Abstract:

Mosses are dominant in many ecosystems where nutrients from deposition are one of the main nutrient sources. However, it is difficult to evaluate mosses’ role in nutrient cycling without knowledge of how mosses use deposited nutrient inputs. To fill this gap, the present study aims to investigate: (i) how nitrogen (N) and phosphorus (P) concentrations of new-grown segments change along a gradient of N or P amount in a pulse treatment? (ii) how do a pulse of major nutrient (N or P) affect N or P translocation rate along a moss shoot? and (iii) to what extent do N or P translocation rates link to nutrient status of the new-grown segments of mosses?

We measured N and P concentrations of segments with different ages in two dominant forest floor mosses, Actinothuidium hookeri and Hylocomium splendens, on 8 days and 1 year after N and P pulse treatment with an in situ experiment in a subalpine fir forest in eastern Tibetan Plateau.

Both mosses were efficient in taking up nutrients from a pulse of either N or P. Nitrogen and P concentrations of new-grown segments were affected by nutrient pulse treatments. These N and P concentration changes were attributed to the initial N and P concentration of the young segments harvested 8 days after nutrient pulse treatments, suggesting that the captured nutrients were reallocated to the new-grown segments via translocation, which was largely controlled by a source–sink relationship. While no significant relationship was found between N translocation rate and N:P ratio of the new-grown segments, P translocation rate explained 21%–23% of the variance of N:P ratio of the new-grown segments, implying importance of P transport in supporting the new-grown sections. These results suggest that nutrient (N, P) translocation is a key process for mosses to utilize intermittent nutrient supply, and thus make mosses an important nutrient pool of the ecosystem.

Key words: forest floor mosses, nutrient resorption, nutrient cycling, nutrient pulse, old-growth forest