Avaliação do efeito de organismos epifilicos no processo de decomposição

Abstract

Epiphyllous organisms (e.g., fungi, lichens, bryophytes) are often found in tropical forests. Their positive and negative effects on the host plant occur at different hierarchical levels ranging from foliar to individual levels. Despite the importance of ir effects on host plants, the understanding of their role as a possible mediator of ecosystem processes remains scarce. Epiphylls require a humid microclimate for their establishment and, therefore, the leaf ability to repel water from external sources (e.g., rain and fog) may influence leaf susceptibility to colonization. On the other hand, epiphylls can alter characteristics related to leaf wetness. For example, the high hydration capacity of bryophytes may result in super hydrophilic leaves when colonized by bryophytes, while the colonization by lichens may result in hydrophobic leaves due to the production of hydrophobic substances. These effects on leaf wetness can lead to important consequences to decomposition process after leaf senescence, however, such effects remain untested. This work had the objective of evaluating the relative contribution of epiphyllous bryophytes and lichen on the rates of litter decomposition due to their influence of leaf water repellency. We propose the following hypothesis: the presence of bryophytes in the leaves will provide greater hydration and higher rates of decomposition, leaves with lichens will be more hydrophobic which will result in lower rates of decomposition compared to leaves without colonization. To test our hypothesis, we performed an experiment with microcosms containing 1g of leaf in four treatments (leaves colonized by bryophyta, by lichen, without colonization and epiphylls removed) of six species of vascular plants were incubated in a climatic chamber for ten weeks. The leaf material was sprinkled with water every 48 hours to replace the evaporated water and maintain conditions favorable to decomposition. At the end of the experiment, the remaining material was collected and dried. The percentage mass loss was calculated as a measure of decomposition. The leaf water repellency for each treatment was measured through the contact angle between a drop of water and the surface of the leaf. Our hypothesis was partially rejected. There was no effect of lichens on water repellency, the presence of bryophytes had an effect on water repellency by making the leaves super-hydrophilic. The decomposition rates differed only between treatment with bryophytes and without colonization. This result suggests that the effect of epiphylls cannot be predicted from the bryophytes and lichens life forms due to the high heterogeneity of characteristics related to the ability to absorb water and the variation of decomposability within the groups. In this sense, for a better understanding of the effects of the epiphylls on the decomposition and the interaction with functional characteristics of the plants, it is necessary to consider the functional traits of these organisms and the functional diversity of the phyllosphere