Journal of Bamboo & Rattan 31 J. Bamboo and Rattan, Vol. 18, Nos. 2, pp. 31 - 43 (2019) www.jbronline.org Phytolith assemblages in the leaves of Guadua bamboo in Amazonia Risto Kalliola1*. Ari Linna1. Linnea Toiviainen1. Kalle Ruokolainen2 Received: 28 June 2019/Accepted:17 August 2019 ©KFRI (2019) Abstract: We studied phytoliths (plant stones) from Introduction 228 leaf samples of Guadua weberbaueri and Guadua sarcocarpa bamboos from eleven collection locations The subfamily of Bambusoideae (Poaceae) inhab- in Southern Peruvian Amazonia and in the state of Acre its a wide range of tropical and subtropical habi- in Brazil. Four leaf-blade transverse thin sections were tats. Bamboos absorb silicon from the soil solu- made by grinding and smoothing them into a 30 µm tion and deposit it as amorphous hydrated silicon thickness, and over 550 phytolith slides created by (SiO .nH O) in the cell wall, cell lumina, and inter- using both the dry ashing and wet oxidation methods. 2 2 Large-sized (up to 50 µm) cuneiform bulliform cells in cellular spaces of various tissues (Piperno, 2006). the intercostal adaxial leaf-blade areas were the most These phytoliths (plant opals, plant stones) can be conspicuous phytoliths in Guadua leaves, but their both abundant and morphologically diverse, and abundance varied even locally. Other recurrent phyto- diagnostic up to the level of tribe or genus. Phyto- lith types included bilobate, saddle, and rondel shaped liths are preserved in the soil even after the organ- short cells; long cells in many different sizes and or- namentations; and prickle hairs, spikes, stomatal, and ic parts of the plant have degraded, making them inter-stomatal cells. We found the definite classifica- useful as microfossils to help paleoecological and tion of phytoliths into morphotypes difficult because of archaeological studies (Ball et al., 2016; Watling their variable sizes, forms, and surface characteristics. et al., 2015). Moreover, phytoliths often occlude Conjoined tricellular cell structures with one to three carbon (PhytOC), which is preserved in the soil mineral-accumulating cells forming a characteristic and contribute to carbon sequestration (Parr et al., mushroom-like constellation were also documented. Fusoid cells forming dense rows attached to the costal 2010). zones locally showed mineralization, indicating their Probably the world’s largest lowland bamboo role in inorganic mineral mobilization and deposition in Guadua leaves. Foliar phytolith assemblages showed forests in their natural state are located in south little variation among the different collection locations western Amazonia in Brazil and Peru, where two compared to the variation found among leaves within species of arborescent semi-scandent bamboos individual sites. (Guadua weberbaueri Pilg. and Guadua sarcocar- pa Londono and Peterson) dominate tropical rain Keywords: Amazonia, bamboo, fusoid cell, Guadua, forests in an area of over 160,000 km2 (de Carval- leaf, phytolith ho et al., 2013). These bamboo species form large patches that flower gregariously and die off after *Corresponding Author the flowering event’(Nelson, 1994). It has been 1 Department of Geography and Geology, University of argued that the pre-Colombian civilization that oc- Turku, FI20014 Turku, Finland cupied at least a part of these present-day bamboo 2 Department of Biology, University of Turku, FI20014 forests utilised the die-off events as a window of Turku, Finland opportunity to clear the forest using the fires fu- E-mail: [email protected] elled by dead bamboo biomass. Hence, Guadua Published online 21 October 2020 32 Journal of Bamboo & Rattan phytoliths in archaeological deposits are among and among different plant structures. For example, the key microfossils of that region (McMichael et in the bamboo genus Aristida, rondels occur in al., 2013; Watling et al., 2016). both the leaves and inflorescences, whereas sad- dles form in the leaves, culms, and inflorescences The relevance of Guadua phytoliths in archaeolo- (Piperno and Pearsall, 1998). Moreover, individu- gy and their potential contributions to carbon se- al plants growing in different habitats may differ in questration call for a closer look to examine their their phytolith compositions (Twiss et al., 1969). characteristics in the living plant. Opal phytoliths in grasses can be variable, depending on when, As such, there are no studies that describe the where, and how silicon deposition occurs in the variation in appearance of foliar Guadua bamboo plant. Phytoliths with bulliform morphology are phytoliths between individuals or populations. common in the family, but many other phytolith The study aims to fill this gap by describing the morphotypes have also been described (Rapp Guadua phytoliths in leaves sampled widely from and Mulholland, 1992). In the Guadua bamboos, eleven different locations across the Amazonian known morphotypes include bulliform, bilobate, bamboo forest area. By using a variety of analyt- saddle, rondel, cross and narrow elliptate phyto- ical methods, we attempt to answer the following liths (Piperno and Pearsall, 1998; Watling et al., research questions: (1) Which kinds of phytoliths 2016). However, the phytolith composition of a do the living Guadua bamboo leaves contain? (2) given plant species can vary from one individu- Where do the different phytolith types occur in the al plant to another (Twiss et al., 1969). Variations leaf structure? (3) How much do the overall phyto- also occur between different parts of a single leaf lith assemblages vary among different individuals blade, between the leaves of an individual plant, or populations? Fig 1. The bamboo sampling locations in the lowland Amazonia. The grey shaded area shows the total distribution of the bam- boo forest formation according to de Carvaljo et al., (2013). 1 = San Carlos, 2 = Ojeayo, 3 = Cumarillo, 4 = Tahuamanu, 5 = Primavera. 6 = Chico Mendes, 7 = Maciopira, 8 = Edmilson, 9 = São Tomé, 10 = Campo Alegre, 11 = Ivo. Journal of Bamboo & Rattan 33 Materials and methods lections made in the Peruvian locations (Table 1). Each leaf sample was taken at a minimum of 30 m The Guadua samples were collected during 2017 apart from another collected culm, so as to repre- and 2018 from eleven different locations in South- sent separate genets. The samples were assigned- ern Peruvian Amazonia and the Brazilian state of consecutive collection numbers from 1 onwards Acre (Fig. 1). The Brazilian samples were on av- in each location. Care was taken to sample leaves erage fewer than those collected from Peru (Table that were healthy-looking. The collected samples 1). Due to difficulty in distinguishing G.sarcocar- were folded, placed in small paper bags, and im- pa from G. weberbaueri in sterile conditions, the mediately deposited in silica gel to achieve rapid common term Guadua bamboo is used throughout drying. the text, acknowledging the possibility that our material could represent two different species (Ol- The laboratory studies were undertaken in the geo- ivier and Poncy, 2009). scientific laboratory at the University of Turku, In each location, the regional abundance of bam- Finland. Three different analytical lineages used boo-dominated forests was confirmed by exam- to produce microscopy slides are shown in Fig 2. ining Landsat TM satellite images wherein these Foliar transverse thin sections were prepared forests are clearly discernible due to their high from four leaf-blade samples. Because phytoliths reflectance in the near-infrared radiation. The tar- are minerals, thin section methodology used in geted bamboo stands in the patches were identified mineralogy and petrology was applied. Air-dried with the help of local inhabitants. All the collec- leaf-blade samples were first embedded into Stru- tion locations were below 200 meters above sea ers EpoFix and air bubbles were removed via a level. Annual rainfall in these locations varies be- low-pressure treatment (200 mbar) for about 20 tween 2000 and 2500 mm per year, and there is a minutes. After the samples had hardened at room distinct dry season, which typically lasts three to temperature for several days, they were levelled at four months. Guadua leaves are commonly ca. 20 the broadest point of the leaf using an Astera Solu- cm long and 2 to 3 cm wide. Foliar samples (about tions precision grinding machine GRN16 (#400 5 cm long) from the central parts of leaves were diamond cup wheel) and then attached with EPO- used for the study, and in total, 228 different leaf TEK 301 into levelled glass that had also been blades were collected from 7 to 41 bamboo ramets produced using the GRN16 (#140). The samples in each location, with the highest numbers of col- were cut with an Astera Solutions precision cut- Table 1. Collection locations with their respective numbers of studied Guadua leaves, transverse section micros- copy samples and dry ashing photographs. Location Country Leaves studied Transverse Dry ashing sections photographs San Carlos Peru 32 1 97 Ojeayo Peru 26 2 82 Cumarillo Peru 41 0 102 Tahuamanu Peru 38 0 96 Primavera Peru 36 1 88 Chico Mendes Brazil 10 0 16 Maciopira Brazil 7 0 10 Edmilson Brazil 11 0 15 Sao Tomé Brazil 10 0 15 Campo Alegre Brazil 10 0 23 Ivo Brazil 7 0 13 Total 228 4 557 34 Journal of Bamboo & Rattan off saw CUT8 and levelled down to 30 µm using The third methodological lineage was wet oxida- the GRN16 (#800). The samples were finalised by tion (Piperno, 2006: 97; Katz et al., 2010) to al- diamond polishing with Saint-Gobain W606AS low individual phytolith examination and photog- slurries and Struers Largo (3 micron), PoliSat1 raphy. The bamboo leaves were first soaked in a (1 micron) and PoliFloc4 (1/4 micron) polishing 1% solution of Alconox detergent and then washed pads. with distilled water. The organic materials were re- moved using nitric acid (HNO ) in a bath of boiling In the second lineage, phytolith spodograms were 3 water by adding pinches of solid potassium chlo- prepared with the dry ashing method (Piperno, rate (KClO ) to speed up the reaction time.