-The objective of this work was to evaluate the ecosystem functions of a natural wetland and of artificially flooded rice areas, managed under organic and conventional systems, by phytomass degradation and by the colonization of this material by benthic macroinvertebrates. The experiment was carried out in a natural wetland area, and in two flooded rice areas managed under organic and conventional systems. Twenty-five decomposition bags filled with 10 g of dry vegetation were installed in each site. At 14, 28, 42, 56, and 70 days after the beginning of the experiment, five bags from each site were collected. Macroinvertebrates were identified and classified by functional trophic group. The number of species of benthic macroinvertebrates increased: natural wetland > organic system > conventional system. The Chironomidae group was present in all areas, confirming its food plasticity and adaptability to different substrates and environmental stress situations. The Amphipoda group was present only in the artificially flooded rice area, and the Acari, only in the natural wetland. The diversity of species in the natural wetland area was higher than in the artificially flooded rice area. Nutrient cycling, provided by phytomass decomposition, is affected by the management system, and the delay in this process causes a reduction of the ecosystem functions in the conventional system. Index terms: Oryza sativa, Aqualf, biomass degradation, ecosystem services, nutrient cycling, paddy soils. Macroinvertebrados bentônicos e degradação da fitomassa como indicadores de funções ecossistêmicas em arroz irrigado por inundaçãoResumo -O objetivo deste trabalho foi avaliar as funções ecossistêmicas de um banhado natural e de lavouras de arroz irrigado por inundação, manejadas nos sistemas convencional e orgânico, por meio da degradação da fitomassa e da colonização desse material por macroinvertebrados bentônicos. O experimento foi realizado em um banhado natural e em duas áreas de arroz irrigado por inundação, manejadas em sistemas orgânico e convencional. Vinte e cinco bolsas de decomposição, cada uma preenchida com 10 g de palha seca, foram instaladas em cada local. Aos 14, 28, 42, 56 e 70 dias após o início do experimento, cinco bolsas de cada local foram retiradas. Os macroinvertebrados foram identificados e classificados por grupo trófico funcional. O número de espécies de macroinvertebrados bentônicos aumentou: banhado natural > sistema orgânico > sistema convencional. O grupo Chironomidae estava presente em todas as áreas, o que confirma sua plasticidade alimentar e adaptabilidade a diferentes substratos e situações de estresse ambiental. O grupo Amphipoda esteve presente somente nas lavouras de arroz artificialmente inundadas, enquanto o grupo Acari, somente no banhado natural. A diversidade de espécies no banhado natural foi maior do que nas áreas de arroz artificialmente inundadas. A ciclagem de nutrientes, por meio da degradação da fitomassa, é influenciada pelo sistema de manejo, e o atraso nesse processo reduz ...

Aim To evaluate the general situation of studies on the decomposition of organic matter in aquatic environments in the subtropical region of South America. Methods We compiled publications (1990-2018) with a combination of words referring to decomposition, debris, aquatic environments and South American countries with subtropical climate. The characteristics of the publications were analysed over time. Results A total of 1,042 publications were found, with 106 specifically addressing the purpose of this study. For subtropical climates in South America, this research topic is incipient. Most studies were carried out in streams (39.6%) and studied the decomposition process and associated invertebrates (42.5%). There is a great deficiency of studies in lentic environments (e.g. lakes, 10%). Conclusion Studies on the decomposition of organic detritus in aquatic ecosystems in the subtropical region of South America are still emerging. While the knowledge about the role of shredders is more or less understood, the importance of microorganisms on the decomposition process still needs to be better evaluated. Finally, our study demonstrated that scientific collaboration boosted publication on the topic.

Shallow lakes favour the development of aquatic macrophytes that can influence the limnological characteristics of these environments. In addition to macrophytes, allochthonous organic matter contributes to the metabolism of lakes through the bed of decomposing detritus. Among the decomposing microorganisms, bacteria can be important in the processing of organic matter when the abundance of fungi and invertebrates is low. The present study evaluated the effects of macrophyte coverage on bacterial-mediated leaf decomposition of allochthonous debris in shallow subtropical lakes. Litter bags were incubated with senescent leaves of Erythrina crista-galli in six shallow lakes, three with high (HML) and three with low (LML) macrophyte coverage.After 2, 7, 15 and 35 days of incubation, a set of litter bags was removed from each lake for bacterial, environmental and mass-loss analyses. Decomposition rates were higher in the LML (49% of remaining mass), compared to the HML (63% of remaining mass). The bacterial density and biomass were higher in the LML. Limnological variables influenced bacterial morphotypes, especially branched filament. Thus, the high coverage of aquatic macrophytes can be a main factor influencing the bacterial colonization in the debris, delaying the decomposition process in these ecosystems.