<emphasis role="strong">Methods</emphasis>
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.
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
maturestands 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, leaf litter was collected from stands C1, C4, C6, C8, C9,
HBM, HBO, JBM, and JBO. Species collected include American beech (C1),
pin cherry (C1, C4, C6, JBM), white birch (C1, C4, C6, HBM, JBM)
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 at the following
citation:
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). Concentrations of X of
NIST SRM 1515 samples were within X% of certified values (see
accompanying QC data). To determine C and N concentrations, a 2-3 mg
subsample was analyzed in a CN analyzer (FlashEA 1112 analyzer, Thermo
Scientific).
