Compostos secundários durante a decomposição foliar de espécies arbóreas em um riacho do sul do Brasil

Abstract

RESUMO -(Compostos secundários durante a decomposição foliar de espécies arbóreas em um riacho do sul do Brasil). Os objetivos deste trabalho foram identificar os compostos secundários e avaliar o comportamento destes em folhas de Sebastiania commersoniana (Baill.) Smith e Downs e Eucalyptus grandis Hill ex Maiden durante diferentes estágios de decomposição em um riacho de primeira ordem do norte do Rio Grande do Sul. Foram incubadas no riacho folhas das duas espécies, sendo essas retiradas do corpo hídrico após zero, um, 30 e 60 dias para determinação da taxa de decomposição e análise química por cromatografia gasosa. Foi possível identificar 14 compostos em S. commersoniana e 25 em E. grandis. O ácido palmítico foi o composto mais freqüente em ambas as espécies durante o experimento, sendo que a quantidade deste e dos demais compostos identificados variou durante o período estudado. A complexidade química das folhas de E. grandis pode ter influenciado na sua decomposição, que foi mais lenta que a das folhas de S. commersoniana. Palavras-chave: Eucalyptus grandis, qualidade ambiental, Sebastiania commersoniana, vegetação ribeirinhaABSTRACT -(Secondary compounds during leaf decomposition of tree species in a stream in southern Brazil). This work aims to identify the secondary compounds and evaluate their behaviour in Sebastiania commersoniana (Baill.) Smith and Downs (Euphorbiaceae) and Eucalyptus grandis Hill ex Maiden (Myrtaceae) leaves during different decomposition stages in a first-order stream in northern Rio Grande do Sul. Leaves of the two species were incubated in the stream and were removed after 0, 1, 30 and 60 days to determine decomposition rate and perform chemical analysis by gas chromatography. Fourteen compounds in S. commersoniana and 25 in E. grandis were identified. Palmitic acid was the most frequent compound in both species throughout the experiment; the amount of this acid and the other compounds varied during the study period. The chemical complexity of E. grandis leaves may have influenced their decomposition, which was slower than that of S. commersoniana leaves.

Nutrient addition does not enhance leaf decomposition in a Southeastern Brazilian stream (Espinhaço mountain range)

“…Although eucalyptus leaves are usually considered relatively refractory to breakdown due to the high concentrations of secondary compounds and toughness and to the relatively low nutrient contents (e.g., Graça et al, 2002), the vegetation of the Cerrado biome is even tougher and more recalcitrant to biological breakdown (Moretti el al., 2007a). The breakdown rates of eucalyptus obtained in this study were faster than breakdown rates obtained in other studies with leaves of E. grandis (Gonçalves Jr., 2005;Hepp et al, 2009) in Brazilian streams. But these faster breakdown rates were probably more related to the characteristics of the stream rather than to the characteristics of the leaf species, which are similar (Gonçalves Jr., 2005;Moretti, 2009).…”

“…Abelho and Graça, 1996;Canhoto and Graça, 1996;Graça et al, 2002), where eucalyptus is also an introduced species, have shown that species of eucalyptus decompose relatively slow in comparison to the natural leaf litter in these streams. Although very few data is available on the decomposition rate of eucalyptus in Brazilian streams, the results obtained by Hepp et al (2009) andGonçalves Jr. (2005) for Eucalyptus grandis (0.0050 to 0.0068 day -1 ) are within the higher range reported (Gonçalves Jr., 2005;Moretti et al, 2007a, b) for breakdown rates of natural vegetation of the Cerrado in several Southeastern Brazilian streams (0.0019 to 0.0063 day -1 ). The main objective of this study was to assess whether nutrient availability may limit the process of leaf decomposition in a mountain stream located at the southern end of the Espinhaço Range Mountain, and, if so, whether macroinvertebrates, microorganisms, or both, mediate the effect.…”

Exotic Eucalyptus leaves are preferred over tougher native species but affect the growth and survival of shredders in an Atlantic Forest stream (Brazil)

“…The intrinsic characteristics and the stage of decomposition of leaf litter determine its quality for consumers [ 28 ]. Therefore, the contents of lignin, cellulose, nutrients, and secondary compounds as well as microbial colonization influence leaf quality [ 29 – 31 ]. It is well known that invertebrate shredders exhibit a feeding preference for high-quality leaves, i.e., with high nutrient contents and low amounts of structural compounds [ 27 , 32 , 33 ].…”

Chemical change of leaves during breakdown affects associated invertebrates in a subtropical stream

“…Both species lost more than 50% of their secondary compounds during the first week of incubation in the stream. Previous studies have suggested that high concentrations of these compounds inhibit colonisation by invertebrates, slowing leaf breakdown (Hepp et al, 2009;Stout, 1989;Wantzen et al, 2002). However, the rapid leaching of these leaf compounds may have reduced the inhibitory effect on invertebrates.…”

“…Leaf chemical characteristics known to increase breakdown rates and nutritional quality of leaves for invertebrates in streams included high N and P (Ardón et al, 2009), low C:N ratio (Enríquez et al, 1993), secondary compounds (Hepp et al, 2009) and lignin content (Ardón et al, 2009). In contrast to the existing information from temperate streams, high diversity of tree species in the tropical riparian vegetation has prompted suggestions that leaf quality plays a more important role on decomposition than in temperate streams (Wantzen et al, 2008).…”