Leaf Decomposition Rates Research Articles

Measuring of leaf litter decomposition rate and flux of carbon dioxide in various land cover in Gunung Bromo Education Forest, Karanganyar

The process of leaf litter decomposition on the soil surface as a source of nutrition and food for soil fauna. Leaf litter decomposition rate is influenced by the activity of soil fauna, which is thought to increase the emission of carbondioxide from the soil. The aim of this research was to investigate the leaf decomposition rate and flux of carbon dioxide in various land cover. The research was conducted from July to November 2020 in Gunung Bromo Education Forest, Karanganyar, Central Java. This research used purposive sampling with nine land covers and three replications. The leaf decomposition rate was measured using the litterbag method, and flux of carbon dioxide was measured using the closed chamber method. The results suggested that the leaf decomposition rate was the fastest in Pine 2016 at 6.17 g/week, and the highest flux of carbon dioxide in Indonesian rosewood (Dalbergia sissoo) rejuvenation was 9,860 mg/CO2/day. The leaf decomposition rate was influenced by air temperature (p = 0.535) compared to humidity (p = - 0.257). Flux carbondioxide is influenced by air temperature (p = 0.854) compared to humidity (p = - 0.677), and the leaf decomposition rate affects the level of flux of carbon dioxide (p = 0.631).

Decomposition of Entandrophragmacylindricum Tree Prunings in Agroforestry System in Onne, Rivers State

A study was conducted at Swamp Forest Research Station, Onne, Forestry Research Institute of Nigeria, to evaluate the rate of decomposition of E. cylindricumtree prunings. The experiment was a 2x8 factorial in a randomized complete block design with three replications. The first factor comprises two placement methods (surface-placed and soil-incorporated) and the second factor comprises eight biweekly sampling intervals (2 – 16 weeks). The litterbag technique was employed. Results indicated that the Total leaf decomposition (100.0%) of soil incorporated leaf litter was obtained at 16th week after litter placement (WALP). Soil-surface placed had 98.00% at 16th WALP. Leaf half-lives of the soil-surface placed and soil incorporated were 5.08 and 2.10 WALP respectively. The turnover coefficients (k1) of the soil surface-placed and soil -incorporated leaf litter of E. cylindricum were 6.93yr-1 and 17.33 yr-1 respectively. The high rate of fresh leaf decomposition and subsequent release of nutrient make E. cylindricum leaf pruning a good source of organic manure for soil fertility restoration.

Do crayfish affect stream ecosystem response to riparian vegetation removal?

Abstract Riparian vegetation management alters stream basal resources, but stream ecosystem responses partly depend on top‐down interactions with in‐stream consumers. Large‐bodied omnivores can exert particularly strong influences on stream benthic environments through consumption of food resources and physical disturbance of the benthos. Trophic dynamics studies conducted within the context of reach‐scale riparian vegetation manipulations can provide insights into the interactions and relative importance of top‐down and bottom‐up controls that determine ecosystem response to riparian change. Here, we examine how top‐down control by native crayfish omnivores (Cambarus bartonii) interacts with abiotic conditions created by reach‐scale removal of riparian rhododendron (Rhododendron maximum) in the southern Appalachian Mountains of the U.S.A. We conducted 32‐day trophic experiments by nesting five pairs of electrified (crayfish excluded) and non‐electrified (crayfish access) plots within each of two 300‐m stream reaches (one control and one rhododendron‐removed) for 1 year pre‐removal and 2 years post‐removal. Algal growth responded positively to the reduced canopy cover (post‐rhododendron removal) only under low flow conditions combined with the absence of top‐down control by crayfish. Leaf decomposition rates were reduced by c. 40% in the absence of crayfish, but higher inputs of rhododendron leaf litter during the summer following rhododendron removal reduced the effect of crayfish presence on decomposition. Riparian rhododendron removal also significantly increased benthic sediment and fine benthic organic matter, but crayfish exclusion did not affect these stream properties. Potential long‐term reductions in crayfish abundance could reduce the top‐down effects of crayfish and ultimately lead to higher algal growth and reduced leaf decomposition rates in streams where rhododendron is managed through removal.

Decomposition of Herbivore-Damaged Leaves of Understory Species Growing in Oak and Pine Stands

Leaves are the largest component of forest litter. Their decomposition rate depends mainly on plant species, leaf chemical composition, microorganism biodiversity, and habitat conditions. It is known that herbivory by insects can modify the chemical composition of leaves, such as through induction. The aim of this study was to determine whether the rate of leaf decomposition is related to the susceptibility of the plant species to insect feeding and how leaf damage affects this rate. For our research, we chose six species differing in leaf resistance to insect damage: Cornus sanguinea, Frangula alnus, and Sambucus nigra (herbivore resistant), and Corylus avellana, P. padus, and Prunus serotina (herbivore susceptible). The decomposition of these plant leaves was examined in two monoculture forest stands, deciduous (Quercus robur) and coniferous (Pinus sylvestris). Litter decay rate k and change of litter mass, content of defensive metabolites (total phenols (TPh) and condensed tannins), and substances beneficial for organisms decomposing litter (nitrogen (N) and nonstructural carbohydrates (TNC)) were determined. Contrary to our expectations, leaf litter of herbivore-resistant species decomposed faster than that of herbivore-susceptible species, and damaged leaves decayed faster than undamaged leaves. We found that faster decaying leaf litter had a lower content of defensive compounds and a higher content of TNC and N, regardless of the plant species or leaf damage. Leaf litter decomposition caused a large and rapid decrease in the content of defensive compounds and TNC, and an increase in N. In all species, the tannin content was lower in damaged than in undamaged leaves. This pattern was also observed for TPh, except in S. nigra. We interpret this as the main reason for faster decay of damaged leaves. Moreover, the loss of leaf mass was greater under oak than pine stands, indicating that the microorganisms in deciduous stands are more effective at decomposing litter, regardless of leaf damage.

Fungal assemblages in predictive stream bioassessment: A cross-taxon comparison along multiple stressor gradients

Degradation of freshwater ecosystems requires efficient tools for assessing the ecological status of freshwater biota and identifying potential cause(s) for their biological degradation. While diatoms and macroinvertebrates are widely used in stream bioassessment, the potential utility of microbial communities has not been fully harnessed. Using data from 113 Finnish streams, we assessed the performance of aquatic leaf-associated fungal decomposers, relative to benthic macroinvertebrates and diatoms, in modelling-based bioassessment. We built multi-taxon niche -type predictive models for fungal assemblages by using genus-based and sequence-based identification levels. We then compared the models’ precision and accuracy in the prediction of reference conditions (number of native taxa) to corresponding models for macroinvertebrates and diatoms. Genus-based fungal model nearly equalled the accuracy and precision of our best model (macroinvertebrates), whereas the sequence-based model was less accurate and tended to overestimate the number of taxa. However, when the models were applied to streams disturbed by anthropogenic stressors (nutrient enrichment, sedimentation and acidification), alone or in combination, the sequence-based fungal assemblages were more sensitive than other taxonomic groups, especially when multiple stressors were present. Microbial leaf decomposition rates were elevated in sediment-stressed streams whereas decomposition attributable to leaf-shredding macroinvertebrates was accelerated by nutrients and decelerated by sedimentation. Comparison of leaf decomposition results to model output suggested that leaf decomposition rates do not detect effectively the presence of multiple simultaneous disturbances. The rapid development of global microbial database may soon enable species-level identification of leaf-associated fungi, facilitating a more precise and accurate modelling of reference conditions in streams using fungal communities. This development, combined with the sensitivity of aquatic fungi in detecting the presence of multiple human disturbances, makes leaf-associated fungal assemblages an indispensable addition in a stream ecologist’s toolbox.

Decomposição foliar da serapilheira de dois sistemas agroflorestais no Cerrado Sul-Mato-Grossense

Um dos indicadores importantes para um ecossistema é a serapilheira, pois ela fornece nutrientes e matéria orgânica que são essenciais para o funcionamento do ambiente. Assim sendo, o objetivo deste estudo foi avaliar a taxa de decomposição foliar da serapilheira e correlacioná-la com índices meteorológicos, em duas áreas com sistemas agroflorestais (SAF1) formado por diversas espécies de plantas e (SAF2) formado por Heveicultura e abacaxi, em uma região de Cerrado, no município de Pedro Gomes, MS. Para avaliação da decomposição da serapilheira folhas recém-caídas foram coletadas das áreas de estudo e transferidas à estufa por 96 horas. Em seguida, foram pesadas frações de 10 gramas e inseridas em litterbags. Foram alocados 20 litterbags em cada área de estudo e a remoção das amostras ocorreu aos 30, 60, 90 e 120 dias, retirando-se 5 amostras por área e época avaliada. Foi estimada a massa foliar remanescente dos litterbags, o tempo de meia vida (t ½) e a constante de decomposição (k). Posteriormente, a correlação de Pearson (r) entre as variáveis climáticas e k. A perda da massa foliar foi maior na área do SAF2, e em ambas as áreas a temperatura e precipitação tiveram influência na decomposição foliar da serapilheira.

Flood and Edge Effects on Leaf Breakdown in Wetlands of the Cerrado Savanna to Amazonia Ecotone

We studied the rates of leaf decomposition and loss of leaf constituents (lignin and cellulose) of a native plant species using the litterbag experiment during different seasonal periods (flood and drought) in periodically flooded ecosystems, locally known as “Ipucas”. The effects of flood, edge and fungal colonization on leaf degradation were evaluated. The results show that leaf decomposition is very slow, and influenced by seasonality, flooding and leaf chemical quality. Low moisture and leaf structural components contribute to the slow rate of decomposition. In addition, the fungal biomass was sensitive to the edge effect, with higher values in the center, probably due to the edge losing moisture earlier than the center after the end of rainy season. In addition, the positive correlation of fungal biomass with flooding demonstrates the importance of seasonality in these temporally flooded ecosystems, indicating that global changes in rainfall patterns may disrupt carbon cycling and probably nutrient cycling in periodically flooded environments.

CLUSIA HILARIANA, A KEY SPECIES ON NUTRIENT CYCLING IN SAND DUNE VEGETATION THICKETS

Interspecific plant-plant interactions studies showed that C lusia hilariana plays a facilitation role in the scattered vegetation thickets of the Brazilian sandy coastal plain vegetation (Restinga). In the Clusia open formation in the Jurubatiba Restinga National Park there are thickets differing in the presence and senescence of Clusia : (1) healthy Clusia thickets (HCT); (2) senescent Clusia thickets (SCT); and also (3) thickets without Clusia (TWC). The aim of this long term study was to assess soil chemistry, litterfall mass and nutrient input and its leaf-litter decomposition in Clusia thickets, testing the hypotheses that: (1) the presence of Clusia increases soil nutrient concentrations in the thickets; (2) litterfall mass and nutrient input are dependent on the senescence stage of Clusia , being higher in HCT than in SCT; (3) decomposition and nutrient release of Clusia leaves are faster in HCT than in SCT, evaluating if C. hilariana promotes an improvement in nutrient cycling according to its presence and senescence in the thickets and reinforcing the role of Clusia as a nurse plant. Collection of nutrients in soils, litterfall and Clusia leaf decomposition rates were measured between 2001 and 2008. The HCTs presented higher annual litterfall mass and nutrient input than the SCTs, Clusia leaf-fall contributed the bulk of the total litterfall (70 % HCT, 34 % SCT). Nitrogen, as all other nutrient inputs from Clusia leaf-litter, was higher in HCT, although Clusia leaves had low N concentrations and a higher C/N ratio. Clusia -leaf decomposition was faster in HCT than in SCT during the first year of the experiment. The slow decomposition and nutrient release from Clusia leaf-litter, may be an important mechanism of nutrient conservation. We concluded that C. hilariana acts as a key species, and as a nurse plant, in relation to nutritional dynamics, organic matter, nutrient input, and decomposition via its litter, which decreased according to its senescence.

Effects of the organic UV-filter, 3-(4-methylbenzylidene) camphor, on benthic invertebrates and ecosystem function in artificial streams

In the last decades, the use of organic ultraviolet-filters (UV-filters) has increased worldwide, and these compounds are now considered emerging contaminants of many freshwater ecosystems. The present study aimed to assess the effects of 3-(4-methylbenzylidene) camphor (4-MBC) on a freshwater invertebrate community and on associated ecological functions. For that, artificial streams were used, and a natural invertebrate benthic community was exposed to sediments contaminated with two concentrations of 4-MBC. Effects were evaluated regarding macroinvertebrate abundance and community structure, as well as leaf decomposition and primary production. Results showed that the macroinvertebrate community parameters and leaf decomposition rates were not affected by 4-MBC exposure. On the other hand, primary production was strongly reduced. This study highlights the importance of higher tier ecotoxicity experiments for the assessment of the effects of low concentrations of organic UV-filters on freshwater invertebrate community structure and ecosystem functioning.

Different Patterns Of Nutrient Cycling In Contiguous Phytophysiognomies Of Atlantic Forest, Brazil

ABSTRACT The present study aimed to evaluate fine aboveground litterfall, deposition of nitrogen and phosphorus from total litterfall and leaf litter decomposition in areas of tall forest (Mata Alta) and low forest on sandy soils (Mussununga) in southeastern Brazil. Fine litterfall was collected monthly for two years (from June/2007 to May/2009) in 10 conical collectors (0.25 m2) in each phytophysiognomy (1 ha plots). The material was subsequently separated into leaves, branches, flowers and fruits, and unidentified material. Leaf decomposition rates were evaluated using 15 litterbags, three of which were collected every 30 days. Higher litterfall occurred in both phytophysiognomies during the rainy season, with leaves predominating. The lowest litterfall, nutrient input, and leaf litter decomposition values appeared to be nutrient conservation strategies, contributing to the ecological functioning of the Mussununga where soil fertility was lower than in the Mata Alta.

Leaf decomposition in a cool‐temperate broad‐leaved forest established on serpentine soil on Mount Oe, Japan

AbstractSerpentine ecosystems are characterized by soil with high heavy metal and low nutrient content, both of which are likely to influence the rate of leaf decomposition. Here, we report how leaf chemistry and the microbial community influence the leaf decomposition rate in a serpentine ecosystem. Fresh Clethra barbinervis and Quercus serrata leaves collected from serpentine and non‐serpentine sites in cool‐temperate forests were placed at both sites for several months, after which changes in leaf mass were determined. The N concentration in the initial Q. serrata leaves from the serpentine site was lower than in those from the non‐serpentine site. The Ni concentration in the initial C. barbinervis leaves from the serpentine site was higher than in those from the non‐serpentine site. The leaves from the serpentine site decomposed slower than those from non‐serpentine sites for both species. Although we expected that serpentine soil would have a negative influence on microbial decomposers, the Q. serrata leaves placed in the serpentine site decomposed faster than those placed in the non‐serpentine site, suggesting that the serpentine soil had no adverse effect on microbial decomposers. However, microbial respiration and biomass in an in vitro experiment were not high in the leaves decomposed on serpentine soil. Future work should reveal the mechanism behind this contradiction. Our results suggest that the change of leaf quality is key to understanding the leaf decomposition rate in a serpentine ecosystem.

Leaf litter decomposition of sweet chestnut is affected more by oomycte infection of trees than by water temperature

Abstract Riparian forests are subjected to multiple disturbances, such as tree diseases caused by invasive pathogens, whose consequences on stream functioning are unknown. We assessed the impact of Phytophthora cinnamomi infection, and interactions with temperature, on microbial decomposition of Castanea sativa leaves. Leaves from healthy, symptomatic and highly symptomatic trees were incubated in the laboratory at 13 and 18 °C for 64 d. Infection significantly increased polyphenolic concentration and leaf toughness, reducing leaf decomposition and microbial respiration rates irrespective of temperature. Aquatic hyphomycete communities differed significantly in leaves from highly symptomatic trees. Fungal biomass was highest at 18 °C, irrespective of tree health status. None of the parameters were influenced by the tree health status × temperature interaction, suggesting that temperature rise may not synergistically increase the cross-ecosystem effects caused by P. cinnamomi in streams where litter decomposition is microbial-driven. Infection by P. cinnamomi alters the nutritional quality of leaves affecting the functioning of aquatic ecosystems.

Changes in decomposition rate and litterfall in riparian zones with different basal area of exotic Eucalyptus in south-eastern Brazil

Exotic species in riparian environments can influence the quantity and quality of litterfall in the ecological system. The objective of this study was to evaluate the influence of Eucalyptus leaves on litterfall and terrestrial and aquatic leaf decomposition in a riparian forest in São Paulo state, Brazil. Three riparian zones were evaluated, and they were designated as areas of low (L), medium (M) and high (H) Eucalyptus basal area, respectively. Each riparian area was evaluated by surveying its structure and floristic composition. The amount of litterfall was evaluated over one year, and leaves were collected in terrestrial and vertical collectors. We evaluated the rates of aquatic and terrestrial decomposition of Eucalyptus and native leaves within litterbags. In general, area H had lower species richness, a higher edge effect and high Eucalyptus litterfall. Area L had higher species diversity (H′, Shannon– Wiener index), higher Pielou’s equitability index (J′), and smaller amounts of Eucalyptus litterfall. Eucalyptus leaves had higher extractive and lignin content compared with that of native trees. Eucalyptus leaves had a lower decomposition rate, except for the aquatic environment in area M. Our results show that the presence of Eucalyptus in riparian zones can increase litterfall and reduce the rate of leaf decomposition, but more studies are needed to evaluate any changes in ecosystem function from Eucalyptus presence.

Landscape patterns in top-down control of decomposition: omnivory disrupts a tropical detrital-based trophic cascade.

Detrital-based trophic cascades are often considered weak or absent in tropical stream ecosystems because of the prevalence of omnivorous macroconsumers and the dearth of leaf-shredding insects. In this study, we isolate top-down effects of three macroconsumer species on detrital processing in headwater streams draining Trinidad's northern mountains. We separated effects of different macroconsumers by experimentally manipulating their temporal access to isolated benthic habitat over the diel cycle. We found no evidence that omnivorous macroconsumers, including a freshwater crab (Eudaniela garmani) and guppy (Poecilia reticulata), increased leaf decomposition via consumption. By contrast, above a waterfall excluding guppies, the insectivorous killifish, Anablepsoides hartii, reduced the biomass of the leaf-shredding insect Phylloicus hansoni 4-fold, which consequently reduced leaf decomposition rates 1.6-fold. This detrital cascade did not occur below the barrier waterfall, where omnivorous guppies join the assemblage and reduce killifish densities; here killifish had no significant effects on Phylloicus or decomposition rates. These patterns of detrital processing were also observed in upstream-downstream comparisons in a landscape study across paired reaches of six streams. Above waterfalls, where killifish were present, but guppies absent, leaf decomposition rates and Phylloicus biomass were 2.5- and ~35-fold lower, respectively, compared to measurements below waterfalls. Moreover, the strength of top-down control by killifish is reflected by the 20- and 5-fold reductions in variability (±SE) surrounding mean Phylloicus biomass and leaf decomposition rates in upstream relative to downstream reaches where no top-down control was detected. Findings show a clear, detrital-based trophic cascade among killifish, a leaf-shredding insect, and leaf decomposition rates. Results also show how omnivorous guppies disrupt this cascade by depressing killifish densities, thereby releasing invertebrate shredders from predation, and significantly increasing decomposition rates. Moreover, this combination of direct and indirect trophic interactions drives patterns in decomposition rates in stream networks at a landscape scale, resulting in significantly lower rates of decomposition above vs. below barrier waterfalls. Our findings reveal that omnivory can result in significant indirect effects on a key ecosystem process, illustrating the importance of these hidden trophic pathways in detrital-based systems and suggesting that resource control in tropical systems may be even more complex than previously envisioned.

Traits or habitat? Disentangling predictors of leaf‐litter decomposition in Amazonian soils and streams

AbstractQuantifying the relative contributions of plant physicochemical traits and environmental conditions to leaf decomposition is essential to increase our understanding of ecosystem processes in forested terrestrial and aquatic habitats. This is particularly crucial in tropical rainforests that display high levels of tree diversity and environmental heterogeneity over relatively small spatial scales. For example, in Amazonia, detritus from hundreds of tree species fuels carbon cycling in watersheds, but much remains to be learned about how species traits interact with environmental conditions to mediate decomposition. We investigated the leaf‐litter decomposition of 17 tree species with contrasting traits in soil and stream habitats in Yasuní National Park, Ecuador. We hypothesized that (1) habitat type would be the major determinant of leaf decomposition (faster in stream than soil systems), (2) species would be ranked similarly in terms of leaf decomposition rates, according to decomposability traits (i.e., litter quality), within each habitat, and (3) the variability of leaf decomposition within habitats would be greater for soil than for stream systems. Contrary to our first hypothesis, we found that leaf‐litter decomposition rates for any given tree species were similar in stream and soil systems. However, we found that the relative importance of litter traits for decomposition such as concentrations of micronutrients (Mn and Cu, in particular) was consistent across habitats. Finally, we found that decomposition was equally highly variable in both terrestrial and aquatic systems. This variability was explained by differences in microhabitat within soils, but appeared to be more stochastic in streams. Overall, we found that plant traits had an overwhelming effect on the decomposition process in the intertwined aquatic and terrestrial matrices of the Yasuní rainforest, with significant effects of microhabitat features. This study sheds light on the fate of the pool of dead organic matter in tropical rainforests and highlights the need for further studies of the mechanisms underlying microhabitat variability.

Direct and indirect effects of zinc oxide and titanium dioxide nanoparticles on the decomposition of leaf litter in streams.

As the production of metallic nanoparticles has grown, it is important to assess their impacts on structural and functional components of ecosystems. We investigated the effects of zinc and titanium nanoparticles on leaf decomposition in freshwater habitats. We hypothesized that nanoparticles would inhibit the growth and activity of microbial communities leading to decreased decomposition rates. We also hypothesized that under natural light, the nanoparticles would produce reactive oxygen species that could potentially accelerate decomposition. In the lab, whole Ficus vasta leaves were placed in containers holding one liter of stream water and exposed to either 0, 1, 10 or 100 mg/L of ZnO or TiO2 nanoparticles for six weeks (referred to as Exp. 1). We measured leaf mass loss, microbial metabolism, and bacterial density at 2, 4, and 6 weeks. In a second experiment (referred to as Exp. 2), we measured the effects of light and 10 and 100 mg/L ZnO or TiO2 nanoparticles on leaf mass loss, bacterial density and the bacterial and fungal community diversity over a 2 week period. In Experiment 1, mass loss was significantly reduced at 10 and 100 mg/L after 6 weeks and bacterial density decreased at 100 mg/L. In Experiment 2, there was no effect of ZnO nanoparticles on leaf mass loss, but TiO2 nanoparticles significantly reduced mass loss in the dark but not in the light. One possible explanation is that release of reactive oxygen species by the TiO2 nanoparticles in the light may have increased the rate of leaf decomposition. Bacterial and fungal diversity was highest in the dark, but nanoparticles did not reduce overall diversity.

Do genetically-specific tree canopy environments feed back to affect genetically specific leaf decomposition rates?

In forest ecosystems, trees may have genetically distinct patterns in leaf decomposition. Trees also can have genetically distinct canopy environments which modify temperature, moisture, and microbial communities on the forest floor. The interaction between these factors may result in underexplored interactions between microenvironment and leaf decomposition at the genotype level. We compare litter decomposition rates for distinct genotypes of Fremont cottonwood (Populus fremontii) grown in a common garden environment under three different riparian conditions: 1) under a 16-tree stand of the same genotype, 2) under a 16-tree stand of another genotype, and 3) under a 16-tree stand of 16 different genotypes. Genotypes differed in canopy size and phenology. While genotype exerted a strong effect on decomposition, this effect was most pronounced when litter was decomposed under a self-similar (“home”) canopy. The strongest driver of decomposition rates across all factors (including litter quality and environmental factors) was spring (leaf-out) and fall (leaf-drop) phenology, but responses were variable by genotype. The influence of genetics on litter decomposition, canopy environment, and tree phenology provides justification for the inclusion of stand-level traits like canopy cover into models of decomposition and complicates the results of studies that rely on litter quality traits alone.

Contribution of Litter and Leaf Decomposition of Byrsonima gardneriana

ABSTRACT The litter in tropical ecosystems is one of the compartments responsible for the transference of nutrients to the soil, having great importance for the conservation and maintenance of biodiversity. Thus, this study aimed to quantify the contribution and stock of litter and the leaf decomposition rate of Gardneriana byrsonima A. Juss (murici) in two areas of Caatinga, semiarid region of Alagoas State. Litter production was measured monthly from March of 2012 to February of 2013. The litter decomposition rate and the remaining leaf mass of the murici were also calculated and analyzed for its material chemically. The leaf decomposition was measured in litter bags and the material was chemically analyzed. In the area of Olho D'Agua Casado, the litter produced was over Delmiro Gouveia. The leaf fraction contributed to the higher percentage in the litter training in both areas. The leaf material showed slow decomposition to high levels of lignin, cellulose, hemicellulose, and high C:N ratio.

DECOMPOSIÇÃO DE ESPÉCIES UTILIZADAS COMO ADUBAÇÃO VERDE EM SISTEMA AGROFLORESTAL EXPERIMENTAL, SANTARÉM, PARÁ

Os sistemas agroflorestais são consórcios que possuem em seus arranjos culturas alimentares e madeireiras, tendo sua sustentabilidade estabelecida em função das interações do fluxo de decomposição das espécies existentes. Nesse sentido, a adubação verde é a nova prática utilizada para promover a ciclagem de nutrientes nos sistemas de produção, sendo as leguminosas as espécies mais indicadas para compor esse tipo de adubação. Dessa forma, este trabalho teve por objetivo avaliar a taxa de decomposição foliar das espécies feijão de porco (Canavalia ensiformis (L.) DC.), gliricídia (Gliricidia sepium (Jacq.) Walp.), guandú (Cajanus cajan L.) e leucena (Leucaena leucocephala (Lam.) de Wit.), utilizadas como adubação verde em sistema agroflorestal (SAF) adotando-se do método de litter bags. O estudo foi realizado no SAF experimental, Universidade Federal do Oeste do Pará (UFOPA) no período de abril a setembro de 2017. Analisou-se a decomposição da fração foliar durante 5 períodos de tempo, com coletas aos 30, 60, 90, 120 e 150 dias. Os dados gerados foram ajustados por meio de equação não-linear para obtenção da constante de decomposição (k) e cálculo do tempo de meia vida, sendo analisados estatísticamente pelo teste de Tukey a 5% de probabilidade. A gliricídia apresentou maior taxa de decomposição em relação às demais espécies avaliadas, contudo o guandú embora tenha obtido taxa mais lenta, pode auxiliar na manutenção da cobertura e umidade do solo. A decomposição de todas as espécies se mostrou mais acentuada durante os 90 primeiros dias de experimento.PALAVRAS-CHAVE: Biomassa, Decomposição foliar, Leguminosa.

Interactive Effects of Pesticides and Nutrients on Microbial Communities Responsible of Litter Decomposition in Streams.

Global contamination of streams by a large variety of compounds, such as nutrients and pesticides, may exert a high pressure on aquatic organisms, including microbial communities and their activity of organic matter decomposition. In this study, we assessed the potential interaction between nutrients and a fungicide and herbicide [tebuconazole (TBZ) and S-metolachlor (S-Met), respectively] at realistic environmental concentrations on the structure (biomass, diversity) and decomposition activity of fungal and bacterial communities (leaf decay rates, extracellular enzymatic activities) associated with Alnus glutinosa (Alnus) leaves. A 40-day microcosm experiment was used to combine two nutrient conditions (mesotrophic and eutrophic) with four pesticide treatments at a nominal concentrations of 15 μg L-1 (control, TBZ and S-Met, alone or mixed) following a 2 × 4 full factorial design. We also investigated resulting indirect effects on Gammarus fossarum feeding rates using leaves previously exposed to each of the treatments described above. Results showed interactive effects between nutrients and pesticides, only when nutrient (i.e., nitrogen and phosphorus) concentrations were the highest (eutrophic condition). Specifically, slight decreases in Alnus leaf decomposition rates were observed in channels exposed to TBZ (0.01119 days-1) and S-Met (0.01139 days-1) than in control ones (0.01334 days-1) that can partially be explained by changes in the structure of leaf-associated microbial communities. However, exposition to both TBZ and S-Met in mixture (MIX) led to comparable decay rates to those exposed to the pesticides alone (0.01048 days-1), suggesting no interaction between these two compounds on microbial decomposition. Moreover, stimulation in ligninolytic activities (laccase and phenol oxidase) was observed in presence of the fungicide, possibly highlighting detoxification mechanisms employed by microbes. Such stimulation was not observed for laccase activity exposed to the MIX, suggesting antagonistic interaction of these two compounds on the ability of microbial communities to cope with stress by xenobiotics. Besides, no effects of the treatments were observed on leaf palatability for macroinvertebrates. Overall, the present study highlights that complex interactions between nutrients and xenobiotics in streams and resulting from global change can negatively affect microbial communities associated with leaf litter, although effects on higher trophic-level organisms remains unclear.