Red maple (Acer rubrum L.) trees demonstrate acclimation to urban conditions in deciduous forests embedded in cities

Abstract

The impacts of urbanization, such as urban heat island (UHI) and nutrient loads, can influence tree function through altered physiology and metabolism and stress response, which has implications for urban forest health in cities across the world. Our goal was to compare growth-stimulating and stress-mitigating acclimation patterns of red maple (Acer rubrum) trees in deciduous forests embedded in a small (Newark, DE, US) and a large (Philadelphia, PA, US) city. The study was conducted in a long-term urban forest network on seventy-nine mature red maple trees spanning ten forests across Newark and Philadelphia. We hypothesized that red maples in Philadelphia forests compared to Newark forests will be healthier and more acclimated to warmer temperatures, elevated CO 2 concentrations and reactive nitrogen (N r) deposition, and higher nutrient/heavy metal loads. Therefore, these red maples will have higher foliar pigments, nutrients, and stress-indicating elements, enriched δ 15 N isotopes and increased free polyamines and amino acids to support a growth-stimulating and stress-induced response to urbanization. Our results indicate red maples are potentially growth-stimulated and stress-acclimated in Philadelphia forests experiencing a greater magnitude of urban intensity. Red maples in Philadelphia forests contained higher concentrations of foliar chlorophyll, %N, δ 15 N, and nutrients than those in Newark forests. Similarly, lower foliar magnesium and manganese, and higher foliar zinc, cadmium, lead, and aluminum reflected the difference in soil biogeochemistry in Philadelphia forests. Accumulation patterns of foliar free amino acids, polyamines, phosphorous, and potassium ions in red maples in Philadelphia forests shows a reallocation in cellular metabolism and nutrient uptake pathways responsible for physiological acclimation. Our results suggest the approach used here can serve as a model for investigating 'plant physiology' and the use of urban trees as a biomonitor of the impacts of 'urban pollution' on urban forests. The results suggest that cellular oxidative stress in trees caused by pollutant uptake is mitigated by the accumulation of free amino acids, polyamines, and nutrients in a larger city. Our study provides a framework for determining whether trees respond to complex urban environments through stress memory and/or acclimation.

Thermal, water, and land cover factors led to contrasting urban and rural vegetation resilience to extreme hot months

“…This may be in part because warmer nighttime temperatures can reduce frost damage to leaves during the phenological transition seasons ( 49 , 50 ). Another factor may be acclimatization in photosynthesis and respiration in the warmer parts of the city ( 51 , 52 ), which has the possibility of being transient and hence not reflected in the optimal temperatures calculated from multiyear data at annual level ( SI Section 1.2.4 ) ( 53 ). Also, the warmer parts of a city may be more built-up, with more nighttime lighting that alters vegetation phenology ( 28 , 54 ).…”

Is foliar tissue drying and grinding required for reliable and reproducible extraction of total inorganic nutrients? A comparative study of three tissue preparation methods

“…This portion of nutrients contains Ca present as CaOx with 2 N HCl or 5% PCA (Minocha et al, 2015a). However, scientists in the biogeochemistry field have always made use of the total inorganic nutrient concentrations and analyze these by first drying and grinding the leaf tissue (Crim et al, 2019;Mcdermot et al, 2020;Arseneau et al, 2021;Hong et al, 2022). Therefore, to bridge this gap and to be able to make more direct comparisons among both types of reported studies, the present study was designed to explore an efficient and reproducible way to conduct total inorganic nutrient analyses using a subsample of the same pool of wet tissue as is often used for metabolomic and genomic analyses.…”

“…According to these records, even when branches were sampled from within the mid-canopy area for a given study, but the distance from the top of the canopy varied more than two meters for the same trees, the concentrations of nutrients and metabolites in the foliage would be significantly different. Reported literature shows that under abiotic and biotic stress dilute acid-soluble inorganic nutrients and metabolites changed in concert in order to maintain homeostatic balance within cells (Minocha et al, 1997;Bubier et al, 2011;Schaberg et al, 2011;Ma et al, 2020;Mcdermot et al, 2020;Minocha et al, 2021;Blagden et al, 2022;Majumdar et al, 2022). Thus, the current practices of pooling foliar tissue (as described above) followed by drying and grinding before total inorganic nutrients analyses, though economical, are not the best if the goal is to advance our understanding of the collaborative role of nutrients alongside metabolites in maintaining homeostasis within the plant tissue under study.…”

Native tree seedling growth and physiology responds to variable soil conditions of urban natural areas

“…Scharenbroch and Catania (2012) and Scharenbroch et al (2017) established an urban soil quality index and a rapid urban site index for assessing the quality of street tree planting sites, but similar tools linking urban natural area site conditions and tree performance are lacking. Foliar chemistry of trees in urban natural areas can also provide insight about nutrient cycling and availability, as well as potential toxic effects of urban pollutants (Falxa‐Raymond et al 2014; McDermot et al 2020; Sonti et al 2021). However, these studies are limited and focus on larger trees and long‐term productivity rather than the early establishment of seedlings.…”