing poplar plantations.

中文翻译：

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基于快速生长毛白杨人工林树干直径波动的树木生长模式和水分状况诊断

摘要 树干直径波动 (TDF) 的高分辨率测量为研究短期和长期茎径向变化以及对果树水分胁迫的响应提供了一种手段。然而，缺乏关于快速生长的杨树的 TDF 测量性能的信息。为了阐明年内和年际生长模式并诊断杨树幼树的水分状况，我们监测了人工林的 TDF、叶面积指数、土壤基质势、中午茎水势 (Ψstem) 和主要气象变量两个生长季节（2016 年和 2017 年）的 3 年和 4 年生毛毛杨树。我们进行了两种灌溉处理，灌溉充足 (WW) 和缺水 (WS)。对于这个物种来说，这是第一次，我们根据两种处理的生长速率，准确、定量地确定了具有四个明确阶段的幼龄毛毛松的季节性生长模式和相关参数（生长开始和停止时间、生长季节持续时间、最大生长速率等）。我们确定第二阶段（4 月中旬至 6 月中旬），此时树木表现出最活跃的生长速度，记录的降雨量较少，是灌溉管理最关键的阶段，尤其是当树木长得更大且需水量更大时。在两个试验年中，灌溉不影响生长开始和停止的时间。然而，WW 树的最大生长速率明显高于 WS 树，并且发生得更早。从测试的树干直径波动指标来看，树干生长率 (TGR) 显示出比最大日收缩率 (MDS) 和日生长率 (DG) 更大的评估树木水分胁迫的潜力，对水分胁迫的发生甚至比中午 Ψstem 更敏感。我们得出结论，高分辨率树干测树仪可用于跟踪生长和确定水分胁迫，这使它们成为在快速生长的杨树人工林中安排灌溉的良好候选者。