Abstract

Authors

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Dataset Citation

Verity Salmon, Colleen Iversen, Amy Breen, Holly VanderStel, Joanne Childs. 2019. NGEE Arctic Plant Traits: Plant Aboveground Biomass, NPP and Traits, Kougarok Road Mile Marker 64, Seward Peninsula, Alaska, beginning 2016. Next Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, USA. Dataset accessed on [INSERT_DATE] at https://doi.org/10.5440/1346199.

Dates

2016-07-27 - current

Geographic Location

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Methodology

Aboveground biomass was determined in twelve plots across six vegetation types in July of 2016. Methods employed included destructive harvests to sample understory species ("Understory Clip plots") and shrub surveys combined with existing allometric relationships to determine the aboveground biomass of tall shrub species ("Shrub Clip Plots"). Aboveground Biomass: Understory Clip Plots When sampling understory aboveground biomass we included nonvascular plants, lichen, graminoids, forbs, and dwarf shrub species (including Betula nana and Vaccinium uliginosum). To quantify aboveground biomass for these plants, we clipped all plant material from a 20cm x 50cm area at the level of the moss or soil surface. Some material was sorted within 1-2 days of collection in the UAF lab facility in Nome, but most material was frozen, shipped, and sorted at ORNL. All plant material was separated by species and leaves were separated from stems. Whenever possible, current year stem and leaves were separated from older materials and treated as separate samples. For woody plants, this often meant looking for new stem material with bark was lighter in color and more pliable than the older tissue. Attached dead leaves and wood were separated from live leaves and wood. Inflorescences and fruits were separated when present. Mosses were distinguished at the genus level but only green material was collected. Lichen were collected and sorted to the level of functional type (foliose, crustose, fruticose). After sorting, all materials were dried in an oven at 70 degrees C for 1-2 days, allowed to come to room temperature in a desiccator, and weighed. Aboveground Biomass: Shrub Clip Plots To quantify the biomass of tall shrub species, we surveyed larger vegetation plots (2.5m x 2.5m and 5m x 5m) for the presence of Alnus viridiris ssp fruticosa, Betula glandulosa, Salix alaxensis, Salix glauca, Salix pulcra, and Salix richardsonii. For all individuals of these species in the plot we noted species, measured the max height, and measured the basal diameter of all stems at the ground level. When the stem was not uniformly round, we measured basal area twice and took an average. We then performed a destructive harvest of one individual for each of the tall shrub species present in the plot to determine whether existing allometries could be applied at this site. During the destructive harvest of these tall shrub species, we separated attached dead leaves, inflorescences, live leaves, attached dead wood, live wood, and current year's stem growth in the field. Stem growth of current year was differentiated from old stem growth by the absence of healed leaf bud scars and lighter color bark. While in the field, we measured total fresh weight of live and dead wood using hanging scales and subsamples of these tissues were brought back to the lab. These samples were weighed before and after being dried in an oven to determine % water content for live and dead wood. The water weight in live and dead wood was then subtracted from the field weights of these tissue to get the total dry weight of live and dead wood. After sorting, all plant tissues were dried in an oven at 70 degrees C for 1-2 days, allowed to come to room temperature in a desiccator, and weighed. The aboveground biomass numbers from these harvested shrubs were found to be within the range of existing allometric relationships (See Fig 1. in documentation and Berner et al, 2015). Aboveground Biomass: Tall Alder individuals In one of our vegetation types ("Alder shrubland"), the tall alder shrubs (Alnus viridis spp. fruticosa) were over 3m tall and therefore were too large to sample destructively in 2016. They were also too large to sample using a 2.5x 2.5m plot. For this vegetation type, we therefore setup plots that were 5m x 5m and surveyed the height and basal diameter of all alder stems within the plot. Allometries from Berner et al (2015) were applied to determine aboveground biomass. We collected a wood core and sun and shade leaves from each stem but did not perform a destructive harvest of tall Alder individuals. NPP of leaves and Stems In understory clip plots, current year stem and leaves were separated from older materials and treated as separate samples for quantification of NPP. For woody plants, this often meant looking for new stem material with bark was lighter in color and more pliable than the older tissue. Net primary productivity for stems was the sum of new stem material at the time of harvest. Net primary productivity of leaves was the entire pool of leaves for deciduous species and was the sum of leaves attached to new stem material for evergreen species. Graminoids were assumed to be deciduous, with a leaf pool turning over annually. In shrub clip plots, we did not harvest all shrubs in a plot so extrapolation of stem NPP was necessary. Given the agreement between our field data and Berner et al's allometric equations for aboveground biomass (Fig 1) we relied on these allometries to calculate NPP for the tall shrubs we surveyed but did not harvest. The allometric relationships in Berner et al do not consider secondary stem growth (thickening of existing stems) and do not separate leaf biomass from stem biomass. We therefore used the ratio of leaves to the sum of new leaves plus stem observed in our harvests to separate leaf and stem biomass for all tall shrubs. The ratios in our data (0.80-0.87) were similar to those that Berner observed in a subset of his data (0.80, personal communication). We assumed that leaf NPP for tall shrubs would consist of the entire leaf pool since all the tall shrubs are deciduous. Stem NPP is the sum of primary stem NPP (extension of new stem) plus secondary stem NPP (thickening of existing stems). Primary stem NPP was calculated as the NPP from Berner's allometric equations minus the leaf NPP. Secondary stem NPP was calculated based on ratios of secondary stem growth to primary stem growth observed for Salix and Betula in Bret-Harte et al's study from Toolik Arctic LTER (Bret-harte et al., 2002). The ratio applied to Alder was an average of Salix and Betula. Foliar Traits Foliar data presented here was collected from the Kougarok hillslope site starting in July of 2016. All leaves were collected during the peak of the growing season and were fully mature at the time of collection. See table in documentation for species code assignment. Specific leaf area (SLA) SLA of tall deciduous shrub leaves (Alnus, Betula, Salix) was measured by taking leaf punches with a known diameter from leaves. Leaf punches were counted, pooled, oven dried at 70 degrees C and weighed the neared 0.1 mg. SLA of smaller leaves was measured by scanning the leaves in WinRhizo (Regent Instruments, Inc., Quebec, Canada) to attain leaf area. Leaves were then pooled, dried, and weighed. Specific leaf area was calculated as the cm2 leaf area per g dry leaf weight. Leaf % C and %N All leaf %C values were from analysis on an elemental analyzer (Costech Analytical Technologies, Inc., Valencia, CA, USA). Leaf %N values were either from analysis on the same elemental analyzer or from isotope ratio mass spectrometry (IRMS, Integra CN, SerCon, Crewe, UK). Leaf %P Leaf %P was determined from Kjeldahl digests that were run on a QuikChem 8500 analyzer (Lachat Instruments, Loveland, CO, USA). Leaf δ15N and δ13C All isotopic ratios reported here are from isotopic ration mass spectrometry (IRMS, Integra CN, SerCon, Crewe, UK).

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