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Seed germination and seedling growth of two Pseudobombax species (Malvaceae) with contrasting habitats from Brazilian Cerrado Clesnan Mendes-Rodrigues, Paulo Eugênio Oliveira & Marli Aparecida Ranal Programa de Pós-graduação em Ecologia e Conservação de Recursos Naturais, Instituto de Biologia, Universidade Federal de Uberlândia, Caixa Postal 593, 38400-902 Uberlândia, Minas Gerais, Brazil; [email protected], [email protected], [email protected] Received 22-XI-2010. Corrected 07-IV-2011. Accepted 09-V-2011. Abstract: Pseudobombax tomentosum and P. longiflorum are common trees in the Cerrado region, but the former species is more common in forest edges while the later is present in open cerrado areas. This work aimed to investigate differences in seed germination and seedling growth in these species, from seed collected from Cerrado areas in Central Brazil. For this, a seed germination experiment was designed and included four replicates with 25 seeds per species; seeds were randomly distributed in the germination chamber. To evaluate initial seedling growth, seedlings height was measured up to 67 days after seedling emergence; besides, some of these seedlings were grown for biomass evaluation during nine months. Results showed that seeds of the two species had the same germinability (near 100%) and mean germination time (ca. 12 days). However, P. longiflorum showed a more spread seed germination through time, with higher values of coefficient of variation in germination time and uncertainty index; and lower values of synchronization than P. tomentosum. The two species showed basically the same growth pattern, but lower values for height of apical meristem, diameter of underground structures (mostly roots), dry mass of shoots, underground structure and total mass of seedlings in P. tomentosum were obtained, compared to P. longiflorum. Both species allocated more dry mass to under- ground structures in detriment of shoot. This probably allows resprouting behavior which prevents hydric stress and detrimental fire action typical of the open Cerrado areas. Rev. Biol. Trop. 59 (4): 1915-1925. Epub 2011 December 01. Key words: Cerrado, seed germination measurements, Neotropical savannas, plant growth, seedling growth, Pseudobombax longiflorum, Pseudobombax tomentosum. Seed germination patterns differ in the last seed germinated in experimental conditions same family, genus and even for the same spe- (Souza & Válio 2001, Souza-Silva et al. 2001, cies (Baskin & Baskin 1998). Inside the Bom- Zamith & Scarano 2004, Wittmann et al. 2007, bacaceae, now the subfamily Bombacoideae, Lopes et al. 2008). Other studies for the family Malvaceae sensu lato (APG 2003), there are focused on the ratio between dry mass of roots species with dormant and non-dormant seeds and shoots or on seedling growing under dif- (Vazquez-Yanes 1974, Joly & Crawford 1983, ferent light and soil conditions, without records Danthu et al. 1995), but information about seed for Pseudobombax (Moreira & Klink 2000, germination patterns is not available yet for Scalon et al. 2003). most taxa of this group. Among the species of Bombacoideae from Germination within the large Neotropical cerrado, P. longiflorum and P. tomentosum are genus Pseudobombax is still poorly studied and species that occur in open fire-prone plant for- the few published works are restricted to the mations, but also at the edge or inside gallery, germinability assessment, and sometimes to the deciduous and mesophyllous forests (Gribel speed of the process, based on the first and the 1988, Silva & Scariot 2004). P. longiflorum is Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 59 (4): 1915-1925, December 2011 1915 much more common in open savanna forma- more synchronized germination process and tions and has hanging bat pollinated flowers seedlings would have more mass allocated to (Coelho & Marinho Filho 2002). P. tomento- the stems, favoring light absorption and con- sum is much more common in forest habitats tinuous growth. where its sturdy flowers depend on non-flying mammals passing from crown to crown for MATERIAL AND METHODS pollination (Gribel 1988). Except from the dif- ferences in habitat, the species are similar in Studied species: Pseudobombax longiflo- relation to the distribution, phenology and seed rum (Mart. & Zucc.) Robyns (Bombacoideae, dispersion period (Lorenzi 1992, Silva Júnior Malvaceae) is found in most Cerrado areas. It et al. 2005). The absence of exclusive habitats is fairly common in Minas Gerais and down between the two species reflect the presence of to the North of Paraná State. It is a deciduous physiognomic gradients and transitions among tree, which occurs sparsely in open Cerrado savanna and forest areas in the Cerrado Biome areas (Lorenzi 1992). Flowering occurs from (Ribeiro & Walter 1998). The water stress and July to November and fruits mature during the the occurrence of seasonal fire in the Cerrado next dry season, from July to November (Silva biome select species with ability to resprout Júnior et al. 2005). P. tomentosum (Mart. & after these events, leading to the allocation of Zucc.) Robyns (Bombacoideae, Malvaceae) available resources to the roots or other under- is usually a larger tree, found in Cerradão ground structures in detriment of the shoots in (dense cerrado with almost closed woodland) open formation species while forest species and Cerrado (closed vegetation dominated by show allocation to aerial parts in detriment of trees and shrubs with herbaceous vegetation the roots (Hoffmann & Franco 2003). Inside between them), but mainly in the edges and mesophyllous forest and gallery forest forma- sometimes inside mesophyllous and gallery tions, light is the limiting factor but habitat forests. It occurs in most Cerrado region down shows less oscillations in water regime and to Southern areas of São Paulo and Mato temperature, favoring fast and synchronized Grosso do Sul. It flowers from July to August seed germination whenever gaps or leaf fall and the fruits mature from August to October. cycles improve seedling survival chances as It is a deciduous and heliophyllous plant, also discussed by Garwood (1983). Meanwhile, appearing less frequently in open vegetation, in the savanna habitats, the limiting factors usually on sandy or humic clay soils, but also are water and nutrients, and seed germination on better drained oxisoils common in the Cer- spread in time, and even dormancy, may favor rado region (Lorenzi 1992, P.E. Oliveira, pers. seedling survival (Moreira & Klink 2000, observ.). The voucher specimens can be found Hoffmann & Franco 2003, Oliveira 2008, in Herbarium Uberlandense. Vieira et al. 2008). In this context, vicariant species as the ones Studied area: About 200 seeds of both studied here provide the opportunity to see how species were collected in the Cerrado areas, habitat specialization would be reflected in Neotropical savannas region in Central Brazil germination and seedling growth (Hoffmann & (sensu Ribeiro & Walter 1998). The seeds of Franco 2003). The objective of this paper was P. tomentosum were collected in forest areas, to test, on the one hand, if seed germination of near to Uberlândia city, Minas Gerais state P. longiflorum would be more asynchronous (19º07’ W - 48º22’ S) and the seeds of P. and seedling mass allocated predominantly in longiflorum were collected in adjacent open the underground structures, favoring seedling pasture and areas along the BR050 highway survival in the open savanna areas. On the other (17º06’ W - 47º45’ S), between Uberlândia hand, for P. tomentosum, typical of forest for- and Brasília. Germination and seedling growth mation with less water stress, with an expected experiments were carried out at the Campus 1916 Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 59 (4): 1915-1925, December 2011 of the Federal University of Uberlândia. The synchronization index of germination (ZG) (Z, region climate is characterized as Aw according Ranal & Santana 2006 adapted from Primack to the Köppen scale (Köppen 1948), tropical 1980) were used to describe the germina- humid climate with a dry winter (April to Sep- tion process. Further details on mathematical tember) and rainy summer (October to March) expressions, authorship, intermediate calculus, (Rosa et al. 1991). the sense and the applications of these germi- nation measurements can be found in Ranal & Seed germination: Mature fruits of both Santana (2006) and Ranal et al. (2009). All ger- species were collected in September and Octo- minated seeds were checked for the presence ber 2003. The fruits were collected directly of more than one embryo per seed, known as from the trees and placed to dry at room tem- polyembryony and common in Bombacoideae perature in order to facilitate the extraction of (Mendes-Rodrigues et al. 2005). the seeds. Seeds were stored in paper bags at room temperature (between 25 and 30°C), in a Seedling morphology and height: Seeds dry chamber containing silica gel with humid- germinated in laboratory conditions were trans- ity indicator, and kept until the installation of planted to black plastic bags (30cm high per the experiment, 30 days later. The seeds were 13cm diameter), filled with previously sieved sown on fine vermiculite (expansion volume of open Cerrado oxisol. Seedlings were kept in 0.1m3), inside transparent germination boxes, a greenhouse covered with black plastic net moistened as necessary with distilled water. with 50% shading and moistened when neces- Boxes were kept in a germination chamber sary. Starting from emergence date, periodic (Seedburo Company, model MDG2000) under measurements of the maximum height of each continuous light (mean=11.90, SD=6.52µmol/ plant, considered from ground to the apex of the m2/s of photosynthetically active radiation), at last leaf were carried out (Fig. 1 H-1). The data 25ºC. The experimental units were randomly were adjusted to a linear regression model, as a distributed in the germination chamber, four function of the days from emergence. Some 20 replicates for each species with 25 seeds per P. longiflorum seedlings were evaluated up to replicate. The seed sample size was somewhat 67 days after emergence and 15 P.

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