The moss traits that rule cyanobacterial colonization

BACKGROUND AND AIMS: Cyanobacteria associated with mosses represent a main nitrogen (N) source in pristine, high-latitude and -altitude ecosystems due to their ability to fix N(2). However, despite progress made regarding moss–cyanobacteria associations, the factors driving the large interspecific variation in N(2) fixation activity between moss species remain elusive. The aim of the study was to identify the traits of mosses that determine cyanobacterial colonization and thus N(2) fixation activity. METHODS: Four moss species varying in N(2) fixation activity were used to assess cyanobacterial abundance and activity to correlate it with moss traits (morphological, chemical, water-balance traits) for each species. KEY RESULTS: Moss hydration rate was one of the pivotal traits, explaining 56 and 38 % of the variation in N(2) fixation and cyanobacterial colonization, respectively, and was linked to morphological traits of the moss species. Higher abundance of cyanobacteria was found on shoots with smaller leaves, and with a high frequency of leaves. High phenol concentration inhibited N(2) fixation but not colonization. These traits driving interspecific variation in cyanobacterial colonization, however, are also affected by the environment, and lead to intraspecific variation. Approximately 24 % of paraphyllia, filamentous appendages on Hylocomium splendens stems, were colonized by cyanobacteria. CONCLUSIONS: Our findings show that interspecific variations in moss traits drive differences in cyanobacterial colonization and thus, N(2) fixation activity among moss species. The key traits identified here that control moss-associated N(2) fixation and cyanobacterial colonization could lead to improved predictions of N(2) fixation in different moss species as a function of their morphology.