Functional Trait Trade-off Relationships Across 28 Subtropical Montane Moss Species

Bryophyte is a transitional higher plant group between aquatic and land plants,able to adapt to diverse extreme environments.As such,it occupies a special status in plant evolution,As the haploid dominant terrestrial plant,the reproductive characteristics of bryophytes are unique as compared to other plant groups.However,previous studies on moss traits mostly focused on the gametophyte,and the studies on the sporophyte were limited to taxonomic descriptions of the anatomical and morphological structures for classification.To some extent,sporophyte traits of mosses reflect their sexual reproductive and dispersal capacities.Exploring the effects of specific structures and environmental variations on sporophyte traits can contribute to a better understanding of their unique sexual reproductive strategies.Trade-offs among different functional traits reflect the different strategies of plants in resource acquisition and allocation and have been a hot topic in ecological research in recent years.Most of the existing studies on relationships between functional traits have focused on vascular plants,while related studies on bryophytes are scarce.Due to the small size,weak metabolic ability,and special nutrient absorption and utilization mechanism,the existing functional trait relationships of vascular plants do not necessarily apply to bryophytes.With an integrative perspective,exploring the sporophyte traits and their relationships with gametophyte will help to better understand moss resource allocation strategies between vegetative growth and sexual reproduction.Based on the previous studies on moss sporophyte traits and their effects on the development of gametophyte,the current study proposed the following hypotheses:H1: mosses with seta central strands should have larger and heavier sporophytes;H2: mosses growing at the wetter site(more precipitation)should have larger sporophytes than those growing at the drier site;H3: With increasing seta length,the proportion of the area of transport cells should also increase,thus improves the transport capacity and efficiency;H4: With increasing seta length,the cross-section area should also expand and the shape of the cross-section will tend to be more round;H5: The biomass of sporophyte should be positively related to gametophyte biomass and nutrient concentrations.To test the hypotheses,we collected 28 moss species with sporophytes from Hailuogou glacier,Emei mount,and Dagu glacier of Sichuan Province.The anatomical structure(seta cross-section epidermis cell area,transport cell area,and their ratios),morphological traits(the seta length,crosssectional area,and cross-sectional shape index),biomass(the weights of seta,capsule,sporophyte,and gametophyte,and the ratios of seta to capsule and sporophyte to gametophyte)and gametophyte nutrient content(the carbon,nitrogen,and phosphorus concentrations and their stoichiometric ratios)were measured.Generalized linear mixed models were used to investigate the effects of seta structural characteristics(with or without seta central strands),site,and their interaction on the studied traits.Generalized linear models were used to compare the intra-specific trait variations of the two species collected from two different sites.Principal component analysis and bivariate correlation analysis were used to reveal the trade-off relationships among seta anatomical and morphological traits,the biomass allocation patterns between sporophyte and gametophyte,and the relationships among sporophyte traits and gametophyte economic traits.Lastly,we used standardized major axis regression analysis to determine how the presence of seta central strands affects these relationships.The current mosses were not the dominant species in the study sites,and most of them were acrocarpous mosses.The hypothesis H1 was supported: the presence of seta central strands had significant effects on the growth of moss sporophytes,with longer and thicker setae and heavier sporophytes.However,it was unrelated to the resource allocation between transport cell and mechanical tissue resources and the biomass allocation of sporophytes.H2 was not supported: there were no differences among different sites for the community-mean traits,but intraspecific variations were found.Generally,the Hailuogou Glacier had the more appropriate temperature and precipitation for sporophyte growth as compared to the other two sites.Inconsistent with H3,the variations in seta length were unrelated to the transport cell/epidermis area.In support of H4,the seta cross-sectional area increased and the shape index decreased(thicker and rounder)with increasing seta length.Finally,H5 was partly supported: the biomass of capsule,seta,sporophyte,and gametophyte were positively related,and the resource investment strategies in biomass allocation were different between the mosses with and without central strands.However,there were no relationships between sporophyte traits and gametophyte nutrient concentrations.This study extends the current plant functional trait network and provides evidence for a deeper understanding of the unique ecological adaptation strategies of mosses.