Scaling functional traits to ecosystem processes: Towards a mechanistic understanding in peat mosses

Abstract

The role of trait trade‐offs and environmental filtering in explaining the variability in functional traits and ecosystem processes has received considerable attention for vascular plants but less so for bryophytes. Thus, we do not know whether the same forces also shape the phenotypic variability of bryophytes. Here, we assess how environmental gradients and trade‐offs shape functional traits and subsequently ecosystem processes for peat mosses (Sphagnum), a globally important plant genus for carbon accumulation. We used piecewise Structural Equation Modeling (SEM) to understand how environmental gradients influence vital processes across levels of biological organization. We gathered data on functional traits for 15 globally important Sphagnum species covering a wide range of ecological preferences. Phenotypes lie along well‐established axes of the plant economic spectrum characterizing trade‐offs between vital physiological functions. Using SEM, we clarified the mechanisms of trait covariation and scaling to ecosystem processes. We tested whether peat mosses, like vascular plants, constrain trait variability between a fast turnover strategy based on resource acquisition via fast traits and processes, and a strategy of resource conservation, via slow traits and processes. We parameterized a process‐based model estimating ecosystem processes linking environmental drivers with architectural and functional traits. In our SEM approach the amount of variance explained varied substantially (0.29 ≤ R2 ≤ 0.82) among traits and processes in Sphagnum, and the model could predict some of them with high to intermediate accuracy for an independent dataset. R2 variability was mainly explained by traits and species identity, and poorly by environmental filtering. Some Sphagnum species avoid the stress caused by periodic desiccation in hollows via resource acquisition based on fast photosynthesis and growth, while other species are adapted to grow high above the water‐table on hummocks by slow physiological traits and processes to conserve resources. Synthesis.We contribute to a unified theory generating individual fitness, canopy dynamics and ecosystem processes from trait variation. As for vascular plants, the functional traits in the Sphagnum economic spectrum are linked into an integrated phenotypic network partly filtered by the environment and shaped by trade‐offs in resource acquisition and conservation.

Functional trait evolution in Sphagnum peat mosses and its relationship to niche construction

“…Contrary to some previous observations (Coulson & Butterfield, ; Bragazza et al ., ) and in agreement with others (Thormann et al ., ; Moore et al ., ; Turetsky et al ., ), litter C : N ratio is not significantly correlated with measurements of decomposability or height‐above‐water‐table. No support was found for a relationship between shoot density or bulk density and either height‐above‐water‐table or decomposability in disagreement with previous studies that did not account for phylogeny (Hájek, ; Elumeeva et al ., ; Mazziotta et al ., ). Indeed, even the trade‐off between rates of growth and decomposition per se (Turetsky et al ., ; Laing et al ., ) is only supported for biomass increase per area and mass loss in the laboratory in multivariate evolutionary models consistent with recent analyses that acknowledged that support for such a trade‐off is weak (Mazziotta et al ., ).…”

“…No support was found for a relationship between shoot density or bulk density and either height‐above‐water‐table or decomposability in disagreement with previous studies that did not account for phylogeny (Hájek, ; Elumeeva et al ., ; Mazziotta et al ., ). Indeed, even the trade‐off between rates of growth and decomposition per se (Turetsky et al ., ; Laing et al ., ) is only supported for biomass increase per area and mass loss in the laboratory in multivariate evolutionary models consistent with recent analyses that acknowledged that support for such a trade‐off is weak (Mazziotta et al ., ). It should be noted, however, that the increased probability of type II error associated with small sample size in this study likely contributes in part to the observation of relatively few significant regression models.…”

“…Sphagnum magellanicum Brid. was treated a single taxon in accordance with other recent ecological studies (Bengtsson et al ., , ; Mazziotta et al ., ) despite the current taxonomic status of S. magellanicum sensu lato as a species complex (Hassel et al ., ).…”

Leaf traits interact with management and water table to modulate ecosystem properties in fen peatlands

“…Path models use correlation coefficients and regression analyses to estimate cause-and-effect relationships among multiple variables by using straight, single-headed arrows that denote standardized partial regression coefficients of direct effects (Schumacker and Lomax 2010). Path analysis starts with an initial conceptual model based on a priori knowledge of the functioning of the system, which is then tested against the covariance matrix of the observed data (Maruyama 1998). The model is evaluated by a chi-square (χ 2 ) test of fit, in which a significant p value (p < 0.05) indicates that the covariance structure of the data differs significantly from that of the hypothesized model.…”

Towards a moss sclerophylly continuum: Evolutionary history, water chemistry and climate control traits of hygrophytic mosses

“…In 2007, Hill et al published an extraordinarily large dataset of bryophyte traits, including morphological, reproductive and life‐history traits. Several researchers have studied moss traits in boreal and arctic ecosystems (Elumeeva, Soudzilovskaia, During, & Cornelissen, ; Jonsson et al, ; Kangas et al, ; Mazziotta, Granath, Rydin, Bengtsson, & Norberg, ; Sokołowska, Turzańska, & Nilsson, ; Turetsky et al, ), alpine habitats (Ah‐Peng et al, ; Wang, Liu, Bader, Feng, & Bao, ), tropical forests (Waite & Sack, ) and even in vitro experiments (Löbel & Rydin, ). Despite intensive local research on moss traits and the extremely useful dataset published by Hill, Preston, Bosanquet, and Roy (), however, it has not been until 2018 that, to the best of our knowledge, the first paper focused on the relationship between bryophyte traits, species distributions and environmental conditions was published.…”