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Background and Aims Biological soil crusts, comprising assemblages of cyanobacteria, fungi, lichens and mosses, are common in dryland areas and are important elements in these ecosystems. Increasing N deposition has led to great changes in community structure and function in desert ecosystems worldwide. However, it is unclear how moss crusts respond to increased atmospheric N deposition, especially in terms of growth and physiological parameters. The aim of this study was to understand how Syntrichia caninervis, a dominant species in moss crusts in many northern hemisphere desert ecosystems, responds to added N.

Methods The population and shoot growth, and physiological responses of S. caninervis to six different doses of simulated N deposition (0, 0 center dot 3, 0 center dot 5, 1 center dot 0, 1 center dot 5 and 3 center dot 0 g N m(-2) year(-1)) were studied over a 3 year period.

Key Results Low amounts of added N increased shoot length and leaf size, whereas high doses reduced almost all growth parameters. Moss shoot density increased, but population biomass decreased with high N. Low N augmented chlorophyll b, total chlorophyll content and soluble protein concentrations, but not chlorophyll a or chlorophyll fluorescence. High N was detrimental to all these indices. Soluble sugar concentration declined with increased N, but proline concentration was not affected significantly. Antioxidant enzyme activities generally decreased with low N additions and increased with high doses of simulated N deposition.

Conclusions Low amounts of added N (0-0 center dot 5 g N m(-2) year(-1)) may enhance moss growth and vitality, while higher amounts have detrimental effects.