View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Plant Soil (2007) 291:181–198 DOI 10.1007/s11104-006-9185-1 ORIGINAL PAPER Can isoprenoids in leaves and roots of plants serve as biomarkers for past vegetation changes? A case study from the Ecuadorian Andes Boris Jansen Æ Klaas G. J. Nierop Æ Femke H. Tonneijck Æ Frans W. M. van der Wielen Æ Jacobus M. Verstraten Received: 18 October 2006 / Accepted: 15 December 2006 / Published online: 17 January 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Large-scale clear-cutting and burning suitable records. Such biomarkers could help caused the altitude of the natural upper forest line establish past vegetation dynamics including the (UFL) in the Northern Ecuadorian Andes to UFL position. For an isoprenoid to be a biomar- decline to the point that its ‘natural’ position is ker in soils normally it must be absent from the now uncertain. To obtain a detailed reconstruc- roots of a plant species as roots do not enter soils tion of the dynamics of the UFL over the last few in chronological order. For peat deposits this thousand years, traditional proxies alone do not criteria only needs to be met for the peat species suffice. For instance, pollen analysis suffers from themselves as only roots from peat species will be a low altitudinal resolution due to the large wind- present. Two diterpenes, four phytosterols and six blown component. In an attempt to find new, pentacyclic triterpenoids met the criteria for additional proxies to study past UFL dynamics in biomarker in peat records. Of these, one diter- the Ecuadorian Andes, we investigated the occur- pene, two phytosterols and three pentacyclic rence of isoprenoids (diterpenes, phytosterols and triterpenoids also met the criteria for biomarker pentacyclic triterpenoids) in the roots and leaves in soils. Samples from a soil under forest, a soil of 19 plant species responsible for the dominant under the adjacent pa´ramo and a nearby peat biomass input in soil and peat records along deposit, 14C dated at approximately 1500 cal. AD altitudinal transects covering approximately and 200 cal. AD, were tested for the presence of 500 m above and below the current UFL in two isoprenoids that meet the criteria for biomarker. locations in the Northern Ecuadorian Andes. Such isoprenoids were only found in the peat bog Isoprenoids can serve as biomarker if they are samples. However, we found that changes of uniquely present in a relevant plant species and number and concentrations of isoprenoids with preserved well enough in chronological order in depth might provide additional information re- lated to past vegetation changes. In conclusion, isoprenoids show potential for use in a multi- proxy approach to reconstruct past UFL locations B. Jansen (&) Á K. G. J. Nierop Á F. H. Tonneijck Á F. W. M. van der Wielen Á J. M. Verstraten in the Northern Ecuadorian Andes and other Institute for Biodiversity and Ecosystem Dynamics – ecosystems with similar vegetation and soils. Earth Surface Processes and Materials (IBED-ESPM), Universiteit van Amsterdam, Keywords Andic soil Á Biomarkers Á Nieuwe Achtergracht 166, NL1018 WV Amsterdam, The Netherlands Diterpenes Á Peat Á Pentacyclic triterpenoids Á e-mail: [email protected] Phytosterols 123 182 Plant Soil (2007) 291:181–198 Introduction onset of large-scale human interference. To obtain as detailed as possible a reconstruction of Montane cloud forests and Montane tropical past UFL positions we need to overcome the alpine grasslands (pa´ramo) compose the fragile limitations of pollen and vegetation analysis as ecosystems that nowadays are encountered only recognized by Wille et al. (2002). Therefore, we in selected places in the higher parts of the are investigating the possibility of applying new Ecuadorian Andes. However, cloud forests are additional proxies in conjunction with traditional believed to have once covered much larger areas, pollen and vegetation analysis. Biomarkers con- and human interference through clear-cutting and stitute one such proxy that may offer opportuni- burning is held responsible for a significant ties for reconstructing past vegetation reduction of cloud forest coverage and a depres- compositions including the historic UFL position. sion of the upper forest line (UFL) in the entire Biomarkers are defined as organic chemical Ecuadorian Andes (e.g. Dodson and Gentry 1991; components, or groups of components, exclusive Laegaard 1992). Publications like the one by to relevant plant species and preserved in chro- Laegaard (1992) have been used to justify nological order in suitable records such as peat replanting efforts above the current UFL as a deposits, sediments or soils. In a previous study reconstruction of natural forest destroyed by we successfully tested the occurrence of plant- humans. However, the past ‘natural’ locations of specific combinations of straight-chain lipids in the UFL in the Ecuadorian Andes are subject of plants responsible for the dominant biomass input scientific debate (e.g. Wille et al. 2002). A lower into soil and peat records in our research area, natural UFL than indicated by Laegaard (1992) and tested their preservation (Jansen et al. would mean that replanting efforts may not be 2006a). However, in the case of straight-chain reconstructing past forest vegetation, but destroy- lipids, the distinction of plant species is based on ing a natural pa´ramo ecosystem. Therefore, to the occurrence of unique combinations of other- enable sustainable and ecological management of wise ubiquitous compounds with different carbon the current Montane ecosystems in Northern chain-lengths. As a consequence, unraveling such Ecuador and possible reconstruction of degraded unique combinations from the mixed straight- areas, the question what the ‘natural’ location of chain lipid signal found in soil, peat or sediment the UFL would have been in the absence of records that contain the combined input of many human disturbance must be addressed. plants, is a challenge (Jansen et al. 2006a). In their recent attempt to reconstruct the To help overcome the limitations of straight- natural UFL position in the Ecuadorian Andes, chain lipid biomarkers it would be very helpful to Wille et al. (2002) reconstructed shifts of the UFL have a second set of biomarkers at our disposal, during the last 700 years through a combination based on unique individual components instead of of analysis of the current vegetation and fossil unique combinations of otherwise common com- pollen analysis from peat cores. While important pounds. Isoprenoids may constitute such a class of insights into past UFL positions were born from components. Like straight-chain lipids, isopre- their study, Wille et al. (2002) also recognized the noids and in particular diterpenes, phytosterols limitations of the proxies applied. For instance, and pentacyclic triterpenoids, have been consid- the spatial resolution of pollen analyses is limited ered as biomarkers in the past and have in some by the dispersal of pollen by wind prior to cases been linked to specific plants or groups of deposition, whereas a UFL reconstruction by plants (e.g. Chaffee et al. 1986; Ohsaki et al. 1999; vegetation analysis is only possible if sufficient Simoneit 1986; Volkman 2005). Diterpenes in traces of the original forest remain, which in most paleoecological records mainly originate from areas in the Ecuadorian Andes is not the case. higher plant waxes and resins, and consist of Analogous to the above-mentioned study, we amongst others the abietanes, pimaranes, kaur- are currently attempting a reconstruction of the anes, podocarpanes and labdanes as well as their vegetation history in the Northern Ecuadorian derived acids, alcohols, etc. (Simoneit 1986). Andes covering a period of time predating the Phytosterols occur in all higher plants and derive 123 Plant Soil (2007) 291:181–198 183 from the common precursor cycloartenol, as proxy in reconstructing the upper forest line in opposed to fungal and animal sterols that derive the Northern Ecuadorian Andes. Considering the from lanosterol (De Leeuw and Baas 1986). potential drawbacks mentioned, the goal was Common plant-derived pentacyclic triterpenoids specifically to: (i) construct a database of diterp- include the friedelanes, taraxeranes and ursanes enes, phytosterols and pentacyclic triterpenoids as well as their derived alcohols, acids, etc. present in the plant species responsible for the (Killops and Frewin 1994; Simoneit 1986). For dominant biomass input into paleoecological all three compound classes, it is their distinct, records in our study area, (ii) identify possible predominantly plant-derived origin that makes biomarkers from the compounds found, them potential biomarkers (Killops and Frewin (iii) perform a preliminary assessment of the 1994; Ohsaki et al. 1999; Volkman 2005). In occurrence and preservation of any identified addition, potential persistence of isoprenoids in isoprenoid biomarkers in selected paleological paleological records is indicated by several records in the area. authors (e.g. Jaffe et al. 1996; Simoneit 1986). The component classes under consideration are all lipids (Dinel et al. 1990), which according to Materials and methods the most common definition are organic compo- nents soluble in organic solvents but insoluble in Description of the study sites water (Bull et al. 2000b). As a consequence, vertical mobility in the form of leaching upon Our study area consists of (i) the Guandera dissolution will be limited. At the same time in Biological Station and (ii) the combined area of soil records, leaching in the form of dispersed El Angel Ecological Reserve and Los Encinos colloids is expected to be limited as well, since Biological Station in El Carchi province, Ecua- clay translocation is normally not considered a dor. Both sites are located in an area identified by dominant process in Andosols, due to the difficult Myers (1988) as part of the ‘‘tropical Andes dispersion of amorphous clay minerals (Shoji hotspots’’, characterized by exceptionally high et al.