Methods
Freshly senescent leaves were collected from most of the plots in the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE). More information on this project design can be found at the following citation:
Yanai, R.D., M. Fisk, and T.J. Fahey. 2022. Multiple Element Limitation in Northeast Hardwood Ecosystems (MELNHE): Project description, plot characteristics and design ver 1. Environmental Data Initiative. https://doi.org/10.6073/pasta/bcfc628d26e78b3dff648c34a33da1a3
In 2009 and 2010, freshly senescent leaf litter was collected from three suspended mesh traps per plot in each of 10 stands. Litter was collected in autumn between rain events and separated by species; each species per plot was analyzed for nutrient concentrations.
To obtain foliar calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), sulfur (S), strontium (Sr), and phosphorus (P) concentrations, 0.25 g of sample was oven dried at 60°C, ashed in a muffle furnace at 470°C, digested in 6 N HNO3, and analyzed with ICP-OES. Foliar N concentrations were determined using a CN elemental analyzer (EA1112 elemental analyzer; Thermo Electron Corporation, Waltham, Massachusetts, USA). Concentrations of N and P obtained from reference leaf material (NIST SRM 1515) analyzed with our samples were within 5% of certified values. Strontium values in 2010 were not published due to the fact that values were inexplicably high, perhaps due to calculation errors.
Some samples from 2009 and 2010 were run again in 2023 to check unusual values. If the new results were similar to the original ones, the two estimates were averaged. Eight samples from 2010 for which fresh litter was not collected were estimated by analyzing litter samples collected in litter traps in the same plots in that year. These additions and corrections are indicated in the comments section of the data.
In September 2014, three net traps were hung in each of the four plots of C2. Each net trap was hung approximately 1.5 m above the ground using mesh netting and zip ties. Plots were revisited the following day and leaf litter that had fallen into each trap was collected. Leaves from each net were composited by plot and species. In October 2014, litter that appeared freshly fallen was collected from the ground. For both collection dates, leaves of five species were collected: American beech (Fagus grandifolia), red maple (Acer rubrum), white birch (Betula papyrifera), yellow birch (Betula alleghaniensis), and pin cherry (Prunus pensylvanica). All leaves to be used for subsequent chemical analyses were weighed, photographed (for surface area), dried to constant mass, and weighed again.
In 2015, leaf litter was collected from the same mid-aged and mature stands it was collected from in 2009 and 2010 (C4, C6, C8, C9, HBM, HBO, JBM, JBO), plus the Ca plots of C1, C6, C8, HB, and JB. Leaf litter was collected from beech in all stands, red maple from the mid-aged stands, and sugar maple (Acer saccharum) from the mature stands, except for JBM where sugar maple was collected instead of red maple due to the species composition of that stand. Freshly fallen whole leaves with petioles attached free of disease and damage were collected from each plot during the first two weekends of October 2015 (10/3-10/4 and 10/10-10/11). The litter from the second collection was used for subsequent analyses with the exception of three P concentrations for which values from the first weekend were used. Leaves were stored in paper bags from the field to the lab, then weighed, photographed, dried, and weighed again.
In 2014 and 2015, each sample of leaves was ground to pass through a 20 mm mesh screen. A 0.25 g subsample was ashed and hot plate-digested with 6N nitric acid. The digested samples were analyzed with ICP-OES (Optima 3500 DV ICP-OES, Perkins-Elmer) to determine concentrations of Al, Ca, K, Mg, Mn, Na, P, Sr, and S. To determine C and N concentrations, a 2-3 mg subsample was analyzed in a CN analyzer (FlashEA 1112 analyzer, Thermo Scientific). Concentrations of Ca, K, Mg, Mn, P, Sr, and S of NIST SRM 1515 were within 10% of certified values for most acid digestion batches (see accompanying QC data).
In 2016, freshly fallen leaves were collected from stands C1, C4, C6, C8, C9, HBM, HBO, JBM, and JBO. Litter was collected between October 21 and 23. Species collected include American beech (C1), pin cherry (C1, C4, C6, JBM), white birch (C1, C4, C6, HBM, JBM), and yellow birch (C4, C6, C8, C9, HBM, HBO, JBM, JBO). freshly fallen whole leaves with petioles attached free of disease and damage were collected in mid-October 2016. Care was taken to collect leaves near the base of the same trees that were sampled for green, sunlit foliage in summer 2016; this data can be found in the following data package:
Hong, S.D., K.E. Gonzales, C.R. See, and R.D. Yanai. 2021. MELNHE: Foliar Chemistry 2008-2016 in Bartlett, Hubbard Brook, and Jeffers Brook (12 stands) ver 1. Environmental Data Initiative. https://doi.org/10.6073/pasta/b23deb8e1ccf1c1413382bf911c6be19
In 2016, 0.25 g of sample was digested in 6 N nitric acid using microwave digestion and analyzed with ICP-OES (Optima 3500 DV ICP-OES, Perkins-Elmer). Elements measured include Al, boron (B), Ca, iron (Fe), K, Mg, Mn, Na, P, S, Sr, and Zn (zinc).To determine C and N concentrations, a 2-3 mg subsample was analyzed in a CN analyzer (FlashEA 1112 analyzer, Thermo Scientific). Concentrations of B, Ca, K, Mg, Mn, P, and Sr were within 15% of certified values for NIST SRM 1515, S and Zn were within 20%, Fe was within 25%, and Al and Na were consistently over 25% (see accompanying QC data).
Freshly fallen leaves were then collected from stands HBM, HBO, HBCa, JBM, and JBO in 2021 and from stands C1, C2, C4, C6, C8, and C9 in 2022. Care was taken to choose leaves that matched the criteria for selecting corresponding foliage in the summer (e.g., no insect damage or disease, complete leaves with petioles, relatively small and thick leaves that likely came from sunlit portions of the trees). Between 9 and 30 leaves were collected per species per plot in 2021-22, depending on the number of trees of that species sampled for foliage in that plot (9-10 times the number of trees sampled for foliage).
In the lab, 0.25 g of sample was digested in 6 N nitric acid using microwave digestion and analyzed with ICP-OES (Optima 3500 DV ICP-OES, Perkins-Elmer). Elements measured include Al, B, Ca, Fe, K, Mg, Mn, Na, P, S, Sr, and Zn (zinc).To determine C and N concentrations, a 2-3 mg subsample was analyzed in a CN analyzer (FlashEA 1112 analyzer, Thermo Scientific). Al, Na, and B values are not reported, as Al often did not meet ICP QC criteria (e.g., high relative standard deviations), vials were contaminated with Na, and B was likely not rinsed out of the ICP system in a sufficient manner. Concentrations of Ca, K, Mg, Mn, P, and Sr were within 14% of certified values for NIST SRM 1515, and Fe and Zn were within 21% (see accompanying QC data).
This EDI data package includes a supplemental file with QC data from 2014, 2015, 2016, 2021, and 2022. QC data from nutrients measured using ICP-OES are summarized and color-coded for 2014 and 2015; for 2016, the concentrations reported in mg/g are listed first and the percent recovery is listed in the second set of columns. QC data from aspartic acid and SRM 1515 samples are listed in separate sheets for 2014 and 2015 as well; %N and %C values are listed in bold.
