Comparative wood anatomy of root and stem of Citharexylum myrianthum (Verbenaceae)

Rodriguésia 65(3): 567-576. 2014 http://rodriguesia.jbrj.gov.br DOI: 10.1590/2175-7860201465301 Comparative wood anatomy of root and stem of Citharexylum myrianthum (Verbenaceae) Anatomia comparada da madeira de raiz e caule em Citharexylum myrianthum (Verbenaceae) Carmen Regina Marcati1,4, Leandro Roberto Longo1, Alex Wiedenhoeft2 & Claudia Franca Barros3 Abstract Root and stem wood anatomy of C. myrianthum (Verbenaceae) from a semideciduous seasonal forest in Botucatu municipality (22º52’20”S and 48º26’37”W), São Paulo state, Brazil, were studied. Growth increments demarcated by semi-ring porosity and marginal bands of axial parenchyma were observed in the wood of both root and stem. Many qualitative features were the same in both root and stem: fine helical thickenings, and simple and multiple perforation plates in vessel elements; large quantities of axial parenchyma in the growth rings, grading from marginal bands and confluent forming irregular bands in earlywood to lozenge aliform in latewood; axial parenchyma cells forked, and varied wall projections and undulations; septate fibres; forked and diverse fibre endings. Quantitative features differing between root and stem wood were evaluated using student’s t-test, and vessel frequency, vessel element length, vessel diameter, ray height, and vulnerability and mesomorphy indices differed significantly. Root wood had lower frequency of vessels, narrower and longer vessel elements, and taller rays than wood of the stem. The calculated vulnerability and mesomorphy indices indicated that C. myrianthum plants are mesomorphic. Roots seem to be more susceptible to water stress than the stem. Key words: secondary xylem, semideciduous seasonal forest, wood anatomy. Resumo A anatomia da madeira da raiz e do caule de Citharexylum myrianthum (Verbenaceae) que ocorre em uma área de floresta estacional semidecídua próximo à cidade de Botucatu (22º52’20”S e 48º26’37”W), estado de São Paulo, Brasil, foi estudada. Camadas de crescimento distintas, demarcadas por anel semi-poroso e faixas marginais de parênquima axial foram observadas em ambos os órgãos. As características qualitativas observadas tanto em raiz quanto em caule foram: espessamentos helicoidais finos e placas de perfuração simples e múltiplas em elementos de vaso; grandes quantidades de parênquima axial nos anéis de crescimento, em faixas marginais a confluente formando faixas irregulares no lenho inicial a aliforme losangular no lenho tardio; células do parênquima axial bifurcadas, com projeções e ondulações na parede; fibras septadas; fibras bifurcadas e com diversas terminações. Na análise quantitativa comparativa entre raiz e caule foi aplicado teste t-student que mostrou diferenças significativas na frequência e diâmetro de vasos; comprimento dos elementos de vaso; altura dos raios; índices de vulnerabilidade e mesomorfia. A madeira da raiz teve menor frequência de vasos, vasos com menor diâmetro e elementos mais longos, e raios mais altos. Os índices de vulnerabilidade e mesomorfia indicaram que as plantas de C. myrianthum são mesomórficas. As raízes parecem estar mais susceptíveis ao estresse hídrico do que os caules. Palavras-chave: anatomia da madeira, floresta estacional semidecídua, xilema secundário. Introduction Citharexylum myrianthum Cham., a deciduous tree, reaches 8 to 15 m in height and 20 to 40 cm in breast height diameter, and has a wide occurrence in Brazilian forest formations (latitude 14045’‒31050’S). It occurs in Dense Ombrophilous Forest (Atlantic Rain Forest sensu stricto), semideciduous seasonal forest, riparian areas (Carvalho Universidade Estadual Paulista (UNESP), Faculdade de Ciências Agronômicas (FCA), Depto. Ciência Florestal, R. José Barbosa de Barros 1780, 18610-307, Botucatu, SP, Brazil. 2 Center for Wood Anatomy Research, Forest Products Laboratory, One Gifford Pinchot Dr, Madison, WI, 53726-2398, USA. 3 Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Diretoria de Pesquisas, Lab. Botânica Estrutural, R. Pacheco Leão 915, 22460-040, Rio de Janeiro, RJ, Brazil. 4 Author for correspondence: 1 Marcati, C.R. et al. 568 1994), and also in lowland dry tropical forest (Tabarelli 1992). The rapid growth makes C. myrianthum an important species for restoration of degraded areas (Sansevero et al. 2009). General descriptions of wood anatomy of the genus Citharexylum have already been reported by Metcalfe and Chalk (1950). For C. myrianthum, Gomes et al. (1989) studied stem wood anatomy from trees that occurred in eastern part of Paraná state (South Brazil) and it was the first time that radiate perforation plates in vessels were mentioned in this species. Barros et al. (2001) described the wood anatomy of trees from a seasonally flooded forest of the Reserva Biológica de Poço das Antas (Rio de Janeiro state, Southern Brazil). Cambial activity and the seasonal formation of secondary xylem in stems of C. myrianthum occurring at São Paulo State were studied by Marcati (2000) and annual growth rings were observed in the wood. Seasonal presence of acicular calcium oxalate crystals in the cambial zone, with greater abundance in dry than in wet periods, was reported for this species (Marcati 2000; Marcati & Angyalossy 2005). Across this rich body of work, only stem wood was studied. Perhaps not surprisingly, given the comparative difficulty of collection specimens, root wood anatomy, in general, has received much less attention than stem wood anatomy (e.g. Gasson & Cutler 1990). When studied, physiological and anatomical research demonstrated that within a species, root xylem has wider vessels than stem xylem and that root wood is more vulnerable to embolism than stem wood (Alder et al. 1996; Ewers et al. 1997; Machado et al. 1997; Kavanagh et al. 1999; Kolb & Sperry 1999; McElrone et al. 2004; Psaras & Sofroniou 2004). The objectives of this study were to compare root and stem wood anatomy of Citharexylum myrianthum qualitatively and quantitatively and to relate any anatomical differences between the organs to their function and ecological adaptations. Material and Methods Citharexylum myrianthum were collected in a semi-deciduous seasonal forest in the municipality of Botucatu (22052’20’’S, 48026’37’’W), São Paulo state, south-eastern Brazil. The average annual rainfall is about 1300 mm, with a mean annual temperature of 20°C. July is the driest and coldest month with mean temperature of 15°C, and January is the wettest and warmest month with mean temperature of 25°C. The dry season typically extends from May to September (Fig. 1). Climate data were obtained from the Estação Meteorológica of the Faculdade de Ciências Agronômicas, UNESP, Botucatu, São Paulo State. The Estação Meteorológica was about 11 km from the study site. Stem and main root samples from three adult specimens (Tab. 1) were collected at 1.30 m and 30 cm distal from root collar, respectively. Wood samples from sapwood were fixed in 70% ethanol. Transverse, (...truncated)