Sunlit foliage was sampled from two locations in canopies of dominant and codominant sugar maple and yellow birch trees (>10 cm in diameter at breast height) using a shotgun in most of the plots in the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE). More information on this project design can be found in the following file:
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
Foliage was sampled at Hubbard Brook and Jeffers Brook in 2021 and at Bartlett in 2022; foliage from 85 sugar maple trees and 137 yellow birch trees were sampled in total. Most trees were sampled from the measurement area, though occasionally trees from the buffer were sampled if there were not enough suitable trees there. Three leaves from each tree were selected for stomatal density and length measurements. These leaves were air-dried and pressed in a plant press for at least 72 hours.
Stomata were visualized using clear nail polish impressions. Clear nail polish was applied in three approximately 1 x 1-cm squares on the leaf: one near the base of the leaf, one in the middle of the leaf, and one at the top of the leaf, along but avoiding the midvein. Impressions were mounted on clear slides using transparent tape and viewed using light microscopy at 400x magnification. One photograph was taken of each impression. Care was taken to photograph an area on the impression in which as many stomata were as clear as possible and veins were minimally present, if at all. Photographed stomata were counted in each image using ImageJ software and converted to units of stomata per square millimeter by dividing the count by 0.066 square millimeters.
Length of three stomata were measured in each image for 15 yellow birch trees in JBM and for 35 sugar maple trees across HBM, HBO, and JBM (405 stomata for yellow birch, 945 stomata for sugar maple). Length was measured in micrometers.
An initial pilot study was conducted on sugar maple trees in stand HBM using 200x magnification (i.e., a 20x objective lens), and a second pilot study was done measuring stomata in yellow birch at 100x vs. 400x (10x vs. 40x objective lenses). These density and length data are included as “other entities” in this data package.