Abstract
Aims
Water and nitrogen availability are primary determinants of woody communities in dryland ecosystems and are strongly affected by global change. However, the mechanisms by which resource availability and plant demographic responses regulate woody-herb composition are unclear.
Methods
We investigated plant productivity, shrub demography, and resource availability in a 5-year field experiment involving three levels of precipitation (ambient, + 20% precipitation, + 40% precipitation) and two levels of nitrogen addition (0, 60 kg N ha− 1 yr− 1) in a desert shrubland of northern China.
Results
Increased precipitation had similar positive effects on shrub and herbaceous productivity and, thus, did not alter the community composition. However, nitrogen enrichment dramatically increased herbaceous productivity but tended to decrease shrub productivity. Five years after the experimental manipulation, increased precipitation and nitrogen enrichment significantly altered shrub demography. Increased precipitation decreased the number and cover of small shrubs but increased those of large shrubs. Nitrogen enrichment largely decreased the number and cover of small shrubs, whereas large shrubs showed a higher resistance. Structural equation modeling revealed that nitrogen-enhanced herbaceous competition for water and light potentially reduced shrub growth, especially the growth of small shrubs.
Conclusions
Our results suggest that large shrubs can coexist with herbs, whereas small shrubs tend to be competitively excluded from the system under enhanced precipitation and nitrogen deposition. Nitrogen enrichment may lead to continued declines in shrub recruitment and growth, and a conversion to grassland. Our findings highlight the competitive and demographic mechanisms underlying the responses of woody communities to global change.
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Acknowledgements
This study was jointly supported by the National Natural Science Foundation of China (32001373, 31470711), the Fundamental Research Funds for the Central Universities (BLX201815, 2015ZCQ-SB-02), and the National Key Research and Development Program of China (2016YFC0500905). We thank Shijun Liu, Zhen Liu, **g Zheng, Jie Fu, Na Liu, and the staff of the Yanchi Research Station for their assistance in the field and laboratory work. The authors declare no conflicts of interest.
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She, W., Bai, Y., Zhang, Y. et al. Nitrogen-enhanced herbaceous competition threatens woody species persistence in a desert ecosystem. Plant Soil 460, 333–345 (2021). https://doi.org/10.1007/s11104-020-04810-y
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DOI: https://doi.org/10.1007/s11104-020-04810-y