DOI: 10.6073/pasta/f0ef599895ae16be914843566133bed1
title: Foliar and sapwood nutritional and metabolic responses to Ca-treatment at the Hubbard Brook Experimental Forest, 2000 – 2015

description: Background Acidic deposition has caused a depletion of calcium (Ca) in the northeastern forest soils. One time application of wollastonite (CaSiO3 - 1.2 Mg ha-1 of Ca) was done at watershed 1 (WS1) of the Hubbard Brook Experimental Forest (HBEF) in 1999 to evaluate its effects on various functions of the HBEF ecosystem. This rate of application was intended to increase the existing base saturation of the soil from 10% to approximately 19%, and to increase the soil pH to the level that was estimated to exist ~50 years prior to treatment. More details on the treatment can be found at http://www.hubbardbrook.org/research/longterm/calcium/w1_overview/index.html. The overall objective of this study was to evaluate changes in foliar and sapwood metabolic parameters and microbial diversity as indicators of stress and overall health in trees exposed to Ca-supplementation. Raw data from Ca-treated WS1 are compared with WS3 (reference watershed) for cellular metabolites, exchangeable foliar chemistry (not totals) 2000-2015. These watersheds are in close proximity (less than 1.5 Km apart) with similar geology, temperature, soils, and overall climate. For more details see a list of references given below Ca-Supplementation-Metabolic Study (WS1 & along eastern edge of WS3) SUMMARY: The effects of Ca addition on foliar soluble (extractable in 5% HClO4) ions, chlorophyll, polyamines, and amino acids were studied in three hardwood species, namely sugar maple, yellow birch, and American beech. We further analyzed these effects in relation to elevation at Ca-supplemented WS1 and reference WS3 watersheds. During the earlier years foliar soluble Ca increased significantly in all species at mid and high elevations at Ca-supplemented WS1. This was accompanied by increases in soluble P, chlorophyll, and two amino acids, glutamate and glycine. A decrease in known metabolic indicators of physiological stress (i.e. the amino acids, arginine and γ-aminobutyric acid (GABA), and the diamine, putrescine) was also observed. In general, these changes were species-specific and occurred in an elevation dependent manner. Despite an observed increase in Ca at high elevation for all three species, only sugar maple exhibited a decrease in foliar putrescine at this elevation indicating possible remediation from Ca deficiency. At higher elevations of the reference WS3 site, foliar concentrations of Ca and Mg, as well as Ca:Mn ratios were lower, whereas Al, putrescine, spermidine, and GABA were generally higher. Comparison of metabolic data from these three species reinforces the earlier findings that sugar maple is the most sensitive and American beech the least sensitive species to soil Ca limitation. Furthermore, there was an increase in sensitivity with an increase in elevation. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES). The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station.