Open Geosci. 2016; 8:503–513 Research Article Open Access Amir Hossein Jafarzadeh-Haghighi, Jusop Shamshuddin*, Jol Hamdan, and Norhazlin Zainuddin Structural composition of organic matter in particle-size fractions of soils along a climo-biosequence in the Main Range of Peninsular Malaysia DOI 10.1515/geo-2016-0034 Keywords: alkyl C, O-alkyl C, pedogenesis, scanning elec- Received November 28, 2015; accepted March 21, 2016 tron microscopy, solid-state 13C CPMAS NMR spectroscopy Abstract: Information on structural composition of or- ganic matter (OM) in particle-size fractions of soils along a climo-biosequence is sparse. The objective of this study 1 Introduction was to examine structural composition and morphologi- cal characteristics of OM in particle-size fractions of soils Climatic factors and vegetation types are believed to con- along a climo-biosequence in order to better understand trol structural composition of soil organic matter (SOM) [1]. the factors and processes aecting structural composi- Climate and vegetation are considered as two indepen- tion of soil organic matter. To explore changes in struc- dent variables in the state-factor model [2]. According to tural composition of OM in soils with dierent pedoge- this model, climo-biosequences allow evaluating eects nesis, the A-horizon was considered for further analyses of climate and vegetation on soil development [3]. Climo- including particle-size fractionation, solid-state 13C nu- biosequences can also be used to examine changes in clear magnetic resonance (NMR) spectroscopy and scan- the structural composition of SOM as inuenced by cli- ning electron microscopy (SEM). Due to the increase in the mate and vegetation. In addition, climate-gradient stud- thickness of organic layer with increasing elevation, the ies (i.e. climosequences) by substituting space for time of- A-horizon was situated at greater depth in soils of higher fer further insight into the eects of climate on such struc- elevation. The relationship between relative abundances tural alterations occurring over longer periods of time [4]. of carbon (C) structures and particle-size fractions was Studies on structural composition of SOM along the cli- examined using principal component analysis (PCA). It matic and bioclimatic gradients have focused on bulk soil, was found that alkyl C (20.1-73.4%) and O-alkyl C (16.8- e.g. [1, 5, 6] and often disregarded fractions of SOM. 67.7%) dominated particle-size fractions. The proportion Several chemical and physical fractionation schemes of alkyl C increased with increasing elevation, while O- have been proposed to isolate SOM fractions with simi- alkyl C showed an opposite trend. Results of PCA con- lar chemical/physical composition [7]. Physical fractiona- rmed this nding and showed the relative enrichment of tion of soil based on the size and/or density of particles alkyl C in soils of higher elevation. Increase in the propor- leads to the separation of uncomplexed organic matter tion of alkyl C in 250-2000 µm fraction is linked to selective (OM) and organo-mineral complexes [8, 9]. Such fraction- preservation of aliphatic compounds derived from root lit- ter. SEM results showed an increase in root contribution to the 250-2000 µm fraction with increasing elevation. For the <53 µm fraction, pedogenic process of podzolization *Corresponding Author: Jusop Shamshuddin: Depart- ment of Land Management, Faculty of Agriculture, Universiti is responsible for the relative enrichment of alkyl C. This Putra Malaysia, 43400 Serdang, Selangor, Malaysia, E-mail: study demonstrates that changes in structural composi- [email protected]; phone number: +60389474865 tion of OM in particle-size fractions of soils along the stud- Amir Hossein Jafarzadeh-Haghighi, Jol Hamdan: Department ied climo-biosequence are attributed to site-specic dier- of Land Management, Faculty of Agriculture, Universiti Putra ences in pedogenesis as a function of climate and vegeta- Malaysia, 43400 Serdang, Selangor, Malaysia Norhazlin Zainuddin: Department of Chemistry, Faculty of Sci- tion. ence, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia © 2016 Amir Hossein Jafarzadeh-Haghighi et al., published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. The article is published with open access at www.degruyter.com. 504 Ë Amir Hossein Jafarzadeh-Haghighi et al. ation procedure yields OM fractions that are more chemi- analyzed by 13C CPMAS NMR spectroscopy and scanning cally homogenous compared to the bulk soil [10]. Particle- electron microscopy (SEM), respectively. size fractionation aims to separate OM associated with pri- mary particles (i.e. sand, silt, and clay) after complete dis- aggregation [11]. SOM pools obtained from particle-size 2 Materials and methods fractionation are directly related to the structure and func- tions of SOM in situ [12]. For example, of the OM pools isolated via particle-size fractionation, the OM in the sand 2.1 Study area and soil sampling fraction known as particulate organic matter (POM) shows The study area was located along an elevation gradient in the most structural similarities to the original plant in- the Main Range of Peninsular Malaysia (04°14’–04°31’N, put [10]. This normally labile fraction provides a source of 101°18’–101°23’E) (Figure 1). Variation in climate and veg- energy and nutrients for microorganisms [13]. Solid-state etation was a major cause of dierences in pedogenesis 13 C cross-polarization magic angle spinning nuclear mag- along the respective elevation gradient. After preliminary 13 netic resonance ( C CPMAS NMR) spectroscopy has been eld studies, a group of four soil proles (P1-P4), represen- widely used to examine the structural composition of OM tative of major elevation zones, were examined (Table 1). in particle-size fractions, e.g. [14–19]. This method is non- According to the state-factor model [2], this group of soils destructive and doesn’t require extraction of OM [20]. The formed a climo-biosequence in which two of the state fac- 13 C CPMAS NMR spectra, which are run under similar ex- tors (climate and vegetation) were allowed to vary and the perimental conditions, allow semi quantitative character- other three were held constant as much as possible. ization of OM in particle-size fractions [15]. Generally, the proportion of alkyl C would increase and O-alkyl C de- crease with decreasing particle-size [21]. Little is known about changes in structural compo- sition of OM in particle-size-fractions of soils along a climo-biosequence. Examining soils within a mountain range is considered as a common form of climosequence and/or climo-biosequence [3]. The Main Range of Penin- sular Malaysia, the backbone mountain range located in the center of the peninsula, extends northward into the Peninsular Thailand and southward to the Indonesian tin islands [22]. Gradients of soil forming factors such as cli- mate and vegetation on fairly uniform parent material in the Main Range [23] enables us to investigate such alter- ations in structural composition of OM. The research ques- tion is whether changes in structural composition of OM in particle-size fractions of soils along a climo-biosequence can be ascribed to dierences in climate and vegetation or Figure 1: Map of the study area showing the location of the investi- pedogenesis as a function of the two variables. Our objec- gated sites (1-4) along an elevation gradient in the Main Range of Peninsular Malaysia (cited from Jafarzadeh-Haghighi et al. [38]) tive was to examine structural composition and morpho- logical characteristics of OM in various particle-size frac- tions of soils along a climo-biosequence in order to bet- With increasing elevation, mean annual temperature ter understand the factors and processes aecting struc- decreased from 26.9 °C recorded at Hospital Tapah mete- tural composition of SOM. We hypothesized that pedo- orological station (04°12’N, 101°16’E; 35.1 m asl) to 18 °C genesis as a function of climate and vegetation controls recorded at Cameron Highlands meteorological station structural composition of OM in particle-size fractions of (04°28’N, 101°22’E; 1545 m asl). The mean annual rainfall soils along a climo-biosequence. To test this hypothesis, was 3282 mm at the Hospital Tapah station and 2977 mm samples from the A-horizon of soils were fractionated into at the Cameron Highlands station. The occurrence and du- three particle-size fractions (250-2000 µm, 53-250 µm, and ration of fog as an additional water input increased with <53 µm). The structural composition and morphological increasing elevation [24]. As a function of climatic fac- characteristics of OM in each particle-size fraction were tors, four vegetation zones occur with increasing eleva- tion, progressing from hill dipterocarp forest (<750 m asl) Structure of OM in soils of a climo-biosequence Ë 505 through upper dipterocarp forest (750-1200 m asl), myr- samples were subjected to chemical dispersion by adding taceous forest (1200-1800 m asl), and ericaceous forest 40 mL sodium hexametaphosphate (5 g L−1) to 10 g of (>1800 m asl) [25]. All sampling sites were situated on sim- the soils (<2 mm) that were previously weighed in 50 mL ilar geomorphic position with slopes ranging from 20 to centrifuge tubes. Soil samples and dispersant were mixed 30%. All soils were developed from granitoid parent ma- for 30 s using vortex mixer. Based on preliminary experi- terial [23]. The granitoid bedrock in the Main Range of ment, 10 5-mm glass beads were added to each centrifuge Peninsular Malaysia is of Triassic age (200-230 Ma) [22, 26]. tube to aid in complete soil dispersion. Samples were then This claim had been proven by U-Pb zircon emplacement shaken for 16 hours on a rotary shaker set to 60 rpm. Wet which indicated the age of granite ranging from late Trias- sieving using stacks of 250 and 53 µm sieves separated sic (230 ± 9 Ma) to early Jurassic (207 ± 14 Ma) with a peak 250-2000 µm (coarse sand) and 53-250 µm (ne sand ) around 210 Ma [27].