Impact of long-term water level draw-down on functional plant trait composition of northern peatlands@en

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). […]我们针对各研究单元内的常见物种，测定了以下维管植物功能性状：株高（单位：cm）、叶面积（leaf size, LS，单位：cm²）、比叶面积（specific leaf area, SLA，单位：cm²·g⁻¹）、叶干物质含量（leaf dry matter content, LDMC，单位：mg·g⁻¹）以及叶片含水量（单位：g·g⁻¹）。我们还测定了以下泥炭藓属（Sphagnum）性状：头状枝密度（capitulum density，单位：枝条数·cm⁻²）、束枝密度（fascicle density，单位：束数·cm⁻¹）、表层密度（surface density，单位：mg·cm⁻³）、头状枝干质量（capitulum dry mass，单位：mg）以及头状枝含水量（cap_wc，单位：g·g⁻¹）。此外，我们在4个光照梯度下测定了净光合速率。 数据采集于芬兰南部的拉卡苏沃泥炭地复合体（Lakkasuo mire complex，坐标：61°47'N；24°18'E）。本研究包含3个样地，分别为富营养沼泽（rich fen）、贫营养沼泽（poor fen）与藓类泥炭沼泽（bog）。2000/2001年，我们在每个样地内设置两个实验单元：未排水对照单元，以及经1年对照期后开挖30cm深沟渠以实施水位下降（water level drawdown, WLD）的处理单元。 光合速率测定于2016年夏季开展，其余性状采样均在2016年8月完成。我们补充测定了维管植物的营养株高（单位：cm），使用叶面积扫描仪（LI-3000，LI-COR公司）测定叶面积（leaf area, LA，单位：cm²·叶⁻¹），并测定叶片鲜质量；样品经40℃烘干至少48小时后，测定叶片干质量（单位：mg·叶⁻¹）。叶干物质含量（LDMC，单位：mg·g⁻¹）由叶片鲜质量与干质量计算得到，比叶面积（SLA，单位：cm²·g⁻¹）则由叶面积与干质量计算得到。叶片性状的测定采用5次生物学重复：每株植物选取10片完全成熟的健康叶片混合取样，取其平均值。 泥炭藓性状的测定采用5次单物种种样重复。每份样包含两部分：一是用土钻（直径7cm，面积38.5cm²，高度3cm）采集的体积特异性样方，以维持群落的自然密度；二是约10株茎长超过5cm的额外个体样。野外采集土钻前，先在4×4cm的样方内计数枝条数，用于计算头状枝密度（cap_dens，单位：枝条数·cm⁻²）。体积特异性样方经清除凋落物与非目标物种后，于40℃烘干至少48小时，以测定表层密度（surf_dens，单位：mg·cm⁻³）。将额外采集的10株泥炭藓个体分为头状枝与茎部（头状枝下方4cm的茎段），计数4cm茎段上的束枝数，用于计算束枝密度（fasc_dens，单位：束数·cm⁻¹）。[…]