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增加。因此，树木必须适应新的气候条件。我们研究了年轻的白桦树（Betula pendula罗斯（Roth）在一项长期（2012-2018）的自由空气湿度操纵实验中，目的是弄清提高相对大气湿度的适应机制。在2016-2018年期间，监测了茎的径向增量（通过树突仪测量）和叶片的脱落，并确定了叶片的氮和磷吸收效率。估计了生物量分配，并评估了叶面氮磷钾储量的季节动态。加湿使氮吸收效率提高了11％。对照中的氮吸收效率的年均值在对照中为41％至52％，在潮湿的林地中为50％至59％。磷的吸收效率受天气条件的影响很大，并且在25％到66％之间变化。在生长季结束时，较高的叶面NPK贮藏量和延迟的叶片落落延长了潮湿地块的生长期，导致茎radial骨生长延长了一周。尽管加湿桦树的茎径增长在5年后恢复，但树高迟缓现象持续了七个研究年，导致加湿条件下茎锥度（直径与高度之比）增加。另外，加湿增加了树皮在茎生物量中的份额以及每树冠长度的分支数量。白桦树适应空气湿度的增加需要改变森林的氮循环和桦木木材的质量。加湿增加了树皮在茎生物量中的份额以及每树冠长度的分支数量。白桦树适应空气湿度的增加需要改变森林的氮循环和桦木木材的质量。加湿增加了树皮在茎生物量中的份额以及每树冠长度的分支数量。白桦树适应空气湿度的增加需要改变森林的氮循环和桦木木材的质量。