Hoehnea 29(2): 151-158. 2 tab., 4 fig., 2002 Soluble carbohydrate similarities between Echinolaena inflexa and Melinis minutiflora (Poaceae) Moemy Gomes Moraes I, Amanda de SouzaI, Rosemeire Aparecida Bom Pessoni I and Rita de Cassia Leone Figueiredo-Ribeiro1,2 Received: 10 September, 2001; accepted: 28 May. 2002 ABSTRACT - (Soluble carbohydrate similarities between Echinolaena inj7exa and Melin is lIIinutijlora - Poaceae). Echinolaena inj7exa (Poir.) Chase is a native grass species with high biomass production, with abundance in the cerrado comparable to Melinis lIIinlltijlora Beauv., a forage grass of African origin, wide pread in the cerrado, displacing some native herbaceous species. In the present study, sugars from both species were analysed in two distinct periods of their annual developmental cycle. Water-soluble carbohydrates varied significantly in both species between summer and winter. Soluble carbohydrate contents were higher in winter in different tissues of both species, but sugar alcohols were higher in E. inj7exa. The presence of these sugars and other low molecular weight carbohydrates is discussed with respect to stress tolerance and the establishment of both species in the cerrado. Key words: soluble carbohydrates, cerrado, grasses, biological invasion RESUMO - (Similaridade de carboidratos soluveis em Echinolaena inj7exa e Melinis lIIinutijlora - Poaceae). Echinolaena inj7exa (Poir.) Chase e uma gramfnea nativa, amplamente distribufda em areas de cerrado e com biomassa aerea companlvel a de Melinis minutijlora Beauv., que e uma gramfnea de origem africana, tambem largamente distribufda nessas areas, onde compete com as especies herbaceas de ocorrencia natural. No presente trabalho foram analisados os carboidratos soluveis de ambas as especies, em duas esta~6es anuais, sendo observadas varia~6es no conteudo e na composi~ao desses compostos, com tendencia a um aumento no inverno, em todos os tecidos analisados. Destacou-se 0 teoI' de a~ucares alcoois de E. inj7exa, que foi cerca de 10 vezes maior que 0 de M. min/ltijlora no inverno. A presen~a marcante de a~ucares alcoois e de outros carboidratos de baixo peso molecular nessas especies poderia estar associada atolerancia a estresses ambientais, favorecendo seu estabelecimento no cerrado. Palavras-chave: carboidratos soluveis, cerrado, gramfneas invasao biol6gica Introduction Pivello et al. (1999a, and references therein), this factor also contributed significantly for the success of Comparative physiological and ecological studies the invasive grass Eragrostis lehmanniana (Lehmann on the invasion of neotropical savannas by African lovegrass) in the Arizona arid grassland. grasses have been calTied out in the last ten years Melinis minutiflora Beauv., an African species, (Klink & Joly 1989, Bilbao & Medina 1990, Anten et was introduced in Brazil due to its high forage value. al. 1998, Pivello et al. 1999a, b). These species invading This species has been propagating rapidly in the native areas have drastic effects on native plant species cerrado, perhaps because of the suitable climate and and they may contribute directly to changes in soil conditions for its growth (Filgueiras 1990). The ecosystems processes (Williams & Baruch 2000). high light intensity ofthe savanna open fields (Medina However, a clear comprehension ofthe process is not & Motta 1990) and the degree of environmental available yet, although high seed production and viability, disturbance (Pivello et al. 1999a and references seedling establishment, rapid growth and an efficient therein) could also favour its propagation in the celTado. vegetative reproduction have been pointed out as Among several other alien grasses, M. minlltiflora is important biological attributes for successful invader notably the most prominent species occupying natural species (Klink 1996). In addition to the factors reserves of the Brazilian cerrado, thus outcompeting previously cited, the high biomass production is also native herbs (pivello 1992). Results obtained by Pivello an important feature on competition. According to et al. (l999a) in one preserved area of cerrado in I. Sec;:ao de Fisiologia e Bioqufmica de Plantas, Instituto de Botanica. Caixa Postal 4005, 0 I061-970 Sao Paulo, SP, Brasil. 2. Corresponding author: [email protected] 152 Hoehnea 29(2), 2002 southeastern Brazil showed that this species has similar species of Asteraceae, Poaceae and Leguminosae phytossociological patterns and spatial distribution (Mantovani & Martins 1993). when compared to the native grass Echinolaena Plants of Echinolaena inflexa and Melinis inflexa (Poir.) Chase. minutiflora were harvested in the Biological Reserve Rapid changes in soluble carbohydrate metabolism of Moji-Guayu during summer and winter, in the underground organs ofnative herbaceous species corresponding to wet and dry seasons, respectively. from the cerrado (Figueiredo-Ribeiro & Dietrich 1983), £. inflexa is a perennial, rhizomatous grass species in addition to the accumulation of high amounts of native from the cerrado. It occupies both shaded (KJink fructans, have been considered as adaptive features & Joly 1989) and sunny habitats and exhibits C-3 ofthe plants to survive under unfavourable conditions, photosynthetic metabolism (Medina et al. 1999), particularly related to low temperature and drought differently from M. minutij7.ora, a C-4 species that (Figueiredo-Ribeiro et al. 1991, Tertuliano & occurs mainly in sunny and disturbed areas (Filgueiras Figueiredo-Ribeiro 1993, Vieira & Figueiredo-Ribeiro 1990, Pivello et al. 1999b). In the sampling site 1993, Carvalho et al. 1997). According to Mc Cue & E. inflexa plants flowered during summer, while Hanson (1990), the accumulation of several M. minutiflora flowered mainly in winter. Plants were metabolites, including fructans and polyols or sugar harvested in a sunny habitat from an area close to a alcohols in plants could be one indication of an track besides the border of the reserve. alternative metabolic mechanism operating in response From each of two species, tillers with the same to adverse environmental conditions, mainly drought. number of leaves were harvested from four plants In the present work we describe changes in randomly chosen ofeach species. The harvested tillers soluble carbohydrates from leaf blades, leaf sheaths represented the predominant phenological phase ofthe and stems of Echinolaena inflexa and Melinis species in the area. The sampling was performed minutiflora during winter and summer aiming to assess between 5 and 6 hours after sunrise. the role of those sugars in the association of both Carbohydrate extraction and analysis: immediately species in the cerrado. after harvesting, intact plants were hand cleaned from soil particles and placed in thermal boxes containing Material and methods solid CO2 (dry ice). In the laboratory they were separated into leaf blades, leaf sheaths and stems, Study site and studied species: the Biological Station constituting different samples, which were of Moji-Guayu (SP, Brazil) is a border cerrado area immediately wrapped in aluminium foil, frozen, occupying 343 ha within the rectangle 22°15'- 22°16'S Iyophilised and then finely ground through a 0.5 mm and 47°08'- 47°12'W. The climate fits into Koppen's screen in a Tecator-Cyclotec mill (USA). Carbohydrate Cwa. The soil is deep, acid and sandy with little organic extraction was performed using 5 mg cm-3 deionised matter and nutritionally poor. The altitude varies from water 95°C for 15 min, followed by centrifugation for 560 m to 700 m. The monthly temperature and rainfall 15 min at 1500 x g. This procedure was repeated twice. records registered over the years of 1996 and 1997, Supernatants were pooled and the pH adjusted to period when plants were harvested, ranged from 22.9°C neutrality before concentrating under vacuum at 37°C to 34.9°C during summer and from 10.4 °C to 30°C (Chatterton & Harrison 1997). The extracts were during winter; and from 0 mm in winter to 275 mm deionised using Sep-Pack Acce11 Plus QMA and CM during the summer months, respectively. There is a cartridges and hydrophobic compounds were removed rather definite dry season, which coincides with the using Sep-Pack tC l8 cartridges. All cartridges used cooler months (Eiten 1972, Mantovani & Martins 1993). were supplied by Waters Chromatography Division of As reported by Nardoto et al. (1998), water content Millipore Co. (USA). decreases in the outer layers of the soil, reaching Total sugars were measured using the phenol­ values lower than the permanent wilting percentage sulphuric acid procedure (Dubois et al. 1956), using to commercial crops (-1.5 MPa, soil water potential) glucose as standard. at the end of the dry period. The vegetation is High-performance anion exchange predominantly open and varies from "campo cerrado" chromatography with pulsed amperometric to "cerrado" (sensu stricto). The herbaceous detection (HPAEC-PAD) was used to perform component ofthe cerrado flora is composed mainly of quantitative analysis on a CarboPac PA-l column M.G. Moraes, A. Souza, R.A.B. Pessoni, R.C.L. Figueiredo,Ribeiro: Sugars in grasses from the cerrado 153 (4 X 250 mm) in a Dionex System Mod. DX-300 summer and winter are shown in figure 1. For both (USA). Quantification of individual sugars was also species and for all analysed tissues WSC were performed according to Timmermans et al. (1994) significantly higher in winter (Tukey 0.05). Differences by the external standard method using authentic were found among the plant parts,