Evergreen trees stimulate carbon accumulation in urban soils via high root production and slow litter decomposition

• Published in: The Science of the total environment Vol. 774; p. 145129
• Main Authors: Lu, Changyi, Kotze, D. Johan, Setälä, Heikki M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.06.2021
• Subjects: Carbon; carbon dioxide; carbon sequestration; Cities; Deciduous tree; Ecosystem; ecosystems; environment; Finland; Forests; grasses; Home field advantage; Lawn; lawns and turf; organic matter; Plant functional type; plant litter; Soil; Trees; Urban park; urbanization; Finland; Cities; Urban park; Lawn; Plant functional type; Deciduous tree; Home field advantage
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.145129

Urban soils can, when not sealed, store a considerable amount of carbon (C) especially under cool climates. Soil C sequestration is controlled by plant functional type, but the mechanisms by which plant types affect C accumulation in urbanised settings is poorly known. We selected 27 urban parks of varying ages (young: 5–15, old: >70 years) and 10 reference forests (>80 years) in southern Finland to study whether the ability of soils to store C relates to (i) the decomposition rate of different litter types (recalcitrant vs. labile), and/or (ii) organic matter (OM) input via root production among three common plant functional types (deciduous trees, evergreen trees, grass/lawn). Our results suggest that the high soil C accumulation under evergreen trees can result from low needle litter decomposability, accompanied by a low soil CO2 efflux. Furthermore, high root production by evergreen trees compared to deciduous trees and lawns, likely reflects the high % OM under evergreen trees. We showed that plant effects on C inputs and outputs are modulated, either directly or indirectly, by park age so that these effects are accentuated in old parks. Our results suggest that despite the capacity of evergreen trees to accumulate C in soils in urban parks, this capacity is far less compared to soils in forests of the same age. OM content under deciduous trees did not differ between old parks and reference forests, suggesting that the raking of leaves in the fall has a surprisingly small impact on OM and C accumulation in urban parks. Soil OM content is an important measure that controls various ecosystem services in cities and elsewhere. Therefore, increasing the proportion of evergreen trees in urban parks in cool cities is a good option to boost the ecosystem services capacity in the often strongly disturbed urban soils. [Display omitted] •Evergreens improve the capacity of C accumulation in soils in urban parks and forests.•Evergreens had the lowest soil CO2 flux compared to deciduous trees and lawns.•Evergreens had higher root production than deciduous trees and lawns.•Raking tree leaves has a small impact on C accumulation in boreal urban park soils.•Evergreens in natural forests had higher C accumulation than those in old urban parks.