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Enhanced leaf turnover and nitrogen recycling sustain CO2 fertilization effect on tree-ring growth

Nature Ecology & Evolution volume 6, pages 1271–1278 (2022)Cite this article

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Abstract

Whether increased photosynthates under elevated atmospheric CO2 could translate into sustained biomass accumulation in forest trees remains uncertain. Here we demonstrate how tree radial growth is closely linked to litterfall dynamics, which enhances nitrogen recycling to support a sustained effect of CO2 fertilization on tree-ring growth. Our ten-year observations in two alpine treeline forests indicated that annual (or seasonal) stem radial increments generally had a positive relationship with the previous year’s (or season’s) litterfall and its associated nitrogen return and resorption. Annual tree-ring width, annual litterfall and annual nitrogen return and resorption all showed an increasing trend during 2007–2017, and most of the variations were explained by elevated atmospheric CO2 rather than climate change. Similar patterns were found in the longer time series of tree-ring width index from 1986–2017. The regional representativeness of our observed patterns was confirmed by the literature data of six other tree species at 11 treeline sites over the Tibetan Plateau. Enhanced nitrogen recycling through increased litterfall under elevated atmospheric CO2 supports a general increasing trend of tree-ring growth in recent decades, especially in cold and nitrogen-poor environments.

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Fig. 1: Relationships of seasonal stem increment to previous season’s litterfall and its induced N recycling at two alpine treelines during 2007–2017.
Fig. 2: Relationships of annual stem increment to previous year’s litterfall and its induced N recycling at two alpine treelines during 2007–2017.
Fig. 3: Relative contributions of climatic factors and atmospheric CO2 to annual variations of litterfall, N recycling and tree-ring growth at two alpine treelines during 2007–2017.
Fig. 4: Structural equation models quantifying direct effects of climatic factors and atmospheric CO2 and their indirect effects through interactions with litterfall and N-ret/N-res on tree-ring width index at two alpine treelines during 2007–2017.
Fig. 5: Relative contributions of climatic factors and atmospheric CO2 to annual variations of tree-ring width index (since 1986) across 8 tree species and 13 treeline sites on the Tibetan Plateau.

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Data availability

The tree-ring width chronologies collected from the International Tree-Ring Data Bank are available at https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/tree-ring. The time-series data of atmospheric CO2 concentration were obtained from https://www.esrl.noaa.gov/gmd/ccgg/trends/. The time-series data of monthly climatic factors at weather stations were obtained from http://data.cma.cn/data/detail/dataCode/A.0012.0001. All observed data in this study are provided in this article and its associated supplementary information.

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Acknowledgements

We thank X. S. Liu for his help with the observation of stem radial increment and the Southeast Tibet Station for Alpine Environment Observation and Research, Chinese Academy of Sciences, for help in the fieldwork. This work was funded by the Second Tibetan Plateau Scientific Expedition and Research Programme (grant no. 2019QZKK0106) and the National Natural Science Foundation of China (grant nos. 41830649 and 41571046).

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Author notes

  1. These authors contributed equally: Ying Guo, Lin Zhang.

Authors and Affiliations

  1. Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China

    Ying Guo, Lin Zhang, Liu Yang, Wei Shen & Tianxiang Luo

  2. University of Chinese Academy of Sciences, Beijing, China

    Ying Guo & Liu Yang

  3. USDA Forest Service, Northern Research Station, Durham, NH, USA

    Yude Pan

  4. Hawkesbury Institute for the Environment, Western Sydney University, Penrith, New South Wales, Australia

    Ian J. Wright

  5. Department of Biological Sciences, Macquarie University, North Ryde, New South Wales, Australia

    Ian J. Wright

  6. Center for Ecosystem Science and Society, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA

    Yiqi Luo

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Contributions

T.L. designed the experiment. Y.G., L.Z., L.Y. and W.S. conducted the experiment. Y.G., L.Z., T.L., Y.P., I.J.W. and Y.L. analysed the data. Y.G., L.Z. and T.L. wrote the manuscript. Y.P., I.J.W. and Y.L. revised the manuscript.

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Correspondence to Tianxiang Luo.

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Nature Ecology & Evolution thanks Flurin Babst and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Guo, Y., Zhang, L., Yang, L. et al. Enhanced leaf turnover and nitrogen recycling sustain CO2 fertilization effect on tree-ring growth. Nat Ecol Evol 6, 1271–1278 (2022). https://doi.org/10.1038/s41559-022-01811-1

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