Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena Soil carbon isotope ratios in forest-grassland toposequences to identify vegetation changes in southern Brazilian grasslands Daiane Deckmann Andriollo a , Cristina Gouvêa Redin a , José Miguel Reichert b,⁎ , Leandro Souza da Silva b a Graduate Program in Forest Engineering, Federal University of Santa Maria (UFSM), Av. Roraima 1000, Santa Maria, RS, Brazil b Department of Soil Science, Federal University of Santa Maria (UFSM), Av. Roraima 1000, Santa Maria, RS, Brazil ARTICLE INFO Keywords: Pampa biome Stable carbon isotopes Soils vs. vegetation Vegetation change ABSTRACT The Southern Grasslands or Pampa biome covers 176,496 km 2 (2.07%) of the Brazilian territory, concentrated in the southernmost state with 63% covered by this biome. When adding Uruguay and Argentina, the biome area reaches 750,000 km 2 . Rangelands are being substituted by crops and commercial eucalyptus, with potential impacts on ecological and hydrological response of watersheds and river basins. Studies of isotopic natural abundance may be used to understand vegetation dynamics in the past. We evaluated the natural abundance of 13 C in soil profiles (ten soil layers down to 1.40 m) at different positions of the landscape, in order to associate it with the vegetation dynamics in the studied environment. Two grassland areas and a forest area in the Pampa region of southern Brazil were sampled. Isotopic signature δ 13 C in the soil profile of the two grassland areas was dissimilar: one area is in the range of C4 plant formation, and the other followed the same trend up to the first 1.00 m but from this depth on δ 13 C is in an intermediate range, which could have occurred due to the influence of C3 and C4 plants. Forest vegetation presents a clear change of predominant vegetation in a more-recent past period. Characteristic values of soil formed by C3 photosynthetic cycle plants are predominant in surface layers, whereas those of C4 plants predominate in deeper soil layers. Our hypothesis that soil classes, texture, and position in landscape are related to the presence/absence of riparian forest, as evaluated by the 13 C isotopic abundance in soils from these sites, is accepted. Quantification of isotopic natural abundance allowed verifying changes in vegetation based on photosynthetic types predominant in the environments of grassland and native forests of the Pampa biome, and may provide information to manage this ecosystem. 1. Introduction Rich in biodiversity, the Pampa biome or southern grasslands is a mix of ecological formations in a single eco-landscape with intense flow of matter, energy and wildlife (IBGE, 2004). This biome covers 750,000 km 2 in South America, with 176,496 km 2 of this area in the southernmost Brazilian state where it occupies 63% of the territory and represents 90% of rangelands of the state (MMA, 2016). A mosaic of grassland and forest, the Pampa biome has been af- fected by climate change in past geological times and by the occurrence of natural and anthropic disturbances, such as fire and grazing (Behling, 2002; Overbeck et al., 2007). Geomorphology, hydromorphism, edaphic factors, species origin time on site, wind, and plant dispersal syndromes also contribute to plant distribution patterns in the en- vironment (Rizzini, 1997; Quadros and Pillar, 2002). Grassland is the predecessor to forest in the Pampa biome (Lindman, 1906; Rambo, 1956; Behling et al., 2005). Once dominant in extensive areas from past periods of cold and dry climates, grasslands have been naturally losing ground to forests due to current climate (Behling, 2002). In this context, the geological and climatic events associated to the floristic centers and flows constitute the foundations on which the proposed model to classify the southern Brazilian primary vegetation is built (Leite, 2002). Currently, there is great discussion among scientists and society about the effect of the conversion of grasslands to agriculture and for- estry, in terms of biodiversity loss (Overbeck et al., 2007, 2013; Roesch et al., 2009; Bond and Parr, 2010; Bolzan et al., 2016), water con- sumption and soil degradation (Rodrigues et al., 2014; Reichert et al., 2017). Lack of knowledge on the dynamics between grassland and forest contributes to improper conservation and management of grass- lands and forests. Studies of isotopic natural abundance may be used to fill gaps in the http://dx.doi.org/10.1016/j.catena.2017.08.012 Received 9 February 2017; Received in revised form 7 July 2017; Accepted 16 August 2017 ⁎ Corresponding author. E-mail address: reichert@ufsm.br (J.M. Reichert). Catena 159 (2017) 126–135 0341-8162/ © 2017 Elsevier B.V. All rights reserved. MARK