Do bryophyte shoot systems function like vascular plant leaves or canopies? Functional trait relationships in Sphagnum mosses (Sphagnaceae)

Abstract

Vascular plant leaf traits that influence photosynthetic function form the basis of mechanistic models of carbon exchange. Given their unique tissue organization, bryophytes may not express similar patterns. We investigated relationships among tissue, shoot, and canopy traits, and their associations with photosynthetic characteristics in 10 Sphagnum species. Trait relationships were organized around a primary dimension accounting for 43% of variation in 12 traits. There was no significant relationship between nitrogen content of shoot systems and maximum photosynthesis expressed on mass (A(mass)) or area (A(area)) bases due to nitrogen sequestration and storage within the canopy interior. This pattern differs from the distribution of nitrogen in vascular plant canopies. Thus, nitrogen and its relationship to carbon uptake in Sphagnum shoots does not conform to patterns of either vascular plant leaves or canopies. Species that concentrate biomass and nitrogen in the capitulum have enhanced rates of A(mass) and A(area). Consequently, A(area) was positively associated with N(area) of the capitulum only. Overall, water content and carotenoid concentration were the strongest predictors of both A(mass) and A(area) and these were expressed as inverse relationships. The relationships of plant traits in Sphagnum defines a principal trade-off between species that tolerate environmental stress and those that maximize carbon assimilation.

Higher photosynthetic capacity and different functional trait scaling relationships in erect bryophytes compared with prostrate species

“…However, only a few studies have focused on the functional trait relationships of bryophytes, even though they play important roles in the nutrient cycling and carbon fixation of ecosystems (Chapin et al 1987;Crowley and Bedford 2011;Lindo and Gonzalez 2010;Street et al 2013;Vanderpoorten and Goffinet 2009). Rice et al (2008) and Waite and Sack (2010) suggested that the trait relationship rules observed in vascular plant leaves did not apply to Sphagnum species or tropical forest mosses, whereas our previous study found that moss species growing in temperate forests possessed similar functional trait relationships to vascular plant leaves but with distinct scaling (Wang et al 2014). Considering the lack of studies in this field, as well as the wide distribution and high species diversity of this group, the functional trait scaling relationships of bryophytes require further investigation.…”

“…However, the shoot structures of bryophytes with different growth forms vary greatly (Bates 1998;Glime 2007;Mägdefrau 1982). Various shoot structures reflect different adaptive capacities of the species and, to a certain extent, have potent effects on the photosynthetic efficiency (light interception and CO 2 diffusion) and nutrient allocation of bryophytes Niinemets and Tobias 2014;Rice et al 2008). Nevertheless, few studies have compared bryophyte species with different shoot structures in terms of physiological status.…”

“…The differences in functional trait scaling relationships between bryophytes and vascular plant leaves have primarily been attributed to their distinct morphological structures (Rice et al 2008;Waite and Sack 2010). Because of their small size and weak metabolic capacity, ecophysiological research on bryophytes has generally been conducted at the shoot or canopy scale rather than the leaf scale (Rice and Cornelissen 2014).…”

“…(1) For the same projected area, the thickness (the height) and/or density of an erect bryophyte shoot should be higher than that of a prostrate species (Niinemets and Sack 2006;Rice et al 2008). Thus, the former will possess a higher SMA.…”

Passive warming reduces stress and shifts reproductive effort in the Antarctic moss,Polytrichastrum alpinum

“…By growing in tight cushions, poikilohydric mosses trap water among adjacent gametophytes, creating a dense canopy that reduces overall water loss (Rice et al, 2008). The gametophyte density of P. alpinum cores from our control plots was significantly greater than that of warmed plots (Fig.…”