Natural abundance of 15N in forests across a nitrogen deposition gradient
Natural abundance of 15N in forests across a nitrogen deposition gradient
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DOI：
10.1016/s0378-1127(97)00121-7
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发表时间：
1998-02-01
影响因子：
3.7
通讯作者：
Sleep, D
中科院分区：
文献类型：
--
作者：
Emmett, BA;Kjonaas, OJ;Sleep, D
长期的大气氮沉降可以改变森林生态系统中氮素的内部循环速率，增加氮素淋失的幅度，因为在与氮素富集和氮素损失相关的各种转化中，氮素发生了有利于较轻的N-14的分馏。有人提出，植被的N-15信号可以为评估森林生态系统过去和现在的N状况提供一个有用的工具。在NITREX项目内，跨越欧洲氮沉积梯度的一系列针叶林提供了一个机会，以测试来自大气沉积的氮供应与大片地理区域内植被对土壤的相对N-15丰度之间的关系。地上和地下树木成分、四个深度的土壤、总体降水和/或穿透雨水以及土壤溶液或流出水的大多数增量(15)N值都在其他地方观察到的值范围内，除了少数显著的例外情况。如果不包括威尔士北部的Aber森林，乔木叶片相对于土层的增量(15)N富集量(或富集率)与穿透水中的氮素通量呈显著正相关。ABER现场异常高的浓缩系数表明，该地点的高N循环速率超过了从当前N沉积预测的速率。这归因于与其他地点相比，耕作和植树对阿伯尔相对富含N和粘土的矿物层的影响。土壤表层凋落物氮素通量和硝化速率等氮素循环内部速率参数与土壤肥力因子之间存在极显著的相关关系(P<；0.01)。氮素循环速率与三角洲(15)氮的富集率之间似乎有很强的联系，而不是氮的沉积或硝酸盐本身的淋失。这些结果证实了利用增量(15)氮浓缩因子来确定受氮沉积影响的地点的可能性。然而，应考虑其他立地特征和土地管理措施，这些因素也会影响土壤氮素动态和氮素循环。(C)1998年爱思唯尔科学公司。
Chronic atmospheric nitrogen deposition can alter the rate of internal nitrogen cycling and increase the magnitude of N leaching losses in forested ecosystems, As fractionation of nitrogen in favour of the lighter N-14 occurs during various transformations associated with N-enrichment and nitrogen loss, it has been proposed that the N-15 Signal of vegetation may provide a useful tool in evaluating the past and current N status of forested ecosystems. A series of coniferous forests across a European nitrogen deposition gradient within the NITREX project provided an opportunity to test the relationships between nitrogen supply from atmospheric deposition and the relative N-15-enrichment of vegetation to soil, across a large geographical area. Most delta(15)N values for above-and below-ground tree components, soil at four depths, bulk precipitation and/or throughfall water and soil solution or outflow water values were within those observed elsewhere except for a few notable exceptions. There was a significant positive relationship between the delta(15)N enrichment of the tree foliage relative to the soil horizons (or the enrichment factor), and nitrogen flux in the throughfall if Aber forest, N. Wales, was excluded from the regression analysis. An unusually high enrichment factor at the Aber site indicated that a the high rate of N cycling at the site was in excess of that predicted from current N deposition. This was attributed to the effect of ploughing and tree planting on the relatively N- and clay-rich mineral horizons at Aber compared to other sites. Highly significant relationships (P < 0.01) between enrichment factors and parameters describing internal rates of N cycling, such as litterfall N flux and nitrification rates in upper soil horizons, supported this conclusion. There appears to be a strong link between the rate of N cycling and the delta(15)N enrichment factor, rather than N deposition or nitrate leaching per se. These results confirm the potential use of the delta(15)N enrichment factor to identify sites influenced by nitrogen deposition. However, consideration should be taken of other site characteristics and land management practises which also influence soil N dynamics and N cycling. (C) 1998 Elsevier Science B.V.