Moss functional trait ecology: Trends, gaps, and biases in the current literature

Functional traits are critical tools in plant ecology for capturing organism-environment interactions based on trade-offs as well as making links between organismal and ecosystem processes. While broad frameworks for functional traits have been developed for vascular plants, we lack the same for bryophytes, despite an escalation in the number of bryophyte functional trait studies conducted in the last 45 years and an increased recognition of the ecological roles bryophytes play across ecosystems. In this review, we compiled data from 282 published articles (10005 records) focusing on functional traits measured in mosses, and sought to (a) examine trends in types of traits measured, (b) capture taxonomic and geographic breadth of trait coverage, (c) reveal biases in coverage in the current literature, and (d) develop a bryophyte-function index (BFI) to describe completeness of current trait coverage and identify global gaps to focus research efforts. The most commonly measured response traits (those related to growth/reproduction in individual organisms) and effect traits (those that directly affect community/ecosystem scale processes) fell into the categories of morphology (e.g. leaf area, shoot height) and nutrient storage/cycling, and our BFI revealed that these data were most commonly collected from temperate and boreal regions of Europe, North America and east Asia. However, fewer than 10% of known moss species have available functional trait information. Our synthesis revealed that there is a need for research on traits related to ontogeny, sex, and intraspecific plasticity, and on co-measurement of traits related to water-relations and bryophyte-mediated soil processes.