Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Research paper Carbohydrate concentrations and enzyme activities as inﬂuenced by exchangeable cations, mineralogy and clay content Fatemeh Rakhsh ⁎ , Ahmad Golchin Soil Science Department, Faculty of Agriculture, University of Zanjan, Zanjan, Iran. ARTICLE INFO Keywords: Acid phosphatase Alfalfa residues Alkaline phosphatase Carbohydrate CM-cellulase Homoionic clay ABSTRACT Enzymes can exist in bound or free form within the soil, but the impact of interactions between extracellular enzymes with the amount and type of clay minerals and exchangeable cations on the activities of enzymes and decomposition or retention of carbohydrates in soil is still poorly understood. Appropriate amounts of homoionic Na-, Ca- and Al-clay minerals from Georgia kaolinite, Illinois illite and Wyoming montmorillonite were mixed with pure sand to prepare artiﬁcial soils with diﬀerent clay contents, exchange cations and clay types to examine the eﬀects of exchangeable cations, mineralogy and clay content on the concentrations of hot water and dilute acid extractable carbohydrates and activities of acid and alkaline phosphatases and CM-cellulase. There was a signiﬁcant eﬀect of clay content on the concentrations of carbohydrates and activities of enzymes. The con- centrations of carbohydrates increased when the clay contents of soils increased from 0 to 5 and 10%, respec- tively, showing that the clay contents inﬂuence the capacity of soils for stabilization of carbohydrates. But opposite trends were found in enzyme activities. The enzyme activities decreased signiﬁcantly as the clay contents of the artiﬁcial soils increased. The concentrations of carbohydrates and activities of enzymes were signiﬁcantly aﬀected by exchangeable cations. In soils with 5 and 10% clay, the concentrations of carbohydrates were maximum in Al-soils and minimum in Ca-soils, in contrast, the activities of enzymes were maximum in Ca- soils and minimum in Al-soils. There was a signiﬁcant eﬀect of clay mineralogy on the concentrations of car- bohydrates and activities of enzymes. The concentrations of carbohydrates were highest in soils with Wyoming montmorillonite clay mineral and lowest in soils with Georgia kaolinite clay mineral. But the activities of en- zymes were lower in soils with Wyoming montmorillonite clay mineral than soils with Georgia kaolinite and Illinois illite clay minerals, indicating the inﬂuence of speciﬁc surface area (SSA) and cation exchange capacity (CEC) of clay minerals on carbohydrate retention and enzyme activities. The results of this study indicate that carbohydrates are stabilized in soils through the interaction with clay minerals and a small amount of clay (5%) signiﬁcantly increases carbohydrate retention and reduces enzyme activities in soils. Exchangeable cations exert their inﬂuence on enzyme activities and hence carbohydrate dynamics by controlling the activities of enzymes through modifying the physicochemical characteristics of soils. 1. Introduction Better understanding of carbon cycling is necessary to decrease the emission of greenhouse gases and global climate changes resulted from it. Soil organic carbon (SOC) is a signiﬁcant pool that plays important role in global carbon cycling (Scharlemann et al., 2014; Wang and Hsieh, 2002). The SOC consists of two main fractions; the labile and the non-labile organic fractions. Carbohydrate constitutes an important component of the labile fraction that represents about 5–25% of soil organic matter (SOM) (Uzoho and Igbojionu, 2014). Its fate in soils varies depending on the SOM dynamics and transformation processes, especially decomposition, mineralization and immobilization (Paul et al., 2002). Carbohydrate plays fundamental roles in the soil which include; conservation of soil physical properties (Martins et al., 2012), stabilization of soil aggregates (Youseﬁ et al., 2008) and sustenance of soil microbial activities through the provision of readily available en- ergy (Ros et al., 2003). Besides being a source of energy for microorganisms, the soil car- bohydrates play a signiﬁcant role in the formation of stable aggregates and metal ion complexes (Six et al., 2004). Soil carbohydrates consist of plant- and microbial-derived polysaccharides that are an immediate by- product of microbial utilization of organic carbon (OC). Microbial ex- tracellular polysaccharides are regarded important in ecophysiological processes from the viewpoints of resistance to desiccation and survival https://doi.org/10.1016/j.clay.2018.07.031 Received 25 March 2018; Received in revised form 9 July 2018; Accepted 19 July 2018 ⁎ Corresponding author. E-mail address: rakhsh.fatemeh@znu.ac.ir (F. Rakhsh). Applied Clay Science 163 (2018) 214–226 0169-1317/ © 2018 Elsevier B.V. All rights reserved. T