Apportionment study of calcium nutrition of boreal tree species

本研究的目的是评估钙营养在北方森林树木生长中的作用。密集的森林采伐措施可能有利于增加生态系统中钙的出口，以至于钙可能在氮素之前限制在树木中。空气污染加剧，伴随而来的是雨水酸度的增加和钙的淋失，这只会加剧其出口。因此，有人提出，如果出口的钙超过自然或通过施肥增加的钙，则空气污染和/或北方商业森林的叶钙缺乏和随后的健康问题/生长下降将会发生。这些森林生长在质地粗糙的酸性土壤上，土壤矿物风化缓慢地释放出钙，因此，树木中的钙是那些因风化而被动员到土壤溶液中的钙的范式受到了挑战，研究表明，在一些生态系统中，大气中的钙对树木的贡献非常大，而且树木几乎完全与深层土壤来源的钙脱钩。因此，未来五年的目标将是确定加拿大和斯堪的纳维亚北部具有不同功能特征的树种在土壤矿物风化和利用释放的钙方面的能力，这些树种在有效性低和/或竞争激烈(缺乏)时利用释放的钙。申请者的计划是利用碱土元素比率和锶同位素作为示踪剂来调查钙营养。树种将在生长室和田间沿着土壤肥力、植物竞争和生产力的梯度进行研究。然后，结果将被用来寻找最佳的钙供应和树木生长指标，并在景观生产力模型中实施，永久立地变量(例如，气候和排水)和氮素作为驱动变量。从森林管理的角度来看，这些指标很重要，因为它们将使科学家和森林管理人员能够更好地预测林木生长速度，从而更好地规划森林利用。从长远来看，这项研究将有助于确定一些林分是否对钙的出口敏感，以及这些森林的完整性是否因采伐而受到威胁。

The goal of this research is to assess the role of calcium (Ca) nutrition on tree growth in boreal forests. Intense forest harvesting practices may favor increased exports of Ca from the ecosystem to a point that Ca may become limiting to trees before nitrogen. Increased air pollution with a concomitant increase in rain acidity and leaching of Ca will only exacerbate its export. It has therefore been suggested that foliar Ca deficiencies and subsequent health problems/growth declines will occur in air polluted and/or commercial boreal forests if Ca exports are in excess of those added naturally or by fertilization. These forests grow on coarse-textured acidic soils that slowly release Ca from soil mineral weathering and thus, the paradigm that the Ca in trees are those mobilized into the soil solution from weathering is being challenged by studies showing that contributions of atmospherically derived Ca to the trees in some ecosystems is very large and that the trees are almost fully decoupled from Ca coming from deeper soil sources. The next five years will therefore aim at determining the capacity of Canadian and Scandinavian boreal tree species with different functional traits to promote soil mineral weathering and make use of the released Ca when availability is low and/or being intensely competed for (deficient). The applicant's plan is to investigate Ca nutrition by using alkali earth element ratios and strontium isotopes as tracers. Tree species will be studied in growth chambers and in the field along gradients of soil fertility, plant competition, and productivity. The results will then be used to find the best indicators of Ca supply and tree growth and implement them in landscape productivity models with permanent site variables (e.g., climate and drainage) and nitrogen as driver variables. These indicators are important from a forest management perspective as they will allow scientists and forest managers to better forecast growth rates of forest stands and therefore, make better planning of forest utilization. In the long term, this research will help identify if some stands are sensitive to exports in Ca and whether the integrity of these forests is jeopardized by harvesting.