The moss traits that rule cyanobacterial colonization

Abstract

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 N2. However, despite progress made regarding moss-cyanobacteria association, the factors driving the large interspecific variation in N2 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, N2 fixation activity. Methods Four moss species varying in N2 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% variation in N2 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 N2 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, N2 fixation activity among moss species. The here-identified key traits that control moss-associated N2 fixation and cyanobacterial colonization could lead to improved predictions of N2 fixation in different moss species as a function of their morphology.

New insights into the drivers of moss‐associated nitrogen fixation and cyanobacterial biomass in the eastern Canadian boreal forest

“…These functional traits could lead to host‐specific micro‐habitat conditions and affect light and water availability to cyanobacteria colonies on moss leaves. Recently, Liu and Rousk (2021) showed that the moss hydration rate, which was related to species morphology, was a key trait controlling N 2 ‐fixation and cyanobacterial colonization on feather moss leaves. The link between moss identity and N 2 ‐fixation could also result from the structure of the moss microbiome.…”

“…Recently, Liu and Rousk (2021) showed that the moss hydration rate, which was related to species morphology, was a key trait controlling N 2 -fixation and cyanobacterial colonization on feather moss leaves.…”

Biotic and abiotic controls of nitrogen fixation in cyanobacteria–moss associations

“…All moss species harbour cyanobacteria, albeit to a varying extent. This is reflected in a large range of N 2 fixation rates reported for mosses, and in the biomass of the cyanobacterial colonizers that usually scales well with N 2 fixation activity (Liu & Rousk, 2021). While abiotic factors such as nutrient availability and climate impact N 2 fixation associated with mosses (see below), N 2 fixation activity in mosses growing in the same habitat can differ many fold (Calabria et al ., 2020; Jean et al ., 2020; Stuart et al ., 2021).…”

High nitrogen‐fixing rates associated with ground‐covering mosses in a tropical mountain cloud forest will decrease drastically in a future climate

“…However, none of the liverworts assessed in this study belong to genera already known to form ‘true’ symbioses with diazotrophs (Adams & Duggan, 2008). Specific bryophyte traits are a driving factor of associated N 2 fixation, for example, by controlling bryophyte moisture level and thereby diazotroph colonization and activity (Liu & Rousk, 2021). The liverwort associated with the highest N 2 fixing activity in our study, Herbertus sp., is a ‘leafy’ liverwort, with morphology similar to mosses in terms of size and structure, separated into stem and leaves, which could explain the similar high N 2 fixation activity associated with this liverwort species.…”

“…Nitrogen fixation activity of bacteria hosted by bryophytes is affected by abiotic factors such as temperature and moisture availability (Cusack et al, 2009; Gundale, Nilsson, et al, 2012; Permin et al, 2022; Rousk, Jones, et al, 2013), with desiccation inhibiting activity (Rousk et al, 2014). Also increased N availability can inhibit N 2 fixation in mosses (Rousk, Rousk, et al, 2013; Wang et al, 2021) and moss pH can affect N 2 fixation activity (Alvarenga & Rousk, 2021; Liu & Rousk, 2021). Furthermore, specific morphology traits linked to bryophyte hydration rate (e.g.…”