RESUMO

Consumers can alter decomposition rates through both feces and selective feeding in many ecosystems, but these combined effects have seldom been examined in tropical ecosystems. Members of the detrital food web (litter-feeders or microbivores) should presumably have greater effects on decomposition than herbivores, members of the green food web. Using litterbag experiments within a field enclosure experiment, we determined the relative effects of common litter snails (Megalomastoma croceum) and herbivorous walking sticks (Lamponius portoricensis) on litter composition, decomposition rates, and microbes in a Puerto Rican rainforest, and whether consumer effects were altered by canopy cover presence. Although canopy presence did not alter consumers' effects, focal organisms had unexpected influences on decomposition. Decomposition was not altered by litter snails, but herbivorous walking sticks reduced leaf decomposition by about 50% through reductions in high quality litter abundance and, consequently, lower bacterial richness and abundance. This relatively unexplored but potentially important link between tropical herbivores, detritus, and litter microbes in this forest demonstrates the need to consider autotrophic influences when examining rainforest ecosystem processes.

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We investigated the role of leaf litter chemistry and richness in affecting testate amoeba communities of tropical rainforest in the Ecuadorian Andes. Litterbags containing leaf litter from four dominating tree species (Clusia sp., Myrcia pubescens, Graffenrieda emarginata, and Cecropia andina) with richness 1, 2, and 4 species were established and exposed in the field for 12 months at 2000 m a.s.l. Chemical elements and compounds of leaf litter were analyzed before exposure. At the end of exposure, microbial biomass and litter mass loss were measured, and living testate amoeba species number, density, biomass, and community composition were determined. In total, 125 testate amoeba species colonized the litter in litterbags. The results suggest that high litter nitrogen and low lignin concentrations are indicators of high litter quality for testate amoebae density and species richness. Their species number and density significantly declined in the order 1 > 4 > 2 leaf litter species and varied with leaf litter chemistry being at a maximum in high-quality single leaf litter species and low in low-quality leaf litter. Further, the addition of litter of high-quality to low-quality litter increased testate amoebae biomass and density; however, the values did not exceed the ones in single high-quality litter treatments. Moreover, the structure of testate amoeba communities varied with litter chemistry, with Fe, Na, lignin, and litter C-to-N ratio being of major importance, and indicating that litter chemistry reflects habitat quality for testate amoebae. Overall, the data show that leaf litter chemistry overrides leaf litter richness in structuring testate amoeba communities.

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Plant decomposition is dependant on the activity of the soil biota and its interactions with climate, soil properties, and plant residue inputs. This work assessed the roles of different groups of the soil biota on litter decomposition, and the way they are modulated by soil use. Litterbags of different mesh sizes for the selective exclusion of soil fauna by size (macro, meso, and microfauna) were filled with standardized dried leaves and placed on the same soil under different use intensities: naturalized grasslands, recent agriculture, and intensive agriculture fields. During five months, litterbags of each mesh size were collected once a month per system with five replicates. The remaining mass was measured and decomposition rates calculated. Differences were found for the different biota groups, and they were dependant on soil use. Within systems, the results show that in the naturalized grasslands, the macrofauna had the highest contribution to decomposition. In the recent agricultural system it was the combined activity of the macro- and mesofauna, and in the intensive agricultural use it was the mesofauna activity. These results underscore the relative importance and activity of the different groups of the edaphic biota and the effects of different soil uses on soil biota activity.

RESUMO

Due to the connection between enzymatic activity and degradation of different fractions of organic matter, enzyme assays can be used to estimate degradation rates of particulate and dissolved organic carbon in freshwater systems. The aim of this study was to quantify and model the enzymatic degradation involving the decomposition of macrophytes, describing temporal activity of cellulases (EC 3.2.1.4 and EC 3.2.1.91) and xylanase (EC 3.2.1.8) during in situ decomposition of three aquatic macrophytes (Salvinia sp., Eichhornia azurea and Cyperus giganteus) on the surface and water-sediment interface (w-s interface) of an oxbow lagoon (Óleo lagoon) within a natural Brazilian Savanna Reserve. Overall, the enzymatic degradation of aquatic macrophytes in Óleo lagoon occurred during the whole year and was initiated together with leaching. Xylanase production was ca. 5 times higher than cellulase values due to easy access to this compound by cellulolytic microorganisms. Enzymatic production and detritus mass decay were similar on the surface and w-s interface. Salvinia sp. was the most recalcitrant detritus, with low mass decay and enzymatic activity. E. azurea and C. giganteus decomposition rates and enzymatic production were high and similar. Due to the physicochemical homogeneity observed in the Óleo lagoon, the differences between the decay rates of each species are mostly related with detritus chemical quality.

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RESUMO

Este estudo teve como objetivo determinar os coeficientes de decomposição daparte submersa (PS) e aérea (PA) de Salvinia auriculata em duas profundidades da coluna de água(superfície e sedimento). Também visou avaliar o rendimento do processo de perda de massaassim como a evolução temporal dos teores de fósforo e nitrogênio. As macrófitas foramseparadas em partes; em seguida, foram secas até peso constante. Os materiais vegetais foramdepositados em sacos de decomposição e incubados no reservatório da UHE Lajeado, Tocantins.As análises dos resultados de perda de massa revelaram que não houve diferenças significativasentre os PA-sed e PA-sup (p > 0,05), entretanto, os PA-sed foram significativamente diferentesdos PS-sed (p < 0,05) e dos PS-sup (p < 0,01). Os PA-sed apresentaram k = 0,0102 dia-1 e asincubadas na superfície (PA-sup) um k = 0,0067 dia-1, os PS-sed apresentaram um k = 0,0027dia-1 e os PS-sup um k = 0,0040 dia-1. Durante os primeiros dias de decomposição foramliberadas grandes concentrações de fósforo e nitrogênio pelo processo de lixiviação; a partir do14º dia foi observada uma tendência de aumento nas concentrações de nitrogênio, fatoprovavelmente relacionado com o enriquecimento dos detritos pela biomassa microbiana.(AU)

Thisstudy aimed to determine the decomposition coefficients of the submerged (SP) and aerial part(AP) of S. auriculata at two different depths within water column (surface and sediment). It alsoquantified the decomposition yield of S. auriculata and the temporal changes of nitrogen andphosphorous content of the remaining biomass. The macrophytes were fractionated in parts andwere dried in sequence until attaining constant weight. The litterbags with plant material wereincubated in the reservoir of UHE Lajeado. The results of mass loss showed that there were nosignificant differences among the AP-sed and AP-sur (p > 0.05). However, the AP-sed wassignificantly different from SP-sed (p < 0.05) and SP-sur (p < 0.01). The AP-sed presented adecay coefficient (k) of 0.0102 day-1 and AP-sur a k of 0.0067 day-1. The SP-sed presented a k of0.0027 day-1 and the SP-sur 0.0040 day-1. It was also noticed that during the first days ofdecomposition great amounts of nitrogen and phosphorous were solubilized. This event wasrelated to the leachate process; from the 14th day of decomposition, an increasing trend wasobserved in nitrogen concentrations. This fact was probably related to detritus enrichment bymicrobial colonization.(AU)

Assuntos

RESUMO

Este estudo teve como objetivo determinar os coeficientes de decomposição da parte submersa (PS) e aérea (PA) de Salvinia auriculata em duas profundidades da coluna de água (superfície e sedimento). Também visou avaliar o rendimento do processo de perda de massa assim como a evolução temporal dos teores de fósforo e nitrogênio. As macrófitas foram separadas em partes; em seguida, foram secas até peso constante. Os materiais vegetais foram depositados em sacos de decomposição e incubados no reservatório da UHE Lajeado, Tocantins. As análises dos resultados de perda de massa revelaram que não houve diferenças significativas entre os PA-sed e PA-sup (p > 0,05), entretanto, os PA-sed foram significativamente diferentes dos PS-sed (p < 0,05) e dos PS-sup (p < 0,01). Os PA-sed apresentaram k = 0,0102 dia-1 e as incubadas na superfície (PA-sup) um k = 0,0067 dia-1, os PS-sed apresentaram um k = 0,0027 dia-1 e os PS-sup um k = 0,0040 dia-1. Durante os primeiros dias de decomposição foram liberadas grandes concentrações de fósforo e nitrogênio pelo processo de lixiviação; a partir do 14º dia foi observada uma tendência de aumento nas concentrações de nitrogênio, fato provavelmente relacionado com o enriquecimento dos detritos pela biomassa microbiana.

This study aimed to determine the decomposition coefficients of the submerged (SP) and aerial part (AP) of S. auriculata at two different depths within water column (surface and sediment). It also quantified the decomposition yield of S. auriculata and the temporal changes of nitrogen and phosphorous content of the remaining biomass. The macrophytes were fractionated in parts and were dried in sequence until attaining constant weight. The litterbags with plant material were incubated in the reservoir of UHE Lajeado. The results of mass loss showed that there were no significant differences among the AP-sed and AP-sur (p > 0.05). However, the AP-sed was significantly different from SP-sed (p < 0.05) and SP-sur (p < 0.01). The AP-sed presented a decay coefficient (k) of 0.0102 day-1 and AP-sur a k of 0.0067 day-1. The SP-sed presented a k of 0.0027 day-1 and the SP-sur 0.0040 day-1. It was also noticed that during the first days of decomposition great amounts of nitrogen and phosphorous were solubilized. This event was related to the leachate process; from the 14th day of decomposition, an increasing trend was observed in nitrogen concentrations. This fact was probably related to detritus enrichment by microbial colonization.

Assuntos

RESUMO

Due to the connection between enzymatic activity and degradation of different fractions of organic matter, enzyme assays can be used to estimate degradation rates of particulate and dissolved organic carbon in freshwater systems. The aim of this study was to quantify and model the enzymatic degradation involving the decomposition of macrophytes, describing temporal activity of cellulases (EC 3.2.1.4 and EC 3.2.1.91) and xylanase (EC 3.2.1.8) during in situ decomposition of three aquatic macrophytes (Salvinia sp., Eichhornia azurea and Cyperus giganteus) on the surface and water-sediment interface (w-s interface) of an oxbow lagoon (Óleo lagoon) within a natural Brazilian Savanna Reserve. Overall, the enzymatic degradation of aquatic macrophytes in Óleo lagoon occurred during the whole year and was initiated together with leaching. Xylanase production was ca. 5 times higher than cellulase values due to easy access to this compound by cellulolytic microorganisms. Enzymatic production and detritus mass decay were similar on the surface and w-s interface. Salvinia sp. was the most recalcitrant detritus, with low mass decay and enzymatic activity. E. azurea and C. giganteus decomposition rates and enzymatic production were high and similar. Due to the physicochemical homogeneity observed in the Óleo lagoon, the differences between the decay rates of each species are mostly related with detritus chemical quality.

RESUMO

Due to the connection between enzymatic activity and degradation of different fractions of organic matter, enzyme assays can be used to estimate degradation rates of particulate and dissolved organic carbon in freshwater systems. The aim of this study was to quantify and model the enzymatic degradation involving the decomposition of macrophytes, describing temporal activity of cellulases (EC 3.2.1.4 and EC 3.2.1.91) and xylanase (EC 3.2.1.8) during in situ decomposition of three aquatic macrophytes (Salvinia sp., Eichhornia azurea and Cyperus giganteus) on the surface and water-sediment interface (w-s interface) of an oxbow lagoon (Óleo lagoon) within a natural Brazilian Savanna Reserve. Overall, the enzymatic degradation of aquatic macrophytes in Óleo lagoon occurred during the whole year and was initiated together with leaching. Xylanase production was ca. 5 times higher than cellulase values due to easy access to this compound by cellulolytic microorganisms. Enzymatic production and detritus mass decay were similar on the surface and w-s interface. Salvinia sp. was the most recalcitrant detritus, with low mass decay and enzymatic activity. E. azurea and C. giganteus decomposition rates and enzymatic production were high and similar. Due to the physicochemical homogeneity observed in the Óleo lagoon, the differences between the decay rates of each species are mostly related with detritus chemical quality.