A importância de traços funcionais e do posicionamento do detrito na serrapilheira como mecanismos mediadores dos efeitos da interação entre diversidade de detritos e foto-oxidação na decomposição
Studies over the last two decades have pointed to an important role of the litter diversity, especially the functional one, as a determinant of decomposition rates. So far, it has been known that the mechanisms by which the diversity of litter affects decomposition results from biotic mechanisms...
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Formato: | Dissertação |
Idioma: | pt_BR |
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Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/27469 |
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Resumo: | Studies over the last two decades have pointed to an important role of the
litter diversity, especially the functional one, as a determinant of decomposition rates.
So far, it has been known that the mechanisms by which the diversity of litter affects
decomposition results from biotic mechanisms mediated by the interactions between the
decomposing fauna and the detritus. However, abiotic factors such as photodegradation
also have a direct effect on decomposition rates in many ecosystems, especially in
regions or habitats with a high incidence of UV radiation. In this way, it is conjectured
that non-additive effects of the debris diversity in the decomposition should be weak or
nonexistent under environmental conditions that do not favor the decomposition
through biotic mechanisms. In this work, we tested this conjecture through two field
experiments carried out under distinct environmental contexts, in a restinga in the State
of Rio Grande do Norte. In the first experiment (Exp. 1), we verified whether and as
non-additive effects of the richness and functional diversity of litter vary in magnitude
and direction between a habitat more conducive to decay-mediated decomposition (ie
soil under vegetation) and another where Photo-degradation-mediated decomposition
assumes greater relevance (ie soil exposed to direct solar radiation). In the second
experiment (Exp. 2), we observed only in the habitat with high solar exposure if and as
the overlap (ie overlapping or not between) and the position with which the litter is
vertically in the litter (ie in contact with the soil , or on the litter surface) measured the
effects of the diversity of debris on decomposition. In the Exp. 1 litter of four species,
presenting discrepant values of specific leaf area (AFE) were placed to decompose in
monocultures and all possible bicultures over 6 months in litterbags. In Exp. 2 the
decomposition was also evaluated in litterbags over 6 months, but only for monocultures and mixtures formed by two species that presented more discrepant
values of AFE, Erythrina velutina (Ev) and Sterculia chicha (Sc). The results of Exp. 1
showed that the rate of decomposition at sites exposed to the direct action of
photodegradation was on average 34% higher than that observed in shaded sites under
vegetation. There was no significant effect of species richness on decomposition in any
of the environmental contexts, indicating that on average the decomposition of the
detritus mixtures can be predicted through the decomposition of their monocultures.
However, this effect was not homogeneous among the bicultures. The functional
dissimilarity between the bicultures had a significant effect on the decomposition, but
only in the environment exposed to the sun. In general, combinations of foliar litter with
greater discrepancy in the AFE values presented slower decomposition in bicultures
than in monocultures. This result was mediated by a trade-off between effect and
response of the debris of different species to shade. Species with higher AFE were more
sensitive to shading, while species with lower AFE had a greater shading effect. In
addition, in Exp. 2 we observed that the overlap and vertical positioning of the detritus
also modify the effects of diversity on decomposition. Effects of the debris diversity on
decomposition occurred only in the treatments with overlapping litter. However, the
effects were significant only for the S. chicha (Sc) species, whose decomposition in the
near-soil (less exposed to the sun) and surface (more exposed to the sun) differed from
their monoculture decomposition (ie major and minor respectively ). Contrary to our
expectations, abiotic mechanisms from photodegradation determine non-additive effects
of the functional diversity of debris that consistently retard decomposition in
environments exposed to the sun, but such effects have been shown to be dependent on
the vertical position of the debris in the litter. Together, the results show that the
functional diversity of the detritus, as well as factors that determine the vertical position
of the debris in the litter (ie phenological pattern) can act as important mechanisms of
carbon retention in the soil in regions, ecosystems or habitats, with high exposure solar. |
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