Institute of Ecology and Earth Sciences, University of Tartu, Lai 40, 51005, Tartu, Estonia.
Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Kreutzwaldi 5, 51006, Tartu, Estonia.
Oecologia. 2020 Jun;193(2):449-460. doi: 10.1007/s00442-020-04688-8. Epub 2020 Jun 17.
Climate models predict increasing amounts of precipitation and relative atmospheric humidity for high latitudes in the Northern Hemisphere. Therefore, tree species must adjust to the new climatic conditions. We studied young silver birches (Betula pendula Roth) in a long-term (2012-2018) free air humidity manipulation experiment, with the aim of clarifying the acclimation mechanisms to elevated relative atmospheric humidity. In 2016-2018, stem radial increment (measured by dendrometers) and leaf abscission were monitored, and the leaf N and P resorption efficiencies were determined. Biomass allocation was estimated, and the seasonal dynamics of foliar NPK storage was assessed. Humidification increased N resorption efficiency by 11%. The annual means of N resorption efficiency varied from 41 to 52% in control and from 50 to 59% in humidified stands. The P resorption efficiency was strongly affected by weather conditions and varied between years from 25 to 66%. Higher foliar NPK storages at the end of growing season and delayed leaf fall allowed to extend the growth period in humidified plots, which resulted in a week longer stem radial growth. Although stem diameter growth of humidified birches recovered after 5 years, tree height retardation persisted over the seven study years, resulting in increased stem taper (diameter to height ratio) under humidification. Additionally, humidification increased the share of the bark in stem biomass and the number of branches per crown length. The acclimation of silver birches to increased air humidity entails changes in forest N cycle and in birch timber quality.
气候模型预测，北半球高纬度地区的降水量和相对大气湿度将会增加。因此，树种必须适应新的气候条件。我们在一个长期（2012-2018 年）的自由空气湿度控制实验中研究了年轻的银桦（Betula pendula Roth），旨在阐明适应高相对大气湿度的适应机制。在 2016-2018 年，监测了茎的径向增量（通过树木测高计测量）和叶片脱落，并确定了叶片氮和磷的再吸收效率。估计了生物量分配，并评估了叶片 NPK 储存的季节性动态。增湿使氮再吸收效率提高了 11%。对照和增湿林中氮再吸收效率的年平均值分别在 41-52%和 50-59%之间变化。磷再吸收效率受天气条件的强烈影响，每年在 25-66%之间变化。生长季末较高的叶片 NPK 储存和延迟的叶片脱落，使增湿区的生长时间延长，导致茎的径向生长延长一周。尽管增湿桦木的茎直径生长在 5 年后恢复，但树高的延迟在七年的研究中仍持续存在，导致增湿下树干的锥度（直径与高度的比值）增加。此外，增湿增加了树皮在树干生物量中的份额和树冠长度上的树枝数量。银桦对空气湿度增加的适应需要改变森林氮循环和桦木木材质量。
