Soil Science Society of America Journal †These authors contributed equally to this study. Soil Sci. Soc. Am. J. doi:10.2136/sssaj2015.10.0383 Received 26 Oct. 2015. Accepted 2 May 2016. *Corresponding author (lwarburton@chicagobotanic.org). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved. Impact of Restoration and Management on Aggregation and Organic Carbon Accumulation in Urban Grasslands Soil & Water Management & Conservation Understanding the patterns of soil organic carbon (SOC) accumulation in restored grasslands is necessary to determine their potential to seques- ter atmospheric CO 2. Patterns of SOC accrual after grassland restorations are generally based on studies in former agricultural ields, and these stud- ies show an increase in SOC and aggregated-associated OC over time. In this study, we quantiied SOC accrual in a series of restored grasslands situ- ated within the matrix of the Chicago metropolitan region. Soil samples were collected from unmanaged (no restoration), short-term (<7 yr), and lon- ger-term restorations (>10 yr) and from native prairie remnants located on Mollisols or Alisols and analyzed using a combination of physical fraction- ation (aggregate size) and chemical measurements (organic C [OC], 13 C/ 12 C natural abundance). We found that (i) total SOC declined after restoration and remained signiicantly lower in restored than unmanaged soils, (ii) pat- terns of aggregate OC in longer-term restorations were more similar to those in unmanaged than to prairie sites, and (iii) microaggregate OC levels and C 4 –C inputs into aggregate fractions were signiicantly higher in short- than longer-term restorations. Thus, an increasing time under management did not enhance SOC accrual. For all sites, path models showed that SOC accrual was correlated with soil N, texture, and moisture, whereas C 4 –C inputs were signiicant model terms only in short-term restorations and prairie sites. Taken together, these results indicate the need to consider inter-relationships among vegetation and soil factors as inluences on SOC accrual rather than simply time under management. Abbreviations: OC, organic carbon; PCA, principle components analysis; SOC, soil organic carbon; SOM, soil organic matter. O ver the last 200 yr, anthropogenic activities have resulted in substantial decreases in soil organic carbon (SOC) and increases in atmospheric CO 2 concentrations (Lal, 2004; Stockmann et al., 2013). There is now an urgent need to mitigate these impacts through management strategies that re- build the depleted SOC and offset CO 2 emissions. Studies have broadly demon- strated that the restoration of agricultural soils to perennial grasslands may reverse the loss of SOC and thus act as a potential sink for CO 2 (Baer et al., 2010; Conant et al., 2001; Schmidt et al., 2011; Stockmann et al., 2013). Fewer studies, how- ever, have examined how restoration efforts in degraded urban lands might achieve similar goals (Chen et al., 2013; Raciti et al., 2011). In this study, we examined the extent to which the conversion of degraded old fields to perennial grasslands may promote SOC accrual in an urban setting. The replacement of row crop agriculture by deep-rooted C 4 grasses and forbs has been shown, for the most part, to result in a rapid accrual of SOC with restora- tion age (Baer et al., 2010; Hernández et al., 2013; Jastrow, 1987, 1996; Kalinina et al., 2015; Matamala et al., 2008; McLauchlan et al., 2006), but some research- Jenifer L. Yost† Univ. of Wisconsin-Madison Dep. of Soil Science FD Hole Soils Lab 1525 Observatory Drive Madison, WI 53706 Louise M. Egerton-Warburton*† Chicago Botanic Garden 1000 Lake Cook Road Glencoe, IL 60022 Northwestern Univ. Program in Plant Biology and Conservation 2205 Tech Drive Hogan Hall Evanston, IL 60208 Kathryn M. Schreiner Univ. of Minnesota Duluth Large Lakes Observatory and Dep. of Chemistry and Biochemistry 2205 E. 5th Street Duluth, MN 55812 Corey E. Palmer Northwestern Univ. Program in Plant Biology and Conservation 2205 Tech Drive Hogan Hall Evanston, IL 60208 Alfred E. Hartemink Univ. of Wisconsin-Madison Dep. of Soil Science FD Hole Soils Lab 1525 Observatory Drive Madison, WI 53706 Core Ideas • Few studies have examined SOC accrual in restored urban grasslands. • We examined SOC accrual in 14 restored and native grasslands in Chicago. • Short-term (<7 yr) restoration increased microaggregate OC toward levels in native prairies. • Longer-term restoration did not improve total SOC or aggregate OC. • Differences in SOC were linked to soil moisture, N, texture, and inputs of C 4 –C among sites. Published August 1, 2016