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Abstract
We examined photosynthetic responses of two dominant pleurocarpous mosses, Actinothuidium hookeri (Mitt.) Broth. and Hylocomium splendens (Hedw.) Schimp. to low-level nitrogen (N) addition. The study was conducted in an old-growth fir forest on the eastern Tibetan Plateau. The added N, 1 g N/m2, was mainly absorbed by the new-growth. The concentrations of chlorophyll a and b both increased 8 days after N addition. The quantum yield of Photosystem II (ΦPSII) also increased. However, no significant changes were found in terms of gas exchange parameters. The mass-based CO2 assimilation rate, chlorophyll a content, and chlorophyll a/b ratio (which is related to antenna size of the photosystem), of H. splendens were all higher than those of A. hookeri. Shoot mass per area (SMA) of H. splendens was lower than that of A. hookeri. We conclude that the photosynthetic rate was less sensitive to low-level N addition than chlorophyll contents and chlorophyll fluorescence parameters, suggesting other limiting factors in the photosynthetic process. Additionally, the faster growing H. splendens has a higher photosynthetic capacity than A. hookeri, allocating fewer resources to structural tissue.
Acknowledgements
We thank the Administration Bureau of Dagu Glacier Park, particularly Huaxiang Tang, for the support and facilities for field research. We also thank anonymous reviewers for their valuable comments and suggestions on a previous version of this manuscript. We acknowledge Wei Wang for improving the language of the manuscript. This work was funded by the Strategic Priority Research Program of the Chinese Academy of Science (No. XDA05070306) and the National Science & Technology Pillar Program in 12th Five-year Plan of China (No. 2011BAC09B0402).
Taxonomic Additions and Changes: Nil.