Leaf Functional Traits Vary in Urban Environments: Influences of Leaf Age, Land-Use Type, and Urban–Rural Gradient

Abstract

An increasing number of studies have focused on the response and adaptation of plants to urbanization by comparing differences in leaf functional traits between urban and rural sites. However, considerable uncertainties remain because differences in land-use type have not frequently been taken into account when assessing the effect of urbanization on leaf traits. In this study, we sampled the needles of Chinese pine (Pinus tabuliformis Carr.) in areas with three land-use types (roadsides, parks, and neighborhoods) along an urban–rural gradient in Beijing, China to determine the effect of urbanization on leaf functional traits. There were significant differences in the values of leaf functional traits between the needles of the current and previous year and across land-use types. Pines growing on roadsides had leaves with smaller length, width, and area, as well as lower stomatal density, compared with those growing in parks and neighborhoods. This implies that on roadsides, plant capacity to acquire resources (e.g., light and carbon dioxide) was degraded. Stomatal density, leaf width, and leaf P concentration increased with increasing distance from the city center, while leaf K concentration decreased with increasing distance from the city center. Importantly, there were significant differences in the urban–rural gradient of leaf functional traits between leaves of different ages, and across land-use types. Leaf age was the most important factor influencing leaf nutrient traits, while land-use type was the most important factor influencing leaf morphological traits in urban environments. Thus, considering the effects of the plant characteristic and land-use type on traits is important for assessing the urban–rural gradients of plant functional traits.

Cities of the Anthropocene: urban sustainability in an eco-evolutionary perspective

“…The observed adaptation of Daphnia to urban heat islands, toxic cyanobacteria and pesticides might determine the net effect of urban water pollution strategies [84]. Su et al [82] examined trait changes of the Chinese pine (Pinus tabuliformis Carr. ), a species that is native to China.…”

“…Su et al . [82] examined trait changes of the Chinese pine ( Pinus tabuliformis Carr. ), a species that is native to China.…”

“…[82] found that the leaf functional traits of Chinese pine, which may affect the ability of trees to capture carbon or mitigate air pollution, have changed, although the genetic basis of these trait changes has not been determined.

Figure 4Examples of urban-driven evolutionary changes in traits that affect the ability of organisms to perform important ecosystem functions include: (i) the effect of urbanization on bumblebee body size, which affects pollination [128]; (ii) the genetic differentiation in physiology and structured pace-of-life syndromes in the water flea Daphnia magna , which affects water quality [84]; (iii) the effect of rapid evolution in root traits of a dominant marsh sedge on carbon accumulation and soil surface accretion, which affects marsh resilience to sea-level rise [126]; (iv) the copper-tolerance of red-rust bryozoans and its impact on local ecosystems [129]; and (v) the effects of urban land-use on leaf nutrient and morphological traits of Chinese pines, which influences their ability to mitigate atmospheric pollution and carbon emissions [82].

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Assessment of NO2 Purification by Urban Forests Based on the i-Tree Eco Model: Case Study in Beijing, China

“…The green cover rate in Beijing has steadily increased from 47.4% to 48.5% during the period of 2014-2019 [24]. There is a gradient pattern for urban forests in Beijing, with significant differences in species and functional traits between urban and suburban districts [28,29].…”

“…For the Yanqing District, the average annual absorption was 1883 tons, and emission was 1447 tons, with absorption exceeding emissions by 436 tons. The uneven distribution pattern of NO 2 absorption between urban areas and suburban areas may be influenced by the large differences in population density, building density, forest cover, and the quality of urban forests between the different districts in Beijing [23,28,29]. According to the deposition flux model (Equation ( 1)) and the total absorption amount model (Equation ( 6)), it can be inferred that the total absorption of NO 2 by urban forests has a positive linear relationship with atmospheric NO 2 concentration and the effective leaf area of urban forests, while the absorption per unit of green cover is mainly related to the local air pollutant concentration.…”