Quantifying nitrogen uptake and translocation for mature trees: an in situ whole-tree paired 15N labeling method

Author:

Zhu Feifei123,Dai Luming14,Hobbie Erik A5,Qu Yuying13,Huang Dan13,Gurmesa Geshere A13,Zhou Xulun14,Wang Ang123,Li Yinghua4,Fang Yunting123

Affiliation:

1. CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China

2. Qingyuan Forest CERN, Shenyang 110016, China

3. Key Laboratory of Stable Isotope Techniques and Applications, Shenyang, Liaoning Province 110016, China

4. School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China

5. Earth Systems Research Center, Morse Hall, University of New Hampshire, Durham, NH 03824-3525, USA

Abstract

Abstract Nitrogen (N) is one of the major nutrients limiting plant growth in terrestrial ecosystems. To avoid plant–microbe competition, previous studies on plant N uptake preference often used hydroponic experiments on fine roots of seedlings and demonstrated ammonium preference for conifer species; however, we lack information about N uptake and translocation in the field. In this paper, we described a method of in situ paired 15N labeling and reported the rates and time course of N uptake and translocation by mature trees in situ. We added 15N-enriched ammonium or nitrate, together with the nitrification inhibitor dicyandiamide, to paired Larix kaempferi (Lamb.) Carr (larch) trees from 30-, 40- and 50-year-old plantations. Fine roots, coarse roots, leaves and small branches were collected 2, 4, 7, 14 and 30 days after labeling. Nitrate uptake and translocation averaged 1.59 ± 0.16 μg 15N g−1 day−1, which is slightly higher than ammonium (1.08 ± 0.10 μg 15N g−1 day−1), in all tree organs. Nitrate contributed 50–78% to N uptake and translocation, indicating efficient nitrate use by larch in situ. We observed no age effect. We suggest that sampling leaves after 4 days of 15N labeling is sufficient to detect mature tree N uptake preference in situ. Whole-tree 15N-ammonium recovery equaled that of 15N-nitrate 30 days after 15N addition, implying the importance of both ammonium and nitrate to mature larch N use in the long run. We conclude that our method is promising for studying mature tree N uptake preference in situ and can be applied to other conifer and broadleaf species. We suggest using highly enriched 15N tracer to overcome soil dilution and a nitrification inhibitor to minimize ammonium transformation to nitrate. Our study revealed mature tree N preference in situ and demonstrated the strong contribution of nitrate toward mature larch growth on soils rich in nitrate.

Funder

National Key Research and Development Program of China

National Natural Science Foundation of China

Publisher

Oxford University Press (OUP)

Subject

Plant Science,Physiology

Reference83 articles.

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