Ecosystem N Distribution and δ15N during a Century of Forest Regrowth after Agricultural Abandonment
Ecosystem N Distribution and δ15N during a Century of Forest Regrowth after Agricultural Abandonment
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DOI：
10.1007/s10021-007-9087-y
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发表时间：
2007-09
期刊：
影响因子：
3.7
通讯作者：
J. Compton;T. D. Hooker;S. Perakis
中科院分区：
文献类型：
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作者：
J. Compton;T. D. Hooker;S. Perakis
陆地生态系统氮(N)库稳定的同位素比值反映了陆地生态系统氮的内部过程和投入产出平衡。干扰一般会增加N的循环和损失，但很少有研究在干扰-恢复序列上研究生态系统δ15N。采用时序法研究了农业弃耕后森林再生长过程中N的分布和δ-15N。立地年龄从10年到1150年不等，具有相似的土壤、气候、土地利用历史和覆盖植被(白松)。叶片N和δ15N随着林分年龄的增长而减少，这与农田森林再生期间N循环的逐渐收紧相一致。随着时间的推移，叶片δ15N变得更负，表明沿矿化-菌根-植物吸收途径的分馏增加。生态系统总氮在整个时间序列中保持不变，但在115a的时间里，从矿物土壤到植物和凋落物发生了大量的内部N再分配(占生态系统N的25%或1,610公斤/公顷−1)。土壤δ~(15)N的时间趋势总体上反映了矿质土壤向发育中O层的贫化N的重新分配。尽管植物和土壤δ15N在生态系统发展的千年时间尺度上是耦合的，但我们观察到的植物和土壤之间的差异表明，在干扰-再生长序列中，它们可以解耦。在百年尺度上，生态系统δ15N大约减少了2‰，这意味着大气N的显著吸收，这是传统的生态系统N核算所没有检测到的。考虑时间趋势和干扰遗产可以提高我们对气候或N沉积等更广泛因素对生态系统N平衡和δ15N的影响的理解。
AbstractStable isotope ratios of terrestrial ecosystem nitrogen (N) pools reflect internal processes and input–output balances. Disturbance generally increases N cycling and loss, yet few studies have examined ecosystem δ15N over a disturbance-recovery sequence. We used a chronosequence approach to examine N distribution and δ15N during forest regrowth after agricultural abandonment. Site ages ranged from 10 to 115 years, with similar soils, climate, land-use history, and overstory vegetation (white pinePinus strobus). Foliar N and δ15N decreased as stands aged, consistent with a progressive tightening of the N cycle during forest regrowth on agricultural lands. Over time, foliar δ15N became more negative, indicating increased fractionation along the mineralization–mycorrhizal–plant uptake pathway. Total ecosystem N was constant across the chronosequence, but substantial internal N redistribution occurred from the mineral soil to plants and litter over 115 years (>25% of ecosystem N or 1,610 kg ha−1). Temporal trends in soil δ15N generally reflected a redistribution of depleted N from the mineral soil to the developing O horizon. Although plants and soil δ15N are coupled over millennial time scales of ecosystem development, our observed divergence between plants and soil suggests that they can be uncoupled during the disturbance-regrowth sequence. The approximate 2‰ decrease in ecosystem δ15N over the century scale suggests significant incorporation of atmospheric N, which was not detected by traditional ecosystem N accounting. Consideration of temporal trends and disturbance legacies can improve our understanding of the influence of broader factors such as climate or N deposition on ecosystem N balances and δ15N.