Trait coordination in boreal mosses reveals a bryophyte economics spectrum

The study of plant trait spectra and their association with trade-offs in resource use strategy has greatly advanced our understanding of vascular plant function, yet trait spectra remain poorly studied in bryophytes, particularly outside of the Sphagnum genus. Here, we measured 25 traits related to carbon, nutrient and water conservation in 60 moss canopies (each dominated by one of 15 moss species) across diverse boreal forest habitats and used bi-variate correlations and multi-variate analyses to assess trait coordination and trait spectra. We found substantial trait coordination along a main principal components axis driven by trade-offs in carbon, nutrient and water conservation strategies. Along this trait spectrum, traits varied from resource-acquisitive at one end (e.g. high maximum photosynthetic capacity, high tissue nitrogen content, low water-holding capacity) to resource-conservative at the other end, in line with resource economics theory. Traits related to carbon turnover (photosynthesis and respiration rates, litter decomposability) were positively related to nitrogen content and to desiccation rates, in line with global trait spectra in vascular plants. However, architectural traits of the moss shoots and of the moss canopy were generally unrelated to the main axis of trait variation and formed a secondary axis of trait variation, contrary to what is observed for vascular plants. Resource-conservative trait spectra dominated in moss canopies from open and wet habitats (i.e. mires), indicating that high irradiance and possibly high moisture fluctuation induce a resource-conservative trait strategy in mosses. Synthesis. Our work suggests that trait relationships that are well established for vascular plants can be extended for bryophytes as well. Bryophyte trait spectra can be powerful tools to improve our understanding of ecosystem processes in moss-dominated ecosystems, such as boreal or arctic environments, where bryophyte communities exert strong control on nutrient and carbon cycling.

Automated summary

This study measured trait spectra in bryophytes and found trade-offs in carbon, nutrient, and water conservation strategies. The architectural traits of moss shoots and canopies formed a secondary axis of trait variation in contrast to vascular plants. Resource-conservative strategies dominated moss canopies in open and wet habitats.