Legacy effects from historical grazing enhanced carbon sequestration in a desert steppe Juanjuan Han a , Jiquan Chen c, b , Guodong Han d , Changliang Shao a, b , Hailian Sun e , Linghao Li a, * a Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China b Department of Environmental Science, University of Toledo, Toledo, OH 43606, USA c International Center for Ecology, Meteorologyand Environment (IceMe), Nanjing University of Information Science & Technology, Nanjing 210044, China d College of Ecology and Environmental Science, Inner Mongolia Agricultural University, Huhhot 010018, China e Institute of Forage Science, Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences, Huhhot 010031, China article info Article history: Received 13 September 2013 Received in revised form 24 March 2014 Accepted 26 March 2014 Available online 17 April 2014 Keywords: Carbon exchange Precipitation Semi-arid region Vegetative traits abstract Legacy effects are the ecological inheritances produced by preceding actions, which have been under- lined more on agricultural land use, wildfire, invasive and removal species, forest management, and extreme climates in previous research; however, very few studies have shown concern toward the grazing legacy effects on key ecosystem functions such as the carbon cycle. A nested random block design was employed in 2012, with historical grazing as the block factor and precipitation as a nested factor, to explore the regulatory mechanisms on the carbon fluxes in a desert steppe. This long-term grazing practice had exerted unique legacy effects on community composition through increasing the proportion of Stipa breviflora Griseb.(P stipa ) by 61.53%, and decreasing species richness (R sp ) by 30.70%, cover by 21.87%, aboveground biomass (AGB) by 31.34%, and carbon allocation (the ratio of ANPP/BNPP) by 15.18%. Moreover, plants had differential adaptations to herbivores. Remarkably, these grazing legacies indirectly promoted plant photosynthesis (GEE) and carbon gain (NEE). Precipitation, as expected, accounted for the variability of GEE by 43% and NEE by 33%. The results revealed that precipitation controlled the magnitude of carbon fluxes while grazing legacies offset the adverse effects of current grazing and, therefore, mediated carbon sequestration. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Legacy effects are the impacts from previous disturbances that continue to affect an ecosystem’s structure and function (Bain et al., 2012; Kostenko et al., 2012; de Vries et al., 2012). In the semi-arid regions of Eurasia, such as on the Mongolian Plateau, grazing has been the primary land use or disturbance whose influence does not cease after the grazing enclosure (Adler et al., 2004). Understanding the long-lasting effects of grazing in this region is crucial for ac- curate forecasting of ecosystem functions as well as for developing future management plans. In Midwestern Inner Mongolia, the prohibition of grazing under the national policy of China has created an increasing number of “land closures” in recent decades (Qi et al., 2012). These policy-induced land enclosures create great opportunities for us to assess the legacy effects of the historic grazing. Historic grazing, which differs from current grazing, is the ecological inheritance of herbivores on forage grasses, where these changes persist extensively and evolve to form the unique structure and function of the pasture ecosystem after the ceasing of this activity (Coughenour, 1985). While grazing directly changes the community structure and composition of an ecosystem, it also produces indirect effects on ecosystem functions such as carbon cycling. Herbivory, through selective foraging, excreta, and trample, exerts substantial effects on aboveground communities and, thus, alters the quality of the plant litter (Rossignol et al., 2011) and causes asymmetric effects on differential species (Guitian and Bardgett, 2000; Medina-Roldan et al., 2012) and belowground characteristics via alterations in the soil community (Klumpp et al., 2009; Kotzé et al., 2013; Kulmatiski and Beard, 2011; Tessema et al., 2011; van de Voorde et al., 2011) and triggers root exudation (Hamilton and Frank, 2001). These changes in community * Corresponding author. Tel.: þ86 62836282. E-mail address: llinghao2012@gmail.com (L. Li). Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv http://dx.doi.org/10.1016/j.jaridenv.2014.03.007 0140-1963/Ó 2014 Elsevier Ltd. All rights reserved. Journal of Arid Environments 107 (2014) 1e9