Jiangsu Engineering Lab of Water and Soil Eco-Remediation, School of Environment, Nanjing Normal University, Nanjing, 210046, China.
Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun, 130102, China.
Oecologia. 2024 Oct;206(1-2):1-10. doi: 10.1007/s00442-024-05605-z. Epub 2024 Aug 12.
The N-fixing trees Alnus spp. have been widely encroaching into boreal peatlands, but the nutrient responses of native vascular plants remain unclear. Here, we compared nutrient concentrations and isotope signal of six common plants (Betula fruticosa, Salix rosmarinifolia, Vaccinium uliginosum, Rhododendron tomentosum, Chamaedaphne calyculata, and Eriophorum vaginatum) between Alnus hirsuta island and open peatland and assessed plant nutrient responses to A. hirsuta encroachment in boreal peatlands. Alnus hirsuta encroachment increased nitrogen (N) concentration of leaf, branch, and stem. Despite no significant interspecific difference in branch and stem, the increment magnitude of leaf N concentration varied among species, with greatest magnitude for R. tomentosum (55.1% ± 40.7%) and lowest for E. vaginatum (9.80% ± 4.40%) and B. fruticosa (18.4% ± 10.7%). Except for E. vaginatum, the significant increase in δN occurred for all organs of shrubs, with interspecific differences in change of leaf δN. According to the mass balance equation involving leaf δN, R. tomentosum and E. vaginatum, respectively, obtained highest (40.5% ± 19.8%) and lowest proportions (-14.0% ± 30.5%) of N from A. hirsuta. Moreover, the increment magnitudes of leaf N concentration showed a positive linear relationship with the proportion of N from A. hirsuta. In addition, A. hirsuta encroachment reduced leaf phosphorus (P) concentration of deciduous shrubs (i.e., B. fruticosa, S. rosmarinifolia, and V. uliginosum), thus increasing N:P ratio. These findings indicate that Alnus encroachment improves native plant N status and selectively intensifies P limitation of native deciduous shrubs, and highlight that the N acquisition from the symbiotic N-fixing system regulates plant N responses in boreal peatlands.
固氮树种桤木属（Alnus spp.）广泛侵入北方泥炭地，但本地维管束植物的养分响应仍不清楚。在这里，我们比较了六种常见植物（毛赤杨（Betula fruticosa）、柳兰（Salix rosmarinifolia）、越橘（Vaccinium uliginosum）、杜鹃（Rhododendron tomentosum）、圆头高山茶（Chamaedaphne calyculata）和水毛茛（Eriophorum vaginatum））在桤木属岛屿和开阔泥炭地之间的养分浓度和同位素信号，并评估了桤木属在北方泥炭地对植物养分的侵占响应。桤木属的侵入增加了叶片、枝条和茎的氮（N）浓度。尽管枝条和茎的种间差异不显著，但叶片 N 浓度的增量幅度在物种间有所不同，其中杜鹃的增幅最大（55.1%±40.7%），而水毛茛和毛赤杨的增幅最小（9.80%±4.40%和 18.4%±10.7%）。除水毛茛外，所有灌木器官的 δN 均显著增加，叶片 δN 的变化存在种间差异。根据涉及叶片 δN 的质量平衡方程，杜鹃和水毛茛分别从桤木属获得最高（40.5%±19.8%）和最低（-14.0%±30.5%）的 N 比例。此外，叶片 N 浓度的增量幅度与桤木属的 N 比例呈正线性关系。此外，桤木属的侵入减少了落叶灌木（如毛赤杨、柳兰和越橘）的叶片磷（P）浓度，从而增加了 N:P 比。这些发现表明，桤木属的侵入改善了本地植物的 N 状况，并选择性地加剧了本地落叶灌木的 P 限制，突出了共生固氮系统中从 N 获得的 N 调节了北方泥炭地植物的 N 响应。
