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Post‐disturbance conifer tree‐ring δ15N reflects openness of the nitrogen cycle across temperate coastal rainforests
Journal of Ecology ( IF 5.3 ) Pub Date : 2020-07-31 , DOI: 10.1111/1365-2745.13482 J.M. Kranabetter 1 , K. McKeown 2 , B.J. Hawkins 2
中文翻译：
扰动后的针叶树环δ15N反映了温带沿海雨林中氮循环的开放性
更新日期：2020-07-31
Journal of Ecology ( IF 5.3 ) Pub Date : 2020-07-31 , DOI: 10.1111/1365-2745.13482 J.M. Kranabetter 1 , K. McKeown 2 , B.J. Hawkins 2
Affiliation
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- Post‐disturbance losses in nitrogen (N) may diminish forest productivity, and soils with inherently ‘open’ N cycles are considered the most vulnerable to leaching losses of
. Monitoring ongoing N depletion from soil profiles is challenging, but tree‐ring δ15N of regenerating stands may offer an effective method for assessing site‐specific, long‐term soil N dynamics. Evidence to date is mixed, however, and includes increasing, unchanging or decreasing tree‐ring δ15N in young stands following stand‐level disturbances, possibly because of contrasting soil N availability among study sites. In addition, a consensus on post‐disturbance N trajectories is hampered by the inconsistent patterns in tree‐ring δ15N found between tree species of differing mycorrhizal association. - We compared tree‐ring δ15N of two conifer species (Picea sitchensis with ectomycorrhizal fungi and Thuja plicata with arbuscular mycorrhiza) from a replicated silviculture trial across temperate rainforests of Vancouver Island (Canada). A natural gradient in soil N status across the six sites, driven largely by topography and parent materials, was demonstrated by in situ increases in N mineralization and nitrification rates with declining C:N ratios for both organic horizons and mineral soils.
- Five decades after timber harvest, the overall trend in tree‐ring δ15N was positive, indicating a loss of nitrate from the system, but among individual plots the slope of δ15N ranged from nearly 0 to 0.13. We found the gains in tree‐ring δ15N with time were consistent between mycorrhizal types and escalated (up to 6‰) with increasing N mineralization, although less so on flat terrain with seasonal water tables. The most recent sapwood was also enriched in 15N on soils with higher N mineralization rates, perhaps slightly more so for T. plicata than P. sitchensis.
- Synthesis. The alignment of tree‐ring δ15N with soil N cycles may be especially strong in regenerating forests because of ontogeny effects, including the expansion of rooting depth and increases in N resorption efficiency with stand age. Sharp increases in tree‐ring δ15N underscore the vulnerability of low C:N soils with open N cycles to post‐disturbance N losses, and highlight how multiple, frequent harvesting cycles may risk substantial N depletion from these productive rainforest ecosystems.
中文翻译：
扰动后的针叶树环δ15N反映了温带沿海雨林中氮循环的开放性
- 扰动后氮（N）的损失可能会降低森林的生产力，并且具有固有“开放” N循环的土壤被认为最容易遭受淋溶损失。从土壤剖面监测正在进行ň枯竭的挑战，但年轮δ 15再生看台的N可提供用于评估特定地点，长期土壤氮动态的有效方法。迄今为止的证据是混合的，但是，包括增加，不变或减少树木年轮δ 15中幼林下待机水平紊乱N，对比研究站点间土壤氮可用性可能是因为。另外，关于后扰动Ñ轨迹的共识是由不一致的图案阻碍了树轮δ 15在不同菌根联系的树种之间发现N。
- 我们比较了树轮δ 15两个针叶树种N（北美云杉与外生菌根真菌与美西侧柏与丛枝菌根）来自全国各地温哥华岛（加拿大）的温带雨林复制的造林试验。六个地点土壤氮状况的自然梯度主要是由地形和母体材料驱动的，这通过有机矿层和矿质土壤中氮矿化率和硝化率的原位增加以及C：N比下降而得到证明。
- 五个十年的木材采伐后，在树木年轮的总体趋势δ 15 n为正，表明从系统中硝酸盐的损失，但个别地块中的δ坡度15 n的几乎为0范围到0.13。我们发现在树环增益δ 15 n，其中时间分别为菌根类型之间是一致的和升级（最多6‰）随氮的矿化，虽然少等季节性地下水位平坦的地形。在边际氮矿化率更高的土壤中，最新的边材还富集了15 N，也许对于T而言略多。蚌比P。西加。
- 综合。树轮的δ对准15 n，其中土壤N周期可以是在再生的个体发育因为影响森林，包括与支架年龄生根深度和增加的N再吸收效率的膨胀特别强。夏普增加树木年轮δ 15 ň下划线低C的漏洞：N的土壤开N个周期后扰动氮素损失，并突出如何多，频繁的收获周期可以从这些富有成效的热带雨林生态系统的风险大幅ñ枯竭。
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