Data from: Potential contributions of root decomposition to the nitrogen cycle in arctic forest and tundra

1. Plant contributions to the nitrogen (N) cycle from decomposition are likely to be altered by vegetation shifts associated with climate change. Roots account for the majority of soil organic matter input from vegetation, but little is known about differences between vegetation types in their root contributions to nutrient cycling. Here, we examine the potential contribution of fine roots to the N cycle in forest and tundra to gain insight into belowground consequences of the widely-observed increase in woody vegetation that accompanies climate change in the Arctic. 2. We combined measurements of root production from minirhizotron images with tissue analysis of roots from differing root diameter and colour classes to obtain potential N input following decomposition. In addition, we tested for changes in N concentration of roots during early stages of decomposition, and investigated whether vegetation type (forest or tundra) affected changes in tissue N concentration during decomposition. For completeness, we also present respective measurements of leaves. 3. The potential N input from roots was two-fold greater in forest than in tundra, mainly due to greater root production in forest. Potential N input varied with root diameter and colour but this variation tended to be similar in forest and tundra. As for roots, the potential N input from leaves was significantly greater in forest than in tundra. Vegetation type had no effect on changes in root or leaf N concentration after one year of decomposition. 4. Our results suggest that shifts in vegetation that accompany climate change in the Arctic will likely increase plant-associated potential N input both belowground and aboveground. In contrast, shifts in vegetation might not alter changes in tissue N concentration during early stages of decomposition. Overall, differences between forest and tundra in potential contribution of decomposing roots to the N cycle reinforce differences between habitats that occur for leaves.

1. 植被残体分解对氮循环（nitrogen cycle）的贡献，可能会因气候变化伴随的植被群落转变而发生改变。植被输入的土壤有机质（soil organic matter）中，根系贡献占绝大多数，但目前学界对不同植被类型的根系在养分循环（nutrient cycling）中的贡献差异仍知之甚少。本研究聚焦森林与苔原（tundra）生态系统，探究细根（fine roots）对氮循环的潜在贡献，以期深入理解北极（Arctic）地区气候变化伴随的木本植被扩张这一普遍观测现象所带来的地下生态后果。2. 本研究结合微根窗（minirhizotron）图像获取的根系生产力数据，与不同直径、颜色分级的根系组织分析结果，以估算分解过程中的潜在氮输入量。此外，我们检测了分解初期根系的氮浓度变化，并探究植被类型（森林或苔原）是否会影响分解过程中根系组织的氮浓度变化。为保证研究完整性，我们同时补充了叶片的对应测定数据。3. 森林生态系统中根系的潜在氮输入量约为苔原的两倍，这主要源于森林的根系生产力更高。潜在氮输入量随根系直径与颜色分级存在差异，但该差异在森林与苔原中表现出相似的趋势。与根系结果一致，森林的叶片潜在氮输入量也显著高于苔原。经过一年的分解后，植被类型对根系或叶片的氮浓度变化无显著影响。4. 本研究结果表明，北极地区气候变化伴随的植被群落转变，可能会提升植物相关的地下与地上潜在氮输入量。与之相对，植被转变或许不会改变分解初期的组织氮浓度变化趋势。总体而言，森林与苔原在分解根系对氮循环的潜在贡献上的差异，进一步强化了二者在叶片相关生境间的固有差异。