The Sphagnome Project: enabling ecological and evolutionary insights through a genus-level sequencing project.

Considerable progress has been made in ecological and evolutionary genetics with studies demonstrating how genes underlying plant and microbial traits can influence adaptation and even 'extend' to influence community structure and ecosystem level processes. Progress in this area is limited to model systems with deep genetic and genomic resources that often have negligible ecological impact or interest. Thus, important linkages between genetic adaptations and their consequences at organismal and ecological scales are often lacking. Here we introduce the Sphagnome Project, which incorporates genomics into a long-running history of Sphagnum research that has documented unparalleled contributions to peatland ecology, carbon sequestration, biogeochemistry, microbiome research, niche construction, and ecosystem engineering. The Sphagnome Project encompasses a genus-level sequencing effort that represents a new type of model system driven not only by genetic tractability, but by ecologically relevant questions and hypotheses.

Canopy structure affects temperature distributions and free convection in moss shoot systems.

PREMISE OF THE STUDY: Nonvascular plants play important roles in exchange of water and heat at the soil-atmosphere interface. Differential evaporative cooling may cause temperature gradients within bryophyte canopies, influencing convective heat and mass transport. Understanding mechanisms that affect fluxes through moss layers should improve models of forest floor function. METHODS: A three-dimensional thermal imaging system measured temperature distributions within moss shoot systems that were used to explore relationships among canopy structure, temperature gradients, evaporation, and conductance to water vapor (gs ). We studied five moss species under dark and light conditions in the lab. Also, these properties were measured in two species that differed in canopy structure during drying. KEY RESULTS: Differential evaporative cooling led to a 1.4 to 5.0°C range in shoot temperatures within canopies. Samples displayed -0.5 to -0.9°C/cm temperature gradients with cooler apical temperatures. Gradient magnitudes did not differ among species, but taller canopies expressed greater temperature differences. Light enhanced both the gradient and the temperature difference. Rates of evaporation were significantly related to canopy height in the light, but not in the dark, although gs was positively associated with canopy height in both. Rayleigh (Ra) numbers characterize whether temperature gradients likely generate free convection. In tall canopies, Ra numbers exceeded the value indicative of free convection and turbulent flow. As plants dried, temperature gradients decreased. CONCLUSIONS: When moss canopies are wet, cooler apical temperatures create thermal instabilities within the canopies that appear sufficient to enhance convective transport of water vapor and heat in tall canopies with low bulk density.

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

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.

Laser scanning reveals bryophyte canopy structure.

We evaluated laser scanning as a method to provide depth measurements for bryophyte canopies at fine spatial scales to derive surface roughness (Lr), a structural parameter. Depths to the first vertical canopy contact were measured on 5 x 5 cm2 areas of 27 bryophyte canopies using a contact probe, a commercial laser scanner and a scanner employing a laser diode striper (LED scanner). Laser scanning adequately distinguished structural types, but scanner configuration led to differences in the magnitude of Lr. LED scanning did not damage photosystem II function in three bryophyte species, Bazzania trilobata, Sphagnum girgensohnii and Pleurozium schreberi, as evidenced by no change in the chlorophyll fluorescence parameter FV/FM following LED scanning, but a decrease when subjected to high light. A previously published boundary layer conductance model was parameterized with surface roughness values determined using a laser scanner and compared with the results obtained with contact probe measures. The resulting parameters of the functional models did not differ significantly from each other.

Cushion size, surface roughness, and the control of water balance and carbon flux in the cushion moss Leucobryum glaucum (Leucobryaceae).

We explored the size dependence of water balance and carbon flux in the cushion moss Leucobryum glaucum (Leucobryaceae). Conductance to water vapor (g(a)) was modeled empirically using 4-24 cm diameter cushions (N = 14) evaluated across wind speeds from 0.7 to 4.3 m/s in a wind tunnel. Model parameters included wind speed (u), kinematic viscosity (v), cushion diameter (L(d)), and surface roughness (L(r)). The model g(a) = -9.62(u/v)(1.21) · L(d)(-0.35) · L(r-in)(-1.85) (where L(r-in) represents a dimensionless form of L(r); R(2) = 0.88) indicates negative relationships between g(a) and both L(d) and L(r). These predictions were evaluated during a 5-d field experiment where water loss and net carbon exchange (estimated by ΔF/F(m)') were monitored. In the field (N = 18, 4-34 cm diameter cushions), L(r), but not L(d), controlled rates of evaporation due to additional turbulence that reduced size dependence of cushions along the forest floor. However, the duration of positive net carbon gain varied from 1.4 to 4.4 d and was significantly longer in larger diameter cushions. Thus, under field conditions, size-dependent changes in surface-area-to-volume relationships influence the duration of net carbon gain more than differences in water flux and lead to a strong size dependence of water balance and carbon flux.