High nitrogen resorption efficiency of forest mosses.

Nutrient resorption from senescing tissue is a key mechanism for plants to conserve nutrients, and can affect ecosystems' nutrient dynamics. Yet, our limited knowledge of nitrogen (N) resorption and release from mosses hampers our understanding of the role of mosses as N sources and thereby, N cycling in moss-dominated ecosystems. The aims of this study were to estimate N resorption efficiency (NRE) of two moss species, identify the pathways of N release from the mosses, as well as to provide a better understanding of N cycling and budgeting strategies of mosses.The dynamics of N allocation along annual moss segments of two dominant moss species (Actinothuidium hookeri and Hylocomium splendens) were assessed in old-growth fir forests using an in situ15N tracer experiment.Nitrogen resorption efficiency of A. hookeri and H. splendens was 61% and 52%, respectively. While the mosses lost 23% and 33% N from live tissues via leaching, 15% and 14% of N remained in senesced tissues (> 3 years old) in A. hookeri and H. splendens, respectively.Both mosses resorbed the majority of their tissue N, but a considerable amount of N was lost from live segments. Our results highlight the crucial role mosses play as N sinks in ecosystems, since N retention (resorbed and sequestered in senescent tissue) outweighed N loss via leaching. However, the sink strength depends on temperature and precipitation, which will change in a future climate. The here estimated values for NRE, leaching etc. can help improve biogeochemical models aiming to complete N budgets for moss-abundant ecosystems.