Climate and lawn management interact to control C₄ plant distribution in residential lawns across seven U.S. cities

Abstract

In natural grasslands, C4 plant dominance increases with growing season temperatures and reflects distinct differences in plant growth rates and water use efficiencies of C3 vs. C4 photosynthetic pathways. However, in lawns, management decisions influence interactions between planted turfgrass and weed species, leading to some uncertainty about the degree of human vs. climatic controls on lawn species distributions. We measured herbaceous plant carbon isotope ratios (δ13C, index of C3/C4 relative abundance) and C4 cover in residential lawns across seven U.S. cities to determine how climate, lawn plant management, or interactions between climate and plant management influenced C4 lawn cover. We also calculated theoretical C4 carbon gain predicted by a plant physiological model as an index of expected C4 cover due to growing season climatic conditions in each city. Contrary to theoretical predictions, plant δ13C and C4 cover in urban lawns were more strongly related to mean annual temperature than to growing season temperature. Wintertime temperatures influenced the distribution of C4 lawn turf plants, contrary to natural ecosystems where growing season temperatures primarily drive C4 distributions. C4 cover in lawns was greatest in the three warmest cities, due to an interaction between climate and homeowner plant management (e.g., planting C4 turf species) in these cities. The proportion of C4 lawn species was similar to the proportion of C4 species in the regional grass flora. However, the majority of C4 species were nonnative turf grasses, and not of regional origin. While temperature was a strong control on lawn species composition across the United States, cities differed as to whether these patterns were driven by cultivated lawn grasses vs. weedy species. In some cities, biotic interactions with weedy plants appeared to dominate, while in other cities, C4 plants were predominantly imported and cultivated. Elevated CO2 and temperature in cities can influence C3/C4 competitive outcomes; however, this study provides evidence that climate and plant management dynamics influence biogeography and ecology of C3/C4 plants in lawns. Their differing water and nutrient use efficiency may have substantial impacts on carbon, water, energy, and nutrient budgets across cities.

Urbanization drives convergence in soil profile texture and carbon content

“…Previous studies on urban soil biophysical properties, and especially urban soil carbon, have shown that urbanization creates novel patterns in soil profiles ( Schifman et al 2018 , Trammell et al 2019 , Canedoli et al 2019 ). Based on previous work, there is a consistent literature indicating widespread urban ecological homogenization, where ecosystem-level properties (e.g.…”

Influence of Climate and Management on Patterns of Taxonomic and Functional Diversity of Recreational Park Vegetation

“…However, while the physiological traits of the C3 turf in Baltimore and the C4 turf in Palm Springs were similar, the range of trait values was smaller in Palm Springs. This result is indicative of fewer varieties of C4 turf grass for planting compared to C3 varieties in nurseries throughout the country (Trammell et al, 2019).…”

Urban Grassland Management Implications for Soil C and N Dynamics: A Microbial Perspective

“…This definition constitutes a range of land uses, spatial scales, and interconnectivity, from sports fields or golf courses to residential lawns or roadsides (Figure 1). In all cases, urban grasslands are herbaceous, perennial landscapes of primarily turf-forming grass species, although dominant species composition is regionally adapted (Thompson and Kao-Kniffin, 2017;Trammell et al, 2019). Moreover, different types of urban grasslands experience a wide range of management intensities (Figure 2).…”

“…Wang et al (2014) concluded that reducing fertilizer applications could reduce denitrification in the low input lawns and that lawns composed of warm-season C 4 grasses could reduce irrigation and fertilization needs while still maintaining high productivity and N retention. The proportion of C 3 /C 4 grasses present in lawns across the United States is a function of the mean annual temperature of the region, elevated urban temperatures due to heat island effects, elevated CO 2 and lawn management dynamics (Bijoor et al, 2008;Trammell et al, 2019). More research is needed to determine how the C 3 /C 4 composition of urban grasslands affects soil microbiome composition and function as it relates to urban biogeochemical processes.…”

“…Urban grasslands have been shown to accumulate soil C, and retain N for decades after establishment. There is great variability in regional climates that affect urban grassland plant species composition (Trammell et al, 2019), productivity and nutrient retention and accumulation (Qian and Follett, 2012;Smith et al, 2018), and the need for supplemental inputs to maintain urban grassland quality. The management intensity of urban grasslands also varies as a function of intended use, of numerous social-ecological factors (Cook et al, 2012), and of personal preference by property owners and managers.…”