Urbanization aggravates imbalances in the active C, N and P pools of terrestrial ecosystems

Abstract

Urbanization causes increases in temperature and alters soil carbon (C), nitrogen (N), and phosphorus (P) cycles, but the degree to which these processes vary in temperature sensitivity along the urban-rural gradient are unclear. We selected three typical vegetation types (forests, shrub, and lawn) along an urban-subruban-rural gradient in Nanchang, China, and collected topsoil (at 0–15 cm depth) from 27 plots in each to measure the C, N, and P mineralization rates using thermostatic incubation. This was performed at ambient temperatures of 5 °C, 15 °C, 25 °C, 35 °C and 45 °C, respectively. Our results showed that soil microbial C and N content, as well as the rates of soil C mineralization, nitrification, and P mineralization generally decreased along the urban-rural gradient (P < 0.05). Moreover, the temperature sensitivity (Q10) of soil C mineralization was highest at urban sites, followed by suburban, then at rural sites. In contrast, the Q10 value of ammonification was lower in urban than suburban and rural sites, and a difference in nitrification response to temperature alteration was only found at urban sites. The phosphorus mineralization rate showed minimal variation across incubation temperatures. Taken together, we found that soil C and nutrient fluxes in response to elevated temperature might be more asynchronous in urban than in rural sites, and thus urbanization may aggravate imbalances in the active C, N and P pools of terrestrial ecosystems. Global warming may thus help accelerate soil organic C decomposition, N leaching, and P enrichment in urban vegetations in subtropical China.