Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest
Tree growth and soil acidification in response to 30 years of experimental nitrogen loading on boreal forest
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DOI：
10.1111/j.1365-2486.2006.01102.x
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发表时间：
2006-03-01
影响因子：
11.6
通讯作者：
Tamm, CO
中科院分区：
文献类型：
--
作者：
Högberg, P;Fan, HB;Tamm, CO
氮素负荷、土壤酸化和森林生长之间的关系已根据短期(15年)试验或跨氮沉积梯度的调查进行了评估，调查还可能包括土壤条件和其他污染物的变化，这混淆了对氮本身影响的解释。我们报告了一项对树木和土壤的影响，这是一项独特的长期(30年)实验，在一片未受污染的北方森林中进行年度氮素负荷。在重复(N=3)的0.09公顷小区中，分别添加34和68 kg N ha(-1)yr(-1)的N1和N 2两种剂量。第三个治疗，N3,108千克Nha(-1)Yr(-1)，在20年后终止，允许在10年内评估恢复情况。树木的生长最初对所有N处理都是积极的，但长期的反应是高度依赖于速率的，在N3没有增加，在N2增加了50m(3)ha(-1)树干，在N1比对照(N0)增加了100m(3)ha(-1)。高N处理导致矿质土壤交换性盐基阳离子(Ca~(2+)、Mg~(2+)、K~+)损失高达70%，pH降低，交换性Al~(3+)增加。相比之下，施N处理小区的有机质表层(森林地面)每公顷交换性盐基阳离子含量与N0处理相似。施N的地块中，镁的含量甚至更高，这提供了树木从矿质土壤中向上抬升的证据。树木生长与土壤钙铝比(土壤酸度对树木生长影响的预测因子)无关。施氮处理的小区出现缺硼现象，但在早期已得到纠正。施N处理的土壤和矿质土壤中可提取态NH4+和NO(3)(-)含量较高，而NH4+只在N3小区的MOR中升高。N3处理停止施氮10年后，矿质土pH值显著升高，土壤碱基状况和叶片中盐基离子浓度也有升高的趋势。我们的数据表明，去除N-负荷后，土壤化学性质的恢复，特别是pH，可能比预期的更快。我们的长期试验证明了施氮量相对于施氮量的基本重要性，特别是在树木生长和碳固存方面。因此，短期内添加高剂量N的实验并不能模拟较低速率下N沉积的长期影响。
Relations among nitrogen load, soil acidification and forest growth have been evaluated based on short-term (< 15 years) experiments, or on surveys across gradients of N deposition that may also include variations in edaphic conditions and other pollutants, which confound the interpretation of effects of N per se. We report effects on trees and soils in a uniquely long-term (30 years) experiment with annual N loading on an un-polluted boreal forest. Ammonium nitrate was added to replicated (N=3) 0.09 ha plots at two doses, N1 and N2, 34 and 68 kg N ha(-1) yr(-1), respectively. A third treatment, N3, 108 kg N ha(-1) yr(-1), was terminated after 20 years, allowing assessment of recovery during 10 years. Tree growth initially responded positively to all N treatments, but the longer term response was highly rate dependent with no gain in N3, a gain of 50 m(3) ha(-1) stemwood in N2 and a gain of 100 m(3) ha(-1) stemwood in excess of the control (N0) in N1. High N treatments caused losses of up to 70% of exchangeable base cations (Ca2+, Mg2+, K+) in the mineral soil, along with decreases in pH and increases in exchangeable Al3+. In contrast, the organic mor-layer (forest floor) in the N-treated plots had similar amounts per hectare of exchangeable base cations as in the N0 treatment. Magnesium was even higher in the mor of N-treated plots, providing evidence of up-lift by the trees from the mineral soil. Tree growth did not correlate with the soil Ca/Al ratio (a suggested predictor of effects of soil acidity on tree growth). A boron deficiency occurred on N-treated plots, but was corrected at an early stage. Extractable NH4+ and NO(3)(-)were high in mor and mineral soils of on-going N treatments, while NH4+ was elevated in the mor only in N3 plots. Ten years after termination of N addition in the N3 treatment, the pH had increased significantly in the mineral soil; there were also tendencies of higher soil base status and concentrations of base cations in the foliage. Our data suggest the recovery of soil chemical properties, notably pH, may be quicker after removal of the N-load than predicted. Our long-term experiment demonstrated the fundamental importance of the rate of N application relative to the total amount of N applied, in particular with regard to tree growth and C sequestration. Hence, experiments adding high doses of N over short periods do not mimic the long-term effects of N deposition at lower rates.