Nitrogen nutrition of native and introduced forest tree species in N-limited ecosystems of the Qinling Mountains, China
Root N uptake capacity and soil C, N status indicate superior performance of a mixed forest stand with Larix and Quercus compared with the monocultures of Picea and Larix under N limitation condition.
Nitrogen availability and uptake capacity are key factors influencing forest growth and development in N-limited terrestrial ecosystems. With the aim to determine how species and forest management affect tree N nutrition, we conducted root N uptake experiments as well as soil N analyses at three forest stands with different native and introduced tree species (i.e. Larix principis-rupprechtii Mayr., Quercus aliena var. acutiserrata Maxim. ex Wenz. and Picea wilsonii Mast.) and two management approaches (i.e. monoculture versus mixed stand) in the Qinling Mountains of China. Across the native and introduced species studied, in general, investigated trees take up both, organic and inorganic N compounds, but prefer organic N (Gln- and Arg-) over inorganic NH4 +–N. The introduced conifer species (L. principis-ruprechtii) showed higher root N acquisition capacities compared to a native conifer species (P. wilsonii) under N-limited conditions. Moreover, the mixed forest stand with L. principis-ruprechtii and Q. alinea var. acutesserata accumulated more nitrogen in soil pools and showed improved C and N retention capability through the whole soil profile as compared to the monocultures of P. wilsonii or L. principis-ruprechtii. Similar acquisition strategies were observed for specific N sources (i.e. organic versus inorganic) across all investigated tree species. Still the introduced species Larix exhibited a superior root N acquisition capacity and, therefore, may be a good candidate for afforestation programs in the studied region. The present results underpin the significance of forest management practices that achieve a mixed species structure with broadleaved tree species such as Quercus for restoration of soil C and N pools in order to stabilize forest ecosystems and to achieve sustainable forest development.
KeywordsRoot nitrogen uptake capacity Soil microbial biomass Larix Quercus Picea Qinling Mountains
Stable isotope analyses of plant material were carried out at the Freiburg Zentrum für Biosystemanalyse (ZBSA) and soil analyses were conducted at the Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology (KIT). We appreciate Dr. Boris Bonn for the statistical expertise supports. We also thank Mrs. Erika Fischer and Dr. Gustavo Saiz for technical assistance in the laboratory and Mr. Pengxiang Gao for assistance in the field work. Additionally we acknowledge that an anonymous Communicating Editor made us to use GLMM for additional statistical analysis of the data.
This study was financially funded by the National Natural Science Foundation of China (41573079) for MZ; the 2011–2012 project of Introduction of Foreign Experts of China for HR, SB and JS; the Deutsche Forschungsgemeinschaft (DE) (GRK 1305 - International Graduate School of Signal Systems in Plant Model Organisms) and the Basic Research Funds for talent with foreign doctorate by the Central government, Shaanxi province (Z111021507) & Northwest A&F University (Z109021406), China for BH respectively. The authors also extended their sincere appreciations to the Deanship of Scientific Research at King Saud University for funding this Prolific Research group (PRG-1436-24).
BH, MH Zh, JS, SX Zh and HR designed the experimental setup, BH, MH Zh, SB, XP Liu, LH, HCh, SX Zh and JS implemented it in the field, BH, MH Zh, MD, SB, SA and JS analysed the root and soil samples in the laboratory and drafted the paper. BH, MH Zh, BB, KBB and HR have contributed significantly to the data analysis, discussing the results, writing and reading of the paper.
Compliance with Ethical Standards
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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