Urbanization Drives SOC Accumulation, Its Temperature Stability and Turnover in Forests, Northeastern China

Chang Zhai,Xingyuan He,Bo Zhang,Wei Zhou,Lu Xiao,Wenjie Wang

doi:10.3390/f8040130

Abstract

Global urbanization is a vital process shaping terrestrial ecosystems but its effects on forest soil carbon (C) dynamics are still not well defined. To clarify the effects of urbanization on soil organic carbon (SOC) variation, 306 soil samples were collected and analyzed under two urban–rural gradients, defined according to human disturbance time and ring road development in Changchun, northeast China. Forest SOC showed a linear increase with increasing human disturbance time from year 1900 to 2014 (13.4 g C m−2 year−1), and a similar trend was found for the ring road gradient. Old-city regions had the longest SOC turnover time and it increased significantly with increasing urbanization (p = 0.011). Along both urban–rural gradients SOC stability toward temperature variation increased with increasing urbanization, meaning SOC stability in old-city regions was higher than in new regions. However, none of the urban–rural gradients showed marked changes in soil basal respiration rate. Both Pearson correlation and stepwise regression proved that these urbanization-induced SOC patterns were closely associated with landscape forest (LF) proportion and soil electrical conductivity (EC) changes in urban–rural gradients, but marginally related with tree size and compositional changes. Overall, Changchun urbanization-induced SOC accumulation was 60.6–98.08 thousand tons, accounting for 12.8–20.7% of the total forest C biomass sequestration. Thus, China’s rapid urbanization-induced SOC sequestration, stability and turnover time, should be fully estimated when evaluating terrestrial C balance.

Highlights

multivariate analysis of variance (MANOVA) results (Table 1) show that SOC density (SOCD), soil basal respiration rate (SR), Q10, and turnover time (TT) differed among two urban–rural gradients related to human distance time (p < 0.05) and ring road (p < 0.01)
Using the F-value as an indicator of the magnitude of the effects of both urban–rural gradients, SOCD and TT were most affected by human disturbance time (7–31% higher F-values) while SR and
Our study provides a case study about the influence of urbanization on forest soil organic carbon (SOC) sequestration, basal respiration, temperature stability and carbon turnover time in Changchun, a medium-sized mid-latitude city in Northeast China

Summary

Introduction

Urbanization constitutes an important land use and land cover change process, with impacts on both terrestrial and aquatic carbon pools, and understanding and quantifying carbon flows in cities offers a powerful lens into urban ecosystems and provides a compact metric of urban sustainability [1]. A science research agenda grounded in sustained and intense observations, focusing on a statistically significant sampling of cities, is crucial for estimating urban carbon pools and fluxes as well as the processes controlling them, and will increase our understanding of the carbon cycle [1]. A small change in soil carbon may radically alter the balance of terrestrial ecosystems and the global carbon cycle [4]. It is important to scientifically understand the effects of urbanization on forest carbon dynamics, especially the underground soil organic carbon (SOC)

Results

Discussion

Conclusion