1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions. 2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day )1 and are among the slowest reported. They were significantly (F ¼ 20.12, P < 0.05) lower than in the temperate stream (0.0046-0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 lg g )1 , (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 lg g )1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g )1 ). 3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F ¼ 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves. 4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L )1 ), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source.

No abstract

The objectives of this study were to investigate leaf breakdown in two reaches of different magnitudes, one of a 3 rd (closed riparian vegetation) order and the other of a 4 th (open riparian vegetation) order, in a tropical stream and to assess the colonization of invertebrates and microorganisms during the processing of detritus. We observed that the detritus in a reach of 4 th order decomposed 2.4 times faster than the detritus in a reach of 3 rd order, in which, we observed that nitrate concentration and water velocity were greater. This study showed that the chemical composition of detritus does not appear to be important in evaluating leaf breakdown. However, it was shown to be important to biological colonization. The invertebrate community appeared not to have been structured by the decomposition process, but instead by the degradative ecological succession process. With regards to biological colonization, we observed that the density of bacteria in the initial stages was more important while fungi appeared more in the intermediate and final stages.

We assessed leaf breakdown of five native riparian species from Brazilian Cerrado (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense, and Protium heptaphyllum), incubated in single and mixed species packs in two headwater streams with different physico-chemical properties in the Espinhac¸o Mountain range (Southeastern Brazil). Leaves were placed in plastic litter bags (15 cm  20 cm, 10 mm mesh size) and the experiments were carried out during the dry seasons of 2003 and 2004. Leaf nitrogen and phosphorus contents were similar in all species, but polyphenolic contents were different (Po0.001). M. guyanensis showed higher polyphenolics content (8.48% g À1 dry mass) and leaf toughness. Individually, higher breakdown rates were found in M. guyanensis at Indaia´stream (k ¼ 0.006370.0005 d À1 ) and in Ocotea sp. at Garcia stream (k ¼ 0.008870.0006 d À1 ). However, P. brasiliense and P. heptaphyllum showed lower breakdown rates at Indaia´and Garcia streams (Indaia´: k ¼ 0.002070.0002 and 0.001970.0001 d À1 ; Garcia: k ¼ 0.004270.0001 and 0.004070.0002 d À1 ). Single and mixed breakdown processes of each species were not statistically different on both streams. However, all species showed higher breakdown rates at Garcia stream (Po0.01). These results suggest that leaf breakdown is not altered when litter benthic patches are composed by a mixture of species in the same proportions that they occur on riparian leaf falls.

We evaluate the composition and structure of invertebrate assemblages during leaf breakdown of five native tree species (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense and Protium heptaphyllum) and a mixture of them in a headwater stream, Southeastern Brazil. Coarse mesh litter bags were used over a 120-day period. P. heptaphyllum showed the slowest breakdown rate, while Myrcia showed the fastest. Total densities and biomass values of associated invertebrates were different among leaf types and incubation periods. The highest values of total abundance were found in P. heptaphyllum, while Ocotea sp. and Miconia were few colonized. Gathering-collectors feeding group dominated all leaf types, followed by predators and shredders. Shredders were more abundant in Myrcia than in Miconia and the mixed pack.