Litter in a first–order stream of a temperate deciduous forest (Margaraça Forest, central Portugal)

Abstract To evaluate the importance and fate of organic matter inputs in forested streams, we determined the litterfall inputs and the benthic coarse particulate organic matter (CPOM) in one headwater stream flowing through a mixed deciduous forest, during one year. Both vertical traps and the stream bottom were sampled monthly. The material collected was sorted into four main categories: leaves, fruits and flowers, twigs and debris. Litter production was 715 g m-2 y-1 and seasonal, with 73% of the annual total during October–December (autumn). Leaves comprised the largest litter component. Benthic organic matter was 1880 g m-2 y-1, and was also seasonal. Highest accumulation was attained in spring, and twigs and branches comprised the major component

From litterfall to breakdown in streams: a review

This paper is a review of recent (< or =10 years) information on litterfall, standing stock of benthic organic matter, breakdown rates, and fungal colonization of organic matter in streams. In some cases, recent research reinforces the findings of classic reference papers. In other cases, the additional knowledge provided by recent research introduces a higher variation in the processes analyzed. In many aspects, especially those concerning stream organic matter, the review is biased towards the temperate North American streams, reflecting the fact that most research was carried out there. However, during the 1990s European studies increased enormously, especially those related with instream processes, such as leaf litter decomposition. The first part of this review analyzes the origin of allochthonous organic matter to streams (litterfall, retention, and storage), and it provides data on the amounts estimated in different streams and on the methodology used in the studies. The second part analyzes the fate of detritus in streams: mechanisms of leaf breakdown, relative importance of fungi and bacteria, factors affecting the activity of microbial decomposers, and chemical changes of leaf litter during decomposition. A list of breakdown rates of several different leaf species is given, together with the methodology used, and the main characteristics of the incubation streams

Litter movement pathways across terrestrial–aquatic ecosystem boundaries affect litter colonization and decomposition in streams

Streams and their riparian zones are connected by spatial flows of organic matter and constitute a model example of a meta-ecosystem. Fluxes of leaf litter from the riparian zone to the stream are a major energy source in stream food webs. Leaf litter can enter the stream vertically, falling from the tree and into the stream, or laterally, washing into the stream after a period of exposure in the terrestrial ecosystem. The latter can contribute up to 23% to the total amount of litterfall entering streams. To determine if decomposition, microbial and invertebrate colonization of lateral litter inputs are similar to those of vertical inputs, we assessed leaf decomposition of alder, poplar and a 1:1 mixture of the two species in three scenarios across a gradient of terrestrial:aquatic exposures. Overall, decomposition was explained by a negative exponential model and decreased with the increase in the period of terrestrial exposure in all cases. Invertebrate colonization tended to decrease with the increase in the period of terrestrial exposure, but total invertebrate richness and biomass were more affected by litter type than by the exposure scenario, attaining higher values in the mixture than in the species alone. As the length of exposure in the terrestrial ecosystem increased, in-stream decomposition rates of leaf litter decreased. Comparing leaf species treatments, alder decomposition rates were faster than poplar and the alder–poplar mixture. The richness of the aquatic hyphomycete community colonizing leaf litter after submergence decreased, and sporulation rates were strongly inhibited with an increasing terrestrial exposure period. While fungi colonizing leaf litter exposed only in the stream invested in rapid reproduction, fungi colonizing litter with prior terrestrial exposure built up more biomass. We conclude that the path taken by the litter fluxes has important effects on the functioning of the receiving ecosystem. Studies relying only on the fate of freshly abscissed leaf litter (vertical inputs) may not present a complete picture of the decomposition process in streams and may have been overestimating the overall richness and reproductive activity of the aquatic hyphomycetes colonizing leaf litter

El papel del carbono, nitrógeno y fósforo en la descomposición de hojarasca mediada por hongos acuáticos

The aquatic microbial decomposition of leaf litter has been the subject of many field studies throughout the world. However, field experiments cannot always separate the effects of the multiple biotic and abiotic factors involved in the process. In this laboratory experiment, we controlled the abiotic factors and the fungal decomposer community during decomposition of alder, oak and eucalypt leaf litter in order to determine if variation in leaf carbon, nitrogen and phosphorus (CNP) ratios during decomposition was similar among the three species. Initial CNP values differed among the three species with alder being the richest (C:N = 16, C:P = 903, N:P = 57) and oak being the poorest (C:N = 55, C:P = 1779, N:P = 32) species. In all leaf species, nitrogen was immobilized during decomposition (final < initial C:N ratios), while phosphorus was released (final > initial C:P ratios). Final CNP values were lowest in alder (C:N = 11, C:P = 2495, N:P = 224) but there was a change in the ranking of oak and eucalypt regarding nutrient contents. Leaf species were similar regarding the variation in C:N (final/initial = 0.7 to 0.8) but C:P and N:P increased more in eucalypt and oak than in alder (final/initial C:P = 5.9, 3.9 and 2.8, final/initial N:P = 7.5, 4.7, 3.9, respectively for eucalypt, oak and alder). The lowest decrease in P of alder leaves may explain the highest mass loss observed in this species, most probably due to a higher fungal colonization despite the controlled fungal decomposer community. In conclusion, CNP ratio in leaves seems to determine the fungal-mediated mass loss of leaf litter.La descomposición microbiana acuática de la hojarasca ha sido objeto de muchos estudios de campo en todo el mundo. Sin embargo, en los experimentos de campo es imposible separar los efectos de los múltiples factores bióticos y abióticos involucrados en el proceso. En este experimento de laboratorio, controlamos los factores abióticos y la comunidad de hifomicetos acuáticos durante la descomposicion de hojarasca de aliso, roble y eucalipto para determinar si la variación en los cocientes de carbono, nitrógeno y fósforo (CNP) durante la descomposición fue similar entre los tres especies. Los valores iniciales de CNP difirieron entre las tres especies con el aliso siendo el más rico (C:N = 16, C:P = 903, N:P = 57) y el roble siendo el más pobre (C:N = 55, C:P = 1779, N:P = 32). En todas las especies foliares, el nitrógeno fue inmovilizado durante la descomposición (C:N final inicial). Los valores finales de CNP fueron los más bajos en aliso (C:N = 11, C:P = 2495, N:P = 224) pero hubo un cambio en el ranking de roble y eucalipto con respecto a los contenidos de nutrientes. Las especies foliares fueron similares con respecto a la variación en C:N (final/inicial = 0.7 a 0.8) pero C:P y N:P aumentaron más en eucalipto y roble que en aliso (final/inicial C:P = 5.9, 3.9 y 2.8, final/inicial N:P = 7.5, 4.7 y 3.9, respectivamente para eucalipto, roble y aliso). La disminución más baja en P de las hojas del aliso puede explicar la pérdida de masa más alta observada en esta especie, lo más probablemente debido a una colonización de hongos más alta a pesar de la comunidad fúngica controlada. En conclusión, los cocientes CNP en las hojas parecen determinar su destino durante la descomposición

Once upon a time a leaf... : from litterfall to breakdown in streams

Tese de doutoramento em Biologia (Ecologia) apresentada à Fac. de Ciências e Tecnologia da Univ. de CoimbraOs ribeiros de floresta são basicamente heterotróficos, i.e., obtêm a maior parte da sua energia do ecossistema que os rodeia. A matéria orgânica alóctona produzida na floresta adjacente entra no rio, é retida e decomposta in situ, fornecendo energia para todo o ecossistema. As cadeias alimentares dos ribeiros de floresta são pois baseadas na decomposição microbiana da matéria orgânica alóctona, principalmente folhas. Os fungos, em particular os hifomicetos aquáticos, são os principais decompositores de folhas em rios. Os hifomicetos aquáticos colonizam as folhas acelerando a sua degradação através de um efeito directo no tecido foliar e indirectamente por aumentarem a palatabilidade dos detritos para os detritívoros. Os detritos são finalmente fragmentados em pedaços progressivamente mais pequenos através da actividade alimentar dos macroinvertebrados e da abrasão física. Os ribeiros de floresta são pois diferentes da maior parte dos ecossistemas no sentido em que obtêm a maior parte da sua energia através da decomposição de matéria orgânica alóctona. O objectivo desta tese é a elucidação de alguns dos aspectos da decomposição de folhas em ribeiros de floresta, com ênfase no papel dos microorganismos no processo. A tese cobre a ligação entre o ribeiro e a floresta circundante, i.e., a entrada de matéria orgânica alóctona no sistema, assim como o destino das folhas dentro do ribeiro. Os resultados obtidos mostram que as generalizações obtidas em ribeiros de outras áreas geográficas são aplicáveis a ribeiros de floresta da zona temperada/mediterrânea: (1) a matéria orgânica alóctona é a principal fonte de energia em ribeiros de florestas caducifólias mistas locais, a maior entrada de matéria orgânica ocorre no Outono e é composta maioritariamente por folhas, (2) a importância relativa dos factores determinantes das taxas de decomposição varia em função de um extenso conjunto de factores internos e externos e (3) os fungos são os principais decompositores microbianos de folhas em rios, pelos menos em termos de biomassa. Os resultados desta tese mostram também que existe um gradiente latitudinal geográfico nas taxas de decom-posição de folhas em rios devido ao desenvolvimento mais rápido (em termos de biomassa) dos decompositores microbianos nos rios tropicais

Measurements of litter dry mass remaining, fungal and invertebrate colonization

Data collected in the fiel

Litter movement pathways across terrestrial–aquatic ecosystem boundaries affect litter colonization and decomposition in streams

Streams and their riparian zones are connected by spatial flows of organic matter and constitute a model example of a meta-ecosystem. Fluxes of leaf litter from the riparian zone to the stream are a major energy source in stream food webs. Leaf litter can enter the stream vertically, falling from the tree and into the stream, or laterally, washing into the stream after a period of exposure in the terrestrial ecosystem. The latter can contribute up to 23% to the total amount of litterfall entering streams. To determine if decomposition, microbial and invertebrate colonization of lateral litter inputs are similar to those of vertical inputs, we assessed leaf decomposition of alder, poplar and a 1:1 mixture of the two species in three scenarios across a gradient of terrestrial:aquatic exposures. Overall, decomposition was explained by a negative exponential model and decreased with the increase in the period of terrestrial exposure in all cases. Invertebrate colonization tended to decrease with the increase in the period of terrestrial exposure, but total invertebrate richness and biomass were more affected by litter type than by the exposure scenario, attaining higher values in the mixture than in the species alone. As the length of exposure in the terrestrial ecosystem increased, in-stream decomposition rates of leaf litter decreased. Comparing leaf species treatments, alder decomposition rates were faster than poplar and the alder–poplar mixture. The richness of the aquatic hyphomycete community colonizing leaf litter after submergence decreased, and sporulation rates were strongly inhibited with an increasing terrestrial exposure period. While fungi colonizing leaf litter exposed only in the stream invested in rapid reproduction, fungi colonizing litter with prior terrestrial exposure built up more biomass. We conclude that the path taken by the litter fluxes has important effects on the functioning of the receiving ecosystem. Studies relying only on the fate of freshly abscissed leaf litter (vertical inputs) may not present a complete picture of the decomposition process in streams and may have been overestimating the overall richness and reproductive activity of the aquatic hyphomycetes colonizing leaf litter

Salinity Affects Freshwater Invertebrate Traits and Litter Decomposition

We evaluated the effect of seawater intrusion in coastal ecosystems on the freshwater invertebrate community and on leaf litter decomposition under realistic scenarios in six outdoor freshwater mesocosms containing fauna and flora, to which increasing volumes of seawater were added. The resulting salinity values were 0.28 (control, freshwater only), 2.0, 3.3, 5.5, 9.3, and 15.3 mS cm1. The effect of salinity was assessed for 65 days after seawater intrusion, by computing the deviation of values in each treatment in relation to the control. Our results show that seawater intrusion into freshwaters will affect the invertebrate communities and organic matter decomposition, with salinities of up to 3.3–5.5 mS cm1 having opposite effects to salinities of more than 9.3 mS cm1. There was a net negative effect of the two highest salinities on mass loss and richness of the invertebrates associated with the decomposing leaves. Regarding the invertebrate communities of the mesocosms, there was a net negative effect of the intermediate salinity levels on abundance and richness. Invertebrate life cycle traits conferring resilience and resistance tended to increase with low and decrease with high salinity values, while avoidance traits showed an opposite trend, and these responses were more pronounced on the later stage community. These wave-like responses of the invertebrate species traits to increasing salinity suggest that the life-history and physiological adaptations most suitable to cope with osmotic stress will differ between low and high salinity levels

Appendix C. PCA factor loading scores for the two species of litter decomposing among three habitats.

PCA factor loading scores for the two species of litter decomposing among three habitats

Appendix A. Characteristics of soils across study sites.

Characteristics of soils across study sites