Predicted climate changings can affect hemi-boreal forests especially for soil conditions with low water-holding capacity and susceptibility to soil water deficits. In our study, species-specific sap flux, transpiration and water use efficiency of growth (WUE) were investigated at a mixed hemi-boreal forest ecosystems, especially during temporary moderate dry periods in the main growing season. Therefore, two representative forest sites with different drought susceptibility were selected in Northwest-Lithuania. The aim of our investigations was to identify the responsible factors influencing transpiration and WUE from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L. H. Karst.) and birch (silver birch: Betula pendula Roth. and downy birch: B. pubescens Ehrh.) during temporary drought incidents at a water-limited, oligitrophic sand dominated forest site and at a water saturated, mesoeutrophic organic peat forest site for the whole vegetation period and two moderate short-term drought incidents in 2016. During the dry periods Norway spruce trees exhibited lowest sap flux compared to Scot pine and birch while similarly showing highest WUE. Up-scaled to a virtual pure stand none of the species were differing in species specific transpiration. Thus, we found no evidence for extended drought sensitivity of Norway spruce at the water limited site during the first investigation year. Sap flux of Scots pine trees was more or less constantly high during the main growing season and the dry periods at both plots, while WUE was quite low during the “dry periods”. Thus, we assume that Scots pine trees are less affected by temporarily drought events than Norway spruce. Birch trees exhibited significantly highest sap flux during dry periods at the water limited site whereas quite low WUE was not differing between sites. Thus, birch may compete with Scots pine trees at the study sites in terms of water consumption and growth in future.

中文翻译：

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松树、云杉和桦树的特定树液通量、蒸腾作用和水分利用效率对半北方地区干湿林地混交林中暂时缓和干旱期的响应

预测的气候变化会影响半北方森林，特别是对于保水能力低且对土壤水分亏缺敏感的土壤条件。在我们的研究中，在混合的半北方森林生态系统中研究了特定物种的树液通量、蒸腾作用和水分利用效率 (WUE)，特别是在主要生长季节的临时中等干旱期。因此，在立陶宛西北部选择了两个具有不同干旱敏感性的代表性森林地点。我们调查的目的是确定影响苏格兰松 (Pinus sylvestris L.)、挪威云杉 (Picea abies LH Karst.) 和桦木（银桦：Betula pendula Roth. 和绒毛桦：B. pubescens Ehrh.) 在限水的临时干旱事件期间，在整个植被时期和 2016 年的两次中度短期干旱事件中，贫营养沙占主导的森林场地和水饱和的中富营养有机泥炭森林场地。在干旱时期，与苏格兰松树和桦树相比，挪威云杉树的树液通量最低，而同样显示最高的 WUE。放大到一个虚拟的纯林地，没有一个物种在物种特定的蒸腾作用上有所不同。因此，在第一个调查年期间，我们在限水地点没有发现挪威云杉长期干旱敏感性的证据。在两个地块的主要生长季节和干旱期，苏格兰松树的树液通量或多或少一直处于较高水平，而在“干旱期”期间，WUE 相当低。因此，我们假设与挪威云杉相比，苏格兰松树受临时干旱事件的影响较小。白桦树在缺水地点的干旱时期表现出显着最高的树液通量，而相当低的 WUE 在地点之间没有差异。因此，在未来的耗水量和生长方面，桦树可能会与研究地点的苏格兰松树竞争。