Effects of light and nitrogen on morphological plasticity of the mossCalliergonella cuspidata

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Abstract
In a short‐term experiment we studied the effects of increased light and nitrogen (N) availability on the mossCalliergonella cuspidataby cutting vascular plants and adding nitrogen in a calcareous fen in the mountainous region of central Switzerland. Shoots ofCalliergonellagrowing in plots with reduced vascular plant competition showed smaller increments in length of the main axis and produced shorter offshoots, but showed higher branching densities at the main axis, higher number of offshoots and higher dry mass per unit length. Although the growth forms of pleurocarpous bryophytes are quite different from stolon‐ and ramet‐producing clonal vascular plants, the overall morphological responses to changing light levels are very similar and, at least in part, comparable to the ‘spacer and branching’ strategy exhibited by some stolon‐bearing vascular plants. The observed morphological plasticity ofCalliergonellawould in principle allow for foraging of heterogeneously distributed resources. Nitrogen supply, on the other hand, had no effects on either dry mass or shoot morphology ofCalliergonella. Moreover, interactions between the effects of removal of vascular plants and increased nutrient supply on biomass and shoot morphology ofCalliergonelladid not occur. This could be explained by the short duration of the experiment. However, since above‐ground biomass of vascular plants was increased by the nutrient supply, it cannot be excluded that in the long run, increased N inputs will have serious secondary consequences onCalliergonella, e.g. due to heavy shading by vascular plants.