ALBERT

Description: We measured the following vascular plant functional traits: plant height (cm), leaf size (LS, cm2), specific leaf area (SLA, cm2 g-1), leaf dry matter content (LDMC, mg g-1) and leaf moisture content (g g-1) from the most common species in each research unit. We measured the following Sphagnum traits: capitulum density (number of shoots cm-2), fascicle density (number cm-1), surface density (mg cm-3), capitulum dry mass (mg) and capitulum moisture content (cap_wc, g g-1). In addition, rate of net photosynthesis was measured at four light levels. The data was collected from Lakkasuo mire complex located in Southern Finland (61° 47' N; 24° 18' E). The study includes three sites called rich fen, poor fen, and bog. At each site two experimental units were established in 2000/2001: an undrained control unit and a Water level drawdown (WLD) unit that was surrounded by a 30 cm-deep ditches after a control year. Photosynthesis measurements were carried out during summer 2016, while other traits were sampled during August 2016. We measured vascular plant vegetative height (cm), leaf area (LA, cm2 leaf-1) with a leaf area scanner (LI-3000, LI-COR Inc.), leaf fresh mass and leaf dry mass after the sample was dried at 40 °C for at least 48h (mg leaf-1). Leaf dry matter content (LDMC mg g-1) was calculated from fresh and dry mass, while specific leaf area (SLA, cm2 g-1) was calculated from LA and dry mass. Leaf traits were measured from five replicate plants as an average of a sample of ten fully grown healthy leaves from each plant. Sphagnum moss traits were measured from five replicates of single-species samples. Each sample consisted of two parts: a volume-specific sample collected with a core (diameter 7 cm, area 38.5 cm2, height 3 cm) to maintain the natural density of the stand and an additional sample of ca. 10 individuals, with stems more than 5 cm at length. Before collecting the core in the field, the number of shoots was counted from a 4 × 4 cm square for capitulum density (cap_dens, number of shoots cm-2). The volume-specific sample was cleaned of litter and unwanted species before drying at 40 °C for at least 48h to determine the surface density (surf_dens, mg cm-3). The additional sample of ten moss individuals was divided into capitula and stems (4 cm below capitula). We counted the number of fascicles on the 4 cm stem segments (fasc_dens, number cm-1). The capitula were thoroughly moistened and placed on top of tissue paper for 2 minutes to drain, before weighing them for water-filled fresh mass (cap_fw, mg). The samples were dried at 60 °C for at least 48h to measure the capitulum dry masses (cap_dw, mg). The moisture contents of capitula (cap_mc, g g-1) were then calculated as the ratio of water-filled to dry mass. Height growth (mm growing season-1) was measured in the field with the modified cranked wire method (Clymo 1970) as a difference in height between the beginning (mid-May) and end (mid-October) of the growing season 2017. For both vascular plants and mosses, we measured net photosynthesis rate, with a fully controlled, flow-through gas-exchange fluorescence measurement systems (GFS-3000, Walz, Germany; LI6400, LI-COR, USA). For mosses the living apical parts (~0.5 to 1 cm) were harvested right before the measurement and placed on a custom-made cuvette. For vascular plants, leaves, or in the case of shrubs, segments of branches were enclosed within the cuvette without disturbing the connection to the rooting system. Net photosynthesis rate (A, µmol m-2 g-1 s-1) was measured at 1500, 250, 35, and 0 µmol m-2 s-1 photosynthetic photon flux density (PPFD). The cuvette conditions were kept constant (temperature 20°C, CO2 concentration 400 ppm, flow rate 500, impeller in level 5). Relative humidity (Rh) of incoming air was set to 40% for vascular plants and 60% for mosses; for mosses this setting retained the cuvette Rh at around 80%. The setting enabled mosses to remain moist to ensure photosynthesis but protected the device from excess moisture. The data was collected to find out the impact of long-term WLD on functional traits of vascular plants and mosses, and how this impact is modulated by nutrient status (rich fen, poor fen, bog). We first assess (i) how peatland species differ in their traits and their intraspecific trait variability, to quantify (ii) how WLD impacts community level traits at different peatland sites.

Description: We estimated plant community composition as the projection cover of each vascular plant and moss species. We measured the following vascular plant functional traits: plant height, leaf size (LS), specific leaf area (SLA) and leaf carbon (C) and nitrogen (N) contents from the most common species in each site. We measured the following Sphagnum traits: stand density (number of shoots cm-2), capitulum width (cap_width, mm) and dry weight (cap_dw, mg), fascicle density (number cm-1), capitulum dry matter content (CDMC, mg g-1), capitulum water content (cap_wc, g g-1) and capitulum C and N contents and C:N ratio. The data was collected from 47 northern peatlands located in land uplift regions in Finland, Sweden and Russia: Sävar on the west coast of Bothnian Bay (63o50'N, 20o40'E, Sweden), Siikajoki (64°45' N, 24°43', Finland) and Hailuoto island (65°07' N, 24°71' E, Finland) on the east coast of Bothnian Bay, and Belomorsk-Virma (63°90' N, 36°50' E, Russia) on the coast of the White Sea. The data was collected from the different areas as follows: Siikajoki sites were sampled in August 2016, Sävar sites at the end of June 2017, Hailuoto sites during July 2017 and Belomorsk sites at the end of August 2017. We determined the plant community composition by visually estimating the projection cover of each species separately for field (vascular plants) and moss layer using the scale 0.1%, 0.25%, 0.5%, 1%, 2%, 3%, etc. There were fifteen 50 x 50 cm plots in each peatland at Siikajoki and Belomorsk-Virma, and 10 at Sävar and Hailuoto. The sample plots were located five meters apart along a transect starting from the generally treeless peatland margin and heading towards the peatland center. Plant traits were measured as follows: To measure SLA (i.e., the one-sided area of a fresh leaf divided by its oven-dry mass, cm2 g-1), the freshly picked leaf or a sample of 3 leaves in case of shrubs with small leaves was pressed flat between a board and a glass and a standardized photo was taken. The leaf size (LS, cm2) was analysed from the photos with ImageJ. The leaf samples were stored in paper bags and dried at 60°C for a minimum of 48h. The dried samples were weighed, and SLA calculated. The SLA samples were used for carbon (C) and nitrogen (N) content analysis. Leaves from each species from each site were pooled into one sample, which was milled (Retsch MM301 mill) and analyzed for C and N concentrations and for C:N ration on a CHNS–O Elemental analyzer (EA1110) (University of Oulu). Sphagnum moss samples for trait measurements were collected with a corer (7 cm diameter, area 38 cm2, height at least 8 cm) to maintain the natural density of the stand. Stand density was measured as the number of mosses in the sample. From ten individuals we measured the width of the capitula and counted the number of fascicles from a five cm segment below capitulum. We separated the ten moss individuals into capitulum and stem (5 cm below capitula) wetted them and allowed to dry on top of tissue paper for 2 min before weighing them for water filled fresh weight. Samples were placed on paper bags and dried at 60 °C for at least 48h after which the dry mass of capitula and stems were measured. CDMC and cap_wc were calculated from the fresh and dry weight. We used the capitula samples for analyses of C and N concentrations and for C:N ratio, and treated them similarly to vascular plant samples. The data was collected to find out how functional diversity and trait composition of vascular plant and Sphagnum moss communities develops during peatland succession across land uplift regions.