Leaf breakdown in a tropical stream: comparison between the exotic Eucalyptus grandis and two native species

Abstract

Aim We evaluated the leaf decomposition in a first order stream of the exotic Eucalyptus grandis and two native species Lithraea molleoides and Maytenus aquifolium common riparian trees in a tropical forest. Besides seasonal effects on leaf decomposition of the three species were evaluated. Methods The dried leaves were incubated in litter bags” of 20 x 20 cm with 10 mm of mesh opening in two different treatments and at two times of the year (dry and rainy): i) 48 “litter bags” containing 4 g of leaves, being 24 “litter bags” with leaves of L. molleoides and 24 with E. grandis and ii) 48 “litter bags” containing 4 g of leaves, being 24 “litter bags” with of M. aquifolium and 24 with leaves of E. grandis. After 2, 7, 14, 21, 28 and 60 days of immersion, randomly removed four “litter bags” of each species to carry out the analyzes. Results The weight loss in the first two days was between 20% and 40% in both experiments and in both seasons of the year. Leaf decomposition was higher in L. molleoides (k=0.0062 ± 0.0002 day-1) than in E. grandis (k=0.0039 ± 0.0005 day-1) in the dry season and higher in L. molleoides (k=0.0185 ± 0.0002 day-1) than E. grandis (k=0.0164 ± 0.0003 day-1) in the rainy season. In the second experiment the decomposition rates were higher in M. aquifolium (k=0.0151 ± 0.0009 day-1) than E. grandis (k=0.0149 ± 0.0006 day-1) in the dry season and higher in M. aquifolium (k=0.0174 ± 0.0001 day-1) than E. grandis (k=0.0164 ± 0.0002 day-1) in the rainy season. Besides, the results indicate that there is an effect of both the dry and rainy season and the native or exotic species on the decomposition rates. Conclusions Our findings indicate that, the seasons are likely to influence leaf decomposition, and future studies should consider seasonality. Furthermore, the exotic species had a lower decomposition rate compared to native species, which reinforces that the replacement of native riparian vegetation by exotic species such as eucalyptus can interfere on the quality of allochthonous resources and on the cycling of nutrients in neotropical streams.

Interrelationships among litter chemistry, plant species diversity, and litter decomposition in tropical stream environments: a review

“…Tropical riparian forests are constantly invaded by exotic plant species (van Kleunen et al, 2015), and most studies evaluating the impacts of these species (e.g., Eucalyptus species) on streams have reported changes in the seasonality, quantity, and quality of litter entering streams (Molinero and Pozo, 2004) (Figure 1). These changes can reduce (Pelizari et al, 2022), increase (Gomes et al, 2018) or do not affect (Gonçalves et al, 2012) litter decomposition, which is related mainly to higher or lower chemical and physical compounds in exotic species (i.e., N and P content and presence of refractory compounds such as lignin and cellulose) compared to native species, and to the type of community involvement in the decomposition process (microorganisms and shredder invertebrates) (Ferreira et al, 2019). In regions where shredder invertebrates are not important decomposers and litter decomposition is microbial-driven primarily, as is often the case in tropical regions [e.g., Gonçalves et al (2007)], the litter decomposition may be less affected by invasive exotic plant species since their effects are more potent for streams where shredders are well represented (Ferreira et al, 2016;Ferreira et al, 2019), although invasion by these species can have significant impacts on microbial colonization and decomposition (Gomes et al, 2018).…”