Effects of Leaf Litter Species on Macroinvertebrate Colonization during Decomposition in a Portuguese Stream (original) (raw)
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Leaf-Litter Mixtures Affect Breakdown and Macroinvertebrate Colonization Rates in a Stream Ecosystem
International Review of Hydrobiology, 2009
Previous work in terrestrial and aquatic ecosystems has suggested that the relationship between breakdown rates of leaf litter and plant species richness may change unpredictability due to nonadditive effects mediated by the presence of key-species. By using single-and mixed-species leaf bags (7 possible combinations of three litter species differing in toughness; common alder [Alnus glutinosa], sweet chestnut [Castanea sativa], and Spanish oak [Quercus ilex ilex]), I tested whether leaf species diversity, measured as richness and composition, affects breakdown dynamics and macroinvertebrate colonization (abundance, richness and composition) during 90 days incubation in a stream. Decomposition rates were additive, i.e., observed decomposition rates were not different from expected ones. However, decomposition rates of individual leaf species were affected by the mixture, i.e., there were species-specific responses to mixing litter. The invertebrate communities colonizing the mixtures were not richer and more diverse in mixtures than in single-species leaf bags. On the opposite, mixing leaf species had a negative, non-additive effect on rates of shredder and taxa colonization and on macroinvertebrate diversity.
II. Leaf Litter Processing and Invertebrates Leaf Breakdown Rates: a Measure of Water Quality
International Review of Hydrobiology, 2001
The breakdown rates of Alnus glutinosa leaves and the structure of macroinvertebrate communities were used to evaluate the impact of the village of Montalegre (Portugal) on the water quality of the Cávado river. Chemical and microbial analyses of stream water indicated a high organic load in the vicinity of the village. The abundance of macroinvertebrates associated with leaves increased along the pollution gradient, whereas richness of the community decreased. Biotic indices and multivariate analysis applied to aquatic macroinvertebrate communities discriminated polluted from non-polluted sites. Exponential breakdown rates of alder leaves were high (0.014 to 0.060 day -1 ) and the differences observed among sites suggested that nutrient enrichment stimulated leaf breakdown significantly. Leaf breakdown rates have not reflected improved biotic conditions as assessed by biotic indices at the most downstream site. These results suggest that both data from the structure and function of a stream are important for assessing water quality.
Leaf-litter breakdown in 3 streams in temperate, Mediterranean, and tropical Cerrado climates
Journal of the North American Benthological Society, 2006
The objectives of our study were to assess leaf-litter breakdown in 3 streams in 3 climates and to determine the contributions of associated microbial and invertebrate communities to the process. We incubated leaves of Alnus glutinosa in 1 stream in each of 3 climate zones: temperate (mountains of Central Portugal), Mediterranean (South Portugal), and tropical Cerrado (Minas Gerais, Brazil). Leaf-litter breakdown rates (/d) were faster in temperate (k ¼ 0.023-0.017) than in tropical (k ¼ 0.014) or Mediterranean (k ¼ 0.014-0.009) streams. Leaf-litter breakdown rates (/degree day) also were higher in the temperate stream (k ¼ 0.0018-0.0032) and similar between the other 2 streams (k ¼ 0.008-0.0012). Colonization of leaves by aquatic hyphomycetes was faster in the temperate stream (maximum ¼ 421 lg ergosterol/g of leaf by day 24) than in the tropical Cerrado or Mediterranean streams. However, peak ergosterol content was highest in the tropical Cerrado stream (573 lg/g on day 75). Ergosterol content was lowest in the Mediterranean stream (maximum ¼ 341 lg/g on day 7). Total microbial biomass (as ATP) was higher in the tropical Cerrado stream (maximum ¼ 531 nmoles/g on day 75) than in the Mediterranean (maximum ¼ 108 nmoles/g on day 92) and temperate (maximum ¼ 93 nmoles/g on day 7) streams. These results suggest either that not all microorganisms associated with leaves were involved in leaf-litter breakdown or that other less efficient microorganisms than fungi were involved in leaf-litter breakdown in the tropical stream. Leaves exposed to invertebrates (coarse-mesh bags) decomposed significantly faster than leaves protected from invertebrate feeding (fine-mesh bags) only in the temperate stream. This result suggests that invertebrates were important mediators of leaf-litter breakdown only in the temperate stream. A larger proportion of invertebrates recovered from decomposing leaves were shredders in the temperate stream (nearly 5%) than in the Mediterranean (1%) and tropical Cerrado (0%) streams. Leaf-litter processing rates increased with discharge and NO 3 concentration in the water. Our results suggest that the positive effect of temperature on breakdown rates of allochthonous organic matter in streams can be overridden by nutrient content in the water and the presence of invertebrate shredders.
Hydrobiologia, 2010
The objective of this study was to evaluate the influences of detritus from the leaves of different species, and of exposure time on invertebrate colonization of leaves in a shaded Cerrado stream. We hypothesized that the exposure time is the main factor that influences the colonization of leaves by invertebrates. We used leaves of five tree species native to the Brazilian Cerrado: Protium heptaphyllum and Protium brasiliense (Burseraceae), Ocotea sp. (Lauraceae), Myrcia guyanensis (Myrtaceae), and Miconia chartacea (Melastomataceae), which are characterized by their toughness and low-nutritional quality. Litter bags, each containing leaves from one species, were placed in a headwater stream and removed after 7, 15, 30, 60, 90, and 120 days. The dominant taxon was Chironomidae, which comprised ca. 52% of all organisms and ca. 20% of the total biomass. The taxonomic richness of colonizing organisms did not vary among the leaf species. However, the density and biomass of the associated organisms varied differently among the kinds of detritus during the course of the incubation. The collector-gatherers and shredders reached higher densities in the detritus that decomposed more rapidly (Ocotea sp. and M. guyanensis), principally in the more advanced stages of colonization. The collector-filterers reached higher densities in the detritus that decomposed more slowly (P. heptaphyllum, P. brasiliense, and M. chartacea), principally in the initial stages of incubation. A cluster analysis divided the detritus samples of different leaf species according to the exposure time (initial phase: up to 7 days; intermediate phase: 7-30 days; advanced phase: 30-120 days), suggesting some succession in invertebrate colonization, with differences in taxon composition (indicator taxa analysis). These results suggest that regardless of the leaf-detritus species, exposure time was the main factor that influenced the colonization process of aquatic invertebrates.
research paper, 2021
Detritivorous invertebrates play major roles in organic matter processing and nutrient cycling in headwater streams. In this study, three common leaf species in upland Kenyan streams (Vernonia myriantha, Syzygium cordatum and the exotic Eucalyptus globulus) were used to determine the influence of deployment period (14 vs 28 days) on relative decomposition rates and colonization by detritivorous invertebrates in headwater streams of the Nzoia River Basin. Leaf decomposition rates were measured by placing 216 litterbags made of coarse-and fine-mesh in six streams draining forested (n =3) and agricultural (n = 3) land-use during the dry months of February-March 2020. For each stream, physico-chemical water characteristics and habitat quality were determined. Measurements of electrical conductivity, pH, temperature, dissolved oxygen concentration and salinity were performed in situ using portable probes. There were no major differences in physical and chemical characteristics between forested and agricultural streams, except for significantly higher canopy cover (p < 0.05) in forested streams, and electrical conductivity and mean water temperature in agricultural streams. Decomposition rates were faster during the first 2 weeks (day 14), and differences between fine-and coarse-mesh litterbags were significant for Vernonia and Syzygium, but not for Eucalyptus. After 14 days, differences between microbial and shredder + microbial breakdown of leaves were clearer than after 28 days, suggesting that short deployment periods (14 days) are enough to establish relative roles of shredders and microbes in leaf litter decomposition experiments in tropical streams. There were inter-specific differences in colonization rates of the leaves by detritivores (shredders) with Vernonia having the highest number of shredder taxa and abundance followed by Syzygium and Eucalyptus. However, there were minimal differences in taxon richness and abundance of shredders and non-shredders between day 14 and day 28. Therefore, this study recommends shorter deployment periods of 14 days rather than long periods of one month or more when studying leaf litter decomposition and colonization by detritivores in tropical streams.
Leaf decomposition and invertebrate colonization responses to manipulated litter quantity in streams
Journal of the North American Benthological Society, 2008
Resource availability is an important ecosystem attribute that can influence species distributions and ecosystem processes. We manipulated the quantity of leaf litter, a critical resource in streams, in a replicated field experiment to test whether: 1) greater litter quantity promotes microbial leaf decomposition (through greater microbial inoculum potential), and 2) reduced litter quantity enhances decomposition by leaf-shredding invertebrates (because shredders aggregate on rare resource patches). In each of 3 streams, we identified reaches in which litter quantity was either: 1) augmented, 2) depleted, or 3) left unchanged. We determined decomposition rates and macroinvertebrate colonization of alder leaves placed in coarse-and fine-mesh litter bags, an approach intended to allow or prevent access to leaves by leaf-shredding macroinvertebrates. Responses to litter manipulations were complex. In 2 streams, litter quantities differed among treatments, but high quantities of litter in the control reach of the 3 rd stream produced an overall variable pattern. Microbial decomposition was similar across litter treatments. In contrast, in the 2 streams where litter manipulation was successful, decomposition in coarse-mesh bags tended to be faster where litter was scarce than where it was abundant. Abundances of total and leaf-shredding macroinvertebrates in litter bags did not differ among litter manipulations in these 2 streams. However, a litter-consuming amphipod (Gammarus fossarum) tended to be most abundant in bags placed in litter-depleted reaches in the 2 streams, indicating that this large and highly mobile shredder might have been instrumental in causing differences in decomposition in response to litter manipulations. Overall, the effects caused by alteration of litter quantities on leaf decomposition and macroinvertebrate colonization were relatively weak. Nevertheless, results from 2 of the 3 streams where litter manipulation was successful were consistent with the hypothesis that short-term changes in resource availability might influence ecosystem processes by determining the spatial distribution of key consumers.
Freshwater Biology, 2007
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.
Hydrobiologia, 2014
We hypothesized that (i) the importance of shredders for leaf breakdown is more evident in terms of their biomass than their abundance, due to the large bodies and high-feeding efficiencies of some typical shredders; (ii) non-shredder invertebrates select more refractory leaves because these are a more stable substrate for colonization or to obtain other forms of food. To test these hypotheses, we performed a decomposition experiment with leaves of contrasting chemical composition in a tropical stream, and determined the changes in the ash-free dry mass (AFDM) of the litter, and the invertebrate abundance and biomass during a 44-day period. The biomass of shredders showed a positive relationship with AFDM remaining, whereas their abundance was unrelated to AFDM. While shredder abundance represented only 4-12% of total invertebrate abundance, shredder biomass constituted 19-36% of total invertebrate biomass. We conclude that (i) shredder biomass expresses better than abundance the role of this guild in the decomposition of leaf detritus, demonstrating that they are important for the functioning of tropical streams; (ii) incubation time rather than stability of leaf litter as a substrate influences colonization by nonshredder invertebrates.