The Influence of Tree Size and Microenvironmental Changes on the Wood Anatomy of Roupala Rhombifolia
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88 IAWAIAWA Journal Journal 34-1 34-1 (2013) (2013) 88–106 THE INFLUENCE OF TREE SIZE AND MICROENVIRONMENTAL CHANGES ON THE WOOD ANATOMY OF ROUPALA RHOMBIFOLIA Viviane Jono*, Giuliano Maselli Locosselli and Gregório Ceccantini Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, Rua do Matão 277, CEP 05508-090, Cidade Universitária, São Paulo, SP, Brazil *Corresponding author; e-mail: [email protected] AbsTracT We analysed how variation in microenvironmental conditions and stem size affects the wood anatomy of Roupala rhombifolia in three contrasting habitats in the same study area: open field, hilltop forest and riparian forest. The wood anatomy features analysed were: vessel area and density, vessel element length, fibre length, and ray width and height. Vegetation cover and soil attributes were also quantified and integrated into the analyses. Separate analyses were performed on i) raw anatomical data and ii) residuals from linear fits between wood anatomical features and plant height and stem diameter. Raw data showed a clear difference between specimens from riparian forest and open fields, which represented the most mesic and xeric anatomical features respectively. After residual extraction to correct size-related variation, only fibre length and ves- sel area differed between habitats. Vessel areas in riparian forest differed from those in hilltop forest, but were similar to those in open fields. This result can be explained when vegetation cover and soil are considered together. While open field and hilltop forest have similar soils and lower moisture availability when compared to riparian forest, water demand in open fields is lower, presumably resulting in higher water availability. Keywords: Proteaceae, ecological anatomy, stem size, wood maturity, residual extraction. InTroducTion The anatomical structure of wood records environmental influences and ontogenetic processes experienced throughout its development. Decades of ecological wood anat- omy studies have demonstrated that the relative influences of environment and plant size on wood anatomy are often difficult to disentangle (Baaset al. 1984). While it has been suggested that plants of similar size should be studied to remove the influence of stem diameter and plant height on anatomical data (Lev-Yadun & Aloni 1995), it is frequently impracticable to restrict plant size along environmental gradients since the latter may modulate both anatomical variation and plant size. For example, both wood anatomy and plant height vary with elevation in Rhododendron spp. (Noshiro et al. 1995). © International Association of Wood Anatomists, 2013 DOI 10.1163/22941932-00000008 Published by Koninklijke Brill NV, Leiden Downloaded from Brill.com10/04/2021 11:42:55AM via free access Jono et al. – Tree size, environment, anatomy of Roupala 89 Over the years, many classical studies of ecological wood anatomy have demon- strated that species show different phenotypes as a result of different selective pressures from the environment (e.g. Baas et al. 1983; Barajas-Morales 1985; Carlquist 1975, 1988; Van den Oever et al. 1981). These responses reflect the organization of conductive tissues, which results from a trade-off between safety and efficiency in water transport (Carlquist 1977). This balance, taking into account phenotypical plasticity within the conductive tissue and phylogenetic aspects, allows plants to survive in different en- vironments, including those in which conditions are suboptimal (Walter 1985). These trends have been found at a wide range of altitudes and latitudes, and under a variety of different macro- and microclimatic conditions (e.g. Baas 1973; Roig 1986; Baas & Schweingruber 1987; Lindorf 1994; Alves & Angyalossy-Alfonso 2000; Bosio et al. 2010; Noshiro et al. 2010; Sonsin 2012). However, environmental influences on wood anatomy may not be completely iso- lated from other factors, such as plant size. This sampling artifact can result in biased data which interfere with tests of ecological hypotheses (Lev-Yadun & Aloni 1995). It is known that plant size influences wood anatomy (e.g. Preston et al. 2006; Fichtler & Worbes 2012). Many studies that have used age variation of wood anatomical char- acters have shown that they vary with stem diameter, to a larger degree in softwoods and a lesser degree in hardwoods. Stem diameter is not the only plant size variable that may influence wood anatomy. Plant height has also been shown to introduce a bias in wood anatomical attributes, as shown by a study of dwarf trees (Baas et al. 1984). Even when only mature wood is analysed, correlations between plant size and wood anatomy may be found (Noshiro & Suzuki 2001). By examining wood anatomy, plant size, latitude and altitude of provenance, Noshiro et al. (2010) showed a correlation between vessel area ratio (%) and stem diameter and height. In that study the dependence was not considered important, since vessel area ratio was not correlated with altitude, which was the focus of the study. The aim of our study was to analyse the effect of microenvironmental and stem size variation on the wood anatomy of Roupala rhombifolia Mart. ex Meisn. (Proteaceae). The study site included three different habitats, which allowed us to sample in distinct microenvironmental conditions while avoiding macroclimatic variation in factors such as precipitation and incident solar radiation. To better understand the results, we used a simple method of data analysis to remove the influence of stem diameter and height. Besides, plant density/biomass was quantified via multispectral satellite images and soils were sampled in order to characterise each habitat. MaTerial and MeTHods Sampling took place in the Serra do Cipó (Minas Gerais state, Brazil), a mountain chain rich in endemism and characterised by a vegetation type known as campo rupestre (rocky field). The region shows a broad range of edaphic conditions (Meguro et al. 1996) and also harbours forested vegetation types. These are semideciduous montane forests with trees up to 15 metres tall, which grow both along rivers and distant from water bodies. Mean temperature is 19.3 ºC and total annual precipitation is 1312 mm Downloaded from Brill.com10/04/2021 11:42:55AM via free access 90 IAWA Journal 34-1 (2013) (data from the Diamantina climate station, National Institute of Meteorology - INMET). The rainy season is between October and April, and the dry season between May and September (Fig. 1). We studied two different forest habitats and the open fields surrounding them, all three closely located within the Serra do Cipó National Park (Santana do Riacho, Brazil – 19º 15' 36" S, 43º 32' 37" W). These habitats have different microenvironmen- tal conditions but identical macroclimates (Fig. 2). Sampling sites differed in proxim- ity to water and slightly in altitude. Although water availability varies between these habitats, none of them suffers flooding. In order to better characterise the habitats, satellite images were used to produce a normalised difference vegetation index (NDVI) image. A multispectral image from the CBERS2 satellite, acquired in July 2005, was analysed with IDRISI ANDES software. NDVI values were used to estimate biomass and vegetation cover (Thiam & Eastman 2006) from the remote sensing data. Additionally, soils were characterised via three samples collected at a depth of 15 cm in each habitat, in July 2006. Soil samples were analysed by the Agronomic Institute of Campinas (IAC) via standard methods for determining water content at saturation, field capacity, wilting point, soil density, and organic matter content. A multivariate cluster analysis was used to group similar soil samples by Ward’s hierarchical method applied to standardised data in the R program (R Development Core Team 2011). The study species was Roupala rhombifolia Mart. ex Meisn. (Proteaceae), which usually grows in seasonal higher-elevation environments (Prance & Plana 1998). Our observations suggest that this evergreen species is a pioneer that probably plays a role in the formation and expansion of forest islands in the Serra do Cipó. Although R. rhombifolia seems to behave as a pioneer species, the wood density of Roupala spp. is reported to be relatively high ranging from 0.8 to 1.2 g/cm3 (Record & Hess 1943). First, wood maturity was analysed in a branch of a forest specimen by measuring the length of 30 fibres and vessel elements at each millimetre from cambium to pith after maceration (Franklin 1945). This preliminary analysis was helpful to indicate the limits of trunk size for sampled specimens, especially the open field specimens that were relatively small. Wood samples of the five biggest open field individuals were obtained at their base. For the other habitats, samples were taken from the trunk at breast height, using a handsaw, a chisel and a hammer. Wood samples of eight specimens from each forest formation and five specimens from the open field were collected and deposited at the University of São Paulo xylarium (SPFw). The height and diameter of each sampled specimen were recorded. For these wood samples the following anatomical variables were measured: fibre and vessel element length, vessel area, vessel density, and ray height and width. Sam- ples near the cambium were macerated (Franklin 1945) to measure fibre and vessel element length. Samples of approximately 1.5 × 1.5 × 2 cm were sectioned to measure other variables. In addition, wood samples were softened with 10% ethylenediamine (Carlquist 1982 adapted) and soaked in PEG 1500 (Rupp 1964) to produce transverse and tangential sections using a Leica SM 2000R sliding microtome. Thirty measure- ments were taken for each variable analysed, except for ray height and width, for which Downloaded from Brill.com10/04/2021 11:42:55AM via free access Jono et al. – Tree size, environment, anatomy of Roupala 91 300 50 100 40 80 30 60 20 40 Temperature (°C)Temperature Precipitation (mm) 10 20 0 0 J A S O N D J F M A M J Month Figure 1. Climatic diagram from the climate station of Diamantina, MG, Brazil (National Institute of Meteorology - INMET). 0.10 0.40 0.70 Figure 2.